Ind. Eng. Chem. Res. 2005, 44, 3213-3219
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SEPARATIONS Sulfate Removal from Alunitic Kaolin by Chemical Method Mine O 2 zdemir* and Halil C ¸ etis¸ li Faculty of Engineering and Architecture, Osmangazi University, 26480, Eskisehir, Turkey, and Faculty of Arts and Sciences, Pamukkale University, 20020, Denizli, Turkey
The removal of sulfate from alunitic kaolin by a chemical method, in which alunitic kaolin + potassium compound (KCl and KOH) was calcined at different temperatures and sulfate was extracted by distilled water, was studied in a batch reactor. The effects of calcination temperature, sample type, potassium compound amount, and sample preparation method on the sulfate removal were investigated. Sulfate removal yield varied with the selected parameters relative to the completion of the solid-phase reaction in which the sulfate in the alunitic kaolin was converted to soluble potassium sulfate. Maximum sulfate removal yield was obtained under the following working conditions: calcination temperature, 700 °C; sample type, alunitic kaolin + KCl; potassium compound amount, 17.8% (15% more than the stoichiometric ratio); and solution phase method used for sample preparation. Maximum sulfate removal yield was 97%. By this way, the sulfate content of alunitic kaolin was decreased from 12.97% to below 1%. 1. Introduction Kaolin is a naturally occurring earth material mainly containing the mineral kaolinite, Al2O3‚2SiO2‚2H2O. The impurities in kaolin are cations such as sodium, potassium, calcium, magnesium, iron, titanium, and manganese, and anions such as sulfate, carbonate, and phosphate, according to the formation conditions in nature. Kaolin containing more than 3% SO3 is known as alunitic kaolin. There are significant kaolin and alunite reserves in Turkey. These kaolin reserves contain alunitic impurities which hinder their usage in the ceramics, paper, and cement industries. Only onefourth of the kaolin reserves in Turkey have properties suitable for use in these industries. Turkey has over 13 million tons of alunitic kaolin reserves, which are located in the western part of Anatolia. It is being estimated that the kaolin and alunite demands will increase with rapid developments in the ceramics, paper, and fertilizer industries in our country. DPT (the State Planning Organization of Turkey) encourages researchers to study the beneficiation of alunitic kaolin.1-3 Therefore, the sulfate content of alunitic kaolin must be removed for making the kaolin a useful raw material in the ceramic, paper, cement, and alumina industries. Furthermore, the removed potassium sulfate is a useful raw material in fertilizer industries. A large number of studies were done on kaolin4-13 and alunite14-25 (K2O‚3Al2O3‚4SO3‚6H2O) for using them as raw materials in different industries. The study of the sulfate removal from alunite is based on two methods. In the first method, alunite is calcined at about 900 °C according to the following reaction: * To whom correspondence should be addressed. Tel.: + 90222-239 3750. Fax: + 90-222-239 3613. E-mail: mnozdemi@ ogu.edu.tr.
Al2(SO4)3‚K2SO4‚4Al(OH)3 f 3Al2O3 + K2SO4 + 3SO3 + 6H2O (1) Thus, the aluminum sulfate present in the structure is decomposed to sulfur trioxide and aluminum oxide. From the solid residue obtained after this calcination, potassium sulfate, the only soluble component, may be extracted with hot water and the insoluble residue containing alumina and silica remains. Therefore, the produced alumina should be purified. However, R-alumina formed at high temperature does not dissolve readily in caustic solutions.14,15,18 Because of the increase in cost and the elimination of the kaolin’s plastic property by calcination at a high temperature, this method does not appear to be suitable technically and economically. In the other method, alunite is thermally decomposed at a lower temperature (500-600 °C) in the presence of alkali metal salts according to the following reaction:
Al2(SO4)3‚K2SO4‚4Al(OH)3 + 6KCl f 3Al2O3 + 4K2SO4 + 6HCl + 3H2O (2) The aluminum sulfate in the structure is completely converted to potassium sulfate and then the potassium sulfate is obtained at a high ratio by extraction with hot water. In addition, the γ-alumina produced at a lower temperature is more soluble in alkali than R-alumina.20-23 Therefore, the second method appears to be attractive. There are a few studies concerning the sulfate removal from alunitic kaolin. In these studies, the sulfate compositions of the alunitic kaolins were decreased from 2-13% SO3 to 0.4-3% SO3 only by calcination at 900 °C,26 calcination was performed with KCl and NaCl at 700 °C,27 and flotation was applied by using sodium oleate as collector.28 Despite these studies, we have found no detailed study on sulfate removal from alunitic kaolin by a
10.1021/ie040177s CCC: $30.25 © 2005 American Chemical Society Published on Web 03/19/2005
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Table 1. Chemical Composition of Alunitic Kaolin (%, w/w)
Al2O3
SiO2
K2O
SO3
SO4
H2O
38.05
34.75
2.41
10.82
12.97
13.97
Table 2. Parameters Employed in parameter sample type
Experimentsa value
AKb
AK + KCl AK + KOH
potassium compound amount KCl (%, w/w) 14.7 15.5 16.2 17.0 17.8 KOH (%, w/w) 11.0 11.6 12.2 12.8 13.4 sample preparation method BG BG AG AG SPc
SP
a
Calcination temperature for all samples was 100-1000 °C. b AK: alunitic kaolin. c Sample preparation method used in Figures 1 and 3-11.
chemical method. For that reason, the aim of this study was to investigate sulfate removal from alunitic kaolin calcined with KCl and KOH by extraction in distilled water. 2. Materials and Methods The alunitic kaolin used in the study was provided from the Bursa-Mustafakemalpasa Region, Turkey. It was crushed, ground, and sieved by ASTM standard sieves and dried at 110 °C for 2 h. The particle size fraction between 100 and 120 mesh (average 0.13 mm) was used in the experiments. The chemical composition of the alunitic kaolin shown in Table 1 was determined by classical gravimetric method in which silicates are melted with sodium carbonate. The experimental parameters examined were calcination temperature, sample type, kind and amount of potassium compound, and the method of sample preparation, as given in Table 2. The method of sample preparation used in most studies (Figures 1 and 3-11) is asterisked. The samples used in the experiments were prepared with and without a potassium compound (KCl and KOH) separately. The samples containing potassium compounds were produced by the three different preparation methods. In the first (BG) and the second (AG) methods, the dried alunitic kaolin was mixed with the solid potassium compound in a ball grinder and an agate mortar. In the last (SP) method, it was mixed with the aqueous solution of potassium compound; the sample was dried in open air at room temperature for 48 h and
then dried in an oven at 110 °C for 4 h. In all preparation methods, potassium compounds were added in the stoichiometric ratio, 5% less than the stoichiometric ratio, and 5%, 10%, and 15% more than the stoichiometric ratio by weight. These samples were characterized by differential thermal analysis (DTA) and X-ray diffraction (XRD). DTA curves were recorded using Netsch 404 EP equipment with R-Al2O3 as a reference material, in the temperature range between the room temperature and 1200 °C, and in air atmosphere at a heating rate of 10 °C/min. XRD was carried out in Rigaku GeigerflexD-Maxll TC equipment with Cu KR radiation. In the first part of experiments related to the thermal decomposition of samples, 3 g of sample was placed in an open porcelain crucible. This crucible was left in a cold Heraus furnace. The sample was calcined at each working temperature for 1 h in the Heraus furnace, in air atmosphere at a heating rate of 10 °C/min, and cooled in a desiccator. Then it was weighed in order to determine its weight loss statically. In the second part of experiments related to the extraction from samples, extraction experiments were carried out in a batch heater-jacketed reactor of 150mL capacity. The reactor was kept at desired temperatures by circulating water from a MGW Lauda model constant-temperature bath with (0.1 °C sensitivity. The reactor was fitted with a condenser to prevent losses by evaporation. A Heidolph MR 3001 model magnetic stirrer was used for constant stirring. In the extraction experiments, first 100 mL of distilled water was placed in the reactor and it was heated to the reaction temperature of 75 °C. Then, the previously calcined sample was added into the reactor. The reactor content was stirred at 1250 rpm for 2 h and filtered. The sulfate content in the filtrate was determined by gravimetric analysis using BaCl2 solution. The aluminum content was determined by volumetric analysis using EDTA solution and xylenol orange.29,30 The extracted amounts of sulfate and aluminum were calculated in terms of sulfate and aluminum in alunitic kaolin, respectively. For each experimental condition, the experiment was repeated twice, and the arithmetic average of the results of the two experiments was given. Chemical analysis, DTA, and XRD were applied to the
Figure 1. DTA curve of (a) the alunitic kaolinite, (b) the alunitic kaolinite + 16.2 KCl, and (c) the alunitic kaolinite + 12.2 KOH.
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Figure 3. Effect of calcination temperature on the weight loss. Figure 2. XRD of the alunitic kaolinite.
remaining solid product for observing the chemical and structural changes occurring in alunitic kaolin after extraction. 3. Results and Discussion 3.1 Thermal Decompositions of Alunitic Kaolin Samples. The chemical analysis, DTA, and XRD of the clay show that it consists of alunitic kaolin (Table 1, Figures 1a and 2). According to these analyses, the chemical formula of alunitic kaolin can be given as K2SO4‚Al2(SO4)3‚4Al(OH)3‚4[2(Al2O3 2SiO2 2H2O)] (I). Thus, the alunitic kaolin consists of 27.80% alunite and 72.20% kaolinite approximately. In the DTA curve of the alunitic kaolin, two endothermic peaks at 560 and 790 °C and an exothermic peak at 980 °C are observed (Figure 1a). The first peak indicates the dehydroxylation of kaolinite and alunite and the formation of metakaolinite, and the second peak indicates the decomposition of aluminum sulfate in alunitic structure into alumina and sulfur trioxide. The third peak at 1000 °C is related to the conversion of γ-alumina to R-alumina and the formation of mullite (3Al2O3‚2SiO2). According to DTA results, the thermal decomposition of alunitic kaolin up to 850 °C can be given by the following reaction:6,14-18
I f K2SO4 + 11Al2O3 + 16SiO2 + 3SO3 + 22H2O (3) The weight loss of alunitic kaolin is small up to 450 °C, and it is about 14% within 450-650 °C in which the first endothermic peak appears. Then, weight loss increases gently in the range 600-700 °C. After 700 °C, it increases largely by the decomposition of aluminum sulfate. Finally, after 850 °C, at which the decomposition of sulfate was completed, the total weight loss is increased slightly (Figure 3). Alunitic kaolin was mixed with KCl and KOH for removal of the sulfate present in its structure by chemical method. The thermal decompositions of alunitic kaolin + KCl and alunitic kaolin + KOH can be written as follows:7,8,20-23
I + 6KCl f 4K2SO4 + 11Al2O3 + 16SiO2 + 6HCl + 19H2O (4) I + 6KOH f 4K2SO4 + 11Al2O3 + 16SiO2 + 25H2O (5) Two endothermic peaks that appeared in the DTA curve of the alunitic kaolin are also observed in the DTA curve of the alunitic kaolin + KCl. These endothermic peaks
are wider than those of the alunitic kaolin (Figure 1b). This is due to hydrolysis of KCl during the dehydroxylation and during the decomposition of aluminum sulfate. No peak below its dehydration temperature suggests that alunitic kaolin does not react with KCl in this region. Similar behaviors were also observed in other studies.9,11,13,22,23 It was reported that this reaction was started with the dehydroxylation of clay and accelerated because of high solubility of the salt and small size of the alkali ion, and that the water liberated dissolved adjacent salt particles and catalyzed the reaction.8 As shown in Figure 1c, the DTA curve of the alunitic kaolin + KOH has three endothermic peaks. The effect of KOH on alunitic kaolin is more than that of KCl. This situation is brought about by the high solubility of KOH in water. KOH has a lower melting point than the dehydroxylation temperature, and the first peak that appeared at 300 °C can represent the melting of KOH. Furthermore, before its dehydroxylation, alunitic kaolin can react with KOH in the presence of free water in the alunitic kaolin + KOH without releasing the hydroxyl content. As given in Figure 3, the weight losses of the samples of alunitic kaolin + potassium compound are higher than that of alunitic kaolin alone up to 650 °C and at 650 °C due to the volatilization of HCl and water coming from the reaction with KCl and with KOH, respectively, and the weight losses are suppressed above 650 °C. The total weight loss of alunitic kaolin + KCl below and at 800 °C is lower than the theoretical value (19.24%). The results show that alunitic kaolin + KCl decomposes according to eq 4. Previous researchers found that the temperatures of DTA peaks varied within 500-600 °C according to the type of potassium compound and its weight loss was higher than that of natural clay, and they observed that HCl was formed only after the release of the hydroxyl content of the kaolin.7-11 Thus, the release of the hydroxyl content as water from the structure and the conversion of the sulfate in alunitic structure to potassium sulfate occur simultaneously or consequently. The total weight loss of alunitic kaolin + KOH below and at 800 °C is higher than the theoretical value (15.52%). According to this result and DTA of the samples, the alunitic kaolin + KOH do not decompose with respect to eq 5. The weight loss of the sample at a definite calcination temperature varies with respect to the amount of potassium compound in the sample and the methods of sample preparation (Figure 4 and Table 3). This situation indicates that the conversion of solid phase reaction increases with the amount of potassium compound and the SP method. The potassium cation required for the solid phase reaction is supplied easily by SP method due to the preparation of samples at
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Figure 4. Effect of potassium compound amount on the weight loss.
Figure 6. Effect of KCl amount and calcination temperature on the sulfate removal yield.
Table 3. Effect of Sample Preparation Method on the Weight Loss (sample type ) alunitic kaolin + KCl; potassium compound amount ) 16.2%) calcination temperature (°C)
BG
weight loss (%) AG
SP
600 650 700
14.01 14.54 15.12
12.57 14.58 15.85
15.35 15.56 16.04
solution phase, and thus its diffusion rate into alunitic kaolin increases. 3.2 Extraction of Sulfate from Alunitic Kaolin Samples with Distilled Water. To compare the chemical treatment with the calcination treatment in terms of the sulfate removal yield, the alunitic kaolin without a potassium compound was calcined within 100-1000 °C for 1 h, and extracted with distilled water at a temperature of 75 °C for 2 h. The experimental sulfate removal yields were plotted against the calcination temperatures (Figure 5). The thermal treatment is unsuccessful in extraction of sulfate from the alunitic kaolin as seen in Figure 5. The maximum sulfate removal yield of about 24% is reached at a calcination temperature of 650 °C. Beyond this temperature sulfate removal yield decreases due to vaporization of the sulfur trioxide resulting from the decomposition of sulfate in alunitic structure. It is not possible to take sulfate into the solution from the alunitic kaolin by calcination alone. When the alunitic kaolin is calcined at temperature as high as 1000 °C, it is possible to remove all of the sulfate in the structure. However, it is clear that the solid product obtained does not have kaolin properties since the structure collapses completely at this temperature and it transforms into mullit as discussed in Section 3.1.6 To observe the effect of calcination temperature on the sulfate removal yield, experiments were carried out in the ranges of 500-800 °C and 100-800 °C using KCl and KOH as potassium compound, respectively, because
Figure 5. Effect of calcination temperature on the sulfate removal yield.
Figure 7. Effect of KOH amount and calcination temperature on the sulfate removal yield.
alunitic kaolin + KOH decomposes at a lower temperature than that of alunitic kaolin + KCl. The calcination temperature is an important parameter affecting the sulfate removal yield for alunitic kaolin + potassium compound as shown in Figures 6 and 7. The sulfate removal yields increase from 41 to 95% over the range of 500-700° C and from 74 to 99% over the range of 100-700° for alunitic kaolin + 16.2% KCl and alunitic kaolin + 12.2% KOH, respectively. These yields increase because of the conversion of the sulfate in the alunitic structure into soluble potassium sulfate at these calcination temperatures. Similar behavior was also observed in another study.27 When KCl is used as the potassium compound, the calcination temperature has a large effect on the sulfate removal yield. As indicated in Figure 5, the chemical substances added to the alunitic kaolin are one of the important parameters for conversion of the sulfate in alunitic structure into a soluble compound. The chemical substance added must bind sulfate stronger than alumina and form a water-soluble product. While the sulfate removal yields are about 24 and 19% for the alunitic kaolin calcined at 650 and 700 °C, respectively, those of the alunitic kaolin calcined at 700 °C adding KCl and KOH in 5% less than the stoichiometric ratio (14.7% KCl and 11.0% KOH) are about 90 and 96%, respectively (Figures 6 and 7). Thus, in the case of using potassium compound there is an increase of about 300400% in the sulfate removal yield in comparison with alunitic kaolin calcined at 650 and 700 °C. The sulfate removal yields increase with increasing amount of potassium compound. The low calcination temperature leads to large effect of potassium compound on the sulfate removal yield. In the range of 14.7-17.8% KCl, while sulfate removal yield increases as much as 22% at 500 °C, it increases as much as 8.4% at 700 °C (Figure 6). Also, they are 17% at 500 °C and 3.9% at 700 °C in the range of 11.0-13.4% KOH (Figure 7). The maximum sulfate removal yields of approximately 97% and 99%
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Figure 8. Effect of sample type on the aluminum extraction yield. Table 4. Effect of Sample Preparation Method on the Sulfate Removal Yield (sample type ) alunitic kaolin + KCl; potassium compound amount ) 16.2%) sulfate removal yield (%) AG SP
calcination temperature (°C)
BG
600 650 700
55.36 63.81 61.77
50.36 80.39 92.97
74.45 81.18 95.16
are obtained at 700 °C by calcination of samples containing potassium compound in 15% more than the stoichiometric ratio for 17.8% KCl and 13.4% KOH, respectively. As seen in Figures 6 and 7, the amount of KCl in 5% more than the stoichiometric ratio (16.2% KCl and 12.2% KOH) can be accepted as the optimum potassium amount. The sulfate removal yields obtained in this case are about 95% and 99% for the respective samples at a calcination temperature of 700 °C. Even more than 95% of the sulfate is extracted in the sample containing KOH in 5% less than the stoichiometric ratio. When KOH is used as potassium compound instead of KCl, the sulfate removal yield increases as shown in Figure 5. A large difference was observed in the sulfate removal yields between alunitic kaolin + KCl and alunitic kaolin + KOH at calcination temperature below 650 °C. This result is in agreement with the data of weight loss, and indicates that the fractional conversion of the solid phase in the sample containing KOH is high below this temperature. However, KOH in this sample melts below the dehydroxylation temperature during calcination, and the calcined sample has a hard mass
preventing the extraction treatment. Thus, before extraction, it is necessary to grind this calcined sample. For that reason, the use of KCl instead of KOH as potassium compound is suitable. The sulfate removal yield varies according to the sample preparation method for sample containing a definite amount of KCl calcined at the given temperature (Table 4). The effect of sample preparation methods on the sulfate removal yield were examined using alunitic kaolin + KCl samples prepared by three different sample preparation methods, namely in a ball grinder in solid phase (BG), in an agate mortar grinder in solid phase (AG), and in solution phase (SP), in which these samples are calcined in the temperature range of 500-800 °C. The sulfate removal yields are lower for the samples prepared by the BG and AG methods than for those prepared by the SP method. These results show that the sulfate removal from the alunitic kaolin + potassium compounds depends on the completion of the solid-phase reaction at the high fractional conversion. To control whether aluminum was taken into the solution or not, the amount of aluminum in the solution was determined. The results obtained are given in Figure 8. The maximum aluminum extraction yield is found as about 5.6% at 650 °C. After this temperature the aluminum extraction yield decreases. This is due to the formation of the less soluble alumina. The amount of aluminum extracted from alunitic kaolin + potassium compound is much lower than that of the alunitic kaolin. This situation shows that the aluminum in the structure formed by the thermal decomposition of the alunitic kaolin + potassium compound remains in the form of insoluble alumina in the solid containing silica. 3.3 Chemical and Structural Changes occurring in Alunitic Kaolin + Potassium Compound after Extraction. Chemical analysis, DTA, and XRD were applied to the solid product remaining after sulfate removal from samples prepared at the optimum conditions as explained in Section 3.2. These analysis results are given in Table 5 and Figures 9-11. As can be seen in Table 5, the sulfate content in solid product decreases with an increase in the calcination temperature from 500 to 700 °C. The solid products obtained from the sample (AK + 16.2% KCl) calcined at 700 and 650 °C by extraction are suitable for usage
Figure 9. DTA curve of the remaining solid product after sulfate removal (calcination temperature ) (a) 500 °C, (b) 600 °C, (c) 650 °C).
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Table 5. Chemical Composition of Solid Product calcination temperature (°C)
Al2O3
component (%, w/w) SiO2 K2O SO3
500 650 700
44.29 46.17 47.18
40.63 44.87 45.84
2.81 3.70 3.95
7.44 2.50 0.71
SO4 8.93 3.00 0.85
phous silica structure containing quartz and very little alunite (Figures 10 and 11). DTA and XRD indicate that the solid product obtained by the sulfate removal from the alunitic kaolin with the chemical method does not consist of kaolinite. Therefore, after some physical tests such as plasticity, strength, shrinkage, brightness, and whiteness, the suitability of this solid product for use as a raw material in ceramics and paper industries can be decided. Furthermore, potassium sulfate, an important artificial fertilizer imported to our country will be able to be recovered from the filtrate coming from the extraction by crystallization. Conclusions
Figure 10. XRD of the remaining solid product after sulfate removal (calcination temperature ) 500 °C).
Figure 11. XRD of the remaining solid product after sulfate removal (calcination temperature ) 650 °C).
in the ceramics, paper, and cement industries as raw materials due to their sulfur trioxide compositions less than 1 and 5%, respectively. 1,2 As shown in Figure 9, the first peak (550-600 °C) indicating the release of hydroxide water from the structure appears slightly for the sample calcined at 500 °C, and it does not appear at all for the samples calcined at 600 and 650 °C. The second peak (∼780 °C) showing the release of sulfur trioxide from the structure is also observed slightly for the sample at 500 °C, and it is not observed for the samples calcined at 600 and 650 °C. DTA indicates that it is necessary to calcine the sample at 600 °C for conversion of the sulfate in the alunitic kaolinite into the potassium sulfate. These results are in agrement with the chemical analysis shown in Table 5. The alunitic kaolin + KCl sample calcined at 600 °C consists of 40.36% Al2O3, 34.58% SiO2, 13.86% K2O, and 11.20% SO3. Thus, the chemical formula of this calcined sample can be given as 2.7Al2O3‚3.9SiO2‚K2SO4. This result indicates that the solid-phase reaction is completed at this temperature. XRD of the solid products remaining after sulfate removal show that kaolinite is present at 500 °C, and almost disappeared at calcination temperatures over 500 °C. The alunitic kaolinite decomposes to the amor-
Sulfate removal from alunitic kaolin calcined with KCl and KOH by extraction with distilled water was investigated under the conditions of different calcination temperatures, sample types, potassium compound amounts, and sample preparation methods, and constant calcination time of 1 h, extraction temperature of 75 °C, and extraction time of 2 h. The major conclusions derived from the present work are as follows. (i) It was found that the sulfate removal yield varied with calcination temperature, sample type, potassium compound amount, and sample preparation method relative to the completion of the solid-phase reaction with which the sulfate in the alunitic structure was converted to soluble potassium sulfate. Sample type is the most important parameter affecting the sulfate extraction process, as well as calcination temperature, sample preparation method, and potassium amount. (ii) It was found that alunitic kaolin + 16.2-17.8% KCl should be calcined at 650-700° C for 1 h, and extracted at 75 °C for 2 h for the effective sulfate removal yield. (iii) The working conditions under which the maximum sulfate removal yield was obtained were found as follows: calcination temperature, 700 °C; sample type, AK + KCl; potassium compound amount, 17.8% (15% more than the stoichiometric ratio); sample preparation method, the SP method. Maximum sulfate removal yield of 97% was reached under these conditions. The sulfate amount of solid product was 3% and less than 3% for calcination temperature in the range of 650-700 °C. A detailed analysis of this solid product should be made to determine its suitability for industrial use. Literature Cited (1) DPT, The State Planning Organization. Report 2418; Turkey, 1995. (2) DPT, The State Planning Organization. Report 2611; Turkey, 2001. (3) DPT, The State Planning Organization. Report 2607; Turkey, 2001. (4) Brindley, G. W.; Nakahira, M. The structure of Kaolinite. Mineral. Magn. 1946, 27, 242. (5) Brindley, G. W.; Nakahira, M. Kinetics of Dehydroxylation of Kaolinite and Halloysite. J. Am. Ceram. Soc. 1957, 40, 346. (6) Grim, R. E. Applied Clay Mineralogy; McGraw-Hill: New York, 1962. (7) Heller-Kallai, L. Reactions of Salts with Kaolinite at Elevated Temperatures I. Clay Miner. 1978, 13, 221. (8) Heller-Kallai, L.; Frenkel, M. Reactions of Salts with Kaolinite at Elevated Temperatures II. In International Clay Conference; Amsterdam, The Netherlands, 1979; p 629. (9) Yariv, S.; Mendelovici, E.; Villalba, R. The Study of The Interaction Between Cesium Chloride and Kaolinite by Thermal Methods. In International Conference on Thermal Analysis; Miller, B., Ed.; Queen’s University, Kingston, ON, 1982; Vol. 1, p 533.
Ind. Eng. Chem. Res., Vol. 44, No. 9, 2005 3219 (10) Gabor, M.; Po¨ppl, L.; Ko¨ro¨s, E. Effect of Ambient Atmosphere on Solid State Reaction of Kaolin-Salt Mixtures. Clays Clay Miner. 1986, 34, 529. (11) Gabor, M.; Po¨ppl, L.; Izvekov, V.; Bayer, H. Interaction of Kaolinite with Organic and Inorganic Alkali Metal Salts at 251300 °C. Thermochim. Acta 1989, 148, 431. (12) Yariv, S.; Nasser, A.; Deutsch, Y.; Michaelian, K. H. Study of The Interaction Between Caesium Bromide and Kaolinite by Differential Thermal Analysis. J. Therm Anal. 1991, 37, 1373. (13) Thomspson, J. G.; Gabbitas, N.; Uwins, P. J. R. The Intercalation of Kaolinite by Alkali Halides In The Solid State: A Systematic Study of The Intercalates and Their Derivatives. Clays Clay Miner. 1993, 41, 73. (14) Sokal, S. Improvements in or Relating to Process for Obtaining Alumina. Brit. Patent 569008, 1945. (15) Haff, R. C. Process for Treating Alunite Ores and The Like. U.S. Patent 2,398,425, 1946. (16) Knizek, J. O.; Fetter, H. Alunite and Clays. Trans. Brit. Ceram. Soc. 1947, 46, 22. (17) Bayliss, N. S.; Koch, D. F. A. Thermal Decomposition of Alunite. Australian J. Appl. Sci. 1955, 6, 298. (18) Gu¨lensoy, H. Investigation of Turkish Alunites by Thermogravimetric and Microcalorimetric Methods and The Solubility of Thermal Decomposition Products In Water and Sulfuric Acid. MTA Enstitu¨ su¨ Dergisi 1968, 71, 93. (19) Wang, R.; Bradley, W. F.; Steinfink, H. The Crystal Structure of Alunite. Acta Crystallogr. 1965, 18, 249. (20) Williams, J. F. Process for The Benefication of Mineral Alunite. English Patent 1,547,420, 1979. (21) Gedikbey, T.; I˙ rez, G., Kul, I˙ . The Thermal Decomposition Products of Alunite Potassium Floride Mixture. Kimya ve Sanayi Dergisi 1989, 159.
(22) S¸ engil, A. The Thermal Decomposition of S¸ aphane AlunitePotassium, Sodium, Barium and Calcium Chloride Mixtures. J. Eng. Environ. Sci. 1991, 15, 436. (23) O ¨ zdemir, M.; Gedikbey, T.; O ¨ zdemir, M. Thermal Decomposition Products of Alunite-Salt Mixtures and Salt Solutions. VIII. National Chemistry and Chemical Engineering Symposium; Istanbul, Turkey, 1992; Vol. I, p 7. (24) O ¨ zdemir, M. Leaching of Alunite in Acidic Medium and Leaching Reaction Kinetics. M.S. Thesis, Ana. University, Eskis¸ ehir, Turkey, 1990. (25) O ¨ zacar, M.; S¸ engil, A. Optimum Conditions for Leaching Calcined Alunite Ore In Strong NaOH. Can. Metall. Quart. 1999, 38 (4), 249. (26) Su¨mer, G. Benefication of Alunitic Kaolin. M.S. Thesis, Ana. University, Eskis¸ ehir, Turkey, 1991. (27) Genc¸ , S. Removal Sulphate of Alunitic Kaolins. Ph.D. Thesis, Ana. University, Eskis¸ ehir, Turkey, 1994. (28) Yapa, N. Benefication of Alunite Bearing Kaolinite. Ph.D. Thesis, Istanbul Teknik University, Istanbul, Turkey, 1993. (29) TSE 1428. Potassium Sulphate for Industrial Uses Determination of Sulphate ContentsBarium Sulphate Gravimetric Method, 1973. (30) Merck, E. Complexometric Assay Methods with Titriplex; Darmstadt, 1982.
Received for review June 16, 2004 Revised manuscript received January 24, 2005 Accepted January 26, 2005 IE040177S
