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ISSN 2522-1841 (Online) AZERBAIJAN CHEMICAL JOURNAL № 4 2023 55
ISSN 0005-2531 (Print)
UDC 549.762.11 x 553.492.6 x552.33.549
DETERMINATION OF OPTIMAL CONDITIONS FOR EXTRACTION OF ALUMINUM OXIDE FROM KAOLIN CLAY OF CHOVDARDAGH DEPOSIT
S.G.Efendiyeva, S.T.Jafarova, A.A. Heydarov, E.B.Gahramanova, A.I.Abbasova,
G.M.Ganzayeva
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, Ministry of Science and Education
of the Republic of Azerbaijan
Received 18.01.2023 Accepted 04.04.2023
The increasing demand for aluminum around the world is increasing interest in developing alternative technologies for the production of alumina from non-bauxite sources, especially from clay. In this work, the extraction of aluminum from kaolin in the process of leaching using an aqueous solution of hydrochloric acid as a leaching agent is investigated. For this study, samples of burnt kaolin clay from the Chovdardagh deposit were used. Before leaching, crude kaolin was calcined; calcination achieves dehy-droxylation of kaolinite, which is the main mineralogical phase of kaolin, and its transformation into metakaolin, an amorphous phase of Al-Si, from which aluminum is easily leached. The calcination of the raw kaolin used in this work was carried out at 7500C for 2 h, taking into account that these conditions were recognized as optimal in the corresponding experimental studies to achieve the maximum yield of alumina in solution. It was revealed that the leaching of kaolin clay in order to extract aluminum oxide is achieved using samples of kaolin clay calcined under the above conditions, with 20% hydrochloric acid for 2 hours at a leaching temperature of 950C. The degree of extraction of aluminum and iron oxide under these conditions is 96.7 and 94.1%, respectively.
Keywords: kaolin clay, calcination, hydrochloric acid, solubility, aluminum oxide.
doi.org/10.32737/0005-2531-2023-4-55-62
Introduction
The intensive development of industry and construction in recent decades has caused a great demand for the products of the metallurgical industry, and this, in turn, has required expanding the range of products made on the basis of cheap environmentally friendly raw materials. To date, quite a lot of aluminum-bearing deposits of various mineral types have been discovered in Azerbaijan, including deposits of unusual industrial significance. In order to solve the problems facing the enterprise in production, measures were taken to modernize the non-ferrous metallurgy enterprise. In the same time The growth in demand on a global scale increases interest in the development of alternative technologies for the production of aluminum from alunites, bauxites, high-silicon ores and other rocks containing a number of valuable chemical elements such as aluminum, iron, copper, zinc, gold, etc. [1]. In many countries, intensive scientific and technical work is underway in this direction to extract alumina from various natural non-bauxite sources, especially clays.
The growing volume of mining and processing of mineral raw materials, as a rule, leads to an increase in waste and generates environmental problems [2-5].
Clays are common minerals, consisting mainly of aluminosilicate minerals with traces of iron oxides and alkali metal oxides [6-8]. Their deposits are quite widespread, extraction is not difficult, and the amount of aluminum oxide in them reaches 25-40% [9]. Aluminosilicate ores are widely used in various fields of industry. Research is currently underway to explore new areas of their application [10].
Among the various clays, kaolin seems to be the more attractive candidate for alumina production due to its high aluminum content. Kaolin is composed primarily of kaolinite with the representative chemical formula Al2O3 2SiO2.2H2O, which is a two-layer silicate mineral typical of the kaolin group. The main contaminants of kaolin are quartz and mica (1045%), as well as iron oxide (1-10%) [11].
It should be noted that in terms of the diversity of mineral deposits, the Greater and
Lesser Caucasus region can be considered one of the richest regions in the world. Quite a lot of aluminum-bearing deposits of various mineral types, including deposits of industrial importance, have been discovered in Azerbaijan. Clays attract the most attention among aluminum-containing minerals. Creating effective resource-saving technologies, extracting valuable components from ores is an urgent task, but the main problem of processing raw materials containing low-grade aluminum remains unsolved. The presence of large reserves of aluminum-containing raw materials in the republic makes it possible to use it as a source for the purchase of aluminum oxide [12]. The primary source of clayey formations is feldspars, upon the destruction of which, under the influence of atmospheric agents, silicates of the group of clay minerals are formed. The effectiveness of this direction mainly depends on the successful solution of the issues of opening raw materials, cleaning solutions from impurities, and adapting aluminum oxide to the required physical properties. [13]. Taking into account the orientation of the industry to its own resources, a fundamentally new approach is required, combining the use of modern equipment, minimal material flow, and safety for the environment. Based on the analysis of literary sources [14], it is known that there are acid and alkaline methods for processing clay materials. However, the ineffectiveness of alkaline methods for the processing of aluminum-containing raw materials with high silicon content (kaolin, clay, etc.) has led most researchers to focus on the development of acid methods. A promising direction for obtaining metallurgical-grade aluminum oxide is the hydrochloric acid method [15]. Researches on the leaching of high-silica aluminum raw materials in hydrochloric acid and the physicochemical modeling of this process are not only practical but also of undoubted scientific interest in the field of aluminum chemistry and technology. The practical implementation of this method will allow the production of hundreds of thousands of tons of metallurgical alumina per year. This will fully satisfy the demand for
aluminum metal production in the main metallurgical plants [16].
The hydrochloric acid method can be applied to any type of raw material with high silica content. The use of hydrochloric acid has several advantages over other mineral acids:
• the ease with which the ore is broken down by the transfer of alumina into solution;
• the low solubility of silica in HCl and the possibility of complete separation of the solid residue without significant loss of acid;
• the possibility of AlClr6H2O being a selective crystal;
• the industrially adopted technology of capturing HCl by obtaining hydrochloric acid for reuse in the process of dissolving raw materials;
The chemical interaction can be described in the form of the following equations: 2SiO2-Al2O3+6HCW2Si02|-2AlCl3+3H20 (1) 2SiO2-Fe2O3+6HCW2Si02|-2FeCl3+3H20 (2) 2SiO2-TiO2+4HCW2Si02|-TiCl4+2H20 (3) 2SiO2-Ca0+2HCW2Si02|-CaCl2+H20 (4) 2SiO2-K20+2HCW2Si02|-2KCl+H20 (5) 2SiO2-Na20+2HCW2Si02|-2NaCl+H20 (6)
Various purification methods of acid chloride solutions allow for obtaining of alumina with a purity of more than 99.99%. It is the hydrochloric acid technology that operates full-cycle pilot plants in Canada and China [12]. To solve the problem of the use of ores in Azerbaijan, it is necessary to research and develop an efficient method of obtaining metallurgical aluminum oxide with minimal labor and energy consumption and the most complex use of raw materials containing aluminum with the high silicon content. Acid treatment methods for aluminum-containing raw materials include a pre-calcination step to convert them to a more acid-soluble form.
The purpose of this study was to determine the optimal conditions for the decomposition of kaolin clays from the Chovdar mountain deposit with hydrochloric acid with maximum extraction of aluminum oxide in solution.
Experimental part
Materials and research methods. Aluminum-containing ores from the studied Chovdardag deposit were used as the starting material for the experiments, both in raw and pre-baked form. The material composition of the starting materials was determined in a Universal S8 X-ray fluorescence spectrometer manufactured by Bruker (Germany) (Cu-Ka radiation, X=1.54 A, nickel filter). To determine the degree of extraction of useful components from the ore during decomposition with hydrochloric acid, before the start of research, samples of kaolin clays were crushed in a mortar to a particle size of "0.1 mm", followed by drying at a temperature of 1100C. Before starting the study, samples of kaolin clays were crushed in the solution to a particle size of "0.1 mm", then dried at a temperature of 1100C. Before washing, kaolin was calcined at different temperatures (450, 750, and 9500C) in a SUOL muffle furnace, keeping it at each temperature for 2 hours. It was determined that the rate of dehydration of kaolin clay directly depends on the temperature and burning time. The calcination of kaolin used in subsequent experimental studies was carried out at 7500C for 2 hours.
The study of the stages of clay washing was carried out in a thermostatic reactor equipped with a stirrer and a reflux condenser. After reaching the required temperature, the starting material was loaded into the acid decomposition reactor and hydrochloric acid was added to it in certain proportions. At the end of the process, the pulp is filtered. The resulting solid residue is washed, dried and weighed. Oxides of aluminum and iron passing
into the solution were determined by chemical analysis methods.
Results and discussion
To determine the criteria for choosing the optimal conditions for the effective use of kaolin clays, it is necessary to research the raw materials to find out the phase and chemical composition, and the presence of structure-phase transformations in the studied temperature range. The chemical composition of the studied kaolinite clays of the Chovdardagh deposit was determined by X-ray spectroscopic method. The results of the analysis are shown in Table 1.
The main components of the original sample and the study of their phase transformations were evaluated by X-ray phase analysis. The results of the X-ray phase analysis of kaolin clays from the Chovdardag field are shown in Figure 1.
The analysis of the XRD spectra of the original sample shows that the main mineral, kaolinite Al2Si2(OH)4 (the main part of kaolin clay) is present in the main mineral - 48.5%, as well as quartz (SiO2) - 33.6% and pyrophyllite Al2Si2(OH)4 - 17.9% (Figure 1).
At the beginning of the study, clay was fired at different temperatures (450, 750, 9000C). The literature analysis showed that during calcination, these minerals are subjected to thermal destruction and transformation of the crystal structure of a-modifications into a soluble form, i.e., kaolinite turns into a more easily exposed form - metakaolinite. Metakaolin is obtained by roasting kaolinite (mined in the form of kaolin clays) in the temperature range of 500-800°C according to the reaction: AhOs -2SiO2 -2H2O~Al2O3 2SiO2+2H2O (7)
Table 1. Chemical composition of studied kaolinite clays of Chovdardag deposit (composition, weight %)
Components
AI2O3 SiÜ2 Fe2O3 Na2O MgO K2O SO3 CaO TiO2 V2O5 SrO loss
25.67 62.97 0.23 0.08 0.01 0.12 1.02 0.15 0.4 0.061 0.45 8.84
(a)
(b)
Fig. 1. Results of X-ray phase analysis of the initial sample of kaolin clay (a) and kaolin clay calcinated at 7500C (b).
The results of X-ray phase analysis shown in Figure 1(b) showed that calcination at a temperature of 7500C showed that the peaks characteristic of kaolinite disappears, while those of quartz remain unchanged. As the combustion temperature increases to 8500C, and especially to 9000C, the removal of aluminum into the solution decreases, which is explained by the formation of y-Al2O3 and mullite, which are difficult to dissolve in acid [13, 14]. To determine the effect of the calcination temperature of kaolin clay on the extraction rate of alumina in solution, samples of original and baked clay were tested in a 20% hydrochloric acid solution. It has been established that the yield of aluminum oxide in solution hydrochloric acid treatment on samples of unfired clay and clay calcined at 450, 750, 9000C- is 12.8; 69.2; 95.3 and 79.8% respectively. The study results showed that the maximum yield could be obtained in samples calcined at 7500C and processed for 2 hours. Further experiments were conducted with clay samples processed under conditions (T= 7500C, t=2 hours). Table 2 shows the chemical composition of clay samples fired at 7500C according to the main components.
The effect of temperature, concentration, and washing time on the release of Al2O3 into the solution was studied. One of the main factors affecting the process of removing components from the solid residue is temperature. The effect of process temperature on the extraction rate of alumina from calcined kaolin is shown in Figure 2. As can be seen from the data in the table, at 20% acid concentration; the maximum removal of components is observed at 950C, where the degree of removal of Al2O3 and Fe2O3 reaches 89.4 and 94.1%, respectively.
Further studies were devoted to the study of the influence of the duration of the hydrochloric acid decomposition process of kaolin clays. The results are shown in Figure 3. Constant factors: acid concentration - 20%; processing temperature - 950C. As can be seen from the figure, the processing time factor has a great influence on the removal of Al2O3 and Fe2O3. During the experiment, the degree of extraction of aluminum and iron oxides from the composition of calcined clay increases with increasing processing time. It ranges from 94.5 to 85.6% and 96.7 to 94.1% in the range of 90 to 120 minutes, respectively.
Table 2. Chemical composition of kaolinite clays calcined at 750 C in the Chovdardag field (composition, weight %)
Components
Al2Ü3 SiO2 Fe2O3 Na2O MgO K2O SO3 CaO TiO2 V2O5 SrO
27.6 67.709 0.247 0.086 0.11 0.129 1.0967 0.161 0.43 0.0656 0.4838
Fig. 2. Effect of the process temperature on the degree of obtaining aluminum and iron oxides (t-2 hours, chci - 20%, t- 950C, T:L=1:5).
Fig. 3. Effect of the duration of the hydrochloric acid decomposition of kaolin clays on the degree of obtaining aluminum and iron oxides (t-2 hours, CHa - 20%, t- 950C, T: L=1:5).
Fig. 4. Effect of hydrochloric acid concentra iron oxides from kaolin clays (t-2 hours, CHa
A further increase in the processing time did not give a noticeable increase in the rate of removal of components.
The effect of hydrochloric acid concentration on ore fragmentation was studied in the concentration range of 10-20% (Figure 4). The constants in this process were: temperature 950C and process time 120 min. With the increase of acid concentration from 10% to 20%, the removal rate of components increased and reached the maximum value of 43.4-96.7% Al2O3 and 87.6-94.1% Fe2O3. With further increase in acid concentration, the degree of extraction of components from the ore did not change and then decreased. As the acid concen-
+3
tration increases, Al ions prevent the diffusion
tion on the rate of extraction of aluminum and - 20%, t- 950C, T: L=1:5).
of H+ ions into the solid phase, which is likely
+3
due to the destruction of Al particles at this solution concentration.
Conclusion
It was determined that the kaolin clay of the Chovdardag deposit is suitable for the production of alumina to extract alumina. Based on the conducted research, it was concluded that to achieve the maximum yield of alumina in the solution, it is necessary to use clay samples calcined at 7500C for 2 hours. Calcined clay samples were processed with hydrochloric acid solution and optimal conditions for the washing process were found (hydrochloric acid concentration -20%, duration of the process - 2 hours,
temperature - 950C). Under these conditions, the degree of removal of aluminum oxide and iron is 96.7 and 94.1%, respectively.
The work done in this field requires special attention, and since it consists of a careful attitude to natural resources, which are national treasures, their effective use and preservation for future generations is our main task.
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ÇOVDARDAG YATAGININ KAOLÍN GÍLLORINDON ALÜMÍNÍUM OKSÍDÍN ÇIXARILMASININ OPTÍMAL §ORAÍTÍNÍN TAPILMASI
S.Q.Ofandiyeva, S.T. Cafarova, A.O.Heydarov, Y.B.Qahramanova, N.Í.Abbasova, G.M.Ganzayeva
Dünyada alüminiuma artan talabat yûksak silisiumlu manbalardan olmayan manbalardan, xûsusan da gildan alüminium oksidinin istehsali ûçûn alternativ texnologiyalarin içlanib hazirlanmasina maragi artinr. Bu içda halledici vasita kimi xlorid turçusunun sulu mahlulundan istifada edilmakla alüminiumun kaolindan çixarilmasi tadqiq edilmiçdir. Bu tadqiqatlar ûçûn Çovdardag yataginin yandirilmiç kaolin gilinin nümunalarindan istifada edilmiçdir. Hallolma prosesindan avval, xam kaolin kalsine kôzardilmiçdir. Közardilma zamani kaolinin asas mineraloji fazasi olan kaolinitin dehidroksillaçmasina va onun Al-Si-nin amorf fazasi olan metakaolina çevrilmasina va ondan alüminiumun asanliqla hall edilarak çixarilmasina nail olunur. Bu içda istifada olunan xam kaolinin közardilmasi 7500C temperaturda 2 saat arzinda aparilmiç va bu çaraitin mahlulda alüminium oksidinin maksimum çiximina nail olmaq ûçûn mûvafiq eksperimental tadqiqatlarda optimal oldugu nazara alinmiçdir. Malum olmuçdur ki, alüminium oksidinin çixarilmasi ûçûn kaolin gilinin hall olmasi yuxarida göstarilan çartlarda kôzardilmiç nûmunalardan istifada etmakla, 20%-li xlorid turçusu ila 2 saat arzinda 950C temperaturda hayata keçirilmiçdir. Bu çartlarda alûminium va damirin oksidinin çixarilma daracasi mûvafiq olaraq 96.7 va 94.1% taçkil edir.
Açar sözlzr: kaolin gili, köz3rtm3, xlorid turçusu, h3llolma, alüminium oksid
