Method and system for converting sodium-containing and fluorine-containing compounds in waste cathode carbon block of aluminum electrolytic cell

Abstract

The invention relates to a method and system for converting sodium-containing and fluorine-containing compounds in a waste cathode carbon block of an aluminum electrolytic cell. The conversion methodcomprises the step that a conversion agent is used for converting the sodium-containing compound in the waste cathode carbon block of the aluminum electrolytic cell into a fluorine-free soluble sodiumcompound, converting the fluorine-containing compound into an insoluble and harmless mineral fluorine compound and converting a cyanide-containing compound into harmless N2 or NH3 and CO2 in an oxidized manner through a mechanochemical conversion reaction in a conversion mill, and therefore the hazards of fluoride and cyanide in the waste cathode carbon block of the aluminum electrolytic cell arecompletely eliminated. The conversion system comprises a waste cathode carbon block crushing device, a milling device, the conversion mill, a stirred reactor and a solid-liquid separation device which are sequentially connected in series, and the solid-liquid separation device is then directly connected with a concentration or crystallization device and a drying or heat treatment device, and thedrying or heat treatment device is connected to the crushing device. By means of the method and system, the process is simple, mass production is easy, the production cost is low, pollution of three wastes is avoided, and the method and system are environmentally friendly.

Description

technical field [0001] The invention relates to a method and system for converting sodium-containing and fluorine-containing compounds in waste cathode carbon blocks of aluminum electrolytic cells, and belongs to the technical field of harmless and resourceful utilization of solid waste in the electrolytic aluminum industry. Background technique [0002] By 2017, China has built about 45 million tons of aluminum electrolytic production capacity, and the actual output exceeds 36 million tons, accounting for more than 50% of the global electrolytic aluminum production capacity. During the production process of aluminum electrolysis, the carbon cathode expands due to the penetration of fluorine-containing salts, which further causes damage to the electrolytic cell and scraps it. Aluminum electrolytic cells generally need to be shut down for overhaul after about 4 to 6 years of use, and all waste tank lining materials (referred to as overhaul slag) are taken out, and spent catho...

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Problems solved by technology

[0025] The current wet treatment technology has at least the following main problems: first, the large amount of salty and fluorine-containing wastewater produced has not been effectively treated, causing secondary pollution; the produced H 2 、CH 4 , NH 3 The gas is not controlled and utilized, and the generated HF causes serious pollution

Second, the recovered electrolyte and carbon materials contain too many impurities and cannot be used directly

Third, the process route is cumbersome, the technology is complicated, the equipment is severely corroded, and the processing cost is too high

Fourth, due to the influence of factors such as the difference in the capacity and age of the electrolytic aluminum tank, the fluctuation of the composition, and the particle size of the powder, it is difficult to control the process parameters

[0026] The current fire treatment technology has at least the following main problems: First, the tail gas that produces a large amount of entrained HF and dust needs to be treated

Second, the recovery of electrolyte salt is not complete, and it needs further treatment if it remains in carbon materials or slag

Third, the electrolyte salt with a low melting point melts and agglomerates in the furnace, resulting in a large residual amount of incomplete oxidation and combustion of the carbon material. The melting and agglomeration in the furnace leads to deterioration of production conditions and poor production stability

Fourth, it is difficult for the reaction materials to achieve uniform mixing at the molecular level, resulting in incomplete conversion reactions

Fifth, the equipment is seriously corroded and the energy consumption is high

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