Hindawi Publishing CorporationInternational Journal of MetalsVolume 2013 Article ID 352496 6 pageshttpdxdoiorg1011552013352496
Research ArticleAn Analytical Model Approach for the Dissolution Kinetics ofMagnesite Ore Using Ascorbic Acid as Leaching Agent
Nadeem Raza Zafar Iqbal Zafar and Najam-ul-Haq
Institute of Chemical Sciences Bahauddin Zakariya University Multan 60800 Pakistan
Correspondence should be addressed to Nadeem Raza nadeemr8hotmailcom
Received 29 April 2013 Accepted 10 June 2013
Academic Editor Chi Tat Kwok
Copyright copy 2013 Nadeem Raza et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
Ascorbic acid was used as leaching agent to investigate the dissolution kinetics of natural magnesite ore The effects of variousreaction parameters such as acid concentration liquid-solid ratio particle size stirring speed and temperature were determinedon dissolution kinetics of the magnesite ore It was found that the dissolution rate increased with increase in acid concentrationliquid-solid ratio stirring speed and temperature and decrease in the particle size of the ore The graphical and statistical methodswere applied to analyze the kinetic data and it was evaluated that the leaching process was controlled by the chemical reaction thatis 1 minus (1 minus 119909)13 = 1256 times 105119890minus57244119877119879119905 The activation energy of the leaching process was found to be 57244 kJmolminus1 over thereaction temperature range from 313 to 343K
1 Introduction
Magnesium is the third most commonly used structuralmetal after iron and aluminum The applications of mag-nesium involve aerospace automobiles flash photographyflares pyrotechnics Grignard reagent refractory materialsfood fertilizers medicinal products paper textile alloyformation to remove sulfur in the production of iron andsteel fireproof and so forth as described by Jones et al [1]
With increase in population there is continuous increasein demand of magnesium and its compounds To overcomethe increasing demand of magnesium and its compoundsthere is a need to explore ores of magnesium (magnesitedolomite etc) These ores may vary in composition fromdeposit to deposit resulting differences in acidulation pro-cesses These rocks generally contain impurities such ascalcium iron and silica which can cause adverse effects onthe applications of magnesium and its compounds
The leaching and dissolution studies of different ores withdifferent leaching agents are available in the literature [2ndash11]On industrial scales different leaching agents are used to leachores of various compositions to get different metals and theircompounds Inorganicorganic acids or bases and their saltscan be used for leaching ofmagnesite rocks to getmagnesium
and its compoundsFrom the dissolution studies ofmagnesiterocks by inorganic acids such as HCl H
2SO4 it was found
that the dissolution reaction was chemically controlled [1213] The inorganic acids are regarded as good leaching agentswhen relatively fast reaction rates are required Howeverthe use of inorganic acids as leaching agents affords certainlimitations like less selectivity scaling problems high CO
2
pressure corrosion environmental problems froth forma-tion and pH control of reaction medium [14] On contraryto inorganic acids organic acids may be more selective ascompared to inorganic acids and can be used for dissolutionof specific ores where relatively low-acid concentrations arefavorable The reaction mediums involving organic acids asleaching agents have various advantages like low risk of corro-sion and froth accumulation and biodegradability of organicacids Furthermore their corrosion effect can be reducedby the addition of corrosion inhibitors such as benzoic acidand salicylic acid [15] However organic acids may haveless ability to leach some ores at higher temperatures dueto their low boiling points and decomposition problemsThe leaching kinetics of low-grade phosphate rock involvingdilute organic acids such as succinic acid and lactic acidwas carried out [16 17] and it was investigated that theleaching process was chemically controlled The literature
2 International Journal of Metals
concerning the dissolution studies of magnesite in citric acidand in gluconic acid is also available [18 19] In these researchstudies it was evaluated that the dissolution process wascontrolled by chemical reaction Lacin et al [20 21] carriedout data analysis using shrinking core models for fluid solidsystems in the dissolution kinetics study of natural magnesitein acetic acid and lactic acid solutions and found that thedissolution rate was controlled by chemical reaction
Large deposits of magnesite are present in Khuzdararea of Balochistan (Pakistan) These deposits have differentcompositions from ore to ore Studies of leaching reactionkinetics at different conditions of various reaction parametersof these deposits have not been carried out Therefore inthe present research work indigenous magnesite ore hasbeen taken to investigate the dissolution kinetics at differentconditions of various reaction parameters
2 Methods and Materials
21 Sample Preparation andAnalysis Themagnesite ore usedin the present research work was obtained fromKhuzdar areaof Balochistan (Pakistan) Khuzdar area is widely endowedwithmagnesite ore deposits Samples of naturalmagnesite orewere collected and crushed with ball mill andmortar grinderASTM standard sieves were used to obtain the desiredparticle size fractions Orgul andAtalay [22] found that whenminerals are fractionated the chemical composition of eachfraction with definite particle size is usually changed All themagnesite samples were dried in an electric oven at 100∘Ccooled to room temperature and stored in dry plastic bottlesEDXwas used for the analysis of themagnesite rock fractionsalong with the other conventional analytical techniques [23]Analytical results indicating the composition of magnesiteore have been shown in Tables 1 and 2 The EDX patternindicating the elemental composition of the raw magnesiteore has been shown in Figure 1 Different chemicals used indissolution studies of magnesite ore were of reagent grade
The leaching agent used in this research workwas ascorbic acid [(5R)-[(1S)-12-dihydroxyethyl]-34-dihydroxyfuran-2(5H)-one] commonly called vitamin Cabundantly found in citrus fruits It is a naturally occurringorganic compound with antioxidant properties It is a whitesolid very soluble in water to give mildly acidic solutionsAscorbic acid and its salts with sodium potassium andmagnesium usually act as an antioxidant and are usedin curing of different diseases like hypertension Metalsalts of ascorbic acid typically react with oxidants of thereactive oxygen species such as the hydroxyl radical formedfrom hydrogen peroxide and can terminate chain radicalreactions
22 Detection Measurement Scanning electron microscope(Hitachi S-3000H) was used to observe the magnesiumcontents in the magnesite ore
23 Experimental Procedure Different size fractions (150ndash590120583m) were used in a 500mL well-mixed spherical glassbatch reactor equipped with a mechanical stirrer digital
controller unit timer and thermostat Various experimentswere carried out with known amount of ascorbic acid havingdifferent concentrations at various LS ratios Each time aknown amount of the ascorbic acid was added slowly to thereaction vessel containing 5 g of magnesite ore The vesselcontents were stirred at a certain speed along with differenttimes and temperatures At the end of each experiment anice bath was used to stop the reaction in reaction vessel Thecontents of reaction vessel were filtered using suitable filterpaper The filtrate solution was analyzed volumetrically formagnesium contents to evaluate the degree of conversion
3 Mechanism of Leaching
The leaching process of the magnesite ore with ascorbic acidcan be represented as follows
(a) Ionization of C6H8O6
C6H8O6997888rarr 2H+ + C
6H6O6
minus2 (1)
(b) Diffusion of H+ ions to the exposed surface of themagnesite particles
(c) H+ ions attack on the magnesite particles in the rock
2H+ +MgCO3997888rarr H
2CO3+Mg2+ (2)
The H+ ions taking part in these reactions may comefrom the ascorbic acid as well as from the carbonicacid formed in the medium
(d) Reaction between Mg2+ and C6H6O6
minus2
Mg2+ + C6H6O6
minus2997888rarr MgC
6H6O6
(3)
The leaching process can be represented by using the follow-ing general equation
H2Y(aq) +MCO
3997888rarr CO
2+MY +H
2O (4)
Solubility product constant for MgCO3is 746 at 25∘C and
the ionization constants for ascorbic acid are pK1= 410 pK
2
= 116 at 25∘C Dissociation constants for carbonic acid arepK1= 635 pK
2= 1033 at 25∘C The equilibrium direction
for the above reaction (4) remains in forward direction andmay be considered as an irreversible reaction because one ofthe products (CO
2) produced during the reaction conditions
is evacuated from the reaction mixture
4 Results and Discussion
41 Morphology of Magnesite The SEM micrograph of theraw magnesite ore has been shown in Figure 2 whichindicates the morphology of magnesite ore The materialseems to be nongranular with surface roughnessThe surfaceroughness is due to the evolution of volatiles which in thiscase might be CO
2
International Journal of Metals 3
Table 1 Chemical analysis of natural magnesite ore
42 Effect of Reaction Temperature The effect of temperature(40∘C to 70∘C) on rate of conversion of magnesite orewas investigated at different experimental conditions (178micrometer particle size 10 ascorbic acid with liquidsolidratio of 10 1 and 350 rpm) as shown in Figure 3 It wasobserved that the rate of conversion of the magnesite oreincreased with an increase in reaction temperature It wasalso observed that increase in temperature reduced thereaction time required to attain the equilibrium in reactionmedium Furthermore higher temperature (above 70∘C) cancause contamination of CO
2gas stream with ascorbic acid
and water vapors The experimental results indicated thatthe reaction temperature was the most effective parameterin the dissolution kinetics of magnesite ore From theseexperimental observations it was also evaluated that below40∘C the ascorbic acid was not good leaching agent due toits lower solubility
43 Effect of Acid Concentration and Liquid Solid RatioDifferent experiments were carried out to find the effectof concentration of ascorbic acid and liquid solid ratio onleaching kinetics of magnesite ore under various experi-mental reaction conditions as given in Figures 4 and 5The experimental results indicated that an increase in acidconcentration caused an increase in magnesium contentHowever after certain optimum value of acid concentra-tion the increase in acid concentration did not have anappreciable effect It might be considered that when the acidconcentration exceeded its maximum required value thehydrogen ions in themediummight decrease due to decreasein water contents During the leaching study of colemaniteore with acetic acid Ozmetin et al [24] found that higheracid concentration in reaction medium increased the rate ofappearance of product by attaining the saturation value alongwith the formation of sparingly solid film layer resulting in adecrease in dissolution process
From Figure 4 it was found that the acid concentrationof 10 was good for leaching kinetics study of magnesite
0 05 1 15 2 25 3 35 4 45 5 55 6 65 7 75 8 85(keV)
Spectrum 1
C OCa Fe Mg
Figure 1 EDX pattern of natural magnesite ore
Figure 2 SEM image of natural magnesite ore
ore with liquid solid ratio of 10 1 The pH of reactionmedium depends on the ascorbic acid concentration andits degree of ionization at a particular temperature The pHdecreased as the concentration of ascorbic acidwas increasedFigure 5 showed that the rate of dissolution of magnesite oreincreased with an increase in the liquid solid ratio From theexperimental results it was found that the liquid-solid ratioalso had a significant effect on dissolution rate of magnesiteore It may be attributed to the fact that a relatively higherliquid solid ratio may provide a medium of liquid phase tofacilitate the mobility of reactive species produced in thereaction medium
44 Effect of Particle Size In order to investigate the effectof particle size on the leaching of magnesite ore differentexperiments were carried out Four different size fractionsof magnesite ore (150 178 297 and 590120583m) at 60∘C wereused to find the effect of particle size as shown in Figure 6The leaching curves indicated that the rate of dissolutionprocess increased as the particle size was decreased Thissituation might be attributed to the fact that the surface areafor reaction becomes more available with decreasing particlesize resulting an increase in the efficiency of the leachingprocess In separate experiments it was observed that theeffect of stirring speed on the leaching reaction rate wasnot appreciable as compared to the other parameters This
4 International Journal of Metals
0
20
40
60
80
100
0 10 20 30 40 50 60
Con
vers
ion
()
Time (min)
40∘C50∘C
60∘C70∘C
Figure 3 Effect of temperature on leaching of magnesite ore
10
25
40
55
70
85
100
0 10 20 30 40 50 60
Con
vers
ion
()
Time (min)
6810
1214
Figure 4 Effect of ascorbic acid concentration on leaching ofmagnesite ore
situation indicated that the leaching of magnesite ore was notproduct or ash layer controlled process
5 Kinetic Analysis
Fluid solid heterogeneous reaction systems are usuallyinvolved in chemical and hydrometallurgical processes Influid solid reaction systems reaction rate may be controlledby one of the following mechanisms diffusion throughthe fluid films diffusion through ashproduct layer or thechemical reaction at the surface of the core of unreactedmaterials [25] The experimental data was analyzed on thebasis of shrinking coremodel to find rate controlling step and
10
30
50
70
90
0 10 20 30 40 50 60
Con
vers
ion
()
Time (min)
1 61 81 10
1 121 14
Figure 5 Effect of liquid solid ratio on leaching of magnesite ore
10
30
50
70
90
0 10 20 30 40 50 60
Con
vers
ion
()
Time (min)
590120583m297120583m
178120583m150120583m
Figure 6 Effect of particle size on leaching of magnesite ore
kinetic parametersThe reaction between a solid and fluid canbe represented as
If no ashproduct layer over unreacted core is formed thentwo controlling steps may be fluid film diffusion or chemicalreaction If the time of completion of the leaching processis 119896119900 the fractional conversion of magnesite is 119909 and at any
time 119905 the integrated equations for fluid-solid heterogeneousreactions may be represented as follows
For film diffusion control
119905 = 119896lowast[1 minus (1 minus 119909)] (6)
International Journal of Metals 5
0
02
04
06
08
0 10 20 30 40 50 60Time (min)
y = 0002x + 00413
R2 = 099
y = 00046x + 00467
R2 = 0998
y = 0008x + 0019R2 = 09979
y = 0014x + 00491R2 = 09958
40∘C50∘C
60∘C70∘C
1minus(1
minusx)13
Figure 7 1 minus (1 minus 119909) 13 at different reaction temperatures
29 295 3 305 31 315 32
y = minus6885x + 11741
R2 = 09952
1T times10minus3 (Kminus1)
minus11
minus10
minus9
minus8
ln k
(Sminus1)
Figure 8 Arrhenius plot for leaching of magnesite ore
For chemical reaction control
119905 = 119896lowast[1 minus (1 minus 119909)
13] (7)
The value of 119896lowast may vary with reaction parameters accordingto the kinetic models For example according to the chemicalreaction controlled model (7) 119896lowast is
119896lowast=120588119861119877119900
119887119870119904119862119860
(8)
where 119896lowast is the time for complete dissolution (min) 120588119861is the
molar density of the solid reactant (molmminus3) 119877119900is the radius
of the solid particle (m) 119887 is the stoichiometric coefficient ofthe solid 119896
119904is the surface reaction rate constant (mminminus1)
and 119862119860
is the leaching agent concentration (mol dmminus3)The validity of the experimental data into the integral ratewas tested by statistical and graphical methods The kineticanalysis results for the dissolution process were found tobe consistent with a chemically controlled reaction and the
integral rate expression was determined to obey the followingrate equation
1 minus (1 minus 119909)13= 119896119905 (9)
Using the conversion values for various reaction tempera-tures liquid solid ratio stirring speed particle size fractionsand acid concentration applied in leaching kinetics of mag-nesite ore the apparent rate constants 119896 can be evaluated byplotting 1 minus (1 minus 119909) 13 versus 119905 as shown in Figure 7 Usingthe Arrhenius equation the above equationmay be expressedas
1 minus (1 minus 119909)13= 119896119900119890minus119864119886119877119879119905 (10)
Arrhenius plot for the leaching of magnesite ore in ascorbicacid solutions was obtained by plotting the values of slopes ofthe straight lines (apparent rate constant) versus ln (1119879) asshown in Figure 8 and the following values were calculated
1 minus (1 minus 119909)13= 1256 times 10
5119890minus57244119877119879
119905 (11)
The value of activation energy indicates that the leachingof magnesite with ascorbic acid solutions is controlled bychemical reaction and this value agrees with the valuesobtained in the similar research work of fluid solid reactionsystem [26] Abdel-Aal [27] described that the activationenergy of a diffusion controlled process is characterized to befrom 418 to 1255 kJmolminus1 and for a chemically controlledprocess value of activation energy is usually greater than4184 kJmolminus1
6 Conclusions
(i) The experimental results show that the ascorbic acidcan be used as leaching agent to extract magnesiumcontents from the magnesite ore
(ii) Analysis of the kinetic data by different kineticmodelsshows that the leaching of magnesite ore in ascorbicacid solutions follows a chemically controlled processwith activation energy of 57244 kJmolminus1
(iii) In the leaching of magnesite ore with ascorbic acidthe product that is magnesium ascorbate obtainedis an important medical material and can be used incuring of different diseases like hypertension
(iv) Nontoxic techniques in terms of environmental pollu-tion and human safety are the major reasons in usingenvironment friendly leaching agents like ascorbicacid for the dissolution studies of magnesite ores
Explanation of Symbols
119864119886 activation energy (Jmolminus1)119909 dissolved fraction of Mg2+LS liquidsolid ratio (cm3 gminus1)119905 reaction time (min)119879 reaction temperature (K)119896 reaction rate constant (minminus1)EDX energy dispersive X-ray analysis
6 International Journal of Metals
Acknowledgments
The authors thank the Institute of Chemical Sciences BZUMultan and Institute of Chemical Engineering and Technol-ogy NFC Multan for providing the facilities
References
[1] P T Jones B Blanpain P Wollants R Ding and B HallemansldquoDegradation mechanisms of magnesia-chromite refractoriesin vacuum-oxygen decarburization ladles during production ofstainless steelrdquo Ironmaking and Steelmaking vol 27 no 3 pp228ndash237 2000
[2] H T Dogan and A Yartasi ldquoKinetic investigation of reactionbetween ulexite ore and phosphoric acidrdquoHydrometallurgy vol96 no 4 pp 294ndash299 2009
[3] N Demirkyran and A Kunkul ldquoDissolution kinetics of ulexitein perchloric acid solutionsrdquo International Journal of MineralProcessing vol 83 pp 76ndash80 2007
[4] A Ekmekyapar N Demirkiran and A Kunkul ldquoDissolutionkinetics of ulexite in acetic acid solutionsrdquoChemical EngineeringResearch and Design vol 86 no 9 pp 1011ndash1016 2008
[5] N Demirkiran ldquoA study on dissolution of ulexite in ammoniumacetate solutionsrdquo Chemical Engineering Journal vol 141 no 1ndash3 pp 180ndash186 2008
[6] N Demirkiran ldquoDissolution kinetics of ulexite in ammoniumnitrate solutionsrdquoHydrometallurgy vol 95 no 3-4 pp 198ndash2022009
[7] N Habbache N Alane S Djerad and L Tifouti ldquoLeaching ofcopper oxide with different acid solutionsrdquo Chemical Engineer-ing Journal vol 152 no 2-3 pp 503ndash508 2009
[8] S Kuslu F C Disli and S Colak ldquoLeaching kinetics of ulexitein borax pentahydrate solutions saturated with carbon dioxiderdquoJournal of Industrial and Engineering Chemistry vol 16 no 5pp 673ndash678 2010
[9] A Mergen and M H Demirhan ldquoDissolution kinetics ofprobertite in boric acid solutionrdquo International Journal ofMineral Processing vol 90 no 1ndash4 pp 16ndash20 2009
[10] S A Awe C Samuelsson and A Sandstrom ldquoDissolutionkinetics of tetrahedrite mineral in alkaline sulphide mediardquoHydrometallurgy vol 103 no 1ndash4 pp 167ndash172 2010
[11] S Zhang and M J Nicol ldquoKinetics of the dissolution ofilmenite in sulfuric acid solutions under reducing conditionsrdquoHydrometallurgy vol 103 no 1ndash4 pp 196ndash204 2010
[12] L Chou R M Garrels and R Wollast ldquoComparative studyof the kinetics and mechanisms of dissolution of carbonatemineralsrdquo Chemical Geology vol 78 no 3-4 pp 269ndash282 1989
[13] Y Abali M Copur and M Yavuz ldquoDetermination of theoptimum conditions for dissolution of magnesite with H
2SO4
solutionsrdquo Indian Journal of Chemical Technology vol 13 no 4pp 391ndash397 2006
[14] S Hausmanns G Laufenberg and B Kunz ldquoRejection of aceticacid and its improvement by combination with organic acids indilute solutions using reverse osmosisrdquo Desalination vol 104no 1-2 pp 95ndash98 1996
[15] S Bilgic ldquoThe inhibition effects of benzoic acid and salicylicacid on the corrosion of steel in sulfuric acid mediumrdquo Mate-rials Chemistry and Physics vol 76 no 1 pp 52ndash58 2002
[16] M Ashraf Z I Zafar and T M Ansari ldquoSelective leachingkinetics and upgrading of low-grade calcareous phosphate rock
in succinic acidrdquo Hydrometallurgy vol 80 no 4 pp 286ndash2922005
[17] Z I Zafar and M Ashraf ldquoSelective leaching kinetics ofcalcareous phosphate rock in lactic acidrdquo Chemical EngineeringJournal vol 131 no 1ndash3 pp 41ndash48 2007
[18] F Demir B Donmez and S Colak ldquoLeaching kinetics of mag-nesite in citric acid solutionsrdquo Journal of Chemical Engineeringof Japan vol 36 no 6 pp 683ndash688 2003
[19] B Bayrak O Lacin andH Sarac ldquoKinetic study on the leachingof calcined magnesite in gluconic acid solutionsrdquo Journal ofIndustrial andEngineeringChemistry vol 16 no 3 pp 479ndash4842010
[20] O Lacin B Donmez and F Demir ldquoDissolution kinetics ofnaturalmagnesite in acetic acid solutionsrdquo International Journalof Mineral Processing vol 75 no 1-2 pp 91ndash99 2005
[21] F Bakan O Lacin B Bayrak and H Sarac ldquoDissolution kinet-ics of natural magnesite in lactic acid solutionsrdquo InternationalJournal of Mineral Processing vol 80 no 1 pp 27ndash34 2006
[22] S Orgul and U Atalay ldquoReaction chemistry of gold leaching inthiourea solution for a Turkish gold orerdquo Hydrometallurgy vol67 no 1ndash3 pp 71ndash77 2002
[23] N H Furmann StandardMethods of Chemical Analysis D VanNostrand Princeton NJ USA 6th edition 1963
[24] C Ozmetin M M Kocakerim S Yapici and A YartasildquoA semiempirical kinetic model for dissolution of colemanitein aqueous CH
3COOH solutionsrdquo Industrial and Engineering
Chemistry Research vol 35 no 7 pp 2355ndash2359 1996[25] O Levenspiel Chemical Reaction Engineering John Wiley amp
Sons New York NY USA 2nd edition 1972[26] Z I Zafar ldquoDetermination of semi empirical kinetic model
for dissolution of bauxite ore with sulfuric acid parametriccumulative effect on the Arrhenius parametersrdquo ChemicalEngineering Journal vol 141 no 1ndash3 pp 233ndash241 2008
[27] E A Abdel-Aal ldquoKinetics of sulfuric acid leaching of low-gradezinc silicate orerdquo Hydrometallurgy vol 55 no 3 pp 247ndash2542000
concerning the dissolution studies of magnesite in citric acidand in gluconic acid is also available [18 19] In these researchstudies it was evaluated that the dissolution process wascontrolled by chemical reaction Lacin et al [20 21] carriedout data analysis using shrinking core models for fluid solidsystems in the dissolution kinetics study of natural magnesitein acetic acid and lactic acid solutions and found that thedissolution rate was controlled by chemical reaction
Large deposits of magnesite are present in Khuzdararea of Balochistan (Pakistan) These deposits have differentcompositions from ore to ore Studies of leaching reactionkinetics at different conditions of various reaction parametersof these deposits have not been carried out Therefore inthe present research work indigenous magnesite ore hasbeen taken to investigate the dissolution kinetics at differentconditions of various reaction parameters
2 Methods and Materials
21 Sample Preparation andAnalysis Themagnesite ore usedin the present research work was obtained fromKhuzdar areaof Balochistan (Pakistan) Khuzdar area is widely endowedwithmagnesite ore deposits Samples of naturalmagnesite orewere collected and crushed with ball mill andmortar grinderASTM standard sieves were used to obtain the desiredparticle size fractions Orgul andAtalay [22] found that whenminerals are fractionated the chemical composition of eachfraction with definite particle size is usually changed All themagnesite samples were dried in an electric oven at 100∘Ccooled to room temperature and stored in dry plastic bottlesEDXwas used for the analysis of themagnesite rock fractionsalong with the other conventional analytical techniques [23]Analytical results indicating the composition of magnesiteore have been shown in Tables 1 and 2 The EDX patternindicating the elemental composition of the raw magnesiteore has been shown in Figure 1 Different chemicals used indissolution studies of magnesite ore were of reagent grade
The leaching agent used in this research workwas ascorbic acid [(5R)-[(1S)-12-dihydroxyethyl]-34-dihydroxyfuran-2(5H)-one] commonly called vitamin Cabundantly found in citrus fruits It is a naturally occurringorganic compound with antioxidant properties It is a whitesolid very soluble in water to give mildly acidic solutionsAscorbic acid and its salts with sodium potassium andmagnesium usually act as an antioxidant and are usedin curing of different diseases like hypertension Metalsalts of ascorbic acid typically react with oxidants of thereactive oxygen species such as the hydroxyl radical formedfrom hydrogen peroxide and can terminate chain radicalreactions
22 Detection Measurement Scanning electron microscope(Hitachi S-3000H) was used to observe the magnesiumcontents in the magnesite ore
23 Experimental Procedure Different size fractions (150ndash590120583m) were used in a 500mL well-mixed spherical glassbatch reactor equipped with a mechanical stirrer digital
controller unit timer and thermostat Various experimentswere carried out with known amount of ascorbic acid havingdifferent concentrations at various LS ratios Each time aknown amount of the ascorbic acid was added slowly to thereaction vessel containing 5 g of magnesite ore The vesselcontents were stirred at a certain speed along with differenttimes and temperatures At the end of each experiment anice bath was used to stop the reaction in reaction vessel Thecontents of reaction vessel were filtered using suitable filterpaper The filtrate solution was analyzed volumetrically formagnesium contents to evaluate the degree of conversion
3 Mechanism of Leaching
The leaching process of the magnesite ore with ascorbic acidcan be represented as follows
(a) Ionization of C6H8O6
C6H8O6997888rarr 2H+ + C
6H6O6
minus2 (1)
(b) Diffusion of H+ ions to the exposed surface of themagnesite particles
(c) H+ ions attack on the magnesite particles in the rock
2H+ +MgCO3997888rarr H
2CO3+Mg2+ (2)
The H+ ions taking part in these reactions may comefrom the ascorbic acid as well as from the carbonicacid formed in the medium
(d) Reaction between Mg2+ and C6H6O6
minus2
Mg2+ + C6H6O6
minus2997888rarr MgC
6H6O6
(3)
The leaching process can be represented by using the follow-ing general equation
H2Y(aq) +MCO
3997888rarr CO
2+MY +H
2O (4)
Solubility product constant for MgCO3is 746 at 25∘C and
the ionization constants for ascorbic acid are pK1= 410 pK
2
= 116 at 25∘C Dissociation constants for carbonic acid arepK1= 635 pK
2= 1033 at 25∘C The equilibrium direction
for the above reaction (4) remains in forward direction andmay be considered as an irreversible reaction because one ofthe products (CO
2) produced during the reaction conditions
is evacuated from the reaction mixture
4 Results and Discussion
41 Morphology of Magnesite The SEM micrograph of theraw magnesite ore has been shown in Figure 2 whichindicates the morphology of magnesite ore The materialseems to be nongranular with surface roughnessThe surfaceroughness is due to the evolution of volatiles which in thiscase might be CO
2
International Journal of Metals 3
Table 1 Chemical analysis of natural magnesite ore
42 Effect of Reaction Temperature The effect of temperature(40∘C to 70∘C) on rate of conversion of magnesite orewas investigated at different experimental conditions (178micrometer particle size 10 ascorbic acid with liquidsolidratio of 10 1 and 350 rpm) as shown in Figure 3 It wasobserved that the rate of conversion of the magnesite oreincreased with an increase in reaction temperature It wasalso observed that increase in temperature reduced thereaction time required to attain the equilibrium in reactionmedium Furthermore higher temperature (above 70∘C) cancause contamination of CO
2gas stream with ascorbic acid
and water vapors The experimental results indicated thatthe reaction temperature was the most effective parameterin the dissolution kinetics of magnesite ore From theseexperimental observations it was also evaluated that below40∘C the ascorbic acid was not good leaching agent due toits lower solubility
43 Effect of Acid Concentration and Liquid Solid RatioDifferent experiments were carried out to find the effectof concentration of ascorbic acid and liquid solid ratio onleaching kinetics of magnesite ore under various experi-mental reaction conditions as given in Figures 4 and 5The experimental results indicated that an increase in acidconcentration caused an increase in magnesium contentHowever after certain optimum value of acid concentra-tion the increase in acid concentration did not have anappreciable effect It might be considered that when the acidconcentration exceeded its maximum required value thehydrogen ions in themediummight decrease due to decreasein water contents During the leaching study of colemaniteore with acetic acid Ozmetin et al [24] found that higheracid concentration in reaction medium increased the rate ofappearance of product by attaining the saturation value alongwith the formation of sparingly solid film layer resulting in adecrease in dissolution process
From Figure 4 it was found that the acid concentrationof 10 was good for leaching kinetics study of magnesite
0 05 1 15 2 25 3 35 4 45 5 55 6 65 7 75 8 85(keV)
Spectrum 1
C OCa Fe Mg
Figure 1 EDX pattern of natural magnesite ore
Figure 2 SEM image of natural magnesite ore
ore with liquid solid ratio of 10 1 The pH of reactionmedium depends on the ascorbic acid concentration andits degree of ionization at a particular temperature The pHdecreased as the concentration of ascorbic acidwas increasedFigure 5 showed that the rate of dissolution of magnesite oreincreased with an increase in the liquid solid ratio From theexperimental results it was found that the liquid-solid ratioalso had a significant effect on dissolution rate of magnesiteore It may be attributed to the fact that a relatively higherliquid solid ratio may provide a medium of liquid phase tofacilitate the mobility of reactive species produced in thereaction medium
44 Effect of Particle Size In order to investigate the effectof particle size on the leaching of magnesite ore differentexperiments were carried out Four different size fractionsof magnesite ore (150 178 297 and 590120583m) at 60∘C wereused to find the effect of particle size as shown in Figure 6The leaching curves indicated that the rate of dissolutionprocess increased as the particle size was decreased Thissituation might be attributed to the fact that the surface areafor reaction becomes more available with decreasing particlesize resulting an increase in the efficiency of the leachingprocess In separate experiments it was observed that theeffect of stirring speed on the leaching reaction rate wasnot appreciable as compared to the other parameters This
4 International Journal of Metals
0
20
40
60
80
100
0 10 20 30 40 50 60
Con
vers
ion
()
Time (min)
40∘C50∘C
60∘C70∘C
Figure 3 Effect of temperature on leaching of magnesite ore
10
25
40
55
70
85
100
0 10 20 30 40 50 60
Con
vers
ion
()
Time (min)
6810
1214
Figure 4 Effect of ascorbic acid concentration on leaching ofmagnesite ore
situation indicated that the leaching of magnesite ore was notproduct or ash layer controlled process
5 Kinetic Analysis
Fluid solid heterogeneous reaction systems are usuallyinvolved in chemical and hydrometallurgical processes Influid solid reaction systems reaction rate may be controlledby one of the following mechanisms diffusion throughthe fluid films diffusion through ashproduct layer or thechemical reaction at the surface of the core of unreactedmaterials [25] The experimental data was analyzed on thebasis of shrinking coremodel to find rate controlling step and
10
30
50
70
90
0 10 20 30 40 50 60
Con
vers
ion
()
Time (min)
1 61 81 10
1 121 14
Figure 5 Effect of liquid solid ratio on leaching of magnesite ore
10
30
50
70
90
0 10 20 30 40 50 60
Con
vers
ion
()
Time (min)
590120583m297120583m
178120583m150120583m
Figure 6 Effect of particle size on leaching of magnesite ore
kinetic parametersThe reaction between a solid and fluid canbe represented as
If no ashproduct layer over unreacted core is formed thentwo controlling steps may be fluid film diffusion or chemicalreaction If the time of completion of the leaching processis 119896119900 the fractional conversion of magnesite is 119909 and at any
time 119905 the integrated equations for fluid-solid heterogeneousreactions may be represented as follows
For film diffusion control
119905 = 119896lowast[1 minus (1 minus 119909)] (6)
International Journal of Metals 5
0
02
04
06
08
0 10 20 30 40 50 60Time (min)
y = 0002x + 00413
R2 = 099
y = 00046x + 00467
R2 = 0998
y = 0008x + 0019R2 = 09979
y = 0014x + 00491R2 = 09958
40∘C50∘C
60∘C70∘C
1minus(1
minusx)13
Figure 7 1 minus (1 minus 119909) 13 at different reaction temperatures
29 295 3 305 31 315 32
y = minus6885x + 11741
R2 = 09952
1T times10minus3 (Kminus1)
minus11
minus10
minus9
minus8
ln k
(Sminus1)
Figure 8 Arrhenius plot for leaching of magnesite ore
For chemical reaction control
119905 = 119896lowast[1 minus (1 minus 119909)
13] (7)
The value of 119896lowast may vary with reaction parameters accordingto the kinetic models For example according to the chemicalreaction controlled model (7) 119896lowast is
119896lowast=120588119861119877119900
119887119870119904119862119860
(8)
where 119896lowast is the time for complete dissolution (min) 120588119861is the
molar density of the solid reactant (molmminus3) 119877119900is the radius
of the solid particle (m) 119887 is the stoichiometric coefficient ofthe solid 119896
119904is the surface reaction rate constant (mminminus1)
and 119862119860
is the leaching agent concentration (mol dmminus3)The validity of the experimental data into the integral ratewas tested by statistical and graphical methods The kineticanalysis results for the dissolution process were found tobe consistent with a chemically controlled reaction and the
integral rate expression was determined to obey the followingrate equation
1 minus (1 minus 119909)13= 119896119905 (9)
Using the conversion values for various reaction tempera-tures liquid solid ratio stirring speed particle size fractionsand acid concentration applied in leaching kinetics of mag-nesite ore the apparent rate constants 119896 can be evaluated byplotting 1 minus (1 minus 119909) 13 versus 119905 as shown in Figure 7 Usingthe Arrhenius equation the above equationmay be expressedas
1 minus (1 minus 119909)13= 119896119900119890minus119864119886119877119879119905 (10)
Arrhenius plot for the leaching of magnesite ore in ascorbicacid solutions was obtained by plotting the values of slopes ofthe straight lines (apparent rate constant) versus ln (1119879) asshown in Figure 8 and the following values were calculated
1 minus (1 minus 119909)13= 1256 times 10
5119890minus57244119877119879
119905 (11)
The value of activation energy indicates that the leachingof magnesite with ascorbic acid solutions is controlled bychemical reaction and this value agrees with the valuesobtained in the similar research work of fluid solid reactionsystem [26] Abdel-Aal [27] described that the activationenergy of a diffusion controlled process is characterized to befrom 418 to 1255 kJmolminus1 and for a chemically controlledprocess value of activation energy is usually greater than4184 kJmolminus1
6 Conclusions
(i) The experimental results show that the ascorbic acidcan be used as leaching agent to extract magnesiumcontents from the magnesite ore
(ii) Analysis of the kinetic data by different kineticmodelsshows that the leaching of magnesite ore in ascorbicacid solutions follows a chemically controlled processwith activation energy of 57244 kJmolminus1
(iii) In the leaching of magnesite ore with ascorbic acidthe product that is magnesium ascorbate obtainedis an important medical material and can be used incuring of different diseases like hypertension
(iv) Nontoxic techniques in terms of environmental pollu-tion and human safety are the major reasons in usingenvironment friendly leaching agents like ascorbicacid for the dissolution studies of magnesite ores
Explanation of Symbols
119864119886 activation energy (Jmolminus1)119909 dissolved fraction of Mg2+LS liquidsolid ratio (cm3 gminus1)119905 reaction time (min)119879 reaction temperature (K)119896 reaction rate constant (minminus1)EDX energy dispersive X-ray analysis
6 International Journal of Metals
Acknowledgments
The authors thank the Institute of Chemical Sciences BZUMultan and Institute of Chemical Engineering and Technol-ogy NFC Multan for providing the facilities
References
[1] P T Jones B Blanpain P Wollants R Ding and B HallemansldquoDegradation mechanisms of magnesia-chromite refractoriesin vacuum-oxygen decarburization ladles during production ofstainless steelrdquo Ironmaking and Steelmaking vol 27 no 3 pp228ndash237 2000
[2] H T Dogan and A Yartasi ldquoKinetic investigation of reactionbetween ulexite ore and phosphoric acidrdquoHydrometallurgy vol96 no 4 pp 294ndash299 2009
[3] N Demirkyran and A Kunkul ldquoDissolution kinetics of ulexitein perchloric acid solutionsrdquo International Journal of MineralProcessing vol 83 pp 76ndash80 2007
[4] A Ekmekyapar N Demirkiran and A Kunkul ldquoDissolutionkinetics of ulexite in acetic acid solutionsrdquoChemical EngineeringResearch and Design vol 86 no 9 pp 1011ndash1016 2008
[5] N Demirkiran ldquoA study on dissolution of ulexite in ammoniumacetate solutionsrdquo Chemical Engineering Journal vol 141 no 1ndash3 pp 180ndash186 2008
[6] N Demirkiran ldquoDissolution kinetics of ulexite in ammoniumnitrate solutionsrdquoHydrometallurgy vol 95 no 3-4 pp 198ndash2022009
[7] N Habbache N Alane S Djerad and L Tifouti ldquoLeaching ofcopper oxide with different acid solutionsrdquo Chemical Engineer-ing Journal vol 152 no 2-3 pp 503ndash508 2009
[8] S Kuslu F C Disli and S Colak ldquoLeaching kinetics of ulexitein borax pentahydrate solutions saturated with carbon dioxiderdquoJournal of Industrial and Engineering Chemistry vol 16 no 5pp 673ndash678 2010
[9] A Mergen and M H Demirhan ldquoDissolution kinetics ofprobertite in boric acid solutionrdquo International Journal ofMineral Processing vol 90 no 1ndash4 pp 16ndash20 2009
[10] S A Awe C Samuelsson and A Sandstrom ldquoDissolutionkinetics of tetrahedrite mineral in alkaline sulphide mediardquoHydrometallurgy vol 103 no 1ndash4 pp 167ndash172 2010
[11] S Zhang and M J Nicol ldquoKinetics of the dissolution ofilmenite in sulfuric acid solutions under reducing conditionsrdquoHydrometallurgy vol 103 no 1ndash4 pp 196ndash204 2010
[12] L Chou R M Garrels and R Wollast ldquoComparative studyof the kinetics and mechanisms of dissolution of carbonatemineralsrdquo Chemical Geology vol 78 no 3-4 pp 269ndash282 1989
[13] Y Abali M Copur and M Yavuz ldquoDetermination of theoptimum conditions for dissolution of magnesite with H
2SO4
solutionsrdquo Indian Journal of Chemical Technology vol 13 no 4pp 391ndash397 2006
[14] S Hausmanns G Laufenberg and B Kunz ldquoRejection of aceticacid and its improvement by combination with organic acids indilute solutions using reverse osmosisrdquo Desalination vol 104no 1-2 pp 95ndash98 1996
[15] S Bilgic ldquoThe inhibition effects of benzoic acid and salicylicacid on the corrosion of steel in sulfuric acid mediumrdquo Mate-rials Chemistry and Physics vol 76 no 1 pp 52ndash58 2002
[16] M Ashraf Z I Zafar and T M Ansari ldquoSelective leachingkinetics and upgrading of low-grade calcareous phosphate rock
in succinic acidrdquo Hydrometallurgy vol 80 no 4 pp 286ndash2922005
[17] Z I Zafar and M Ashraf ldquoSelective leaching kinetics ofcalcareous phosphate rock in lactic acidrdquo Chemical EngineeringJournal vol 131 no 1ndash3 pp 41ndash48 2007
[18] F Demir B Donmez and S Colak ldquoLeaching kinetics of mag-nesite in citric acid solutionsrdquo Journal of Chemical Engineeringof Japan vol 36 no 6 pp 683ndash688 2003
[19] B Bayrak O Lacin andH Sarac ldquoKinetic study on the leachingof calcined magnesite in gluconic acid solutionsrdquo Journal ofIndustrial andEngineeringChemistry vol 16 no 3 pp 479ndash4842010
[20] O Lacin B Donmez and F Demir ldquoDissolution kinetics ofnaturalmagnesite in acetic acid solutionsrdquo International Journalof Mineral Processing vol 75 no 1-2 pp 91ndash99 2005
[21] F Bakan O Lacin B Bayrak and H Sarac ldquoDissolution kinet-ics of natural magnesite in lactic acid solutionsrdquo InternationalJournal of Mineral Processing vol 80 no 1 pp 27ndash34 2006
[22] S Orgul and U Atalay ldquoReaction chemistry of gold leaching inthiourea solution for a Turkish gold orerdquo Hydrometallurgy vol67 no 1ndash3 pp 71ndash77 2002
[23] N H Furmann StandardMethods of Chemical Analysis D VanNostrand Princeton NJ USA 6th edition 1963
[24] C Ozmetin M M Kocakerim S Yapici and A YartasildquoA semiempirical kinetic model for dissolution of colemanitein aqueous CH
3COOH solutionsrdquo Industrial and Engineering
Chemistry Research vol 35 no 7 pp 2355ndash2359 1996[25] O Levenspiel Chemical Reaction Engineering John Wiley amp
Sons New York NY USA 2nd edition 1972[26] Z I Zafar ldquoDetermination of semi empirical kinetic model
for dissolution of bauxite ore with sulfuric acid parametriccumulative effect on the Arrhenius parametersrdquo ChemicalEngineering Journal vol 141 no 1ndash3 pp 233ndash241 2008
[27] E A Abdel-Aal ldquoKinetics of sulfuric acid leaching of low-gradezinc silicate orerdquo Hydrometallurgy vol 55 no 3 pp 247ndash2542000
42 Effect of Reaction Temperature The effect of temperature(40∘C to 70∘C) on rate of conversion of magnesite orewas investigated at different experimental conditions (178micrometer particle size 10 ascorbic acid with liquidsolidratio of 10 1 and 350 rpm) as shown in Figure 3 It wasobserved that the rate of conversion of the magnesite oreincreased with an increase in reaction temperature It wasalso observed that increase in temperature reduced thereaction time required to attain the equilibrium in reactionmedium Furthermore higher temperature (above 70∘C) cancause contamination of CO
2gas stream with ascorbic acid
and water vapors The experimental results indicated thatthe reaction temperature was the most effective parameterin the dissolution kinetics of magnesite ore From theseexperimental observations it was also evaluated that below40∘C the ascorbic acid was not good leaching agent due toits lower solubility
43 Effect of Acid Concentration and Liquid Solid RatioDifferent experiments were carried out to find the effectof concentration of ascorbic acid and liquid solid ratio onleaching kinetics of magnesite ore under various experi-mental reaction conditions as given in Figures 4 and 5The experimental results indicated that an increase in acidconcentration caused an increase in magnesium contentHowever after certain optimum value of acid concentra-tion the increase in acid concentration did not have anappreciable effect It might be considered that when the acidconcentration exceeded its maximum required value thehydrogen ions in themediummight decrease due to decreasein water contents During the leaching study of colemaniteore with acetic acid Ozmetin et al [24] found that higheracid concentration in reaction medium increased the rate ofappearance of product by attaining the saturation value alongwith the formation of sparingly solid film layer resulting in adecrease in dissolution process
From Figure 4 it was found that the acid concentrationof 10 was good for leaching kinetics study of magnesite
0 05 1 15 2 25 3 35 4 45 5 55 6 65 7 75 8 85(keV)
Spectrum 1
C OCa Fe Mg
Figure 1 EDX pattern of natural magnesite ore
Figure 2 SEM image of natural magnesite ore
ore with liquid solid ratio of 10 1 The pH of reactionmedium depends on the ascorbic acid concentration andits degree of ionization at a particular temperature The pHdecreased as the concentration of ascorbic acidwas increasedFigure 5 showed that the rate of dissolution of magnesite oreincreased with an increase in the liquid solid ratio From theexperimental results it was found that the liquid-solid ratioalso had a significant effect on dissolution rate of magnesiteore It may be attributed to the fact that a relatively higherliquid solid ratio may provide a medium of liquid phase tofacilitate the mobility of reactive species produced in thereaction medium
44 Effect of Particle Size In order to investigate the effectof particle size on the leaching of magnesite ore differentexperiments were carried out Four different size fractionsof magnesite ore (150 178 297 and 590120583m) at 60∘C wereused to find the effect of particle size as shown in Figure 6The leaching curves indicated that the rate of dissolutionprocess increased as the particle size was decreased Thissituation might be attributed to the fact that the surface areafor reaction becomes more available with decreasing particlesize resulting an increase in the efficiency of the leachingprocess In separate experiments it was observed that theeffect of stirring speed on the leaching reaction rate wasnot appreciable as compared to the other parameters This
4 International Journal of Metals
0
20
40
60
80
100
0 10 20 30 40 50 60
Con
vers
ion
()
Time (min)
40∘C50∘C
60∘C70∘C
Figure 3 Effect of temperature on leaching of magnesite ore
10
25
40
55
70
85
100
0 10 20 30 40 50 60
Con
vers
ion
()
Time (min)
6810
1214
Figure 4 Effect of ascorbic acid concentration on leaching ofmagnesite ore
situation indicated that the leaching of magnesite ore was notproduct or ash layer controlled process
5 Kinetic Analysis
Fluid solid heterogeneous reaction systems are usuallyinvolved in chemical and hydrometallurgical processes Influid solid reaction systems reaction rate may be controlledby one of the following mechanisms diffusion throughthe fluid films diffusion through ashproduct layer or thechemical reaction at the surface of the core of unreactedmaterials [25] The experimental data was analyzed on thebasis of shrinking coremodel to find rate controlling step and
10
30
50
70
90
0 10 20 30 40 50 60
Con
vers
ion
()
Time (min)
1 61 81 10
1 121 14
Figure 5 Effect of liquid solid ratio on leaching of magnesite ore
10
30
50
70
90
0 10 20 30 40 50 60
Con
vers
ion
()
Time (min)
590120583m297120583m
178120583m150120583m
Figure 6 Effect of particle size on leaching of magnesite ore
kinetic parametersThe reaction between a solid and fluid canbe represented as
If no ashproduct layer over unreacted core is formed thentwo controlling steps may be fluid film diffusion or chemicalreaction If the time of completion of the leaching processis 119896119900 the fractional conversion of magnesite is 119909 and at any
time 119905 the integrated equations for fluid-solid heterogeneousreactions may be represented as follows
For film diffusion control
119905 = 119896lowast[1 minus (1 minus 119909)] (6)
International Journal of Metals 5
0
02
04
06
08
0 10 20 30 40 50 60Time (min)
y = 0002x + 00413
R2 = 099
y = 00046x + 00467
R2 = 0998
y = 0008x + 0019R2 = 09979
y = 0014x + 00491R2 = 09958
40∘C50∘C
60∘C70∘C
1minus(1
minusx)13
Figure 7 1 minus (1 minus 119909) 13 at different reaction temperatures
29 295 3 305 31 315 32
y = minus6885x + 11741
R2 = 09952
1T times10minus3 (Kminus1)
minus11
minus10
minus9
minus8
ln k
(Sminus1)
Figure 8 Arrhenius plot for leaching of magnesite ore
For chemical reaction control
119905 = 119896lowast[1 minus (1 minus 119909)
13] (7)
The value of 119896lowast may vary with reaction parameters accordingto the kinetic models For example according to the chemicalreaction controlled model (7) 119896lowast is
119896lowast=120588119861119877119900
119887119870119904119862119860
(8)
where 119896lowast is the time for complete dissolution (min) 120588119861is the
molar density of the solid reactant (molmminus3) 119877119900is the radius
of the solid particle (m) 119887 is the stoichiometric coefficient ofthe solid 119896
119904is the surface reaction rate constant (mminminus1)
and 119862119860
is the leaching agent concentration (mol dmminus3)The validity of the experimental data into the integral ratewas tested by statistical and graphical methods The kineticanalysis results for the dissolution process were found tobe consistent with a chemically controlled reaction and the
integral rate expression was determined to obey the followingrate equation
1 minus (1 minus 119909)13= 119896119905 (9)
Using the conversion values for various reaction tempera-tures liquid solid ratio stirring speed particle size fractionsand acid concentration applied in leaching kinetics of mag-nesite ore the apparent rate constants 119896 can be evaluated byplotting 1 minus (1 minus 119909) 13 versus 119905 as shown in Figure 7 Usingthe Arrhenius equation the above equationmay be expressedas
1 minus (1 minus 119909)13= 119896119900119890minus119864119886119877119879119905 (10)
Arrhenius plot for the leaching of magnesite ore in ascorbicacid solutions was obtained by plotting the values of slopes ofthe straight lines (apparent rate constant) versus ln (1119879) asshown in Figure 8 and the following values were calculated
1 minus (1 minus 119909)13= 1256 times 10
5119890minus57244119877119879
119905 (11)
The value of activation energy indicates that the leachingof magnesite with ascorbic acid solutions is controlled bychemical reaction and this value agrees with the valuesobtained in the similar research work of fluid solid reactionsystem [26] Abdel-Aal [27] described that the activationenergy of a diffusion controlled process is characterized to befrom 418 to 1255 kJmolminus1 and for a chemically controlledprocess value of activation energy is usually greater than4184 kJmolminus1
6 Conclusions
(i) The experimental results show that the ascorbic acidcan be used as leaching agent to extract magnesiumcontents from the magnesite ore
(ii) Analysis of the kinetic data by different kineticmodelsshows that the leaching of magnesite ore in ascorbicacid solutions follows a chemically controlled processwith activation energy of 57244 kJmolminus1
(iii) In the leaching of magnesite ore with ascorbic acidthe product that is magnesium ascorbate obtainedis an important medical material and can be used incuring of different diseases like hypertension
(iv) Nontoxic techniques in terms of environmental pollu-tion and human safety are the major reasons in usingenvironment friendly leaching agents like ascorbicacid for the dissolution studies of magnesite ores
Explanation of Symbols
119864119886 activation energy (Jmolminus1)119909 dissolved fraction of Mg2+LS liquidsolid ratio (cm3 gminus1)119905 reaction time (min)119879 reaction temperature (K)119896 reaction rate constant (minminus1)EDX energy dispersive X-ray analysis
6 International Journal of Metals
Acknowledgments
The authors thank the Institute of Chemical Sciences BZUMultan and Institute of Chemical Engineering and Technol-ogy NFC Multan for providing the facilities
References
[1] P T Jones B Blanpain P Wollants R Ding and B HallemansldquoDegradation mechanisms of magnesia-chromite refractoriesin vacuum-oxygen decarburization ladles during production ofstainless steelrdquo Ironmaking and Steelmaking vol 27 no 3 pp228ndash237 2000
[2] H T Dogan and A Yartasi ldquoKinetic investigation of reactionbetween ulexite ore and phosphoric acidrdquoHydrometallurgy vol96 no 4 pp 294ndash299 2009
[3] N Demirkyran and A Kunkul ldquoDissolution kinetics of ulexitein perchloric acid solutionsrdquo International Journal of MineralProcessing vol 83 pp 76ndash80 2007
[4] A Ekmekyapar N Demirkiran and A Kunkul ldquoDissolutionkinetics of ulexite in acetic acid solutionsrdquoChemical EngineeringResearch and Design vol 86 no 9 pp 1011ndash1016 2008
[5] N Demirkiran ldquoA study on dissolution of ulexite in ammoniumacetate solutionsrdquo Chemical Engineering Journal vol 141 no 1ndash3 pp 180ndash186 2008
[6] N Demirkiran ldquoDissolution kinetics of ulexite in ammoniumnitrate solutionsrdquoHydrometallurgy vol 95 no 3-4 pp 198ndash2022009
[7] N Habbache N Alane S Djerad and L Tifouti ldquoLeaching ofcopper oxide with different acid solutionsrdquo Chemical Engineer-ing Journal vol 152 no 2-3 pp 503ndash508 2009
[8] S Kuslu F C Disli and S Colak ldquoLeaching kinetics of ulexitein borax pentahydrate solutions saturated with carbon dioxiderdquoJournal of Industrial and Engineering Chemistry vol 16 no 5pp 673ndash678 2010
[9] A Mergen and M H Demirhan ldquoDissolution kinetics ofprobertite in boric acid solutionrdquo International Journal ofMineral Processing vol 90 no 1ndash4 pp 16ndash20 2009
[10] S A Awe C Samuelsson and A Sandstrom ldquoDissolutionkinetics of tetrahedrite mineral in alkaline sulphide mediardquoHydrometallurgy vol 103 no 1ndash4 pp 167ndash172 2010
[11] S Zhang and M J Nicol ldquoKinetics of the dissolution ofilmenite in sulfuric acid solutions under reducing conditionsrdquoHydrometallurgy vol 103 no 1ndash4 pp 196ndash204 2010
[12] L Chou R M Garrels and R Wollast ldquoComparative studyof the kinetics and mechanisms of dissolution of carbonatemineralsrdquo Chemical Geology vol 78 no 3-4 pp 269ndash282 1989
[13] Y Abali M Copur and M Yavuz ldquoDetermination of theoptimum conditions for dissolution of magnesite with H
2SO4
solutionsrdquo Indian Journal of Chemical Technology vol 13 no 4pp 391ndash397 2006
[14] S Hausmanns G Laufenberg and B Kunz ldquoRejection of aceticacid and its improvement by combination with organic acids indilute solutions using reverse osmosisrdquo Desalination vol 104no 1-2 pp 95ndash98 1996
[15] S Bilgic ldquoThe inhibition effects of benzoic acid and salicylicacid on the corrosion of steel in sulfuric acid mediumrdquo Mate-rials Chemistry and Physics vol 76 no 1 pp 52ndash58 2002
[16] M Ashraf Z I Zafar and T M Ansari ldquoSelective leachingkinetics and upgrading of low-grade calcareous phosphate rock
in succinic acidrdquo Hydrometallurgy vol 80 no 4 pp 286ndash2922005
[17] Z I Zafar and M Ashraf ldquoSelective leaching kinetics ofcalcareous phosphate rock in lactic acidrdquo Chemical EngineeringJournal vol 131 no 1ndash3 pp 41ndash48 2007
[18] F Demir B Donmez and S Colak ldquoLeaching kinetics of mag-nesite in citric acid solutionsrdquo Journal of Chemical Engineeringof Japan vol 36 no 6 pp 683ndash688 2003
[19] B Bayrak O Lacin andH Sarac ldquoKinetic study on the leachingof calcined magnesite in gluconic acid solutionsrdquo Journal ofIndustrial andEngineeringChemistry vol 16 no 3 pp 479ndash4842010
[20] O Lacin B Donmez and F Demir ldquoDissolution kinetics ofnaturalmagnesite in acetic acid solutionsrdquo International Journalof Mineral Processing vol 75 no 1-2 pp 91ndash99 2005
[21] F Bakan O Lacin B Bayrak and H Sarac ldquoDissolution kinet-ics of natural magnesite in lactic acid solutionsrdquo InternationalJournal of Mineral Processing vol 80 no 1 pp 27ndash34 2006
[22] S Orgul and U Atalay ldquoReaction chemistry of gold leaching inthiourea solution for a Turkish gold orerdquo Hydrometallurgy vol67 no 1ndash3 pp 71ndash77 2002
[23] N H Furmann StandardMethods of Chemical Analysis D VanNostrand Princeton NJ USA 6th edition 1963
[24] C Ozmetin M M Kocakerim S Yapici and A YartasildquoA semiempirical kinetic model for dissolution of colemanitein aqueous CH
3COOH solutionsrdquo Industrial and Engineering
Chemistry Research vol 35 no 7 pp 2355ndash2359 1996[25] O Levenspiel Chemical Reaction Engineering John Wiley amp
Sons New York NY USA 2nd edition 1972[26] Z I Zafar ldquoDetermination of semi empirical kinetic model
for dissolution of bauxite ore with sulfuric acid parametriccumulative effect on the Arrhenius parametersrdquo ChemicalEngineering Journal vol 141 no 1ndash3 pp 233ndash241 2008
[27] E A Abdel-Aal ldquoKinetics of sulfuric acid leaching of low-gradezinc silicate orerdquo Hydrometallurgy vol 55 no 3 pp 247ndash2542000
Figure 3 Effect of temperature on leaching of magnesite ore
10
25
40
55
70
85
100
0 10 20 30 40 50 60
Con
vers
ion
()
Time (min)
6810
1214
Figure 4 Effect of ascorbic acid concentration on leaching ofmagnesite ore
situation indicated that the leaching of magnesite ore was notproduct or ash layer controlled process
5 Kinetic Analysis
Fluid solid heterogeneous reaction systems are usuallyinvolved in chemical and hydrometallurgical processes Influid solid reaction systems reaction rate may be controlledby one of the following mechanisms diffusion throughthe fluid films diffusion through ashproduct layer or thechemical reaction at the surface of the core of unreactedmaterials [25] The experimental data was analyzed on thebasis of shrinking coremodel to find rate controlling step and
10
30
50
70
90
0 10 20 30 40 50 60
Con
vers
ion
()
Time (min)
1 61 81 10
1 121 14
Figure 5 Effect of liquid solid ratio on leaching of magnesite ore
10
30
50
70
90
0 10 20 30 40 50 60
Con
vers
ion
()
Time (min)
590120583m297120583m
178120583m150120583m
Figure 6 Effect of particle size on leaching of magnesite ore
kinetic parametersThe reaction between a solid and fluid canbe represented as
If no ashproduct layer over unreacted core is formed thentwo controlling steps may be fluid film diffusion or chemicalreaction If the time of completion of the leaching processis 119896119900 the fractional conversion of magnesite is 119909 and at any
time 119905 the integrated equations for fluid-solid heterogeneousreactions may be represented as follows
For film diffusion control
119905 = 119896lowast[1 minus (1 minus 119909)] (6)
International Journal of Metals 5
0
02
04
06
08
0 10 20 30 40 50 60Time (min)
y = 0002x + 00413
R2 = 099
y = 00046x + 00467
R2 = 0998
y = 0008x + 0019R2 = 09979
y = 0014x + 00491R2 = 09958
40∘C50∘C
60∘C70∘C
1minus(1
minusx)13
Figure 7 1 minus (1 minus 119909) 13 at different reaction temperatures
29 295 3 305 31 315 32
y = minus6885x + 11741
R2 = 09952
1T times10minus3 (Kminus1)
minus11
minus10
minus9
minus8
ln k
(Sminus1)
Figure 8 Arrhenius plot for leaching of magnesite ore
For chemical reaction control
119905 = 119896lowast[1 minus (1 minus 119909)
13] (7)
The value of 119896lowast may vary with reaction parameters accordingto the kinetic models For example according to the chemicalreaction controlled model (7) 119896lowast is
119896lowast=120588119861119877119900
119887119870119904119862119860
(8)
where 119896lowast is the time for complete dissolution (min) 120588119861is the
molar density of the solid reactant (molmminus3) 119877119900is the radius
of the solid particle (m) 119887 is the stoichiometric coefficient ofthe solid 119896
119904is the surface reaction rate constant (mminminus1)
and 119862119860
is the leaching agent concentration (mol dmminus3)The validity of the experimental data into the integral ratewas tested by statistical and graphical methods The kineticanalysis results for the dissolution process were found tobe consistent with a chemically controlled reaction and the
integral rate expression was determined to obey the followingrate equation
1 minus (1 minus 119909)13= 119896119905 (9)
Using the conversion values for various reaction tempera-tures liquid solid ratio stirring speed particle size fractionsand acid concentration applied in leaching kinetics of mag-nesite ore the apparent rate constants 119896 can be evaluated byplotting 1 minus (1 minus 119909) 13 versus 119905 as shown in Figure 7 Usingthe Arrhenius equation the above equationmay be expressedas
1 minus (1 minus 119909)13= 119896119900119890minus119864119886119877119879119905 (10)
Arrhenius plot for the leaching of magnesite ore in ascorbicacid solutions was obtained by plotting the values of slopes ofthe straight lines (apparent rate constant) versus ln (1119879) asshown in Figure 8 and the following values were calculated
1 minus (1 minus 119909)13= 1256 times 10
5119890minus57244119877119879
119905 (11)
The value of activation energy indicates that the leachingof magnesite with ascorbic acid solutions is controlled bychemical reaction and this value agrees with the valuesobtained in the similar research work of fluid solid reactionsystem [26] Abdel-Aal [27] described that the activationenergy of a diffusion controlled process is characterized to befrom 418 to 1255 kJmolminus1 and for a chemically controlledprocess value of activation energy is usually greater than4184 kJmolminus1
6 Conclusions
(i) The experimental results show that the ascorbic acidcan be used as leaching agent to extract magnesiumcontents from the magnesite ore
(ii) Analysis of the kinetic data by different kineticmodelsshows that the leaching of magnesite ore in ascorbicacid solutions follows a chemically controlled processwith activation energy of 57244 kJmolminus1
(iii) In the leaching of magnesite ore with ascorbic acidthe product that is magnesium ascorbate obtainedis an important medical material and can be used incuring of different diseases like hypertension
(iv) Nontoxic techniques in terms of environmental pollu-tion and human safety are the major reasons in usingenvironment friendly leaching agents like ascorbicacid for the dissolution studies of magnesite ores
Explanation of Symbols
119864119886 activation energy (Jmolminus1)119909 dissolved fraction of Mg2+LS liquidsolid ratio (cm3 gminus1)119905 reaction time (min)119879 reaction temperature (K)119896 reaction rate constant (minminus1)EDX energy dispersive X-ray analysis
6 International Journal of Metals
Acknowledgments
The authors thank the Institute of Chemical Sciences BZUMultan and Institute of Chemical Engineering and Technol-ogy NFC Multan for providing the facilities
References
[1] P T Jones B Blanpain P Wollants R Ding and B HallemansldquoDegradation mechanisms of magnesia-chromite refractoriesin vacuum-oxygen decarburization ladles during production ofstainless steelrdquo Ironmaking and Steelmaking vol 27 no 3 pp228ndash237 2000
[2] H T Dogan and A Yartasi ldquoKinetic investigation of reactionbetween ulexite ore and phosphoric acidrdquoHydrometallurgy vol96 no 4 pp 294ndash299 2009
[3] N Demirkyran and A Kunkul ldquoDissolution kinetics of ulexitein perchloric acid solutionsrdquo International Journal of MineralProcessing vol 83 pp 76ndash80 2007
[4] A Ekmekyapar N Demirkiran and A Kunkul ldquoDissolutionkinetics of ulexite in acetic acid solutionsrdquoChemical EngineeringResearch and Design vol 86 no 9 pp 1011ndash1016 2008
[5] N Demirkiran ldquoA study on dissolution of ulexite in ammoniumacetate solutionsrdquo Chemical Engineering Journal vol 141 no 1ndash3 pp 180ndash186 2008
[6] N Demirkiran ldquoDissolution kinetics of ulexite in ammoniumnitrate solutionsrdquoHydrometallurgy vol 95 no 3-4 pp 198ndash2022009
[7] N Habbache N Alane S Djerad and L Tifouti ldquoLeaching ofcopper oxide with different acid solutionsrdquo Chemical Engineer-ing Journal vol 152 no 2-3 pp 503ndash508 2009
[8] S Kuslu F C Disli and S Colak ldquoLeaching kinetics of ulexitein borax pentahydrate solutions saturated with carbon dioxiderdquoJournal of Industrial and Engineering Chemistry vol 16 no 5pp 673ndash678 2010
[9] A Mergen and M H Demirhan ldquoDissolution kinetics ofprobertite in boric acid solutionrdquo International Journal ofMineral Processing vol 90 no 1ndash4 pp 16ndash20 2009
[10] S A Awe C Samuelsson and A Sandstrom ldquoDissolutionkinetics of tetrahedrite mineral in alkaline sulphide mediardquoHydrometallurgy vol 103 no 1ndash4 pp 167ndash172 2010
[11] S Zhang and M J Nicol ldquoKinetics of the dissolution ofilmenite in sulfuric acid solutions under reducing conditionsrdquoHydrometallurgy vol 103 no 1ndash4 pp 196ndash204 2010
[12] L Chou R M Garrels and R Wollast ldquoComparative studyof the kinetics and mechanisms of dissolution of carbonatemineralsrdquo Chemical Geology vol 78 no 3-4 pp 269ndash282 1989
[13] Y Abali M Copur and M Yavuz ldquoDetermination of theoptimum conditions for dissolution of magnesite with H
2SO4
solutionsrdquo Indian Journal of Chemical Technology vol 13 no 4pp 391ndash397 2006
[14] S Hausmanns G Laufenberg and B Kunz ldquoRejection of aceticacid and its improvement by combination with organic acids indilute solutions using reverse osmosisrdquo Desalination vol 104no 1-2 pp 95ndash98 1996
[15] S Bilgic ldquoThe inhibition effects of benzoic acid and salicylicacid on the corrosion of steel in sulfuric acid mediumrdquo Mate-rials Chemistry and Physics vol 76 no 1 pp 52ndash58 2002
[16] M Ashraf Z I Zafar and T M Ansari ldquoSelective leachingkinetics and upgrading of low-grade calcareous phosphate rock
in succinic acidrdquo Hydrometallurgy vol 80 no 4 pp 286ndash2922005
[17] Z I Zafar and M Ashraf ldquoSelective leaching kinetics ofcalcareous phosphate rock in lactic acidrdquo Chemical EngineeringJournal vol 131 no 1ndash3 pp 41ndash48 2007
[18] F Demir B Donmez and S Colak ldquoLeaching kinetics of mag-nesite in citric acid solutionsrdquo Journal of Chemical Engineeringof Japan vol 36 no 6 pp 683ndash688 2003
[19] B Bayrak O Lacin andH Sarac ldquoKinetic study on the leachingof calcined magnesite in gluconic acid solutionsrdquo Journal ofIndustrial andEngineeringChemistry vol 16 no 3 pp 479ndash4842010
[20] O Lacin B Donmez and F Demir ldquoDissolution kinetics ofnaturalmagnesite in acetic acid solutionsrdquo International Journalof Mineral Processing vol 75 no 1-2 pp 91ndash99 2005
[21] F Bakan O Lacin B Bayrak and H Sarac ldquoDissolution kinet-ics of natural magnesite in lactic acid solutionsrdquo InternationalJournal of Mineral Processing vol 80 no 1 pp 27ndash34 2006
[22] S Orgul and U Atalay ldquoReaction chemistry of gold leaching inthiourea solution for a Turkish gold orerdquo Hydrometallurgy vol67 no 1ndash3 pp 71ndash77 2002
[23] N H Furmann StandardMethods of Chemical Analysis D VanNostrand Princeton NJ USA 6th edition 1963
[24] C Ozmetin M M Kocakerim S Yapici and A YartasildquoA semiempirical kinetic model for dissolution of colemanitein aqueous CH
3COOH solutionsrdquo Industrial and Engineering
Chemistry Research vol 35 no 7 pp 2355ndash2359 1996[25] O Levenspiel Chemical Reaction Engineering John Wiley amp
Sons New York NY USA 2nd edition 1972[26] Z I Zafar ldquoDetermination of semi empirical kinetic model
for dissolution of bauxite ore with sulfuric acid parametriccumulative effect on the Arrhenius parametersrdquo ChemicalEngineering Journal vol 141 no 1ndash3 pp 233ndash241 2008
[27] E A Abdel-Aal ldquoKinetics of sulfuric acid leaching of low-gradezinc silicate orerdquo Hydrometallurgy vol 55 no 3 pp 247ndash2542000
Figure 7 1 minus (1 minus 119909) 13 at different reaction temperatures
29 295 3 305 31 315 32
y = minus6885x + 11741
R2 = 09952
1T times10minus3 (Kminus1)
minus11
minus10
minus9
minus8
ln k
(Sminus1)
Figure 8 Arrhenius plot for leaching of magnesite ore
For chemical reaction control
119905 = 119896lowast[1 minus (1 minus 119909)
13] (7)
The value of 119896lowast may vary with reaction parameters accordingto the kinetic models For example according to the chemicalreaction controlled model (7) 119896lowast is
119896lowast=120588119861119877119900
119887119870119904119862119860
(8)
where 119896lowast is the time for complete dissolution (min) 120588119861is the
molar density of the solid reactant (molmminus3) 119877119900is the radius
of the solid particle (m) 119887 is the stoichiometric coefficient ofthe solid 119896
119904is the surface reaction rate constant (mminminus1)
and 119862119860
is the leaching agent concentration (mol dmminus3)The validity of the experimental data into the integral ratewas tested by statistical and graphical methods The kineticanalysis results for the dissolution process were found tobe consistent with a chemically controlled reaction and the
integral rate expression was determined to obey the followingrate equation
1 minus (1 minus 119909)13= 119896119905 (9)
Using the conversion values for various reaction tempera-tures liquid solid ratio stirring speed particle size fractionsand acid concentration applied in leaching kinetics of mag-nesite ore the apparent rate constants 119896 can be evaluated byplotting 1 minus (1 minus 119909) 13 versus 119905 as shown in Figure 7 Usingthe Arrhenius equation the above equationmay be expressedas
1 minus (1 minus 119909)13= 119896119900119890minus119864119886119877119879119905 (10)
Arrhenius plot for the leaching of magnesite ore in ascorbicacid solutions was obtained by plotting the values of slopes ofthe straight lines (apparent rate constant) versus ln (1119879) asshown in Figure 8 and the following values were calculated
1 minus (1 minus 119909)13= 1256 times 10
5119890minus57244119877119879
119905 (11)
The value of activation energy indicates that the leachingof magnesite with ascorbic acid solutions is controlled bychemical reaction and this value agrees with the valuesobtained in the similar research work of fluid solid reactionsystem [26] Abdel-Aal [27] described that the activationenergy of a diffusion controlled process is characterized to befrom 418 to 1255 kJmolminus1 and for a chemically controlledprocess value of activation energy is usually greater than4184 kJmolminus1
6 Conclusions
(i) The experimental results show that the ascorbic acidcan be used as leaching agent to extract magnesiumcontents from the magnesite ore
(ii) Analysis of the kinetic data by different kineticmodelsshows that the leaching of magnesite ore in ascorbicacid solutions follows a chemically controlled processwith activation energy of 57244 kJmolminus1
(iii) In the leaching of magnesite ore with ascorbic acidthe product that is magnesium ascorbate obtainedis an important medical material and can be used incuring of different diseases like hypertension
(iv) Nontoxic techniques in terms of environmental pollu-tion and human safety are the major reasons in usingenvironment friendly leaching agents like ascorbicacid for the dissolution studies of magnesite ores
Explanation of Symbols
119864119886 activation energy (Jmolminus1)119909 dissolved fraction of Mg2+LS liquidsolid ratio (cm3 gminus1)119905 reaction time (min)119879 reaction temperature (K)119896 reaction rate constant (minminus1)EDX energy dispersive X-ray analysis
6 International Journal of Metals
Acknowledgments
The authors thank the Institute of Chemical Sciences BZUMultan and Institute of Chemical Engineering and Technol-ogy NFC Multan for providing the facilities
References
[1] P T Jones B Blanpain P Wollants R Ding and B HallemansldquoDegradation mechanisms of magnesia-chromite refractoriesin vacuum-oxygen decarburization ladles during production ofstainless steelrdquo Ironmaking and Steelmaking vol 27 no 3 pp228ndash237 2000
[2] H T Dogan and A Yartasi ldquoKinetic investigation of reactionbetween ulexite ore and phosphoric acidrdquoHydrometallurgy vol96 no 4 pp 294ndash299 2009
[3] N Demirkyran and A Kunkul ldquoDissolution kinetics of ulexitein perchloric acid solutionsrdquo International Journal of MineralProcessing vol 83 pp 76ndash80 2007
[4] A Ekmekyapar N Demirkiran and A Kunkul ldquoDissolutionkinetics of ulexite in acetic acid solutionsrdquoChemical EngineeringResearch and Design vol 86 no 9 pp 1011ndash1016 2008
[5] N Demirkiran ldquoA study on dissolution of ulexite in ammoniumacetate solutionsrdquo Chemical Engineering Journal vol 141 no 1ndash3 pp 180ndash186 2008
[6] N Demirkiran ldquoDissolution kinetics of ulexite in ammoniumnitrate solutionsrdquoHydrometallurgy vol 95 no 3-4 pp 198ndash2022009
[7] N Habbache N Alane S Djerad and L Tifouti ldquoLeaching ofcopper oxide with different acid solutionsrdquo Chemical Engineer-ing Journal vol 152 no 2-3 pp 503ndash508 2009
[8] S Kuslu F C Disli and S Colak ldquoLeaching kinetics of ulexitein borax pentahydrate solutions saturated with carbon dioxiderdquoJournal of Industrial and Engineering Chemistry vol 16 no 5pp 673ndash678 2010
[9] A Mergen and M H Demirhan ldquoDissolution kinetics ofprobertite in boric acid solutionrdquo International Journal ofMineral Processing vol 90 no 1ndash4 pp 16ndash20 2009
[10] S A Awe C Samuelsson and A Sandstrom ldquoDissolutionkinetics of tetrahedrite mineral in alkaline sulphide mediardquoHydrometallurgy vol 103 no 1ndash4 pp 167ndash172 2010
[11] S Zhang and M J Nicol ldquoKinetics of the dissolution ofilmenite in sulfuric acid solutions under reducing conditionsrdquoHydrometallurgy vol 103 no 1ndash4 pp 196ndash204 2010
[12] L Chou R M Garrels and R Wollast ldquoComparative studyof the kinetics and mechanisms of dissolution of carbonatemineralsrdquo Chemical Geology vol 78 no 3-4 pp 269ndash282 1989
[13] Y Abali M Copur and M Yavuz ldquoDetermination of theoptimum conditions for dissolution of magnesite with H
2SO4
solutionsrdquo Indian Journal of Chemical Technology vol 13 no 4pp 391ndash397 2006
[14] S Hausmanns G Laufenberg and B Kunz ldquoRejection of aceticacid and its improvement by combination with organic acids indilute solutions using reverse osmosisrdquo Desalination vol 104no 1-2 pp 95ndash98 1996
[15] S Bilgic ldquoThe inhibition effects of benzoic acid and salicylicacid on the corrosion of steel in sulfuric acid mediumrdquo Mate-rials Chemistry and Physics vol 76 no 1 pp 52ndash58 2002
[16] M Ashraf Z I Zafar and T M Ansari ldquoSelective leachingkinetics and upgrading of low-grade calcareous phosphate rock
in succinic acidrdquo Hydrometallurgy vol 80 no 4 pp 286ndash2922005
[17] Z I Zafar and M Ashraf ldquoSelective leaching kinetics ofcalcareous phosphate rock in lactic acidrdquo Chemical EngineeringJournal vol 131 no 1ndash3 pp 41ndash48 2007
[18] F Demir B Donmez and S Colak ldquoLeaching kinetics of mag-nesite in citric acid solutionsrdquo Journal of Chemical Engineeringof Japan vol 36 no 6 pp 683ndash688 2003
[19] B Bayrak O Lacin andH Sarac ldquoKinetic study on the leachingof calcined magnesite in gluconic acid solutionsrdquo Journal ofIndustrial andEngineeringChemistry vol 16 no 3 pp 479ndash4842010
[20] O Lacin B Donmez and F Demir ldquoDissolution kinetics ofnaturalmagnesite in acetic acid solutionsrdquo International Journalof Mineral Processing vol 75 no 1-2 pp 91ndash99 2005
[21] F Bakan O Lacin B Bayrak and H Sarac ldquoDissolution kinet-ics of natural magnesite in lactic acid solutionsrdquo InternationalJournal of Mineral Processing vol 80 no 1 pp 27ndash34 2006
[22] S Orgul and U Atalay ldquoReaction chemistry of gold leaching inthiourea solution for a Turkish gold orerdquo Hydrometallurgy vol67 no 1ndash3 pp 71ndash77 2002
[23] N H Furmann StandardMethods of Chemical Analysis D VanNostrand Princeton NJ USA 6th edition 1963
[24] C Ozmetin M M Kocakerim S Yapici and A YartasildquoA semiempirical kinetic model for dissolution of colemanitein aqueous CH
3COOH solutionsrdquo Industrial and Engineering
Chemistry Research vol 35 no 7 pp 2355ndash2359 1996[25] O Levenspiel Chemical Reaction Engineering John Wiley amp
Sons New York NY USA 2nd edition 1972[26] Z I Zafar ldquoDetermination of semi empirical kinetic model
for dissolution of bauxite ore with sulfuric acid parametriccumulative effect on the Arrhenius parametersrdquo ChemicalEngineering Journal vol 141 no 1ndash3 pp 233ndash241 2008
[27] E A Abdel-Aal ldquoKinetics of sulfuric acid leaching of low-gradezinc silicate orerdquo Hydrometallurgy vol 55 no 3 pp 247ndash2542000
The authors thank the Institute of Chemical Sciences BZUMultan and Institute of Chemical Engineering and Technol-ogy NFC Multan for providing the facilities
References
[1] P T Jones B Blanpain P Wollants R Ding and B HallemansldquoDegradation mechanisms of magnesia-chromite refractoriesin vacuum-oxygen decarburization ladles during production ofstainless steelrdquo Ironmaking and Steelmaking vol 27 no 3 pp228ndash237 2000
[2] H T Dogan and A Yartasi ldquoKinetic investigation of reactionbetween ulexite ore and phosphoric acidrdquoHydrometallurgy vol96 no 4 pp 294ndash299 2009
[3] N Demirkyran and A Kunkul ldquoDissolution kinetics of ulexitein perchloric acid solutionsrdquo International Journal of MineralProcessing vol 83 pp 76ndash80 2007
[4] A Ekmekyapar N Demirkiran and A Kunkul ldquoDissolutionkinetics of ulexite in acetic acid solutionsrdquoChemical EngineeringResearch and Design vol 86 no 9 pp 1011ndash1016 2008
[5] N Demirkiran ldquoA study on dissolution of ulexite in ammoniumacetate solutionsrdquo Chemical Engineering Journal vol 141 no 1ndash3 pp 180ndash186 2008
[6] N Demirkiran ldquoDissolution kinetics of ulexite in ammoniumnitrate solutionsrdquoHydrometallurgy vol 95 no 3-4 pp 198ndash2022009
[7] N Habbache N Alane S Djerad and L Tifouti ldquoLeaching ofcopper oxide with different acid solutionsrdquo Chemical Engineer-ing Journal vol 152 no 2-3 pp 503ndash508 2009
[8] S Kuslu F C Disli and S Colak ldquoLeaching kinetics of ulexitein borax pentahydrate solutions saturated with carbon dioxiderdquoJournal of Industrial and Engineering Chemistry vol 16 no 5pp 673ndash678 2010
[9] A Mergen and M H Demirhan ldquoDissolution kinetics ofprobertite in boric acid solutionrdquo International Journal ofMineral Processing vol 90 no 1ndash4 pp 16ndash20 2009
[10] S A Awe C Samuelsson and A Sandstrom ldquoDissolutionkinetics of tetrahedrite mineral in alkaline sulphide mediardquoHydrometallurgy vol 103 no 1ndash4 pp 167ndash172 2010
[11] S Zhang and M J Nicol ldquoKinetics of the dissolution ofilmenite in sulfuric acid solutions under reducing conditionsrdquoHydrometallurgy vol 103 no 1ndash4 pp 196ndash204 2010
[12] L Chou R M Garrels and R Wollast ldquoComparative studyof the kinetics and mechanisms of dissolution of carbonatemineralsrdquo Chemical Geology vol 78 no 3-4 pp 269ndash282 1989
[13] Y Abali M Copur and M Yavuz ldquoDetermination of theoptimum conditions for dissolution of magnesite with H
2SO4
solutionsrdquo Indian Journal of Chemical Technology vol 13 no 4pp 391ndash397 2006
[14] S Hausmanns G Laufenberg and B Kunz ldquoRejection of aceticacid and its improvement by combination with organic acids indilute solutions using reverse osmosisrdquo Desalination vol 104no 1-2 pp 95ndash98 1996
[15] S Bilgic ldquoThe inhibition effects of benzoic acid and salicylicacid on the corrosion of steel in sulfuric acid mediumrdquo Mate-rials Chemistry and Physics vol 76 no 1 pp 52ndash58 2002
[16] M Ashraf Z I Zafar and T M Ansari ldquoSelective leachingkinetics and upgrading of low-grade calcareous phosphate rock
in succinic acidrdquo Hydrometallurgy vol 80 no 4 pp 286ndash2922005
[17] Z I Zafar and M Ashraf ldquoSelective leaching kinetics ofcalcareous phosphate rock in lactic acidrdquo Chemical EngineeringJournal vol 131 no 1ndash3 pp 41ndash48 2007
[18] F Demir B Donmez and S Colak ldquoLeaching kinetics of mag-nesite in citric acid solutionsrdquo Journal of Chemical Engineeringof Japan vol 36 no 6 pp 683ndash688 2003
[19] B Bayrak O Lacin andH Sarac ldquoKinetic study on the leachingof calcined magnesite in gluconic acid solutionsrdquo Journal ofIndustrial andEngineeringChemistry vol 16 no 3 pp 479ndash4842010
[20] O Lacin B Donmez and F Demir ldquoDissolution kinetics ofnaturalmagnesite in acetic acid solutionsrdquo International Journalof Mineral Processing vol 75 no 1-2 pp 91ndash99 2005
[21] F Bakan O Lacin B Bayrak and H Sarac ldquoDissolution kinet-ics of natural magnesite in lactic acid solutionsrdquo InternationalJournal of Mineral Processing vol 80 no 1 pp 27ndash34 2006
[22] S Orgul and U Atalay ldquoReaction chemistry of gold leaching inthiourea solution for a Turkish gold orerdquo Hydrometallurgy vol67 no 1ndash3 pp 71ndash77 2002
[23] N H Furmann StandardMethods of Chemical Analysis D VanNostrand Princeton NJ USA 6th edition 1963
[24] C Ozmetin M M Kocakerim S Yapici and A YartasildquoA semiempirical kinetic model for dissolution of colemanitein aqueous CH
3COOH solutionsrdquo Industrial and Engineering
Chemistry Research vol 35 no 7 pp 2355ndash2359 1996[25] O Levenspiel Chemical Reaction Engineering John Wiley amp
Sons New York NY USA 2nd edition 1972[26] Z I Zafar ldquoDetermination of semi empirical kinetic model
for dissolution of bauxite ore with sulfuric acid parametriccumulative effect on the Arrhenius parametersrdquo ChemicalEngineering Journal vol 141 no 1ndash3 pp 233ndash241 2008
[27] E A Abdel-Aal ldquoKinetics of sulfuric acid leaching of low-gradezinc silicate orerdquo Hydrometallurgy vol 55 no 3 pp 247ndash2542000
