Method for treating aluminum electrolytic cell anode carbon slag by using nacl molten salt extraction method

Abstract

A method for processing the anode carbon slag of an aluminum electrolytic cell by using the NaCl molten salt extraction method is carried out according to the following steps: (1) pulverizing the anode carbon slag of the aluminum electrolytic cell; (2) mixing the pulverized carbon slag with NaCl; (3) loading The crucible is heated to 810-1020°C to obtain the molten salt mixture; (4) the molten salt mixture is condensed; it is stirred and dissolved in water to obtain the suspension in the upper layer and the primary precipitation at the bottom; (5) after the suspension is separated from the precipitation Filtrate and filter residue are obtained by filtration; (6) filter residue is washed and dried to obtain a carbon powder; Secondary precipitation, secondary carbon powder and secondary NaCl salt; secondary precipitation is dried to form electrolyte. The method of the invention saves a lot of pretreatment time and cost; the price of raw materials is low, the treatment process is simple, and environmental protection produces no toxic by-products.

Description

technical field [0001] The invention belongs to the technical field of metallurgy and environmental protection, and in particular relates to a method for treating anode carbon slag of an aluminum electrolytic cell by using a NaCl molten salt extraction method. Background technique [0002] The production of metal aluminum by molten salt electrolysis is the only method for industrial aluminum smelting in the world today. This method uses molten cryolite as a solvent, alumina as a raw material, and carbon bodies as anode and cathode. Metal aluminum is obtained by electrolysis at 920-950°C liquid. At present, the aluminum electrolytic prebaked anode is mainly made of aggregate (petroleum coke) and binder (pitch). During the production of electrolytic aluminum, due to the inconsistent oxidation resistance of the aggregate and binder in the carbon anode, the The erosion and scouring of the upper aluminum liquid and electrolyte caused some petroleum coke particles to fall off fro...

AI Technical Summary

Problems solved by technology

The carbon slag in the electrolytic cell is mainly powdery and granular, which is mainly mixed in the electrolyte or suspended on the upper layer of the electrolyte, which will not only affect the physical and chemical properties of the electrolyte, such as conductivity, fluidity, etc. In this case, the pole distance is reduced, which intensifies the secondary dissolution loss of aluminum on the interface between the electrolyte and the molten aluminum, and finally leads to problems such as a decrease in current efficiency.

Therefore, in order to ensure the normal progress of the aluminum electrolysis production process, the carbon slag in the electrolyte of the aluminum electrolytic cell must be salvaged by workers on a regular basis; during the process of salvaging the carbon slag, a large amount of electrolyte adhering to the surface of the carbon slag is salvaged together, and the proportion usually accounts for 60-80%; According to statistics, about 3-5kg of carbon slag is produced for every 1 ton of primary aluminum produced. In 2017, the output of primary aluminum in my country was 32.27 million tons, and the total amount of carbon slag produced by electrolytic aluminum enterprises was about 290,000 tons. 174,000 tons, resulting in a lot of waste of electrolyte

[0004] At present, the methods for separation and recovery of anode carbon slag in aluminum electrolytic cells mainly include the following: (1) flotation method; the carbon slag is ground to a certain concentration and particle size by adding water, adding flotation reagents for stirring treatment, and then entering the flotation machine and importing The air forms air bubbles; the carbon powder floats up to the upper part of the pulp with the air bubbles and is taken out, and the electrolyte is discharged from the bottom flow of the flotation tank, so as to realize the separation of carbon powder and electrolyte in the carbon residue; although flotation has the advantages of low processing cost, less labor and labor intensity small, good production environment, etc., but the electrolyte recovery rate is low, and the carbon content of the recovered electrolyte is high (about 5%), which is not conducive to returning to aluminum electrolysis production; the recovered carbon still contains about 20% of the electrolyte, which contains About 20% of carbonaceous mud is still not easy to handle, and it is also difficult to obtain recycling; flotation wastewater contains fluoride ions, which need to be treated to increase recycling costs; (2) roasting method; charcoal residue is roasted at a certain temperature to make charcoal The charcoal, hydrogen and other combustibles in the slag are fully burned, and the obtained roasted product is the electrolyte, so as to realize the separation of the electrolyte and the carbon in the charcoal slag; the disadvantage is that high-temperature roasting will cause secondary environmental protection problems; the roasting time is long, and the production efficiency is low. It is not conducive to large-scale treatment of carbon slag; the labor intensity of workers is high, and the working environment is harsh; (3) vacuum smelting method; the carbon slag is ground into fine powder, then added with a suitable binder and pressed into agglomerates, and then used in a vacuum furnace The volatile properties of the electrolyte at high temperature make the electrolyte cool and condense in the upper part of the vacuum furnace, while the carbon stays in the tank, so as to achieve the purpose of separation; The carbon content in the carbon residue is about 74%, and harsh conditions such as a certain degree of vacuum are required, which limits the large-scale application and promotion of this method

Some other methods, such as leaching the electrolyte in the carbon residue with acid or alkaline solution, etc., but these methods cannot completely separate the carbon residue and the electrolyte, and the process is complicated and the cost is high, so they have not been applied in industry

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