564 STUDY OF SODA EFFECT ON THE SINTERING PROCESS OF LOW TITANIUM SLAG Galymzhan Maldybayev 1 , Madali Naimanbaev 2 , Irina Shadrunova 3 , Nyna Lokhova 2 , Rustam Sharipov 4 ABSTRACT The article presents study results of the sintering process of soda with low-titanium-containing slag, where the slag is produced during processing of titanium magnetite concentrate. The purpose of sintering is to change the mineralogical composition of Ti-containing phases and to obtain a product suitable for chemical separation of ti- tanium dioxide from impurities. The X-ray phase analysis revealed that the obtained titanium slag belonged to the spinel-anosovite type. The factors influencing the sintering process were studied: the slag to soda mass ratio, the process duration, the temperature and the size of slag particles. The thermal analysis of the slag and soda sinter- ing process revealed that the optimum process temperature is 900°C. This temperature ensured the formation of sodium titanates and a sinter of sufficient porosity. The results demonstrate that the effective decomposition process requires a pretreatment of titanium slag by fine grinding. It was found that grinding of titanium slag particles to 40 µm contributes to more complete decomposition of the anosovite with a formation of sodium titanates. It was found that during the sintering of titanium slag with soda at a mass ratio of slag:soda = 1:1.05, decomposition of the ano- sovite occurs, and practically all titanium is bound to sodium titanates. The optimum conditions of the process are determined as follows: the mass ratio of slag to soda is 1:1.05, the sintering temperature is 900°C, the duration is 60 minutes and the particle size of the slag is 40 μm. Titanium-containing slag phases are converted into Na 2 TiO 3 and Na 8 Ti 5 O 14 during the sintering. The presence of a significant amount of silicon dioxide and the sodium-magnesium silicate phase was observed in the sinter. Electron microprobe analysis showed that impurity elements are adsorbed on the particles of the formed Na 2 TiO 3 . Keywords: titanium magnetite concentrate, titanium slag, soda, sintering, sodium titanates, anosovite, silicates. Received 17 Octobet 2017 Accepted 10 January 2018 Journal of Chemical Technology and Metallurgy, 53, 3, 2018, 564-571 1 Kazakh National Research Technical University After K.I. Satpayev (KazNITU) Satpayev Str. 22a, Almaty city, 050013, Republic of Kazakhstan E-mail: [email protected]2 JSC Institute of Metallurgy and Enrichment, Shevchenko str./Valikhanov str., 29/133 Almaty city 050010, Republic of Kazakhstan. 3 Institute of Comprehensive Exploitation of Mineral Resources Russian Academy of Sciences, Kryukovsky impasse Moscow, 4111020, Russian Federation 4 JSC Kazakh - British Technical University, Tole bi str. 59 Almaty city, 050000, Republic of Kazakhstan INTRODUCTION Titanium dioxide is widely used as a pigment in paints, paper and cosmetic products, as well as in high-tech devices such as solar cells, semiconductors, biomedical equipment and air-cleaners [1]. There are two main industrial technologies for the production of titanium dioxide pigment - sulfuric acid and chlorine, in which the main raw material is high-titanium-containing slag and/or rutile, obtained from ilmenite concentrate. In the sulfuric acid process, the Ti-containing product is treated with concentrated sulfuric acid to produce a sulfate solution that undergoes hydrolysis and precipi- tation of titanium dioxide, and the iron passes into the solution as sulfates. By chlorine technology, rutile is first exposed to chlorine gas, titanium passes into the form of chloride and further it is converted to a pigment with the removal of chlorine at high temperature in a mixture
Transcript
Journal of Chemical Technology and Metallurgy, 53, 3, 2018
564
STUDY OF SODA EFFECT ON THE SINTERING PROCESS OF LOW TITANIUM SLAG
The article presents study results of the sintering process of soda with low-titanium-containing slag, where the slag is produced during processing of titanium magnetite concentrate. The purpose of sintering is to change the mineralogical composition of Ti-containing phases and to obtain a product suitable for chemical separation of ti-tanium dioxide from impurities. The X-ray phase analysis revealed that the obtained titanium slag belonged to the spinel-anosovite type. The factors influencing the sintering process were studied: the slag to soda mass ratio, the process duration, the temperature and the size of slag particles. The thermal analysis of the slag and soda sinter-ing process revealed that the optimum process temperature is 900°C. This temperature ensured the formation of sodium titanates and a sinter of sufficient porosity. The results demonstrate that the effective decomposition process requires a pretreatment of titanium slag by fine grinding. It was found that grinding of titanium slag particles to 40 µm contributes to more complete decomposition of the anosovite with a formation of sodium titanates. It was found that during the sintering of titanium slag with soda at a mass ratio of slag:soda = 1:1.05, decomposition of the ano-sovite occurs, and practically all titanium is bound to sodium titanates. The optimum conditions of the process are determined as follows: the mass ratio of slag to soda is 1:1.05, the sintering temperature is 900°C, the duration is 60 minutes and the particle size of the slag is 40 μm. Titanium-containing slag phases are converted into Na2TiO3 and Na8Ti5O14 during the sintering. The presence of a significant amount of silicon dioxide and the sodium-magnesium silicate phase was observed in the sinter. Electron microprobe analysis showed that impurity elements are adsorbed on the particles of the formed Na2TiO3.
Journal of Chemical Technology and Metallurgy, 53, 3, 2018, 564-571
1 Kazakh National Research Technical University After K.I. Satpayev (KazNITU) Satpayev Str. 22a, Almaty city, 050013, Republic of Kazakhstan E-mail: [email protected] JSC Institute of Metallurgy and Enrichment, Shevchenko str./Valikhanov str., 29/133 Almaty city 050010, Republic of Kazakhstan.3 Institute of Comprehensive Exploitation of Mineral Resources Russian Academy of Sciences, Kryukovsky impasse Moscow, 4111020, Russian Federation4 JSC Kazakh - British Technical University, Tole bi str. 59 Almaty city, 050000, Republic of Kazakhstan
INTRODUCTION
Titanium dioxide is widely used as a pigment in paints, paper and cosmetic products, as well as in high-tech devices such as solar cells, semiconductors, biomedical equipment and air-cleaners [1]. There are two main industrial technologies for the production of titanium dioxide pigment - sulfuric acid and chlorine, in which the main raw material is high-titanium-containing
slag and/or rutile, obtained from ilmenite concentrate. In the sulfuric acid process, the Ti-containing product is treated with concentrated sulfuric acid to produce a sulfate solution that undergoes hydrolysis and precipi-tation of titanium dioxide, and the iron passes into the solution as sulfates. By chlorine technology, rutile is first exposed to chlorine gas, titanium passes into the form of chloride and further it is converted to a pigment with the removal of chlorine at high temperature in a mixture
of air and oxygen. Currently, sulfuric acid technology is used by Chinese plants with a total capacity of 130,000 tons per year, as well as JSC “Crimean Titan” with a capacity of 80 thousand tons/year [2, 3]. The enterprises of the main producers of pigmentary titanium dioxide are using both sulfuric acid, and chlorine processes, prefer-ring the latter. Thus, the total capacity of the factories of “Millennium Inorganic Chemicals Inc.” company on the first technology is 182 thousand tons/year, and on the second - 350 thousand tons/year. The Kronos Inc. (a subsidiary of “NL Industries Inc.”) produces 24 thousand tons/year by sulfuric acid method, and by chlorine - 230 thousand tons/year of pigment. It should be noted that the factories of “E.I. du Pont de Nemours & Co. Inc.” (“DuPont”) - the largest producer of pigmentary tita-nium dioxide with a total capacity of 1,000,000 tones/year - operating only on chlorine-technology [3]. Since chlorine technology requires high requirements for the initial titanium material and limits the impurity content, hydrometallurgical methods for the production of pig-mentary titanium dioxide have been developed in the last 10 years as an alternative. Many of them lies in the acid leaching of titanium-enriched raw materials [4 - 7].
In 2008, Austpac technology, collectively referred to as “ERMS SR”, including hydrochloric acid leaching of ilmenite, was successfully tested on an industrial scale to produce high purity synthetic rutile [8]. Other studies are based on the sintering of low-Ti-containing slag with various alkaline reagents. When titanium slag is sintered with sodium hydroxide, titanium, silicon, vanadium and aluminum form vanadates, silicates and sodium aluminates. During the aqueous leaching of the sintered vanadium, silicon and aluminum are converted to solution, and the insoluble titanates remain in the sediment and dissolve in sulfuric or hydrochloric acid with further release of titanium acid. The resulting product is converted to the white pig-ment of titanium dioxide by calcination [9 - 12].
In the studies [13, 14], the production of rutile from titanium slag containing 72 - 82 % of TiO2 is based on hydrometallurgical processing of sintering product of titanium slag with calcined soda. When processing the sinter by water, according to the experiment [13], sili-con passes to the solution, and, according to the [14], at aqueous leaching of the sintering product, chrome and silicon extract to the solution in the form of chromates and silicates. The discrepancy in the results can be ex-plained by the fact that, due to the significant discrepancy
between the chemical and mineralogical compositions of titanium slags obtained during the processing of ilmenite and titanomagnetite concentrates of various deposits, during the sintering of titanium slags with soda, phases differing in mineralogical composition are formed.
The discrepancy in the results can be explained by the fact that because of the significant discrepancy between the chemical and mineralogical compositions of titanium slags obtained during the processing of il-menite and titanium magnetite concentrates of various deposits during the sintering process of titanium slag with soda, phases, differing in mineralogical composi-tion, are formed.
The aim of the presented work is to study the be-havior of titanium phases and accompanying elements in the sintering process of titanium slag with soda, as well as determining the influence of the main factors on the formation of sodium titanates.
ЕXPERIMENTAL Methods of analysis
X-ray data were obtained using the apparatus BRUK-ER D8 ADVANCE. X-ray fluorescence analysis was per-formed on a spectrometer with Venus 200 wave dispersion PANalyical B.V. (Holland). The chemical analysis of the samples was carried out on an optical emission spectrom-eter with inductively coupled plasma Optima 2000 DV (USA, PerkinElmer). Mapping of the elemental and phase composition of the samples was carried out on a JXA-8230 electron microprobe analyzer from JEOL (Japan). The ther-mal analysis was performed using a synchronous thermal analysis instrument STA 449 F3 Jupiter. The results were processed using the NETZSCH Proteus software.
Materials l titanomagnetite concentrate of the Tymlay deposit,
provided by “Tenir Logistic” LLP (Republic of Kazakh-stan), chemical analysis is given in Table 1;
l the Shubarkul special coke containing 67.5 mass % carbon and 5.8 mass % volatiles; ash content of 4.0 mass %; humidity 17,9 %;
l sodium carbonate (soda ash), grade “chemical pure”.
Experimental procedure and instrumentsTitanium slag was obtained applying conditions il-
lustrated in [15]. During the sintering process, a sample of titanium slag crushed to a particle size of 63 μm was
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thoroughly mixed with the required amount of anhydrous sodium carbonate in an alundum crucible and placed in an oven. According to the results of the chemical analysis of titanium slag for the formation of sodium titanate, the theoretical mass ratio of slag:soda should be close to 1 : 0.5, but since the reaction takes place in the melted soda, an excess of sodium carbonate is needed; therefore, in some studies, the mass ratio of slag to soda is taken equal to 1:0.85. Melting of titanomagnetite concentrate and sintering of titanium slag with soda were carried out in a chamber furnace XD-1700M at t = 900°C, the temperature stability under steady-state thermal condi-tions was within ± 2°С.
RESULTS AND DISCUSSIONThe chemical composition of the obtained titanium
slag is given in Table 1. The results of X-ray phase analysis (XRD) of titanium slag (Table 2) indicate that it belongs to the spinel-anosovite type. According to [16], during oxidative roasting, the anosovite lattice is destroyed in the interval t = 400 - 900°C with the release of titanium and impurities contained in the ansovite.
Anosovit is a solid solution composition: n[MeO
· 2TiO2] · [Me2O3 · TiO2], where MeO is FeO, MnO, MgO, and Me2O3 is Al2O3, Cr2O3, Ti2O3, V2O5. It can also include a phase, radiographically characterized as a system of Fe-Mg-Ti-O [17].
At least 3 types of anosovite have been established by electron microscopy. In the first case, iron and chro-mium are the main constituents of the formula: [(Fe0,45 · Ti2,05) O5] · [(Cr0.61 · Ti2,39) O5]; in the second - magnesium and manganese: (Mn0.94 · Mg · Ti1.06) O5.
The presence of an anosovite whose composition is characterized by a multicomponent: magnesium, vana-dium, manganese, iron and aluminum are present:[(Fe0.67 · Mg0.86 · Mn0.47 · Ti) O5] · [(Al1.03 · V0, 97 · Ti) O5].
It is known [18] that an anosovite with an increased aluminum content is a difficult-to-hide component.The formation of sodium titanate, contaminated with copper and iron compounds, has been established. It is deter-mined that a small amount of anosovite is present in the slag in the clusters with nepheline. Metal iron with im-purities of titanium, copper and zinc were also detected. Experiments for the effect of temperature on the process of sintering of titanium slag with sodium carbonate at a mass ratio of slag:soda = 1:1 were carried out by thermal
Product Ti Fetotal Si Al Mg Ca Na Mn V Cr C Titanium-magnetite concentrate
analysis (Fig. 1). The amount of the sample was 200 mg, corundum crucible (Al2O3), heated at 10°С for a minute, argon-gas atmosphere, coolled at 15°С for a minute.
On the DTA curve (Fig. 1), the melting of soda is reflected by the endothermic effect with maximum de-velopment at t = 858°C, and subsequent thermal effects reflect the formation of sodium titanates. The manifesta-tion is an intense endothermic effect with an extremum at t = 974°C, which characterizes the melting of the formed sodium dititanate Na2Ti2O5, and the endothermic peak at 1131°C - reflection of the melting of sodium trititanate Na2Ti3O7. The formation of sodium silicate should be noted, the existence of which confirms the endo-effect of melting with a maximum at t = 1094°C.
An increase in the firing temperature above 900°C leads to the formation and crystallization of the vitreous phase, which is characterized by an exothermic effect
with a maximum at 1084°C. The observed process leads to a reflow of the sinter, which makes it difficult to pro-cess. Fig. 2 shows a fragment of the derivatogram of the sintering process of a mixture of titanium slag with soda, reflecting the change in the mass of the sample during heating. The loss of sample mass, which equals to Δm = -13.9 % at t = 124°C, is due to the fact that during the preparation of the charge, adsorption of water vapor from the air on the developed surface of the material occurs, and during heating it is removed. By carrying out further studies, the calculation of soda consumption was carried out taking this fact into account.
A sharp loss of sample mass begins at t = 650°C, and at 870°C it is 11.8 %. In this temperature range, the processes of decomposition of the anosovite into oxides and their interaction with soda occur on top of each other, while part of the soda sublimes. The basic
Fig. 1. Derivatogram fragment of the sintering process of titanium slag with soda.
Fig. 2. Fragment of the derivatogram of the sintering process of titanium slag with soda.
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interaction of soda with the components of the slag and the products formed during heating ends at t = 940°C. The mass loss of the sample at t > 940°C occurs mainly due to the sublimation of sodium carbonate.
Thus, the temperature of sintering process of titani-um slag with soda (900°C) is sufficient for the formation of sodium titanate and provides a porous sinter easily separable from the crucible walls.
Effect of the slag particle sizeThe effect of the slag particle size on the process
of decomposition of titanium slag was studied in the interval dsl = 40 - 160 microns with a sintering time τ = 90 min, a temperature of 900°C and a mass ratio of slag : soda = 1 : 0.85. The results of the experiments are given in Table 3, from which it can be seen that as the particle size increases, the yield of the sinter increases from 77 to 81.3 %.
It is known that the smaller is the particles of re-acting substances, the higher is the reactivity of the system. Therefore, the loss of mass of the charge, in addition to the sublimation of soda, is affected by the amount of charge components involved in the reaction with sodium carbonate that proceeds with the release of carbon dioxide, for example:2TiO2 + Na2CO3 = Na2Ti2O5 + CO2↑,SiO2 + Na2CO3 = Na2SiO3 + CO2↑.
The study of the influence of the particle size at ag-glomeration sintering process of titanium slag with soda on the formation of sodium titanates is interesting for the practice. For clarity in Table 4, based on the results of the X-ray phase analysis, the change in the content of only titanium-containing phases in them is considered. It can be seen that the figures of the decomposition of
the Na-Mg-Ti-O system at dsl = 40 - 63 μm reach the highest values, so pretreatment of the slag requires its fine grinding to efficiently conduct the decomposition process. Thus, particle size reduction of titanium slag to 40 μm promotes a more complete decomposition of the anosovite with the formation of sodium titanates.
Effect of the sintering duration on the formation of sodium titanates
In the course of this study, a series of experiments were performed with different time periods in the range of τ = 30 - 90 min at t = 900°C, dsl = 40 μm and mass ratio slag : soda = 1 : 0.85, the results of which are given in Tables 5 and 6. Data on Tables 5 and 6 show that after 60 minutes of sintering, the process of decomposition of titanium slag is slowed down, while ~ 85 % of titanium is present as sodium titanates. An increase of the process duration did not show a significant effect, so the optimal time for sintering process of titanium slag with soda, necessary for its decomposition, is 60 minutes.
Influence of the mass ratio of slag : soda on the for-mation of sodium titanates
A study of the effect of the specific consumption of soda on the decomposition of titanium slag with the for-mation of sodium titanates during sintering was carried out at t = 900° C, τ = 60 min. Table 7 shows the changes in the chemical composition of the sinter, depending on the amount of soda in the charge, from which it follows that when soda is introduced into a charge of 10.5 g per 10 g of slag, the loss of Na in the form of sodium carbonate is 10 - 12 %.
Table 8 shows the results of X-ray phase analysis of the sinters, from which it can be seen that even a
Table 3. Effect of the size of slag particles on the results of sintering process of titanium slag with soda.
small amount of soda in the charge promotes the de-composition of the Fe-Mg-Ti-O system. In addition, in the sintering process of titanium slag with soda at their mass ratio of 1 : 0.85, decomposition of the anosovite occurs in a partial manner, and with increasing soda consumption to a mass ratio of 1 : 1.05, practically all
titanium is bound to sodium titanates. X-ray spectro-scopic microanalysis of sintered titanium slag with soda, having a phase composition, is given in Table 8. The presence of perovskite particles CaTiO3 and grains of an aluminum-containing anosovite (in a small amount) has been established.
Table 4. Influence of the size of slag particles on the decomposition of anosovite based on the X-ray phase analysis.
The size of slag particles, μm The percentage composition of the system in the sinter, %
The physical and chemical studies of titanium slag obtained by smelting the titanomagnetite concentrate of the Tymlay deposit showed that it belongs to the spinel-anosovit type. Radiographic analysis of sintered titanium slag with soda products allowed to determine the influence of the main factors on the process and to establish the optimal sintering regime: mass ratio of slag : soda = 1 : 1.05; temperature of the process - 900°С; duration of the process - 60 minutes; particle size of the slag - 40 μm.
It was revealed that in the selected conditions of sintering titanium slag with soda the most persistent component is perovskite.
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