RU2540635C2 - Production of alkaline metal hydrocarboaluminate from natural magnesium-bearing stock - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to nonferrous metallurgy and can be used for synthesis of active additives and for deep purification of aluminate solutions of aluminous production from organic impurities and silica. Proposed process comprises heat treatment of natural magnesium-bearing stock selected from brucite, magnesite and dolomite at 500-700°C for 120-240 min for activation of its magnesia portion. Then it is mixed to interact with alkaline aluminate solution for 5-60 min at 80±5°C.

EFFECT: higher yield and rate owing to formation of active metastable Mg-O complex, higher power efficiency.

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Description

The invention relates to the production of alumina, in particular to the production of active additives, hydrocarbon aluminates of alkaline earth metals used for the purification of aluminate solutions from silica and organic compounds.

A method of producing alkaline earth metal hydrocarbon aluminates includes crushing and grinding natural magnesium-containing raw materials to a particle size> 1 mm, heat treatment of the material in the range of 550-700 ° C, interaction of activated raw materials selected from brucite, magnesite and dolomite with an alkaline aluminate solution at a temperature of about 80 ° C for 5-30 minutes, separating the unreacted part by decantation methods, to obtain a mixture of magnesium hydrocarbon aluminates (80-100%) and calcium (20-0%), characterized in that the activation of nature th magnesium raw material is produced by treating temperature in the range 550-700 ° C.

A known method of producing synthetic hydrotalcite and antacid (US patent No. 3650704, publ. 03/21/1972). Magnesium hydrocarboaluminate was prepared by adding an aqueous solution of aluminum sulfate and sodium carbonate to a suspension of magnesium hydroxide. The pulp was then washed with water until complete removal of sulfate ions. The suspension was heated to 85 ° C for 3 hours, the precipitate was dried. As magnesium-containing compounds claimed oxide, hydroxide, magnesium carbonate, as well as water-soluble salts of magnesium, such as chloride, nitrate and magnesium sulfate.

The disadvantages of the method are the duration of the process and the low degree of conversion, the expenditure of expensive salts of magnesium.

A known method of producing crystalline magnesium hydrocarbonaluminate (US patent No. 4539195, publ. 2.09.1985,). The process includes the conversion of aluminum hydroxide and basic magnesium carbonate in the presence of at least one component - magnesium oxide or hydroxide. Mixing occurs stoichiometrically in terms of aluminum or magnesium. The process is carried out at a temperature of 50-100 ° C, the resulting product is subjected to spray drying. The result is a chemically unbound mixture of magnesium carbonate with aluminate compounds.

The disadvantages of the method are the low degree of conversion and the formation of a chemical unbound mixture of magnesium carbonate with aluminum hydroxide.

A known method of producing magnesium aluminate (RF patent No. 2359913, publ. 10.08.2001). It includes a mixture of magnesium hydroxocarbonate or magnesium hydroxide with aluminum hydroxide and heat treatment in the presence of carbon monoxide CO with a partial pressure of 0.02-0.2 atm at a heating rate of 20-100 ° C / h.

The disadvantages of the method is the low efficiency and duration of the process.

A known method of producing a hydrated hydroxoaluminate of the formula Mg6Al ₂ (OH) 18 · 4H ₂ O (RF patent No. 2275331, publ. 07/10/2005), which consists in the interaction of a solution of sodium aluminate with a caustic module 3.64-3.7 with a solution of magnesium chloride with a concentration of magnesium chloride of 5-10 wt.%, the resulting mixture is stirred at a temperature of 80-100 ° C for 1-3 hours

The disadvantage of this method is the low efficiency of the method, the contamination of the aluminate solution with chloride ion.

A known method of producing highly dispersed magnesium aluminate (RF patent No. 2457181, publ. July 27, 2012), in which magnesium hydroxide and aluminum hydroxide in a weight ratio of 2.69: 1 are mixed and subjected to mechanical activation in highly stressed planetary centrifugal mills for 5-15 when the ratio of the weight of the sample to the mass of the ball load is 1: 10-1: 30 and acceleration upon activation of 20-40 g. Activation products are treated with water at temperatures of 20-95 ° C and a time of 0.25-2 hours, filtered, dried and subjected to thermal processing at a temperature not lower than 800 ° C in those ix 2-4 hours. The invention allows to obtain powdered magnesium aluminate with a specific surface area of from 80 to 260 m ² / g. This method allows to obtain an active additive with a developed specific surface area and involves the stage of activation, was selected as a prototype.

The technical result of the invention is to increase the degree and speed of formation of hydrocarbon aluminates of alkaline earth metals from natural raw materials, as well as improving the energy efficiency of the process.

The technical result is achieved by the fact that in the method for producing hydrocarbon aluminates of alkaline earth metals, including crushing and grinding of natural magnesium-containing raw materials selected from brucite, magnesite and dolomite, to activate its magnesian part and subsequent interaction with active stirring with an alkaline aluminate solution, the treatment is carried out at 500 to 700 ° C from 120 to 240 minutes, and interaction with an alkaline aluminate solution is carried out for 5 to 60 minutes at a temperature of 80 ± 50 ° C.

To obtain a high-purity product, the magnesia portion of natural magnesium-containing raw materials must be activated. Otherwise, a low degree of conversion is observed, and the resulting product will contain a large number of impurity phases, which will affect the quality of the product.

The activation of the magnesia portion can be carried out by heating the magnesium-containing compounds in the temperature range of 500-700 ° C. At temperatures below 500 ° C, the final product will contain a significant amount of inactive phases (mainly magnesium hydroxide and carbonate). At temperatures above 700 ° C, less active forms of magnesium oxide are obtained. The effects of inactive forms can be avoided by heating the magnesium-containing raw materials to temperatures below 700 ° C, in order to activate the magnesian part to the active magnesium oxide (MgO _act ).

According to the proposed method, the complete formation of the phase of magnesium hydrocarboaluminate ends within 5-15 minutes, the degree of conversion of more than 95%. If the natural material, in addition to magnesium salt, contains another compound in significant quantities, such as, for example, CaCO ₃ in dolomite, then the latter does not decompose during the heat treatment. The degree of conversion of CaCO ₃ to calcium hydrocarbon aluminate 4CaO · Al ₂ O ₃ · 0.5CO ₂ · 11H ₂ O is controlled by the duration of the interaction of alkaline aluminate solutions with the feed and varies between 0-19% of the CaCO ₃ content in dolomite so that it the share in the prepared preparation did not exceed 20%.

The temperature range was chosen in such a way as to convert the magnesium component into its most active form, and calcium compounds did not undergo any structural changes. This will significantly reduce energy costs for processing raw materials (for the decomposition of calcite, heating to 900-1000 ° C is necessary). Thus, the scheme for the formation of hydrocarbon aluminate phases for calcium and magnesium is described by the equations

Studies of the kinetics of the formation of magnesium hydrocarbon aluminate revealed the transience of the reaction, provided that the carbonate and / or magnesium hydroxide is activated in the temperature range 500-700 ° C. It was also found that the magnesium hydrocarbon aluminate phase recorded already in the first minute of interaction is stable at various temperatures and concentrations for a long time (after 140 hours no changes were detected). It is known that calcium carbonate is also an unstable phase in alkaline-aluminate solutions and, at elevated temperatures, tends to go into the stable phase of a cubic six-water tricalcium aluminate, which occurs through a phase of unsaturated calcium hydrocarbon aluminate. The high reaction rate for the formation of HCAM allows you to "catch" calcium at the stage of hydrocarbonaluminate. Moreover, the degree of transformation of calcite can be controlled by the duration of interaction in the range of 5-60 minutes.

в алюминатном растворе, учитывая каустифицирующий потенциал реакции (1), можно, ограничив степень превращения карбоната кальция значением 20%, что определяется простым расчетом.As follows from reaction (2), the transformation of CaCO ₃ → 4CaO · Al ₂ O ₃ · 0.5CO ₂ · 11H ₂ O is also associated with the conversion of expensive caustic alkali to carbonate, which is extremely undesirable in the context of metallurgical production. Avoid additional accumulation of carbonate ion $$C{O}_3^{2-}$$

in an aluminate solution, taking into account the causticizing potential of reaction (1), it is possible by limiting the degree of conversion of calcium carbonate to 20%, which is determined by a simple calculation.

The activated material is added to an aqueous alkaline aluminate solution, including one containing carbonate ion. The proposed method is carried out in an environment of strong electrolytes, pH greater than 13, which contributes to the implementation of the process within a few minutes.

As the conversion medium, a synthetic solution containing sodium hydroxide, sodium carbonate (optionally in the case of systems with dolomite) and aluminate ion can be used. Real aluminate solutions of alumina production can also be used for the synthesis of substances.

Solutions of alumina production have the following composition, g / l: 120-250 Na ₂ O _to, 20-100 Na ₂ CO _3, 50-120 and Al ₂ O _3. As studies have shown, such a composition favorably affects the quality and yield of the resulting product. It was possible to obtain sufficiently pure samples both in artificial systems and from industrial aluminate solutions.

The synthesis should be carried out at a temperature of 80 ± 5 ° C. Lower temperatures reduce the degree of conversion and reaction rate, higher temperatures increase energy costs and contribute to excessive evaporation of water.

The activated magnesium-containing material in an amount of 30-250 g / l is added to the alkaline aluminate solution heated to the process temperature. The synthesis is carried out with vigorous stirring.

The process is conducted for 5-60 minutes until the completion of the formation of magnesium hydrocarbon aluminate and the necessary degree of conversion of the phase of calcium hydrocarbon aluminate. Time is determined experimentally.

Unreacted residue is separated by decantation, because its deposition rate is at least three times higher than the deposition rate of calcium and magnesium hydrocarboaluminates.

The proposed method provides a high yield and degree of purity of the product, which is more than 95%.

The compounds obtained by this method were analyzed by quantitative, X-ray phase and thermogravimetric methods. The products obtained by the examples below were analyzed on an XRD-7000 diffractometer company "Shimadzu". X-ray phase analysis of the samples (figure 1) showed that the product is a high purity magnesium hydrocarbon aluminate. A comparison of the main diffraction peaks of the synthesized products and the natural analogue - hydrotalcite (magnesium hydrocarbon aluminate of the formula Mg ₆ Al ₂ (OH) ₁₈ CO ₃ · 4H ₂ O) is presented in table 1.

High purity of the sample in the context of this invention means the absence of diffraction lines inherent in other magnesium compounds. The non-existence of uncharacteristic lines in the diffraction pattern indicate the absence of other compounds in any significant quantities.

The degree of crystallization of the substance can be estimated by the width of the peaks. Narrow intense peaks indicate a high degree of crystallization of the samples, as well as their homogeneity and isotropy of physicochemical properties.

The synthesized hydrocarboaluminates have lamellar morphology. The particle size distribution mainly depends on the synthesis conditions and varies within a few hundred nm to micrometers in the horizontal plane. The main plates are characterized by a distinct hexagonal shape and sharp edges. The asymmetric nature of the main particles is also noticeable. An electron micrograph of sample 1 is shown in FIG. 3.

The synthesized substances, having a developed specific surface area of 90-200 m ² / g, can be used as an adsorbent of impurities of organic compounds characteristic of industrial aluminate solutions of Bayer technology, as well as in the purification of aluminate solutions of nepheline technology from silica.

Example 1

The crushed magnesium carbonate (magnesite) in an amount of 50 g was heated to a temperature of 500 ° C for 15 minutes, then cooled in a desiccator. The resulting magnesium oxide, in an amount of 23 g, was added to the synthetic solution.

The solution was prepared by introducing 9 g of aluminum chips of grade A 999 to 200 ml of an aqueous solution containing 200 g / l Na ₂ O _k , an additional carbonate ion was introduced in the form of Na ₂ CO ₃ , in terms of Na ₂ O _kb , = 30.7 g / l The solution was heated to 80 ° C, then activated feed was added. The mixture was stirred (180 rpm) for 180 minutes, then the pulp was filtered. The precipitate was washed and dried at 105 ° C for 12 hours.

The final product, magnesium hydrocarboaluminate with a specific surface of 205 m ² / g, was characterized by a high degree of whiteness and weighed about 54.8 g, which means a yield of at least 95%. The precipitate was analyzed by x-ray phase method, which confirmed the formation of high purity hydrocarbon aluminate. The results of the analysis are presented in table 2.

The resulting hydrocarbonaluminate in an amount of 2 g was added to 100 ml of an evaporated aluminate solution of the Bayer scheme, stirring was carried out for 5 minutes, then the solid was separated by filtration. Received brown cake (hydrocarboaluminate with sorbed organic compounds) and a clarified aluminate solution, the degree of purification from organic substances 48%.

Example 2

The crushed magnesium hydroxide (brucite) in an amount of 25 g was subjected to a heat treatment of 500 ° C for 60 minutes. A period of 60 minutes was chosen to complete the activation process; it is selected in each case, depending on the quantity and size of the material and the processing temperature. Usually, this period varies between 30-120 minutes.

9 g of activated MgO was added to 75 ml of an evaporated aluminate solution of the Nikolaev Alumina Plant, containing, g / l: 90 Al ₂ O ₃ , 260 Na ₂ O _about ; α _k = 4.2. The mixture was heated to 80 ° C and stirred at a speed of 180 rpm for 30 minutes. Then the pulp was filtered, the cake was washed and dried at a temperature of 105 ° C for 12 hours. The resulting sample of red color weighed 21.8 g. An X-ray phase analysis showed the formation of a hydrotalcite phase to a large extent. The results of the analysis are presented in table 3.

Example 3

As a magnesium-containing raw material, dolomite of the composition was taken,%: CaO 28.47, MgO 20.43, Al ₂ O ₃ 0.69, SiO ₂ 3.68, pp 45, 23.

To activate the magnesian part, dolomite in an amount of 100 g was subjected to heat treatment at 500 ° C for 60 minutes.

75 g of activated raw material was added to 200 ml of an evaporated aluminate solution of the Nikolaev Alumina Plant, containing, g / l: 90 Al ₂ O ₃ , 260 Na ₂ O _about ; α _k = 4.2. The mixture was heated to 80 ° C and stirred at a speed of 180 rpm for 15 minutes. The rate of sedimentation of the unreacted residue is approximately 3 times higher than that of hydrocarbon aluminates. The residue was separated by decantation. Then the hydrocarbon aluminate pulp was filtered, the cake was washed and dried at a temperature of 105 ° C for 12 hours. The resulting sample weighed 61 g, a degree of purity of 94%. The mass of unreacted residue after drying is 42 g, the residue is mainly represented by calcium carbonate CaCO ₃ . The results of the analysis are presented in table 4.

FIG. 1 - X-ray diffraction pattern of the synthesized hydrocarboaluminate.

FIG. 2 - Thermogram of the synthesized hydrocarboaluminate.

FIG. 3 - Micrograph of the synthesized hydrocarbonaluminate (× 2500).

Table 1 Natural hydrotalcite (Ural) Synthesized Magnesium Hydrocarboaluminate A mixture of calcium and magnesium hydrocarboaluminates (20% HCAC, 80% HCAM) dÅ I / I ₀ dÅ I / I ₀ dÅ I / I ₀ 7.84 one hundred 7.7 one hundred 7.67 one hundred 3.92 61 3.83 40 3.8 60 2.62 5 2.61 twenty 2.87 8 1.87 2 2.29 17 2.6 24 - - 1.96 8 2.48 8 - - - - 2,3 fourteen - - - - 2.02 2 - - - - 1.86 6

Table 2 m in the initial solution, g m in sediment (according to gravimetric analysis) Theoretical calculation of GKAM g % g % MgO 23 23 42 23 39.7 Al ₂ O ₃ 17 9.3 17 9.8 16.9 CO ₂ 4.36 4.0 7.3 4.2 7.3 Other - 18.5 33.7 20.7 36.1 Total - 54.8 one hundred 57.7 one hundred

Table 3 m in the initial solution, g m in sediment (according to gravimetric analysis) Theoretical calculation of GKAM g % g % MgO 9 9 41.3 8.7 39.7 Al ₂ O ₃ 6.75 3.2 14.7 3,7 16.9 CO ₂ 1,6 1.4 6.4 1,6 7.3 Other - 8.2 37.6 7.9 36.1 Total - 21.8 one hundred 21.9 one hundred

Table 4 m ref, g m in sediment (according to gravimetric analysis) Theoretical calculation of the mixture g % g % MgO 19 18.7 30.7 19 32,7 Cao 26 6.4 10.5 4.4 7.6 Al ₂ O ₃ eighteen 9.9 16,2 10 17,2 CO ₂ (dolomite) twenty 5.41 8.9 3.88 6.7 Other - 20.59 33.7 20.72 35.8 Total - 61 one hundred 58 one hundred

Claims (1)

A method of producing alkaline earth metal hydrocarboaluminates, including the temperature treatment of natural magnesium-containing raw materials selected from brucite, magnesite and dolomite, to activate its magnesian part and subsequent interaction with active stirring with an alkaline aluminate solution, characterized in that the treatment is carried out at from 500 to 700 ° C from 120 to 240 minutes, and interaction with an alkaline aluminate solution is carried out for 5 to 60 minutes at a temperature of 80 ± 5 ° C.

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