OBTAINING ALUMINUM OXIDE FROM LOCAL ANGREN KAOLIN

ABSTRACT

The stepwise duration and temperature of the main kaolin clays of the Angren deposit with mixtures of H2SO4 and HNO3 acids, as well as the concentration of H2SO4 acid, affect the rate and duration of kaolin decomposition. Studies have shown the possibility of processing kaolin at the factory in Angren in an acidic way. Angren kaolin should be rinsed at a temperature of 250 ° C for at least 60 minutes. During the washing process, the acid concentration is a mixture of 92% sulfuric acid and 56% nitric acid. The rate of transition of metal oxides into solution was 100%. The presence of oxides in this solution is observed – the amount of aluminum oxide is 28.26%, and iron is 0.08%.

АННОТАЦИЯ

Поэтапная длительность воздействия смесями кислот H₂SO₄ и HNO₃, а также концентрация кислоты H₂SO₄ и температура, влияют на скорость и на продолжительность разложения каолина, основных каолиновых глин Ангренского месторождения. Исследования показали возможность переработки каолина на фабрике в г. Ангрен кислотным способом. Ангренский каолин следует промывать при температуре 250°С в течение не менее 60 минут. В процессе промывки концентрация кислот представляет собой смесь 92% серной кислоты и 56% азотной кислоты. Скорость перехода оксидов металлов в раствор составила 100%. Наблюдается присутствие оксидов в этом растворе – количество оксида алюминия составляет 28,26%, а железа 0,08%.

Keywords: Angren kaolin, sulfatization, aluminum oxide, aluminum sulfate.

Ключевые слова: Ангренский каолин, сульфатизация, оксид алюминия, сульфат алюминия.

Introduction. Aluminosilicates, i.e. kaolinite, montmorillonite clays, alunites and other minerals are very valuable raw materials in the production of refractories, ceramics and are used to produce paper, aluminum sulfate, alumina and other chemicals.

Chemicals like aluminosilicates, kaolin, alunite, nepheline, bauxite, and montmorillonite are of great economic importance. It is used in the extraction of aluminum from minerals. They are used to make porcelain, ceramics, earthenware, souvenirs, sand-lime brick, bottom powder, etc.

Angren kaolin belongs to the group of  monomineralic clays. Clays differ from kaolinite in the layered dispersion of kaolinite particles, high plasticity, ability to synthesize at high and high temperatures, and contain more than 50% of the kaolinite mineral - Al₂Si₂O₅(OH)₄. Clay particles are dominated by particles smaller than 2 microns, and in kaolin particles, i.e. particles less than 5 microns in size. [1].

Aluminum mineral raw materials are diverse, have a specific composition, appearance and crystalline structure, as a result of which they differ in the yield of main products during acid-base processing. Therefore, for each type of raw material it is necessary to implement separate scientific and technological directions and select the most suitable processing methods. In various regions of the Republic of Uzbekistan there are large reserves of kaolin from large mines, kaolin agalmatolite from the Aktash mine, which are used in the production of fine, unique ceramics [2].

Using the example of kaolin with low aluminum content, it is shown that the costs of energy carriers and reagents are significantly reduced, which ensures high profitability of a hitherto unprofitable technological process [3]. The purpose of the study is to develop acid and chlorine technology for processing argillite using chlorine gas and production waste to obtain aluminum and iron salts [4]. In the production of aluminum, the starting product is metallurgical alumina Al₂O₃ [5].

The paper presents data on the coagulating ability of aluminum sulfate obtained from kaolin from the Angren deposit during the purification of river water. [6].

The invention relates to the field of hydrometallurgy, in particular to methods for processing high-silicon aluminum raw materials to produce aluminum sulfate. [7]. However, kaolinite clays due to their low aluminum content (Al₂O₃ = 13-25%), high iron content (Fe₂O₃ = 1.5-6.0% sometimes up to 12%) and silicon oxide (30-80%) are currently are not processed. On the outskirts of the city of Angren there are more than 0.45 billion tons of gray secondary kaolin, composition Al₂O₃ = 18,5-24,5%; Fe₂O₃ = 1.5-4.5%; SiO₂ = 39,8-57,9%, etc. [8]. It is the development of products that can meet the needs of the new age, based on insights obtained from the synthesis of big data. [9]. This paper presents the results of a study of methods for producing effective zeolite and aluminum oxide adsorbents for conditioning various process streams, including liquefied petroleum and other hydrocarbon gases, using local mineral raw materials and industrial waste, instead of imported ones [10].

One of the pressing issues is the production of microporous synthetic adsorbents from local raw materials containing silicon and aluminum oxides. [11]. The optimal ratio of raw materials, temperature conditions and process times for obtaining a coagulant-adsorbent have been selected. A technology has been developed for producing a coagulant-adsorbent using simplified technological processes. The ability of the obtained coagulant-adsorbent samples to clarify wastewater from textile production was studied [12].

In this experiment, kaolin is washed with concentrated 92% H₂SO₄ and HNO₃ acid at 105 ⁰C for 60 minutes. In this case, water-soluble aluminum and iron salts (aluminum sulfate and iron sulfate) are formed, which under alkaline action form aluminum hydroxides, and then pure aluminum oxide can be obtained.

Goal. To develop a method for producing pure aluminum oxide by acid leaching of kaolin at different temperature sulfurization.

Objectives. To study of the kinetics of kaolin rock compounds destruction of under the influence of active acids with different temperature leaching; to propose a pattern for the leaching of kaolin and a technological scheme for obtaining pure aluminum oxide from an aqueous solution of aluminum sulfate salt.

Methods and materials. Object of study: Angren kaolin, its composition was studied by X-ray diffraction analysis (XRD). X-ray structural analysis was carried out using an XRD-6100 X-ray diffractometer (Shimadzu). Mass chromatograms of the samples were obtained on an Agilent 5977B GC/MSD. The leaching kinetics of the aluminum containing component was studied under three temperature conditions: 105 ⁰C, 250 ⁰C and 600 ⁰C for a duration of 60 minutes. The control aluminum content in the aqueous solution was determined by the residual proportion of aluminum in the solid filtrate.

Results and discussion. The mineral composition of Anrgen kaolin has been studied and presented in Table 1. For leaching, 100 g of kaolin and a mixture of acids were selected: 45 ml of 92% H₂SO₄ and 5 ml of 56% HNO₃. Kaolin was thrown into the metal thicket and the acid mixture was added while moving it [1].

Table 1.

Mineralogical composition of Angren kaolin clay

The resulting thick pulp was placed in an electric oven at 105 ⁰C. The duration of the process is at least 60 minutes. In this case, sulfurization occurs by easily decomposing sulfuric and nitric acid and by the reaction:

Al₂O₃ · 2SiO₂ + 3H₂SO₄ = Al₂(SO₄)₃ + 3H₂O + 2SiO₂              (1)      

Al₂O₃·2SiO₂·2H₂O + 6HNO₃ = 2Al (NO₃)₃ + 5H₂O + 2SiO₂              (2) [2]

The concentrate obtained after thermal sulfurization was placed in a 600 ml glass and 300 ml distilled water was added. Next, the solution was stirred for 1-1.5 hours under heat. After this, the solution is mixed in a Buchner funnel with filter paper under vacuum.

The filtered liquid part was selected for chemical analysis, the solid cake passed to the further process. The resulting ‘wet’ cake was placed in a drying cabinet at 200 ⁰C for 90 minutes. After drying, the dry weight of the cake was carefully measured. Now can we calculate the amount of dissolved aluminum sulfate and iron sulfate by subtracting the weight of the resulting dry cake from the original 100 g of kaolin. The difference ∆ means the number of gr. dissolved aluminum sulfate and iron sulfate, which is located in the liquid part of the filtrate:

100 g initial kaolin – 76.60 g cake = 23.4 g ∆.

The same process was carried out at 250 ⁰C and 600 ⁰C sulfurization for 60 minutes. The obtained data are shown in Table 2.

Table 2.

Results of sulfurization of Angren kaolin at different leaching temperatures

The sequence of the heat treatment process of kaolin during the processing of aluminum sulfate in the composition of Angren kaolin depends on the speed and concentration of sulfuric acid, the temperature and duration of the decomposition process of kaolin with sulfur. Acid solutions were studied according to the graph of aluminum oxide dissolution in solution. Further research is aimed at studying the influence of technological parameters on the degree of extraction of aluminum and iron oxides from Angren kaolin. [1].

In Figure 1 you can see the graphical peaks forming the % elemental composition of kaolin.

The resulting cake samples of 105⁰C, 250⁰C and 600⁰C sulfuric acid leaching were subjected to X-ray diffraction analysis in an XRD-6100 diffractometer (Shimadzu) Japan (Fig. 1).

Where: Al – 52.2%; Si -20.4%; H – 23.3%, O – 4.1%. From the data obtained, a chemical analysis of the solid cake after drying was carried out to determine the content of metals and their oxides.

Table 3.

Dry cake content after sulfuric acid leaching at different sulfurization temperatures

From Table 3 it is clear that when the sulfurization temperature increases from 105 °C to 250 °C, the extraction of aluminum oxide increases from 9.95% to 28.26%, respectively. Iron is the same from 0.05% to 0.08%. However, with sulfate leaching when heated to 600 °C for 60 minutes, the amount of aluminum oxide decreases to 10.62%, and iron, on the contrary, increases to 0.09%. This is explained by the formation of y-Al₂O₃ and mullite, which is sparingly soluble in sulfuric acid [3].

Conclusion. Kaolin processing from the Angren mine into technical metallurgy, metal oxides (aluminum) in accordance with GOST 30558-2017, the composition of mineral kaolin was studied. The process duration and temperature of the process of washing kaolin with acids, the speed and concentration of sulfuric acid, the duration of the process of decomposition of kaolin with acidic solutions, the degree of transition of metal oxide (aluminum) into solution was studied. It showed the possibility of acid processing of kaolin from the Angren mine. To do this, kaolin should be washed at a temperature of 250°C for at least 60 minutes. Washing is carried out in an acidic environment with a mixture of 92% concentrated sulfuric acid and 56% nitric acid. 100% degree of transfer of metal oxides into solution. In this case, the amount of aluminum oxide obtained is 28.26%, iron - 0.08%.