RU2381992C2 - Method of receiving of sandy argil at reprocessing of argil-bearing raw material by method of sintering - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: at reprocessing of low-grade argil-bearing raw material by sintering method aluminium hydrate is extracted from aluminate mud at presence of inoculating aluminium hydrate successively by carbonation and decomposition. At stage of carbonation it is introduced inoculating aluminium hydrate with content of grade - 45 mcm in amount 80-100% and inoculating ratio is kept in the range 0.02-0.25 units. During carbonation of aluminate mud it is possible introduction of crystal growth modifying agent. Received aluminium hydrate is subject to filtering, flushing and calcification. Expected saving rate from receiving of sandy argil is 3.53 mln. dollar per year.

EFFECT: invention provides receiving of uniform by garin-composition aluminium hydrate with minimal content of smalls and coarse grains.

2 cl, 2 dwg, 4 tbl

Description

The invention relates to the field of production of metallurgical alumina in the processing of low-quality alumina-containing raw materials.

A known method of producing alumina from low-quality alumina-containing raw materials (sinter bauxite and nepheline ores), which consists in sintering it with limestone and soda to obtain cake and aluminate solution after leaching, decomposing the resulting solution with sequential use of carbonization techniques and decomposition to separate crystalline aluminum hydroxide and its subsequent calcination [Liner A.I. and others. Production of alumina. Moscow, Metallurgy Publishing House, 1978, p.184-192].

The disadvantage of this method is to obtain alumina powdery type heterogeneous particle size distribution, with a large number of small fractions of 45 microns.

The closest in technological essence and the achieved result is a method for producing alumina in the processing of nepheline ores, including the preparation of a three-component mixture (nepheline + limestone + soda) and its sintering [A. Liner and others. Production of alumina. Moscow, Metallurgy Publishing House, 1978, p.188]. From the cake after the leaching and desiliconization operations, an aluminate solution is obtained, from which aluminum hydroxide is isolated and calcined to obtain alumina in the presence of seed hydroxide, applying sequentially carbonization and decomposition.

The disadvantage of this method is the production of intermediate or powdery alumina of an inhomogeneous particle size distribution with a large amount of up to 35% of small particles less than 45 microns (-45 microns) and large particles larger than 125 microns (+125 microns).

When carrying out the electrolysis process of such alumina, a deterioration in the electrolysis performance is noted compared to imported sand containing not more than 10% classes of -45 microns and not more than 10% +125 microns:

- an increase in alumina losses during transportation and loading into bathtubs due to the large number of fine fractions;

- a decrease in the rate of dissolution of alumina in the electrolyte due to the large number of large fractions;

- an increase in the frequency of anode effects and a decrease in the current output of aluminum;

- a decrease in the rate of alumina outflow in the APG system with the point feed of electrolyzers.

The purpose of the invention is to obtain alumina of a uniform composition, the so-called "sand type" or "Sandi" with a grade of -45 and +125 microns of not more than 10% each, improving the consumer properties of alumina and improving the performance of the electrolysis process.

This goal is achieved by the fact that at the stage of carbonization a small seed hydroxide is used in an amount of 80-100%, obtained by isolating classes of less than 45 microns from production or seed aluminum hydroxide, with a seed ratio (Z.O. = ratio of the amount of alumina contained in the seed, to alumina in solution) 0.02-0.25 units. using crystal growth modifiers (RTOs) to intensify the agglomeration of small particles.

The claimed method, in contrast to the known methods and the method adopted for the prototype, has the presence of new distinctive features.

A distinctive feature of the proposed method is the classification of aluminum hydroxide obtained at the 1st stage of carbonization or at the decomposition stage, with the separation of fractions less than 45 microns from it and returning them to the head of the process for aggregation (agglomeration).

In contrast to the existing carbonization method, in order to accelerate the agglomeration of particles into the aluminate solution supplied to carbonization, a synthetic reagent is introduced - a crystal growth modifier (MRC), which allows to accelerate particle agglomeration. As an RTO, a mixture of organic components is used, which include aliphatic components and surfactants, for example, mineral oils, residues of distillation of fatty alcohols and their derivatives. Surfactant components strongly affect surface adsorption and can reduce the surface tension of the solvent and change the surface composition and structure of the system when applied in small doses. The mechanism of action of surfactants depends on their adsorption on the surface and the formation of mycelia in solution.

The need to improve the particle size distribution of aluminum hydroxide is due to the fact that the particle size distribution of commercial alumina depends on its size and uniformity.

When using unclassified seed in the method adopted for the prototype, in production hydroxide receive up to 22% of the class -45 μm and up to 35% of the class +125 μm (table 1, p. 1). During calcination, the crystals are slightly crushed and up to 25% of the -45 micron class, up to 30% +125 micron is contained in commercial alumina. The number of fractions 45 ÷ 125 microns most favorable for electrolysis does not exceed 50%, against 75-80% in imported alumina.

Table 1 Granulometric composition of products -45 μm,% +125 μm,% ⌀ average, microns Class content 45-125 μm,% 1. Prototype hydroxide 22 35 103 43 alumina 25 thirty 99 45 2. The proposed method hydroxide 7.1 5.2 72.1 87.7 alumina 9.5 3.2 69.8 87.3

table 2 Granulometric composition of the introduced seed -45 μm,% +125 μm,% ⌀ average, microns 1. Prototype 22 35 103 2. The proposed method 98 0 24

Laboratory studies found that the use of unclassified seed (Table 2, p. 1) during carbonization leads to the production of aluminum hydroxide that is heterogeneous in grain size, a more uniform hydroxide is obtained during carbonization without seed, but in alumina it increases to 0.47% alkali content (table 3, p. 1), which is higher than permissible according to GOST.

Putting a small seed into the carbonization stage (Table 2, Clause 2) makes it possible to obtain aluminum hydroxide more uniform in grain size with a low content of large fractions (see Fig. 1) and low alkali content, not more than 0.35%, but the amount of small fractions will remain at the level of 22.6% (Table 3, Clause 2).

In order to reduce the content of fine fractions, a synthetic additive, a growth modifier (MRC), is introduced into the aluminate solution before carbonization, which enhances the agglomeration of fine particles and makes it possible to obtain hydroxide with a fines content of not more than 10%. The content of classes 45 ÷ 125 μm is 87% (table 3, p. 3).

Crystal optical analysis showed that the precipitate consists of homogeneous particles.

The proposed method has been tested on a semi-industrial scale upon receipt of alumina from the Kiya-Shaltyrskoye nepheline in JSC "AGC". The main stages in the processing of nepheline by sintering: preparation of the mixture, preparation of the cake and its leaching, desalination of aluminate solutions, filtration and washing of aluminum hydroxide and its subsequent calcination worked without changing the scheme. In the process of sequential carbonization and decomposition of siliceous aluminate solutions, an additional separation of aluminum hydroxide fractions of less than 45 μm was carried out and their agglomeration.

To do this, in the existing scheme for the production of aluminum hydroxide during sequential carbonization and decomposition of aluminate solutions were additionally introduced (see figure 2):

- a classification unit for the production pulp after the tail decomposers of the soda-alkali branch with the separation of small fractions of -45 μm into a separate product and large fractions of +45 μm in the form of production pulp of aluminum hydroxide with a content of fractions of -45 μm not more than 10%;

- a thickening unit for the selected “fines” on single-layer thickeners with a diameter of 15 m with the addition of a flocculant to increase the deposition rate of fractions of -45 μm to obtain a clean drain;

- a filtration unit, consisting of two BOU-40 drum filters and mixers under them for repulping the obtained cake with a deeply desilinated aluminate solution (10% of the total flow);

- a unit for dosing pulp of fine fractions for agglomeration into the head carbonizers of the soda branch;

- a unit for the preparation and dosage of a crystal growth modifier to increase the efficiency of agglomeration.

Semi-industrial tests of agglomeration on one third of the total flow of an aluminate stream solution showed a decrease in the grade content of less than 45 μm in alumina by 3%, when using the method throughout the stream, the decrease would be at least 10%.

The proposed method will reduce, compared with the prototype, the content of small and large fractions and obtain a homogeneous alumina in structure. When filtering and washing aluminum hydroxide, the moisture content of aluminum hydroxide will decrease by 1-1.5% due to a more even distribution of the material in the filtered layer with a decrease in the amount of fines from 20 to 7% and fuel oil consumption for calcination will decrease, saving $ 44.4 thousand ., see table 4. In electrolysis by reducing the grade of -45 microns from 24.5% to 10% according to the "Technical and Economic Assessment of the Efficiency of Using Alumina with Different Content of the 45 micron Fraction in Aluminum Production", the total profit increase will amount to $ 5.76 / t of aluminum. The total economic effect with a specific consumption of 1.924 tons of alumina per 1 ton of aluminum and the production of 1110 thousand tons of alumina per year will amount to $ 3.53 million.

Table 3 Granulometric composition of products -45 μm,% +125 μm,% ⌀ average, microns Class content 45-125 μm,% The content of R ₂ O total,% Prototype 1. Without seed hydroxide 20.3 8.6 71.7 73.1 0.47 alumina 24.5 6.6 69.1 69.1 0.47 The proposed method 2. Fine seed hydroxide 22.6 0.2 56.6 77,2 0.35 alumina 24.8 0.1 55.1 75.1 0.35 The proposed method 3. With fine seed and modifier hydroxide 7.1 5.2 72.1 87.7 0.35 alumina 9.5 3.2 69.8 87.3 0.35

Table 4 Expected Economic Benefits of Sand Alumina Production Saving article For 1 ton of alumina Price per unit, USD For the production of 1110 thousand tons of alumina per year, dollars Fuel oil savings with a 1.5% reduction in hydroxide moisture 0.0018 t one hundred 200,000 Increased profits from improved electrolysis rates 3 $ 3 3 330 000 Cumulative effect 3,530,000

Claims (2)

1. The method of producing sand-type alumina in the processing of low-quality alumina-containing raw materials by sintering, including the separation of aluminum hydroxide from an aluminate solution in the presence of seed aluminum hydroxide sequentially by carbonization and decomposition, filtration, washing of aluminum hydroxide and its subsequent calcination, characterized in that it is introduced into the carbonization stage seed aluminum hydroxide with a grade of -45 μm in an amount of 80-100%, and the seed ratio is maintained within 0 , 02-0.25 units. 2. The method according to claim 1, characterized in that during carbonization, a crystal growth modifier is introduced.

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