RU2197429C2 - Method of processing aluminum-containing raw material - Google Patents

Abstract

FIELD: processing aluminum-containing raw materials by sintering; production of aluminum hydroxide of pseudoboehmite structure. SUBSTANCE: includes sintering with limestone and alkalicontaining material forming gaseous products and sinter, leaching sinter at obtaining aluminate solution, desiliconization of aluminate solution, dilution of desiliconized solution by aqueous solution, carbonization of diluted solution, separation of sediment formed during carbonization from carbonate solution and flushing the sediment obtaining pseudoboehmite and industrial water. Used as aqueous solution for dilution is carbonate solution; dilution is performed till molar ratio of carbonate alkali to common alkali is equal to 0.15 to 0.6; carbonization is performed with gaseous sintering products at temperature of 10 to 50 C and consumption of CO₂/Al₂O₃ equal to 1.5 cu dm/g; flushing the sediment is performed at temperature of 40 to 100 C; carbonates of alkaline metals are extracted from carbonate solution and industrial water. Soda is used as alkali- containing material at sintering. Aqueous solution for dilution is preliminarily saturated with gaseous sintering products. Molar fraction of potassium is sum of sodium and potassium in solution ranges from 0.2 to 0.8 before carbonization. Proposed method makes it possible to recover liquid waste. EFFECT: enhanced efficiency. 4 cl, 4 tbl, 6 ex

Description

 The invention relates to methods for processing aluminum-containing raw materials, such as bauxite or nepheline, by a sintering method, as well as to a technology for producing aluminum hydroxide of a pseudoboehmite structure.

в область 6,4-6,8

, отличную от бемита кристаллическую структуру (рыхло связанные пористые агрегаты), высокую удельную поверхность, а также ряд других характерных признаков, позволяющих отличить псевдобемит от других форм гидроксидов. Метастабильная фаза - псевдобемит может использоваться при получении осушителей, сорбентов, катализаторов, используемых в химической, металлургической и ряде других отраслей промышленности.Pseudoboehmite is a metastable form of aluminum hydroxide, similar in chemical composition and x-ray characteristics to boehmite. In contrast to boehmite, pseudoboehmite has more diffuse indices on the X-ray diffraction pattern and the shift of the diffraction peak [020] from 6.1-6.2

to the area of 6.4-6.8

a crystalline structure different from boehmite (loosely coupled porous aggregates), a high specific surface, as well as a number of other characteristic features that distinguish pseudoboehmite from other forms of hydroxides. Metastable phase - pseudoboehmite can be used to obtain desiccants, sorbents, catalysts used in the chemical, metallurgical and some other industries.

As a raw material for the production of pseudoboehmite, metal aluminum or aluminum hydroxide is used, as a rule. The most common way to obtain pseudoboehmite is to reprecipitate crystalline aluminum hydroxide by mixing an alkaline and acidic solution, one of which or both contain aluminum. For example, in the method for producing pseudoboehmite according to US Pat. USA 4.154.812, 1977 is a mixture of an aluminate solution and a solution of aluminum sulfate. This method includes holding the pulp at 60-82 ^{° C.} to achieve a final pH in the range of 9.5 to 10.5, separating the precipitate by filtration, washing and drying to obtain pseudoboehmite, sodium sulfate solution and washing from washing the precipitate.

 The disadvantages of the method are the difficulties of phase separation during filtration, as well as the formation of liquid waste, the disposal of which is difficult due to low concentrations. The evaporation of such solutions is associated with high energy costs, which are not comparable with the effect of the sale of the resulting salts. As a result, these wastes pollute the water basin, worsening the environmental situation. In addition, the anion of the acid cannot be completely removed by washing from the precipitate, which affects the quality of the resulting pseudoboehmite.

There is also known a method of producing pseudoboehmite, including the preparation of aluminum hydroxide according to the Bayer method, dissolving this hydroxide in caustic alkali to obtain an aluminate solution with a concentration of 20-200 g / l Al ₂ O ₃ , carbonizing the aluminate solution at a temperature of 0-60 ^o C to obtain a pH of the final solution is 7-11.5 to obtain an X-ray amorphous precipitate, separating the precipitate, washing it with an aqueous solution at a temperature of about 30 ^{° C.} , treating the precipitate with a solution of mineral acid / Pat. France 2.520.722, 1982; European Patent 0.085.592, 1983 /.

The disadvantages of the method are the use of Al (OH) ₃ as a starting material for the preparation of an aluminate solution, difficulties in controlling the process, and the need for waste disposal. Direct carbonization of the solution obtained in the Bayer cycle without preliminary purification from iron and other impurities leads to contamination of the precipitate released during carbonization. Ions of CO ₃ ^2- , obtained as a result of carbonization, and anions of mineral acids are extremely undesirable for the Bayer process. Therefore, the filtrates and promoters obtained by this method must be disposed of in a separate cycle at the appropriate cost for their evaporation. Difficulties of regulation are explained by the relatively short period of precipitation from the solution, since the majority of the carbonization time is devoted to overcoming the buffer capacity of the carbonized solution. Under these conditions, there is a high probability that the regime will go beyond the required range of the pH of the solution and the formation of a crystalline phase, which affects the quality of the final product.

 A known method of processing aluminum-containing raw materials by the sintering method, including sintering with limestone and working materials with the formation of gas products and cake, leaching cake to obtain an aluminate solution, silicification of the aluminate solution, carbonization of the siliconized solution by gas sintering products, separation of the precipitate formed during carbonization from carbonate solution, from which alkali metal carbonates (e.g., soda and potash) are isolated, washing the precipitate to obtain aluminum hydroxide The line in the form of gibbsite / liner AI and others. Production of alumina. M .: Metallurgy, 1978.P. 184 - 193 /.

Carbonization, along with decomposition, is a method for the separation of aluminum hydroxide from aluminate solutions in the processing of alumina-containing raw materials by the sintering method. In contrast to decomposition, carbonization makes it possible to quickly transfer aluminum from solution to precipitate to obtain a solution of alkali metal carbonates, from which soda products are isolated. Sintering gas products contain more than 20% CO ₂ , however, when transporting gases from the furnace unit to the tank in which carbonization is carried out, this concentration decreases to 7-18% CO ₂ .

In the production of alumina by the sintering method, the content of silicon and iron impurities in aluminate solutions before carbonization is such that in the resulting aluminum hydroxide the content of SiO _{2 is} less than 0.02%, and Fe ₂ O ₃ less than 0.01%.

During the carbonization of aluminate solutions with a concentration of 70-120 g / dm ³ Al ₂ O ₃ with gas sintering products containing 7-18% CO ₂ , carbon dioxide is first consumed to overcome the buffer capacity with the subsequent formation of an X-ray amorphous phase, which dissolves in excess caustic alkali:
CO ₂ + ₂ OH ^- = CO ₃ ^2- + H ₂ O; (1)
СО ₂ + 3Н ₂ О = 2Н ₃ О ⁺ + СО ₃ ^2- ; (2)
[Al (OH) ₄ ] ^- + H ₃ O ⁺ = AlOOH + 3H ₂ O; (3)
AlOOH + OH ^- + H ₂ O = [Al (OH) ₄ ] ^- (4)
Under conditions of comparable rates of formation of new particles and crystallization, aluminum trihydroxide is released into the solid phase:
{Al (OH) ₄ ] ^- = Al (OH) ₃ + OH ^- . (5)
Depending on the temperature, gibbsite (at a temperature of more than 50 ^° C) or bayerite (at a temperature of less than 50 ^° C) is precipitated predominantly. With further carbonization, carbon dioxide is spent on the formation of bicarbonate ions in a solution:
CO ₂ + 2H ₂ O = H ₃ O ⁺ + HCO ₃ ^- . (6)
When the pH of the liquid phase is below 10 units. and increasing the content of HCO ₃ ions in it ^- the formation of alkali metal aluminocarbonates occurs:
2АlOOН + 2 (Na, K) ⁺ + 2НСО ₃ ^- = (Na, K) ₂ O • Al ₂ O ₃ • 2CO ₂ • 2H ₂ O. (7)
Upon receipt of metallurgical alumina from aluminum-containing raw materials by the sintering method, the carbonization temperature is not lower than 60-90 ^o C and the precipitate of aluminum hydroxide is represented by gibbsite. Alkali metal carbonates at the end of carbonation are obtained separately from the main precipitate, dissolved and returned back to the closed cycle of alumina production.

The disadvantage of this method is the low specific surface area of Gibbsite precipitated during carbonization (less than 1 m ² / g), its low plastic properties and insufficient mechanical strength of the formed and calcined granules. This does not allow the use of aluminum hydroxide obtained by this method as the basis for the production of desiccants, sorbents, catalysts and in a number of other applications. In addition, obtained by the method of sintering alumina due to high production costs for fuel is always less economical compared to the traditional Bayer method.

The prototype of the invention is a method for producing aluminum hydroxide having a pseudoboehmite structure, including diluting an aluminate solution obtained, for example, according to the Bayer method — sintering from a soda-limestone mixture, passing carbon dioxide through a solution at a temperature of 30-43 ^{° C.} at a gas flow rate of CO ₂ / Al ₂ O ₃ about 0.5 DM ³ / g, repulpation of the precipitate with water at a temperature of 65 - 100 ^o C / Pat. U.S. 3.268.295, 1961; US Pat. UK 1.440.194, 1973 /.

 The disadvantages of the prototype method are the need for an independent source of carbon dioxide, for example gas cylinders, and inconsistency in the quality of the resulting product according to the content of the main substance. At the beginning of carbonization, the formation of bayerite, which pollutes pseudoboehmite, is highly likely. In addition, the prototype method does not provide for the possibility of disposal of solutions after filtering and washing the precipitate.

The technical task of the proposed method is to simplify the process by using CO ₂ formed as a by-product, improving the quality of pseudoboehmite, as well as the complete utilization of liquid waste from its production. The technical result is achieved by processing aluminum-containing raw materials, including sintering with limestone and alkali-containing material with the formation of gas products and cake, leaching cake to obtain an aluminate solution, desalination of the aluminate solution, diluting the siliconized solution with an aqueous solution to obtain a molar ratio of carbonate alkali to total alkali equal to 0 , 15-0.6, carbonization of the diluted solution with gas products of sintering at a temperature of 10-50 ^o C and a flow rate of CO ₂ / Al ₂ About ₃ = 1-5 DM ³ / g, separating the precipitate formed during carbonization from the carbonate solution, washing the precipitate at a temperature of 40-100 ^{° C.} to obtain pseudoboehmite and washing, separating the alkali metal carbonates from the carbonate solution and washing.

 Using the combination of the claimed features within the claimed parameters allows us to simplify the method of obtaining pseudoboehmite, increase the content of the main substance in it to a level of at least 95%, and also utilize the resulting liquid waste.

When diluting siliceous aluminate solutions and subsequent carbonization of aluminate solutions with gas sintering products at a temperature of 10-50 ^° С and their consumption from the calculation of СО ₂ / А1 ₂ О ₃ = 1-5 dm ³ / g, the interaction proceeds mainly by reaction (1). The precipitate formed after washing at a temperature of 40-100 ^o With mainly represents pseudoboehmite. The carbonization of solutions by gas sintering products eliminates the use of cylinders with liquefied gas as a source of CO ₂ , more fully use the original raw materials to obtain pseudoboehmite. Carbonate solutions after separation of the precipitate are used to obtain soda, potash and other salts by stepwise evaporation and crystallization. After crystallization, these products, as well as mother liquors, can be returned to sintering as alkali-containing materials.

As an aqueous dilution solution, a carbonate solution is used, which can be obtained by processing aluminum-containing raw materials by a sintering method, for example, a carbonate solution of carbonization or washing the precipitate. Moreover, the molar ratio of carbonate alkali to total alkali in solution before carbonization (R ₂ O _kb / R ₂ O _o ) should preferably be 0.15-0.6. "Carbonate alkali" (R ₂ O _kb ), stoichiometrically proportional to the amount of CO ₃ ^2- ions present in the solution, is defined in solutions as the difference between the total (R ₂ O _o ) and caustic (R ₂ O _ku ) alkali. Total and caustic alkali are determined by titration according to standard methods adopted in alumina production, as the sum of alkali metal oxides in terms of sodium oxide.

 Carbonate solutions can be used as working up to saturation on the content of alkali metal carbonates, and then used to separate from them alkali metal carbonates (soda and / or potash).

When the consumption of gas products of sintering from the calculation of CO ₂ / Al ₂ O _{3 is} less than 1 dm ³ / g, the formation of bayerite in the precipitate is high, which, being a seed, prevents the formation of pseudoboehmide. When the consumption of gas products of sintering from the calculation of CO ₂ / A1 ₂ O ₃ more than 5 dm ³ / g in the sediment increases the proportion of alkali metal aluminocarbonates.

At a carbonization temperature above 50 ^° C, the content of crystalline phases (gibbsite) increases in the resulting product, and a decrease in temperature below 10 ^° C does not affect the quality of the obtained product, but at the same time, the energy costs of maintaining it increase.

The temperature of washing the precipitate below 40 ^o C is insufficient to remove soluble impurities and completely convert the precipitate to pseudoboehmite, and washing at temperatures above 100 ^o C requires the installation of special equipment for working under pressure.

When the molar ratio of R ₂ O _kb / R ₂ O _about in the solution before carbonization is less than 0.15, it is necessary to take special measures to reduce the carbonate content in technological solutions, which will negatively affect other operations of processing aluminum-containing raw materials by the sintering method. When the ratio of R ₂ O _kb / R ₂ O _about in solution before carbonization of more than 0.6 units increases the proportion of impurities of alkali metal aluminocarbonates in pseudoboehmite.

 As the alkali-containing material during sintering, soda is used, which is separated from the carbonate solution and promvod, which allows to reduce the loss of materials and energy consumption during the implementation of the method.

To simplify the process of obtaining pseudoboehmite, the aqueous solution used to dilute the siliceous aluminate solution, it is advisable to pre-saturate with sintering gas products containing CO ₂ .

Obtaining pseudoboehmite without impurities of crystalline phases is possible only if the gas supply mode is observed, which ensures the constant ratio of СО ₂ / НСО ₃ ^- in the liquid phase. When diluting a silica-free aluminate solution, its buffer capacity is essential. At the beginning of carbonization, the supplied CO ₂ is spent primarily on overcoming the buffer capacity and this period should be as short as possible, otherwise the formation of bayerite is possible. Therefore, the initial period of carbonization upon receipt of pseudoboehmite must be carried out at an increased gas flow rate. However, after the appearance of the solid phase, the rate of carbonation in order to avoid a sharp change in the ratio of CO ₂ / HCO ₃ - in the liquid phase must be reduced. The inertia of the system does not always allow you to quickly do this.

When carbon dioxide is saturated with an aqueous solution, which is diluted with a silica-free aluminate solution, the most favorable conditions are created for quickly overcoming the buffer capacity of the carbonized solution and creating the CO ₂ / HCO ₃ ratio necessary to obtain pseudoboehmite ^- without significantly changing the rate of gas supply to carbonization. This simplifies the regulation of the process.

 It is desirable that the molar fraction of potassium from the sum of sodium and potassium in the solution before carbonization is 0.2-0.8 units. This allows you to get pseudoboehmite with a minimum content of alkali impurities with a fixed amount of water for washing the precipitate and other conditions being equal. With a potassium fraction of less than 0.2 units. the alkali content in pseudoboehmite increases significantly, with a fraction of more than 0.8 units. - does not affect the alkali content in pseudoboehmite. Maintaining the necessary ratio of alkalis is achieved by using the appropriate raw materials or by diluting the silicified solution with an appropriate solution. The following examples of the method justify the feasibility of the claimed parameters.

Example 1
Nepheline concentrate with a moisture content of 0.2%, containing,%: Al ₂ O ₃ -28.56; Na ₂ O-13.02; K ₂ O-7.71; Fe ₂ O ₃ -3.35; SiO ₂ -44.16; CaO-1.47, as well as limestone with a moisture content of 12.4%, containing,%: CaO-53.51; MgO-0.90; SiO ₂ -1.34; Fe ₂ O ₃ -0.59; Al ₂ O ₃ -0.55 and pulp of working alkali-containing materials containing,%: Na ₂ O-2.55; K ₂ O-1.58; Al ₂ O ₃ -2.44; H ₂ O-82,10 was used to prepare the sintering mixture with molar ratios in the mixture, (Na ₂ O + K ₂ O) / Al ₂ O ₃ = 1.04; CaO / SiO ₂ = 1.97. Sintering of the obtained mixture was carried out at a temperature of about 1300 ^o With the formation of cake and gas products containing more than 14% CO ₂ . The cake was leached at 75 ^o With a circulating soda-alkaline solution with the formation of belitic sludge and aluminate solution, which was desalted to obtain a mass ratio of Al ₂ O ₃ / SiO ₂ about 5000. Silicon-free aluminate solution containing, g / l: R ₂ O _o - 91.68; R ₂ About _ku -76.83; R ₂ O _KB -14.85; Al ₂ O ₃ -71.81; SiO ₂ -0.015, was diluted with reverse carbonate solutions and promoters with different contents of R ₂ About _kb . The diluted solution having a molar ratio of K ₂ O / (Na ₂ O + K ₂ O) = 0.31 was carbonized by gas sintering products at a temperature of 25 ^{° C.} , the precipitate formed was separated from the filtrate and washed with a condensate having a temperature of 90 ^° C. after filtration and washing, dried at 105 ^o C to a residual moisture content of less than 1% and analyzed for phase composition by x-ray method. The results obtained in the form of the dependence of the phase composition of the final product on the specific consumption of С0 ₂ at various ratios R ₂ О _кб / R ₂ О _o in the solution for carbonization are presented in table. 1. The filtrate and washes after separation of the precipitate was subjected to stepwise evaporation with the release of soda and potash.

Example 2
The diluted solution obtained as in example 1, containing, g / l: R ₂ O _o -35,21; R ₂ O _ky -29.47; R ₂ About _kb -5.74; Al ₂ O ₃ -27.62, carbonized by gas sintering products based on the consumption of CO ₂ = 2.32 dm ³ / g Al ₂ O ₃ in solution. The precipitate formed was separated from the filtrate and washed with a condensate having a temperature of 90 ^° C. The precipitate, after filtration and washing, was dried at 105 ^{° C.} to a residual moisture content of less than 1% and analyzed for phase composition by X-ray. The results obtained in the form of the dependence of the phase composition of the final product on the carbonization temperature are presented in table. 2.

Example 3
The diluted solution obtained as in example 2, was carbonized at a temperature of 25 ^o With gas sintering products from the calculation of the flow rate of CO ₂ = 2,32 DM ³ / g Al ₂ About ₃ . The precipitate formed was separated from the filtrate and washed. The precipitate after filtration and washing was dried at 105 ^o C to a residual moisture content of less than 1% and analyzed for chemical and phase composition. The results obtained in the form of the dependence of the chemical and phase composition of the final product on the washing temperature are presented in Table 3.

Example 4
Bauxite with a moisture content of 19.05%, containing,%: Al ₂ O ₃ -53.51; Fe ₂ O ₃ -7.25; SiO ₂ -18.20; CaO 0.60; TiO ₂ -2,7, limestone as in example 1, soda containing,%: Na ₂ O; and reverse alkali-containing materials were used to prepare the mixture with molar ratios of Na ₂ O / (Al ₂ O ₃ + Fe ₂ O ₃ + SO ₃ ) = 1.00; CaO / SiO ₂ = 2.00. The mixture was sintered at a temperature of about 1200 ^o With the formation of cake and gas sintering products. The cake was leached with a circulating solution at a temperature of 70 ^o C, the sludge was separated from the aluminate solution and the latter was silicified in two stages until a mass ratio Al ₂ O ₃ / SiO _{2 of} about 2000 was obtained. A silicified aluminate solution containing, g / l: R ₂ O _o - 139.51; R ₂ About _ku -114.15; R ₂ O _KB -25.36; Al ₂ O ₃ -116.14; SiO ₂ -0,050, was diluted with reverse promvod. Diluted solution containing, g / l: R ₂ O _about -41.71; R ₂ O _ky -34.13; R ₂ About _kb -7.58; Al ₂ O ₃ -34.72, with a molar ratio of R ₂ O _kb / R ₂ O _o = 0.18, were carbonized by gas sintering products at a temperature of 25 ^o C based on the consumption of CO ₂ = 2.93 dm ³ / g A1 ₂ O ₃ , the precipitate formed was separated from the filtrate and washed with a condensate having a temperature of 90 ^° C. The precipitate after filtration and washing, dried at 105 ^{° C.} to a residual moisture content of less than 1% by 100%, was represented by pseudoboehmite. After separation of the precipitate, the filtrate and wastes were subjected to stepwise evaporation with the release of soda, which was used as an alkali-containing material for the preparation of the charge.

Example 5
Sintering gas products were passed through the promo to obtain a pH of less than 7 units. and used it to dilute the siliceous aluminate solution obtained as in Example 1. The result was a diluted carbonization solution containing, g / l: R ₂ O-42.51; R ₂ O _ku -35.47; R ₂ About _kb -7.04; Al ₂ O ₃ -33.02. The diluted solution having a molar ratio of K ₂ O / (Na ₂ O + K ₂ O) = 0.31 was carbonized by gas sintering products at a temperature of 25 ^{° C.} based on a consumption of CO ₂ = 1.21 dm ³ / g Al ₂ O ₃ . The precipitate formed was separated from the filtrate and washed with a condensate having a temperature of 90 ^° C. The precipitate, after filtration and washing, was dried at 105 ^{° C.} to a residual moisture content of less than 1% and analyzed for phase composition by X-ray. The dried product 100% consisted of pseudoboehmite, in contrast to the results obtained in example 1 (4.5 - table. 1). The filtrate and wastewater from washing the precipitate were used to dilute the silicified solution and to obtain soda and potash as a result of evaporation and cooling.

Example 6
The siliceous aluminate solution obtained as in Example 1 was diluted with solutions with different ratios of K ₂ O / (Na ₂ O + K ₂ O). Diluted solutions with different ratios of K ₂ O / (Na ₂ O + K ₂ O) were carbonized by gas sintering products at a temperature of 25 ^° C based on the consumption of CO ₂ = 2.32 dm ³ / g Al ₂ O ₃ in solution.

The precipitate formed was separated from the filtrate and washed with a condensate having a temperature of 90 ^° C. The precipitate, after filtration and washing, was dried at 105 ^{° C.} to a residual moisture content of less than 1% and analyzed for chemical and phase composition. The resulting precipitation was represented by pseudoboehmite. The dependence of the chemical composition of pseudoboehmite on the ratio of K ₂ O / (Na ₂ O + K ₂ O) in the carbonized solution is presented in Table. 4. The filtrate and washes from washing the precipitates were used to dilute the silica-free solution and to obtain soda and potash as a result of evaporation and cooling.

Claims (4)

1. A method of processing aluminum-containing raw materials, including sintering with limestone and an alkali-containing material with the formation of gas products and cake, leaching cake to obtain an aluminate solution, desalination of the aluminate solution, diluting the siliconized solution with an aqueous solution, carbonization of the diluted solution, separation of the precipitate formed from the carbonation of the carbonate solution washing the precipitate to obtain pseudoboehmite and a washing agent, characterized in that as an aqueous solution for diluted I use the carbonate solution and dilution is carried out to obtain a molar ratio of alkali carbonate to the total alkali equal to 0.15-0.6, carbonization gas products are sintered at a temperature of 10-50 ^o C and a flow rate of CO ₂ / Al ₂ O ₃ = 1- 5 dm ³ / g, the washing of the precipitate is carried out at 40-100 ^o C, and alkali metal carbonates are isolated from the carbonate solution and the wash.  2. The method according to p. 1, characterized in that soda is used as an alkali-containing material during sintering.  3. The method according to p. 1, characterized in that the aqueous solution for dilution is pre-saturated with gas sintering products.  4. The method according to p. 1, characterized in that the molar fraction of potassium from the amount of sodium and potassium in the solution before carbonization is 0.2-0.8.

Images