MINERALS, MATERIALSAND INDUSTRY
Papers presented at the Fourteenth Congress s>f the Council ofMining and Metallurgical Institutions, organized by the Institution ofMining and Metallurgy and held in Edinburgh, Scotland, from 2 to6 July, 1990
The Institution ofMining and Metallurgy
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Studies on the flotation of mixedoxide-sulphide ores of copper fromMalanjkhand deposit, India
S. PrabhakarNational Metallurgical Laboratory Madras Centre) CSIR Madras Complex) Madras) IndiaG. Bhaskar RajuNational Metallurgical Laboratory Madras Centre) CSIR Madras Complex) Madras) IndiaV. N. MisraKalgoorlie Metallurgical Laboratory) Chemistry Centre) Department of Mines) Kalgoorlie) WesternAustraliaP. R. Khangaonkar~ "hoolof Materials and Mineral Resources Engineering) Universiti Sains Malaysia) Ipoh) Malaysia
Bench scale experiments on the benefi-tion of a mixed oxide-sulphide ore
of copper from Malanjkhand deposit ofHindusthan Copper Limited, India con-ducted with certain modifications incollector systems within the limitsof existing plant operating conditionsyielded better metallurgical results.Sodium isopropyl xanthate (IPX) andsodium diethyldithiocarbamate (DTC)were tried as collectors along withmodifiers, such, as, sodium silicate,
Magnafloc-viz. reagent
pulp etc. wereand optimised.results were
guargum, Magnafloc-140 and351. All the variables,concentration,· pH of theJstematically studied'~proved metallurgicalobtai ned wi th isopropylcombination with sodium silicate\-argum at pH 9.0. The results werealso equally good with dithiocarbamate,a chemisorbing collector.
Hindusthan Copper Limited's MalanjkhandProject (M.P. State), is the biggestopen pit base metal mine in India.The project is designed to produce 2million tonnes of ore per year at itsfull rated capaci ty and concentratethe same by flotation. Malachite isthe predominant copper mineral in the
oxidized capping whereas chalcopyriteand pyrite are the principal mineralsin the primary ore zone1 In the secon-dary enrichment zone, where the presentmining activities are going on, copperoccurs not only as chalcopyrite butalso as covellite and chalcocite. Apartfrom secondary sulphide mineralization,considerable degree of oxide formationwas also observed in the ore from thiszone. The ore exhibits a copper segre-gation tendency in the finer sizes.
carries different proportions of primaryand secondary copper minerals and oxidecopper minerals. The varied natureof the depositrecoveries andtailing 10sses2.
To achieve better metallurgicalresults, specific, more efficientcollector systems are needed to floatthe sluggishly floating covellite andchalcocite and the poorly floatingmalachite.
The present investigation detailscertain modifications in the collectorsystems within the limits of existingoperating conditions of the plant.
MATERIALS AND METHODSThe copper ore used in the investiga-tion was a typical (crushed) sample
containing sulphides and oxides analysingabout 3.0% copper, obtained fromMalanjkhand Copper Project of HindusthanCopper Limited, India. The sample wasagain crushed to 10 mesh using Laboratoryjaw crusher followed by roll crusher,the output of which was further groundin a ball mill to get 60% -0.075 mmfraction. The final product with thesize distribution shown in Table IIwas directlyexperiments.of the head
usedThe
sample
in the flotationchemical analysisis shown in Table 1.
Chemical analysis of headsample
CopperIronS i 1 i c aSulphurCaO
Acid (5% Sulphuricacid) Soluble Copper
%
3.063.2281 .344.752.390.34
Sieve analysis of the headsample
wt.% Cu % TotalCu dis-tribu-tion
% Di s-tri-bution
1 +0.21 1 .22 0.69 0.0084 0.272 -0.21 +0.15 6.95 1 .32 0.0920 3.013 -0.15 +0.10516.87 1 .91 0.3222 10.534 -0.105+0.075 9.95 2.35 0.2338 7.645 -0.075+0.06310.76 2.30 0.2475 8.096 -0.063+0.05310.09 3.63 0.3663 11 .987 -0.053 44.16 4.05 1.7885 58.47
100.00 3 .05 8 7 100 .00
Some of the reagents used in theinvestigation viz. sodium silicate,pine oil, guargum, Magnafloc and sodiumisopropyl xanthate were of commercialgrade whilst sodium diethyl dithiocarba-mate, sodium hydroxide and acetic acidwere of laboratory reagent grades.All the flotation experiments were
carried out in a Dorr-Oliver flotationcell (1 kg capacity) keeping 25-30%solids in a single stage operation.The analysis of copper in the ore, floatand tailings was determined with AtomicAbsorption Spectrophotometer AA 575.All the experiments were duplicatedand the average results obtained arereported.
As a
finespreliminary(-0.075 mm)
extent ofas recei ved
step thein the
sample was determined by screening.These fi nes accounted for about 8% byweight of the sample and analysed 5.8%copper including 1.4% acid (5% Sulphuricacid) soluble copper. This indicatethat the generation of fines at thecrushing stage itself is substantial.
The chemical analysis of the headsample after grinding shown in TableI, revealed the major gangue to besilica. The sieve analysis of thesample after grinding in a ball millis indicated in Table II. It is evidentthat the -0.053 mm fraction accountsfor about 45% by weight. The chemicalanalysis of the individual sievefractions indicated that more than 50%of the total copper remained in thi~fraction.
The concentrator plant at Malanjkhandis presently carrying out the flotatiu'of copper ores ground to 50% -0.075mm using IPX and pine oil at the naturalpH of the water available. A fewpreliminary experiments were carriedout with 1 kg of ground ore, 0.06 kg/tonsodium isopropyl xanthate and 0.04kg/ton pine oil without any modifiersor depressants, i.e. maintaining thesame conditions as in the plant exceptcleaning and scavenging steps. Thetrials resulted a recovery of 73.4%with a float grade of 14.5% copper.
As the tailings werethey were subjected toand the results areTable III. The results
rich in copper,sieve analysispresented inindicated that
5ieve analysis of thetailings
51.No.
Wt. % Cu % Distri- % Dis-bution tribu-
tion+0.21 1.12
-0 .21 +0 .15 5.80-0.15 +0.10514.95-0.105+0.075 9.05-0.075+0.06310.94-0.063+0.05310.12-0.053+ 48.02
100.00
0.5360.3450.4820.7180.6491.3441.166
0.0060.0200.0720.0650.0710.1360.5600.930
0.652.157.746.997.6314.6260.22100.00
the copper loss in fine fractions, i.e.-0.063+0.053 and -0.053 mm alone accoun-ted for more than 65% of total lossof copper in tailings and were responsi-ble for lower recoveries. Further thelow recoveries maypH of the pulp, which isThe earlier work3 on copper oxides(mainly malach'te) from Malanjkhanddeposit revealed the dissolution ofcopper at neutral pH of the pulp. TheIis sol ved cop per ion sin the pu 1P wasfound to create difficulties like gangue'tivation (low grade float) and high
reagent consumption. 50 a separate-~t of experiments was carried out too serve the effect of reagent concen-tration and pH of the pulp.
The effect of isopropyl xanthate concen-tration on the flotation of copper,keeping all the other conditions thesame as above is shown in Table IV.The results showed negligible variationsin both recovery and grade by increasingthe reagent concentration and possiblythe collector dosage may not be thecause for poor recoveries at Malanjkhand.
Effect of IPX concentrationwithout sodium silicate andwithout pH control
Ore 1000 gmPine oil. .. 0.04 kg/ton
IP X Grade Recoverykg/ton % %0.06 14.0 73.30.10 16.2 79 .10.15 16.9 80.50.20 18.3 81.20.25 18.8 80.60.30 17.9 79.8
51.No.
A set of experiments was conducted atdifferent pH values of the pulp at0.25 kg/ton of isopropyl xanthate and0.04 kg/ton of pine oil. The resultspresented in Table V indicate a slight
Effect of pH without sodiumsilicate
Conditions: Ore 1000 gm0.25 kg/ton0.04 kg/ton
Grade Recovery% %
15.80 81.3020.61 83.3420.80 86.7120.20 86.01
51. pHNo.
1 7.02 8.03 9.04 10.0
improvement in both grade and recoveryat pH 9.0. This improvement might beattributed to the flotation of malachitepresent in the ore as the po int of zerocharge (PZC) of malachite lies at aboutpH 9.4 as reported by Attia4 Thisfact is in accordance with the findingsof the authors' earlier work on thebeneficiation of copper oxide minerals3.
Though the recoveryimproved to 86% and 20% Cuwith the modification inpH, the loss of copper
and graderespectivelythe pulp andin tailings
seriously affects the overall efficiencyof the plant. Further the silica inthe float can pose other metallurgicalproblems. From the above experimentalresults it was concluded that this typeof ore needs in depth flotation studiesusing some modifiers/regulating agents/selective collectors to reduce tailingslosses in the form of fines and toreduce silica in float. Keeping thisin view further experiments were carriedout using various regulating agents.
The flotation experiments were carriedout with sodium silicate and othermodifiers such as guargum and Magnafloc
polymers.
flotation, at 0.25 kg/ton of isopropylxanthate, 0.04 kg/ton of pine oil andat pH 9.0 is shown in Table VI. The addi-tion of sodium silicate upto 1.5 kg/ton
Table VI Effect of sodium silicatequantity
Conditions Ore 1000 gmIPX 0.25 kg/tonpH 9.2
Pine oil 0.04 kg/ton
S1 . Sod.Silicate Grade RecoveryNo. kg/ton % %
1 0.5 21 .44 84.3
2 1 .0 23.46 85.2
3 1 .5 25.90 84.6
4 2.0 25.80 84.9
5 2.5 25.85 85.0
was found to result in remarkable impro-vements in copper grade, without affect-ing the recovery. The addition of sodiumsilicate naturally resulted in anincrease in pH of the pulp due to itsbasic nature. To verify the effectof pH in the presence of sodium silicate,a few more experiments were carried
out at different pH values of pulp,keeping the other conditions same asabove.
Effect of pH in the presence of sod i urnsilicate
The experimental results at differentpH values of the pulp are shown inTable VII, from which it is again clearthat the optimum pH is 9.0. It was
also observed that the quantity ofNaOH added to attain the pH 9.0 was notappreciable due to the presence ofsodium silicate in the pulp. From the
Table VII: Effect of pH in the presence
of sodium silicate. .. 1000 gm
... 0.25 kg/ton
... 1.5 kg/ton
... 0.04 kg/ton
IPXSod. silicatePine oil
S 1 . pH GradeNo. %
1 7.0 17.02 7.5 17 .73 8.0 19.74 8.5 21 .35 9.0 25.46 9.5 23.67 10.0 20.2
78.0
80.085.084.485.285.086.1
Recovery%
above studies it was concluded thatthe presence of sodium silicate in thepulp a-nd maintenance of pH at 9.0 can
yield better copper grades with goodrecoveries (85%). For still betterrecoveries it was felt necessary torecover the copper values from thefiner fractions of the sample. Forthis purpose a separate set of experi-
men t s was p 1 ann e d and car r ie1 0 u t wit hother regulating agents, consistingmostly of polymers.
Effect of other regulating agents
The flotation experiments were carriedout with the addition of reagents(polymers) such as guargum Magnafloc-140
The results obtained in the presenceof various regulating agents with0.25 kg/ton of isopropylxanthate, 0.04kg/ton of pine oil and at pH 9.0 withoutdepressant for silica are shown inTable VIII. Guargum was comparatively
Table VIII: Effect of various regulat-ing agents without sodiumsilicate to recover finesthereby recovery
Conditions Ore 1000 gmIPX 0.25 kg/tonpH 9.0
Pine oil 0.04 kg/tonName of regulatingagent and quantity
Grade%
Recovery%
Magnafloc-1400.010 kg/tonMagnafloc-3510.010 kg/ton
Cellulose xanthate0.010 kg/ton
Guargum0.250 kg/ton
more effective in obtaining bettercopper recoveries than other regulatingagents.
In the light of the above, furtherxperiments were carried out with guar-aum at different concentrations bothith and without sodium silicate, and
pH values of the pulp.rect of guargum concentration
The effect of guargum concentrationon the flotability with and withoutsodium silicate is shown in Table IX(a)and IX(b) respectively. There was notmuch variation in copper recovery withincreasing guargum concentration anda dosage of 0.25 kg/ton was found tobe more optimum where the copper reco-very ranged from 89-90%. It was al soobserved that the presence of sodiumsilicate in the pulp improved the gradeby more than 2%.
Effect of guargum concen-tration without sodiumsilicateOre 1000
0.259.00.04
gmkg/tonIPX
pHPine oil
S 1 . GuargumNo. kg/ton1 0.052 0.103 0.154 0.205 0.256 0.307 0.35
Grade%
Recovery%
17.318.716.617.619.918.518.3
83.284.184.586.889.490.388.7
Effect of guargum concen-tration in presence ofsodium silicate
Conditions Ore 1000 gmIP X 0.25 kg/tonSod. silicate .. 1 .5 kg/tonpH 9.0Pine oil 0.04 kg/ton
S 1 . Guargum Grade RecoveryNo. kg/ton % %1 0.05 21 .2 84.32 0.10 22.6 84.23 0.15 22.9 88.44 0.20 22.8 88.75 0.25 23.0 89.56 0.30 23.1 88.87 0.35 22.9 90.0
Effect of pH in the presence of guargumand sodium silicate
few experimentsdifferent pHthe presence
outpulpthe
werevalues
guargum andare shown
Table X. A slight reduction in pHof the pulp was noticed after the addi-tion of guargum. However, the resultsagain confirmed the optimum pH to bearound 9.0.
Effect of pH in the presenceof both guargum and sodiumsilicate
Conditions: OreIPX
1000 gm0.25 kg/ton0.25 kg/ton1.5 kg/ton0.04 kg/ton
GuargumSod. silicate ..Pine oil
S 1 . pH Grade RecoveryNo. % %1 7.0 19.7 85.52 8.0 21. 1 86.23 9.0 23.0 89.54 10.0 22.1 87.0
The above studies resulted in someimprovement in both grade and recoveryby the addition of sodium silicate andguargum at pH 9.0. As discussed earlierthe improvement in grade may be dueto the addition of sodium silicate,a depressant for silica, and betterrecovery due to the pH of the pulp andguargum. Flocculation of fines wasobserved after the addition of guargumbut these flocs may not be stable tofloat completely due to turbulencecaused by agitation and further improve-ment in recovery beyond 90% was notpossible. It is suggested that columnflotation technique may work in thiscase, where the agitation turbulenceis negligible. Further studies on theselines are currently being investigatedin our laboratory.
Chelating agents are powerful, selectiveand specific collectors in flotation.Many researchers have indicated clearlythe possibility of surface chelatesfor floating otherwise difficult mine-rals. Earlier work has reported thecollector action of sodium diethyldithio-carbamate in the flotation of chalco-pyrite5 and copper oxides mainlymalachite3.
In the present, case since theore is a mixture of sulphide and oxideminerals of copper (chiefly chalcopyriteand malachite), the flotation efficiencyof sodium diethyldithiocarbamate wasinvestigated. The effect of the reagentconcentration was studied at pH 9.0with 1.5 kg/ton of sodium silicate and0.04 kg/ton of pine oil. The resultsobtained are presented in Table XIindicative of good grade and recoveryof copper.Though dithiocarbamate belongs
Table X I : Effect of DTC concentrationConditions Ore 1000 gm
Sod. silicate .. 1.5 kg/tonpH 9.0Pine oil 0.04 kg/t
S 1 . DTC Grade RecoveryNo. kg/ton % %1 0.10 19.9 63.32 0.20 19.8 66.23 0.30 20.2 72.14 0.40 19.9 73.85 0.50 21 .0 75.06 0.75 22.7 79.07 1. 00 24.3 85.88 1 .50 24.8 88.39 2.00 24.9 91.410 2.50 25.8 92.3
Jto a category of xanthates, thiouridp.group in diethyldithiocarbamateresponsible for high degree of selecti-vity. Mesomeric electron releas'tendency of (C2H5)2-N- group enhancesthe electron donating ability to metalions to facilitate strong coordinatingbond with metal ion. However, the onlysetback with the use of sodium diethyl-dithiocarbamate is its high cost andconsumption in flotation.Flotation with sodium isopropylxanthatefollowed by sodium diethyldithiocarba-mateSome experiments were conducted atoptimum conditions with xanthate followed
by flotation with DTC mainly to reduce
the consumption of DTC. Five identical
flotation experiments were performed
with xanthate 0.25 kg/ton, 0.15 kg/ton
sodium silicate and 0.04 kg/ton pine
oil at pH 9.0 in the first stage and
the tailings were refloated with dithio-
carbamate (0.05 kg/ton) only. The
average overall grade obtained was
16.8% copper with a recovery of 94.8 %.
The crushing/grinding operations with
Malanjkhand ore body generate more fines
resulting in poor copper recoveries
with lower grades of flotation concen-
trates. The studies carried out on
the ore body have revealed that the
pH of the pulp plays a vital role.
Flotation with sodium diethyldithio-
ORE - Cu : 3.05%
3 x 1 kg
I:+ IPX - 0.25 kg/ton
+Sod. silicate - 1.5 kg/ton
Flotation + Guargum - 0.25 kg/ton
+ pH - 9.0
+Pine oil - 0.04 kg/ton
Float - Cu:21.2%Recovery : 92.7%
+ IPX - 0.1 kg/ton
+ Sod. silicate - 0.5 kg/ton
Float - Cu : 29.4 %Recovery - 92.8%
Overall grade: 29.4 %
Overall recovery: 90.6%
and guargum
Amongst all the above experiments, the
trials with guargum may be considered
more economical and easily adoptable
in commercial plant practice. Specific
experiments were conducted including
cleaning of the float to study the
limits of grade and recovery of copper.
The flow sheet adopted in these trials
and the results obtained are indicated
in Figure 1.
carbamate yielded better results compa-
red to sodium isopropylxanthate. The
addition of modifier viz. guargum,
yielded excellent results for both grade
and recovery of copper possibly through
flocculation of slimes. This technique
could be easily adopted for the flota-
tion of Malanjkhand copper ores.
1. Lane White, Hindustan Copper Limited:
India's Copper Producer, E&MJ , June
1985,p. 26-42.
2. Ghosh, S., Makode, M.N., Raju, M.S.
and Satyanarayana, K. Studies on
the investigation of copper losses
in the flotation plant tailings of
copper concentrator, Malanjkhand
Copper Project Proc. of the Int.
Conf. on Base Metal Tech., Nat. Met.
Lab., Jamshedpur, India, 1989, p.
283-288.
3. Prabhakar, S., Bhaskar Raju, G. and
Khangaonkar, P.R. Studies on the
beneficiation of copper oxide minera-
ls, Proc. XVI Int. Min. Proc. Congo
Stockholm, ed. by K.S. Eric Forssberg,
Elsevier, 1988, p. 1267-1278.
4. Attia, V.A. Surface chemistry of
copper minerals in water, Trans.
Inst. Min. Met., Sec. C, Vol. 84,
1975, p. 221-230.
5. Bhaskar Raju, G and Khangaonkar,
P.R. Electroflotation of chalco-
pyrite fines with sodium diethyl-
dithiocarbamate as collector, Int.
J.Min. Process, Vol.13, 1984, p.211-
221 . (
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