EA015635B1 - Method for processing solid wastes from sludge in aluminum production - Google Patents

Abstract

The invention relates to non-ferrous metallurgy, in particular to methods for processing solid wastes from sludge in aluminum production. The method provides thermal treatment of solid wastes of sludge premixed with cellulose-containing material and surfactants with subsequent grinding and deironing resulting to produce cryolite–aluminous mixture with carbon content being at least 1.5-2.0 wt%.

Description

The invention relates to ferrous metallurgy, and in particular to methods for processing solid waste from a slurry field for aluminum production.

A known method of processing waste sludge field, which allows you to select useful components by converting sulfates into carbonates and flotation to separate coal from cryolite and alumina [1]. However, this method of obtaining a cryolite-alumina mixture requires preliminary washing of the sludge from sulfates and carbonates, followed by flotation of the sludge.

A method for processing solid waste from a sludge field of aluminum production [2] provides for sintering of sludge at a temperature of 750-850 ° C and constant access of air for 20-40 minutes. The resulting cake is ground, leached with water at 70-80 ° C and a ratio of T: W from 1: 3 to 1: 5 for 30-90 minutes. The pulp is filtered, a solution containing sodium aluminate is used as an alkaline coagulant for the treatment of drinking and wastewater, and the precipitate containing cryolite and alumina is dried at 150 ° C for 30-60 minutes and used as raw material for aluminum production.

The disadvantage of this method is the necessity of washing the resulting product from sulfates and sodium aluminate and further drying the resulting cryolite-alumina mixture, which leads to an increase in labor costs and higher cost of the product.

Closest to the claimed invention is a method of processing solid waste from a slurry field of aluminum production [3]. Sludge after natural drying is mixed with a 20-40% surfactant solution in a ratio of T: W from 7: 1 to 10: 1, formed into briquettes, which are dried at a temperature of 100-150 ° C for 1-3 hours and subjected to heat treatment ( sintering) at a temperature of 750-1000 ° C for 2-4 hours with forced removal of combustion products. After sintering (sintering) briquettes are cooled under natural conditions, crushed, sieved and iron removed - the cryolite-alumina mixture obtained in this way with a carbon content of less than 1.5-2.0 wt.% Is used as a raw material for aluminum production. The disadvantages of this method include: uneven sintering, leading to heterogeneous chemical composition of the central and peripheral parts of the briquette, as well as high density and low porosity of the briquettes, which complicates their subsequent grinding. In addition, this method does not provide for the utilization of the heat of the exhaust gases and their purification with the capture of fluorine compounds.

In order to eliminate the existing disadvantages, a method has been developed that involves the preliminary introduction of cellulose-containing materials into the sludge, the combustion of which during heat treatment provides a fairly complete and uniform carbon burnout throughout the entire briquette volume and high briquette porosity.

The method is as follows.

The sludge after natural drying is mixed with cellulose-containing material (wood processing waste - sawdust, wood shavings, wood chips; chopped cotton stalks; dry foliage, etc.) in an amount of 1-3% by weight of the sludge and 20-40% surfactant solution in a ratio of T : W from 7: 1 to 10: 1. The resulting mass is molded into briquettes and dried. Molded briquettes are dried depending on weather and climatic conditions, either under natural conditions or at 100-150 ° C for 1-3 hours. The dried briquettes are subjected to heat treatment (firing), as a result of which various physicochemical processes proceed including intense combustion of carbon. Firing is carried out at 750-1000 ° C for 2-4 hours with constant air access and forced removal of combustion products, which are passed through heat exchangers and soda solution in order to recover heat and trap fluorine compounds. After natural cooling, the briquettes are crushed, passed through a sieve and subjected to iron removal in an electromagnetic trap. The resulting cryolite-alumina mixture containing up to 1.5-2 wt.% Carbon can be used as raw material for the production of aluminum and covering material for the anode array of electrolyzers.

Example.

100 kg of sludge containing, after drying under natural conditions, wt.%: Cryolite 26.7, alumina 18.2, carbon 27.3, sodium sulfate 8.4, sodium carbonate and bicarbonate 6.1, sodium fluoride 3.8, iron oxides 0.8, silicon dioxide 0.7 and moisture 2.5; mixed sequentially with 1.5 kg of sawdust and a surfactant solution obtained by mixing 10 l of water with 2 kg of sodium lignosulfonate. Briquettes were formed from the resulting mass, which were dried in a drying chamber at a temperature of 120 ° C for 2 hours. Then, the briquettes were placed in a furnace, where they were fired at a temperature of 750-1000 ° C for 4 hours with constant access of air and forced removal of combustion products. The combustion products were passed through a heat exchanger and sent to a gas purification system of electrolysis production, in which up to 99% of fluoride compounds were extracted from gaseous products.

After firing, the briquettes were cooled in natural conditions to ambient temperature, then crushed and passed through an electromagnetic trap. The obtained cryolite-alumina mixture contained, wt.%: Cryolite 28.5, alumina 41.2, carbon 1.1, sodium sulfate 2.8, sodium fluoride 8.4, sodium oxide 9.3, iron oxides 1.2, silicon dioxide 1.1.

The method allows for the processing of sludge field waste to obtain raw materials for the production of aluminum and covering material for the anode array of electrolyzers, which leads to lower production costs and improved environmental conditions.

- 1 015635

Information sources:

1. Patent for the invention of T1 147. A method of processing waste sludge field of aluminum production.

2. Eurasian patent No. 003660. A method for processing solid waste from a slurry field of aluminum production. С22В 7/00

3. Small patent for invention No. 345. A method for processing solid waste from a slurry field of aluminum production.

Claims (2)

1. A method of processing solid waste from the slurry field of aluminum production, which consists in the fact that the slurry, after drying under natural conditions, is mixed with a 20-40% surfactant solution in a ratio T: W from 7: 1 to 10: 1, formed into briquettes that are dried at a temperature of 100-150 ° C for 1-3 hours and subjected to heat treatment at a temperature of 750-1000 ° C for 2-4 hours with forced removal of combustion products, after natural cooling, the briquettes are crushed, sieved, subjected to iron removal and get cryolite - alumina mixture containing m less carbon 1.5-2.0 wt.%, characterized in that the sludge is pre-mixed with the cellulose-containing material in an amount of 1-3% by weight of the slurry, and the combustion products are passed through heat exchangers and sodium carbonate solution. 2. The method according to claim 1, characterized in that the briquettes after molding are dried in vivo.