RU2167210C2 - Technology of processing of carbonic slime removed from system of electrolytic winning of aluminum - Google Patents

Abstract

FIELD: non-ferrous metallurgy, production of aluminum and alumina. SUBSTANCE: technology is intended for processing of carbonic slime ( tailings of floatation of carbon duct, dust and slime of gas cleaning of electrolysis ) carrying dispersive particles of carbon, fluoride compounds, cryolite, alumina with humidity up to 40% with neutralization of fluoride compounds, cyanides, with recovery of aluminum oxide, alkali metals, with useful utilization of carbon in technological process, with improved ecology of environment. Carbonic slime removed from system of electrolytic winning of aluminum is added as one of components to charge ( pulp ) containing alumina, soda and limestone of alumina production and is subjected to combined thermal treatment at temperature above 100 C in sintering furnace with production of sintered mass. In process of sintering there take place: burning out of slime carbon, formation of sodium (potassium) aluminates, neutralization of soluble fluorides and cyanides. Produced sinter is subjected to hydrochemical treatment in accordance with known methods of alumina production to recover aluminum and alkali metal oxides in the form of alumina, soda, potassium carbonate. Given technology provides for improvement of ecological state of environment, for recovery about 90% of compounds of aluminum and alkali metals contained in starting material and carbonic slime. EFFECT: raised efficiency of proposed technology, improved ecological state of environment. 1 cl, 2 tbl

Description

 The invention relates to non-ferrous metallurgy, in particular to the production of aluminum and alumina, and can be used in the disposal of carbon sludge derived from the electrolytic aluminum production system.

 Carbon sludge discharged from the aluminum electrolytic production system (coal foam flotation tailings, dust and gas treatment sludge from electrolysis production), containing mainly dispersed carbon particles impregnated with cryolite, alumina, with a moisture content of up to 40%, is a waste of electrolysis production. The amount of this sludge accumulated by the enterprises of the aluminum industry in Russia as of January 1, 1999 amounts to ~ 2.4 million tons and is increasing annually by 150 thousand tons.

 A known method of processing carbonaceous sludge, in particular tailings flotation of coal foam according to the copyright certificate of the USSR N 1141083, class. C 04 B 33/00, published on 85.02.23, which provides, in order to reduce the firing temperature while increasing the strength of wall ceramics, the introduction of additional clay - 15-20% and tailings of coal foam flotation - waste from aluminum production - into the raw material mixture for ceramic production -10%.

 Known proposal Arluka B. I. "Improvement of the processing of aluminate-alkaline nepheline cakes", M., 1978, p. 13, 14, adopted as a prototype, on the introduction of additives that intensify the sintering process in the mixture for sintering of alumina production, in particular dust of electrostatic precipitators and sludge from gas purification of electrolyzers containing fluorine, carbon, etc., in an amount corresponding to, in terms of fluorine, ~ 0.25% of the charge mass.

 The disadvantage of this proposal is that these substances are considered only as carriers of fluorine and carbon to intensify the sintering process.

 The technical task is to provide a comprehensive processing of carbon sludge removed from the system for the electrolytic production of aluminum using carbon sludge in the process, extraction of aluminum oxide, alkali metals from the sludge, neutralization of soluble forms of fluorides, cyanides; the use of residues after the extraction of valuable components and removal (oxidation) of carbon in the production of cement, silicate brick, road construction; improvement of the ecological state of the environment by processing carbon sludge in the technological process for the production of alumina with redistribution of sintering.

 The technical result is achieved by the fact that according to the method, carbonaceous sludge with or without regrinding, in the form of pulp or partially dehydrated with a particle size of less than 1 mm, is introduced into the raw alumina-soda-limestone-containing mixture in an amount of up to 10% (by dry weight), which then sent to a sintering furnace (e.g., rotary) of alumina production. The regrinding of carbon sludge is possible together with the grinding of raw materials (limestone, etc.) in the preparation of the mixture for sintering.

In the above mixture with carbonaceous sludge, limestone is introduced in an amount that ensures the binding of fluorine and silicon of the mixture in the form of cuspidine - CaF ₂ • 3CaO • 2SiO ₂ , dicalcium silicate - 2CaO • SiO ₂ , calcium fluoride - CaF ₂ .

Углеродистый шлам, корректирующие состав пульпы добавки известняка и щелочи могут быть введены в нее в любом удобном по технологии месте перед спеканием.The alkali content for the formation of aluminate and sodium ferrite (potassium) is adjusted according to the composition of the mixture before sintering, providing a molecular ratio

Carbon sludge, correcting the composition of the pulp additives of limestone and alkali can be introduced into it in any place convenient for technology before sintering.

When heat treatment in a sintering furnace at a temperature above 1000 ^o C, the charge components interact with the formation of soluble sodium aluminate, hydrolyzable sodium ferrite, insoluble dicalcium silicate, calcium fluoride, cuspidine and other double, triple compounds.

 The carbon component of the charge burns in the furnace, which reduces the specific fuel consumption supplied to the sintering furnace for the implementation of the process.

 Under the influence of high temperatures, decomposition (neutralization) of cyanides occurs with the formation of nitrogen, carbon oxides and nitrogen.

 The sintered mass obtained in the sintering furnace — sinter — is processed by the traditional methods of alumina production to produce alumina, soda products, soda-lime solution and a solid residue — sludge.

 Fluoride compounds bound in the process of sintering into insoluble forms are removed in the composition of the slurry, which, depending on the composition, is directed to the production of cement, silicate brick (white clay slurry), road construction.

 The possibility of implementing the method tested in laboratory conditions; the research results are shown in tables 1 and 2.

 As follows from table 1, the joint processing of carbon sludge with a raw alumina-containing mixture of alumina production allows you to extract a significant amount of aluminum oxides and alkali metals from it simultaneously with an increase in the total extraction of these components from the raw alumina-containing mixture. From table 2 it follows that the introduction of carbonaceous sludge into the raw material charge leads to a decrease in the specific yield of the residue after leaching (sludge) in relation to the mass of the dry charge, reducing the relative amount of waste residue after leaching.

Using the proposed method will allow:
- to improve the ecological state of the environment at the locations of enterprises of the aluminum industry by binding harmful soluble forms of fluorides into insoluble low-hazard forms, neutralizing, decomposing hazardous cyanides into safe nitrogen and oxides of nitrogen and carbon, eliminating (or significantly reducing) sludge fields, and ensuring practically low-waste technology aluminum production;
- extract from raw materials and carbon sludge about 90% of the compounds of aluminum and alkali metals contained in them;
- use carbon contained in the carbon sludge as an energy carrier and a reducing agent;
- use the solid residue after hydrochemical processing of sinter slurry in the production of cement, silicate brick, road construction;
- increase the economic efficiency of the production of alumina and aluminum.

Claims (2)

1. A method for processing carbonaceous sludge withdrawn from an electrolytic production system for aluminum containing carbon particles, various fluoride compounds, cryolite, alumina, with a moisture content of up to 40%, including mixing it with alumina-soda-limestone-containing mixture of alumina production and combined heat treatment, characterized the fact that carbonaceous sludge is introduced into the alumina-soda-limestone-containing mixture of alumina production in the form of pulp or in a partially dehydrated state in an amount of 2-10% by dry weight, with limestone in the mixture is dosed to the formation CaF _2, CaF ₂ • 3CaO • 2SiO _2, 2CaO • SiO _2. 2. The method according to claim 1, characterized in that the soda (in terms of Na ₂ O) is metered into the mixture from the condition of ensuring the molecular ratio:

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