SU1763369A1 - Method of aluminium hydroxide preparation - Google Patents

Abstract

Usage: the invention can be used in alumina production. SUMMARY OF THE INVENTION: An aluminate solution from the processing of refractory bauxites containing 140-160 g / l NaaOk with a caustic modulus 1.7-1.8 is decomposed with release of aluminum hydroxide in two stages at a temperature of 62-64 ° C in the first stage and the supply to this stage of seed in the amount of 80-120 g / l, using as it a mixture of fine and fine aluminum hydroxide with a specific surface area of 8-10 dm2 / g, respectively, and with a ratio of their surfaces from 1: 1 to 4: 1, and in the second stage, the temperature is reduced to 46-48 ° C and, as a seed, The use form a fine aluminum hydroxide with a specific surface area of 10.8 dm @ 2 / g. 5 tab.

Description

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The invention relates to alumina production and can be used in the decomposition process of high modulus aluminate solutions with an increased concentration (140-160 g / l) according to a two-stage decomposition scheme.

The process of producing aluminum hydroxide from supersaturated aluminate solutions is one of the most complex and expensive conversions in the production of alumina by the Bayer method. The low rate of crystallization, controlled by surface reaction, causes a longer duration of operation and a significant turnover of aluminum hydroxide used as a seed. The growth rate of crystals even in the initial period of the process, with a high supersaturation of the solution, does not exceed 5 µm / h, which complicates obtaining products of a given particle size distribution and does not allow the use of finely dispersed aluminum hydroxide, which has a developed specific surface, as a seed.

A known method of decomposing an alumina solution, to produce aluminum hydroxide of an acceptable size at a sufficiently high productivity of process 1, involves decomposition with feeding of seed aluminum hydroxide in two stages, with fine seed being fed to the 1st stage, and . In the 1st stage, favorable conditions are created for the agglomeration of seed particles (elevated temperature, high ratio of initial supersaturation of solution A s to the surface area of the seed crystals S). At the 2nd stage, the process is conducted under conditions of predominantly linear crystal growth, i.e. with virtually no change in their quantity, by introducing coarse seeds, which provides an increase in the surface area of the particles and an acceptable rate of crystallization.

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The disadvantage of this method is its inefficiency with respect to high modulus solutions (1.7-1.8) with an increased concentration of Na20K (140-160 g / l), since this decreases the degree of decomposition of the solution, increases the turnover of the seed aluminum hydroxide, the modulus of the circulating solution decreases when the mother liquor is evaporated.

The prototype of the method is a scheme for the decomposition of aluminate solutions, which is widely used in domestic alumina refineries / 2 /.

In accordance with this scheme, seed hydroxide (P3 400-600 g / l) is introduced into an alumina solution with elevated Naa C (140-160 g / l) and AK (1.7-1.8) and decomposed within 50-70 h, gradually lowering the temperature. The disadvantages of the prototype method is low productivity of the solution, i.e. the yield of aluminum hydroxide, as well as a significant turnover of seed hydroxide (5–6 times the production one), resulting in the need for substantial areas for thickening and filtration, high energy consumption for mixing, filtration, pumping of the seed.

The aim of the invention is to increase the hydroxide yield.

This goal is achieved by applying a 2-stage decomposition to such solutions of the 1st stage. The amount of seed is 80-120 g / l, and a mixture of fine and fine aluminum hydroxides with a specific surface area of 8-10 dm2 / g is used as a seed. -100-200 dm2 / g with a ratio of their surfaces of 1: 1 to 4: 1, while the 1st stage of decomposition is carried out at a temperature of 62-64 ° C for 6 hours.

Further, at the 2nd stage, the rest (fine) seed is introduced into the hydrated pulp obtained after the 1st stage and the decomposition is continued by gradually lowering the temperature to 46-48 ° C.

Example An industrial aluminate solution containing, g / l: NaaOo - 177.5; No. 20k - 150.7; Na20K6 - 26.8; - 140.8; AK-1.7 is poured into a laboratory de-composer with air mixing, a portion of the seed — industrial aluminum hydroxide from vacuum filters (fine hydroxide), and also fine aluminum hydroxide slurry — are added to the solution. The first stage of decomposition is carried out for 6 hours, then the bulk of the seed is added and the 2nd stage is carried out with a gradual decrease in the temperature of the pulp. The total duration of the operation is 48 hours.

The results of the experiments are given in table. 1-5.

Legend accepted in the tables:

Рз1 - the amount of small seed, introduced at the 1st stage of decomposition (sintering stage), g / l;

Рз2 - the same, at the 2nd stage of decomposition (growth stage), g / l;

РЗ - the total amount of small seed at 2 stages of decomposition, g / l;

5з1 - surface of the small seed, introduced at the 1st stage of decomposition, m2 / l;

5 m - the surface of fine aluminum hydroxide, introduced at the 1st stage of decomposition, m2 / l ;.

“To the caustic modulus of the mother liquor after decomposition;

From the data of table 1, it follows that a decrease in the amount of seed in the first stage below 80 g / l and an increase above 120 g / l leads to a decrease in the yield of aluminum hydroxide.

From tab. 2 shows that the best results were obtained when the ratio of the surfaces of fine and fine seed in the first stage was in the range from 1: 1 to 4: 1 and the specific surface of the fine seed was 8-10 dm2 / g. Going beyond the limits limits the degree of decomposition of the solution, and a decrease in the ratio below 1: 1 also leads to a deterioration in the settling of the hydrated pulp.

In tab. Figures 3, 4 and 5 show, respectively, the effect of the specific surface area of the fine seed, the temperature in the first stage and the final temperature in the second stage. From the above data it follows that the greatest effect is achieved when the specific surface of the fine seed is 100–200 dm2 / g, the temperature in the first stage is 62–64 ° C and the final temperature in the second stage is 46–48 ° C.

Going beyond these limits leads to a decrease in the yield of aluminum hydroxide.

During the decomposition of the solution by a known method in one stage, the yield of Al 2 O 3 was 60.2 g / l.

Thus, the proposed method in comparison with the prototype allows to increase the yield of aluminum hydroxide by 6 g / l.

Claims (1)

Invention Formula A method for producing aluminum hydroxide during the processing of hard-to-open bauxites, including the decomposition of aluminate solutions with a caustic modulus of 1.7-1.8 and a Na20K concentration of 140-160 g / l when seed is fed to them with a decrease solution temperature at the end of decomposition, characterized in that, in order to increase the yield of aluminum hydroxide, decomposition is carried out in two stages, when seed is fed to the first stage in an amount of 80-120 g / l and temperature is 62-64 ° C, and in the second stage decomposition when the temperature is reduced to 46–48 ° C, in the first stage, a mixture of fine and fine aluminum hydroxides with a specific surface area of 8–10 dm / g and 100–200 m2 / g, respectively, is used as a seed and the ratio of their surfaces is 1–4 : 1, and in the second stage, a small seed is used with specific surface 8-10 dm2 / g. T a 6 l and c a 1 Table