RU2327642C1 - Charge for alumina production - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention can be implemented at alumina production out of ferriferrous bauxites by a sintering process. Corundum containing wastes are introduced into the charge besides bauxite, limestone, soda, and utilisable products of alumina production such as white slime and soda solution, at that molecular ratio is kept as Fe₂O₃:Al₂O₃=0.17:0.32.

EFFECT: prevents melting of a cake and formation of crusts which increases efficiency of industrial rotating sintering furnaces; also upgrades sintering quality and allows utilising of corundum containing wastes.

3 tbl

Description

The invention relates to the metallurgy of aluminum and can be used to obtain alumina from bauxite by sintering technology.

The so-called stoichiometrically saturated charge for producing alumina is known (Handbook of non-ferrous metals. Production of alumina. M: Metallurgy, 1970, p. 166), consisting of bauxite, limestone and soda, taken in proportions that ensure the observance of molecular ratios:

The disadvantage of this charge is a violation of the sintering process in rotary tube furnaces in cases where bauxite contains a significant proportion of iron oxide (up to 35%), since the formation of a significant amount of low-melting sodium ferrite in the sintered material contributes to the formation of deposits in the furnaces, and reduces their productivity and the quality of the cake .

Closest to the claimed technical solution (prototype) is a method of processing alumina-containing raw materials according to the author's certificate of the USSR No. 481542, class. C01F 7/04, publ. 08.25.75, BI No. 31, 1975, according to which it is recommended to prepare a mixture providing a molecular ratio for sintering highly iron bauxites

This technique allows you to increase the extraction of alumina from the cake into the solution during subsequent leaching. However, the sintering process was carried out by the authors of the prototype in a laboratory shaft furnace, where the sintered material is stationary. When using industrial rotary kilns, the prototype cannot exclude early melting of cake, formation of deposits, which inevitably entails a decrease in the productivity of furnace units.

The objective of the invention is to eliminate the early melting of cake and the formation of accretions, which will allow 2-3% to increase the productivity of industrial rotary sintering furnaces, improve the quality of the cake and utilize corundum-containing waste.

The technical result is achieved by the fact that corundum-containing wastes are additionally introduced into the charge for producing alumina using sintering technology containing highly iron bauxite, limestone, soda and recycled products of alumina production, while observing the molecular ratio Fe ₂ O ₃ : Al ₂ O ₃ = 0.17 ÷ 0.32.

As corundum-containing wastes, abrasive wastes, dump metallurgical slags of aluminothermic reduction processes, etc. can be used.

The invention consists in the following.

Industrial processing of high-iron high-silica bauxite is currently carried out only by sintering technology with limestone and soda. In addition to this raw material and reagents, alumina production products, for example, white sludge, soda solution, etc. The sintering process is carried out in tubular rotary kilns, in which the mixture is heated to a temperature of 1250 ° C. In the presence of a significant amount of fusible components in the charge, for example, sodium ferrite or its eutectic with silicates, the cake can begin to melt before the main target reactions of the formation of sodium aluminate and dicalcium silicate are completed. The fused spec is subsequently poorly processed and considered to be of low quality. In addition, during the fusion of the cake on the walls of the furnaces, treads are formed, to combat which it is necessary to reduce the supply of the initial charge, that is, to reduce the productivity of the furnace units.

On the other hand, the individual processing of corundum-containing wastes into alumina is a very difficult problem, since corundum (fused α-Al ₂ O ₃ ) is the most persistent polymorphic modification of alumina.

It was experimentally established that the combined processing of highly ferrous bauxite and corundum-containing waste onto alumina allows for high extraction of the target component from both types of raw materials and at the same time increase the productivity of industrial rotary sintering furnaces when the composition of the complex charge corresponds to the molecular (ferritic) ratio of Fe ₂ O ₃ : Al ₂ O ₃ = 0.15 ÷ 0.32. The ferritic ratio is selected by the authors of the invention as the main informative parameter for determining the properties of sintered blends.

Examples of the method

At the first stage, laboratory experiments were performed on the sintering of alumina blends of various compositions based on the same starting components (products 1 and 2, Table 1), taken in different ratios.

Table 1 The composition of the feedstock Product Name of alumina raw materials The content of the main components,% Molecular ratio of Fe ₂ O ₃ : Al ₂ O ₃ Al ₂ O ₃ Fe ₂ O ₃ SiO ₂ Cao TiO ₂ one Bauxite 1 46.9 29.0 9.7 1.3 2.9 0.39 2 Corundum waste 1 65,2 0.5 0.4 9.0 17.1 0.05 3 Bauxite 2 50,0 20.7 12.9 1,2 1.3 0.27 four Corundum waste 2 64,2 8.5 3.4 7.0 13,4 0.08

A preliminary calculation of the charges was carried out to perform stoichiometric relationships according to the prototype (2). Blends were obtained by prolonged dry mixing of the initial alumina raw material with limestone and soda in a special mixer with a high-speed propeller mixer. The finished mixture was moistened and pressed into cylindrical briquettes. The briquettes were dried in air for a day and sintered in a laboratory muffle furnace at a temperature of 1250 ° C. The degree of transition to an alumina solution during percolation leaching under standard conditions with a soda-alkaline solution containing, g / l; Na ₂ O _total 48.9; %: Na ₂ O _ku 21.0; Al ₂ O ₃ 11.4. The results are presented in table.2.

It can be seen from the obtained data that when the ferritic ratio is more than 0.32, the molten cake does not leach out enough. In the case of a ferritic ratio of less than 0.17, a small amount of molten liquid phase is formed during sintering, as a result of which the cooled cake becomes unstable, easily crumbles and dusts. It is known from industrial practice that such a material complicates the operation of furnaces and the subsequent leaching process, since industrial percolators with a trellised bottom require not only sinter porosity, but also sufficient particle strength. If the spec is loose, then when it is crushed, a lot of fines are formed, the leaching of which in percolators is difficult and requires additional equipment.

table 2 The conditions and results of laboratory experiments on sintering and leaching Experience number Mass fraction in the ore mixture,% Molecular ratio of Fe ₂ O ₃ : Al ₂ O ₃ Specification Extraction of alumina from cake to solution,% departure bauxite one 0 one hundred 0.39 fused 84.7 2 5 95 0.37 - // - 85.7 3 fifteen 85 0.32 porous, durable 92.3 four 25 75 0.27 - // - 93.2 5 40 60 0.21 - // - 94.6 6 fifty fifty 0.17 - // - 93.9 7 60 40 0.13 friable, crumbling 94.1 8 one hundred 0 0.08 - // - 91.8

At the second stage, industrial tests were conducted on the joint processing of bauxite and corundum-containing waste added to ore in an amount of 9.5% (products 3 and 4, table 1). On the basis of this raw material mixture and working products of alumina production, an experimental charge (sintering pulp) was compiled, the composition of which is illustrated in Table 3. To compare the indicators in the previous tests, the 6-day control period processed the ore without adding corundum waste.

Table 3 The composition of the sintering mixture The content of the main components,% Molecular ratio of Fe ₂ O ₃ : Al ₂ O ₃ Al ₂ O ₃ Cao Fe ₂ O ₃ Na ₂ O SiO ₂ Experienced charge 21.6 11.3 7.3 19,4 6.3 0.22 Control charge 21,2 12,4 7.7 18.6 6.4 0.23

According to the test results, it was found that the use of an experimental charge allows to increase the productivity of furnaces by 2.7% without deteriorating the quality of the cake. Extraction of alumina from the cake to the solution in the percolation leach remained at the same level.

Thus, comparing the data of laboratory and industrial experiments, it is easy to verify the positive effect of the proposed mixture for the joint processing of highly iron bauxite and corundum-containing wastes subject to the claimed ferritic ratio.

Claims (1)

The mixture for producing alumina by sintering technology, containing highly iron bauxite, limestone, soda and recycled products of alumina production, characterized in that it is additionally introduced corundum-containing waste in compliance with the molecular ratio Fe ₂ O ₃ : Al ₂ O ₃ = 0.17 ÷ 0.32.