RU2302995C1 - Method of purification of the aluminate solutions from the impurities - Google Patents

Abstract

FIELD: nonferrous metallurgy; methods of purification of the aluminate solutions from the impurities.

SUBSTANCE: the invention is pertaining to the field of the nonferrous metallurgy, in particular, to the methods of purification of the aluminate solutions from the impurities at production of the alumina from the aluminum-containing raw material including bauxites. The method of purification of the aluminate solutions from the impurities provides for includes addition into the aluminate solution of the sorbent based on the magnesium compounds interacting with the solution, separation of the sorbent from the purified solution, its regeneration by the thermal treatment and reutilization. The sorbent on the basis of the magnesium compounds is produced by the treatment of the aluminate solution with the magnesium hydroxide and the thermal treatment of the produced solid phase at the temperature of 230-400°C. It is added in the form of the water pulp with the concentration of 100-150 g/dm³ in terms of MgO, and the regeneration of the sorbent conduct at the temperature of 250-380°C. The invention allows to increase the purification efficiency and to reduce the power inputs for realization of the method.

EFFECT: the invention ensures the increased purification efficiency and the reduced power inputs for realization of the method.

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Description

The invention relates to non-ferrous metallurgy, and in particular to a technology for the purification of aluminate solutions from impurities in the production of alumina from aluminum-containing raw materials, including bauxite.

Impurities of iron, silicon, organic substances and other impurities pass from aluminum-containing raw materials to aluminate solutions during leaching. A high level of impurities in solutions is a typical reason that the aluminum hydroxide produced has a whiteness (in terms of 100% TiO ₂ ) of not more than 75%. Non-metallurgical use of such hydroxide in areas where a high level of whiteness is required is impossible.

To obtain alumina with a low content of impurities, including organic substances and iron, a number of technological methods are used, including the interaction of purified solutions with inorganic reagents. Of the inorganic reagents used for purification, magnesium compounds are the most effective.

A known method of removing impurities from aluminate solutions, including their processing with magnesium compounds (sulfate, chloride, nitrate), added in an amount of 0.2-50 g / l (US Pat. Germany No. 2518431, CL CF 7/06, 1975; US No. 4046855, CL C01F 7/00, 1976).

The disadvantage of this method is the formation of a fine, poorly separated by filtration of the solid phase, which also sorb a significant amount of aluminate ions from the liquid phase.

A known method of producing refractory materials from Bayer solutions (US Pat. Germany No. 3214422, CL 04B 35/02, 1982; European Pat. No. 008920028, class 01 F 7/02, 1983), including the interaction of oxide and / or magnesium hydroxide with aluminate solution. According to this invention, after interaction at a temperature of 20-300 ° C, the resulting magnesium and aluminum compounds (in them the molar ratio of MgO: Al ₂ O ₃ from (2: 1) to (52: 1) are burned after washing at a temperature of more than 900 ° C.

The disadvantage of this method is the insufficient degree of sorption of colored impurities. In addition, this method allows to obtain refractory materials, but is not suitable for cleaning, because the preparation of these materials is accompanied by significant losses of aluminate ions from solutions.

A known method of treating wastewater using an adsorbent based on magnesium oxide, comprising treating aluminum-containing water with magnesium oxide and subsequent regeneration of the sorbent by calcining at a temperature of 500-700 ° C (US Pat. No. 7845054 (56-1148), CL 01 F 7/47 , 1976).

The disadvantage of this method is the low efficiency of sorption of impurities.

The most promising both from the point of view of cleaning efficiency and from the point of view of using the compounds obtained after purification are complex carbonate-containing magnesium aluminates. The existence of a number of such compounds is known. For cleaning, one or more magnesium-containing compounds of the hydrotalcite group having the formula

Mg ₆ Al ₂ (OH) _x (CO ₃ ) _y · 4H ₂ O,

where: x - 12-20;

y - 1-3

For example, Mg ₆ Al ₂ (OH) ₁₂ (CO ₃ ) ₃ · 4H ₂ O, or Mg ₆ Al ₂ (OH) ₁₄ (CO ₃ ) ₂ · 4H ₂ O, or Mg ₆ Al ₂ (OH) 16CO ₃ · 4H ₂ O.

The term "hydrotalcite" to the greatest extent refers to a compound having the formula: Mg ₆ Al ₂ (OH) ₁₆ (CO ₃ ) · 4H ₂ O or 6MgO · Al ₂ O ₃ · CO ₂ · 12H ₂ O. In ionic form, hydrotalcite can be expressed as [Mg ₆ Al ₂ (OH) ₁₆ ] ²⁺ [CO ₃ ] ^2- · 4H ₂ O. The main structural module for this compound is “brucite” (magnesium hydroxide in an octagonal sheet-like form with Mg ²⁺ ions established between multiple (OH ^- ) ions). Part of the magnesium in this structure is replaced by trivalent aluminum cations. The sublevels of magnesium and aluminum are created with the main sheet-like brucite structure remaining intact. The instability is compensated for by such substitution by aluminum ions due to the incorporation of carbonate ions (CO ₃ ^2- ) and water molecules into the structure, which leads to the formation of inter-levels between brucite-like levels.

Hydrotalcites are obtained from hydroxide, oxide or magnesium salt and aluminum salt in an aqueous solution in the presence of carbonate ions. So, a US patent. No. 3539306, C01F 5/00, 1967, describes the preparation of hydrotalcite by reacting aluminum hydroxide, or aluminum salt, or an aluminate solution with an oxide or hydroxide or magnesium salt in an aqueous medium in the presence of carbonate ions at pH 8 or more. U.S. Patent Nos. 4,904,457, CL C01B 31/24, 1985 and No. Re34164, C01B 31/24, 1991, include heating carbonate and / or magnesium hydroxide to 500-900 ° C to form active magnesia (MgO), and then mixing the latter with an aqueous solution in which aluminate, carbonate and hydroxyl ions are present.

A known method for the production of aluminum hydroxide with increased whiteness, including the interaction of a Bayer method aluminate solution with a mixture of magnesium aluminum carbonate: 6MgO · Al ₂ O ₃ · CO ₂ · 12H ₂ O and tricalcium hydroaluminate: 3CaO · Al ₂ O ₃ · 6H ₂ O (Pat. US No. 4915930, class C01F 7/02, 1988).

According to this method, magnesium aluminum carbonate and tricalcium hydroaluminate are obtained by reacting the oxides of the corresponding alkaline earth metals with an aluminate solution. Purification of iron cations is carried out by 50% to obtain aluminum hydroxide, in which the content of iron oxide is about 0.004%, and the whiteness of the product is about 95%.

The disadvantage of this method is its cumbersomeness and low productivity associated with the need to introduce fresh portions of the sorbent into the aluminate solution and the absence of its regeneration.

There is also a method of reducing the content of aluminate solutions of impurities, including iron cations, according to US patent No. 5624646, class. С01F 1/00, 1995 and its analogues: Australian patent No. 681711, class. C22B 3/12, 1994; European patent No. 0714853, cl. 01 F 7/47, 1994, including the purification of solutions in two stages. At the first stage, a solution is filtered to remove suspended particles with a size of 50 μm or less using special equipment for separating small particles (separator, press filter, centrifuge, etc.). After removing such particles from the solution, hydroxide having a whiteness of at least 85% can be isolated. At the second stage, the solution is refined using a complex aluminum- and magnesium-containing sorbent regenerated at 400-650 ° С, mainly consisting of hydrotalcite, at the rate of 0.3-1.0 g / l. After purification, a product with a whiteness of up to 92-94% is obtained.

The disadvantage of this method is its bulkiness and low productivity associated with the need for two-stage cleaning and low productivity of equipment for separating the solid phase in the first stage of cleaning. In addition, high energy costs at the stage of regeneration of the sorbent at the stage of post-treatment.

The closest in technical essence and the achieved effect is a method of reducing the content of aluminate solutions of impurities, including iron cations, including the interaction of the aluminate solution with complex compounds of aluminum and magnesium obtained by calcining the recycled material at a temperature of 400-650 ° C (US Pat. No. 5068095, class C01D 1/32, 1990).

According to the prototype method for producing aluminum hydroxide with a low content of impurities, including iron compounds, the aluminate solution is treated with a substance having a porous, skeletal structure: Mg ₆ Al ₂ O ₈ OH) ₂ . In the prototype method, the sorbent consumption is 1-10 g / l of solution, which allows to obtain a whiteness of salable aluminum hydroxide not higher than 80%.

The disadvantages of the prototype are the lack of cleaning efficiency from impurities (so when adding 5 g / l of sorbent, the degree of purification from iron in 30 minutes of processing does not exceed 35%), as well as the high energy consumption for regeneration of a magnesium-containing sorbent at a temperature of 400-650 ° C.

The technical task of the proposed method is to eliminate these disadvantages, namely increasing the efficiency of purification of aluminate solutions from impurities, as well as reducing energy consumption for the implementation of the process.

The technical result is achieved by the fact that in a method for purifying aluminate solutions from impurities, comprising adding a sorbent based on magnesium compounds into the aluminate solution, interacting with the solution, separating the sorbent from the purified solution, regenerating it by heat treatment and reusing, according to the invention, a sorbent based on magnesium compounds is obtained by treating the aluminate solution with magnesium hydroxide and heat treatment of the obtained solid phase at a temperature of 230-400 ° C, add it to the aluminate solution in the form of water pulp with a concentration of 100-150 g / dm ³ in terms of MgO, and the regeneration of the sorbent is carried out at a temperature of 250-380 ° C.

The method is as follows. After regeneration at a temperature of 250-380 ° C, the initially prepared or reverse magnesium-containing sorbent is fed to the purification of aluminate solutions. Cleaning occurs when the sorbent is mixed with the solution to be cleaned. The solid phase after interaction with the solution being cleaned is separated from the liquid phase by filtration and again subjected to heat treatment (regeneration) at a temperature of 250-380 ° C. Under these conditions of regeneration, the sorbent is obtained not in the form of a crystalline phase, as in the prototype method, but in the form of an amorphous substance, which positively affects its efficiency during cleaning.

As a result of using the proposed method, the degree of purification from impurities contained in aluminate solutions is increased compared with the prototype, and energy costs for the process are also reduced due to the use of lower temperatures at the stage of sorbent regeneration.

At a sorbent regeneration temperature above 380 ° C, energy consumption sharply increases (Table 1), and at a regeneration temperature below 250 ° C, the degree of purification of aluminate solutions from impurities significantly decreases (Table 2).

When a sorbent is introduced into the solution to be purified in the form of an aqueous pulp, the sorption of impurities significantly increases. In this case, the sorbent is evenly distributed in the volume of the solution to be purified, and the surface of the sorbent is better prepared for sorption.

At a concentration of less than 100 g / dm ³ in terms of MgO, no improvement in purification indices is observed (Table 3), but there is a significant dilution of the solutions being purified. At a concentration of more than 150 g / dm ^3, even distribution of the sorbent in the volume of the solution to be purified is impeded, which leads to a decrease in the degree of purification.

Example 1

The initial magnesium-containing sorbent was obtained as a result of synthesis from an aluminate solution containing, g / l: Na ₂ O _total - 236.5; Na ₂ O _ku - 201.1; Al ₂ O ₃ - 114.8; Fe ₂ O ₃ - 0.005, organic matter - 20.3 and magnesium hydroxide, taken from the calculation of 50 g MgO _act per 1 liter of aluminate solution with stirring for 45 minutes at a temperature of 80 ° C. The resulting solid phase was separated from the liquid phase by filtration and subjected to heat treatment (regeneration) at a temperature of 230-400 ° C for 80 min. A reverse sorbent was obtained as a result of heat treatment of the used sorbent under the same conditions. The dependence of the specific consumption of equivalent fuel on the heat treatment temperature of the sorbent is presented in table 1.

To purify the aluminate solution after leaching of bauxite, the magnesium-containing sorbent obtained after heat treatment in the form of an aqueous pulp with a concentration of 120 g / dm ³ in terms of MgO was used. The aluminate solution was treated with a sorbent at the rate of 5 g of sorbent per 1 liter of the solution to be purified at a temperature of 80 ° C for 15 min. The used sorbent was separated from the purified solution and returned to heat treatment (regeneration). The cleaning results depending on the heat treatment temperature of the sorbent are presented in table.2.

Example 2

The sorbent obtained as in example 1, after regeneration at 300 ° C in the form of an aqueous pulp, was used to purify an aluminate solution after leaching of bauxite. The aluminate solution was treated with a sorbent at the rate of 5 g of sorbent per 1 liter of the solution to be purified at a temperature of 80 ° C for 15 min. The cleaning results, depending on the concentration of aqueous pulp in terms of MgO, are presented in Table 3.

Example 3

The sorbent obtained as in example 1, after regeneration at 300 ° C in the form of a powder, was used to purify an aluminate solution after leaching of bauxite. The aluminate solution was treated with a sorbent at the rate of 5 g of sorbent per 1 liter of the solution to be purified at a temperature of 80 ° C for 15 min. The degree of purification was,%: organic matter - 63%; Fe ₂ About ₃ - 52%.

Table 1. No pp Temperature of heat treatment (regeneration) of the sorbent, ° С Specific fuel consumption, kg / t one 230 44 2 250 46 3 300 53 four 380 56 5 400 63

Table 2. No pp Heat treatment temperature The degree of purification of the solution,% (regeneration) of the sorbent, ° С From iron oxides From organic matter one 230 37 59 2 250 53 70 3 300 58 72 four 380 58 68 5 400 56 68

Table 3. No pp Sorbent concentration in The degree of purification of the solution,% water pulp, g / dm ³ in terms of MgO From iron oxides From organic matter one 90 57 71 2 one hundred 57 70 3 120 58 72 four 150 58 71 5 160 55 66

Claims (1)

A method of purifying aluminate solutions from impurities, including adding a sorbent based on magnesium compounds to the aluminate solution, interacting with the solution, separating the sorbent from the purified solution, regenerating it by heat treatment and reusing it, characterized in that the sorbent based on magnesium compounds is obtained by treating the aluminate solution with hydroxide magnesium and heat treatment of the obtained solid phase at a temperature of 230-400 ° C, add it to the aluminate solution in the form of an aqueous pulp with a concentration of 100-150 g / dm ³ in terms of MgO, and the regeneration of the sorbent is carried out at a temperature of 250-380 ° C.