Research On Leaching Of Spent Cathode Pot-Lining With Aluminum Anodizing Wastewater

With the substantial increase of electrolytic aluminum production,the spent pot lining generated from aluminum electrolysis cell are also increased year by year.The spent pot lining are hazardous solid waste which contain a lot of soluble fluoride,and cause serious pollution on the surrounding environment when the spent pot lining are open dumpped or direct landfilled.Meanwhile,In order to improve the surface properties of aluminum and aluminum alloys,the alloys need to be used as an anode immersed in acid to obtain a dense energized surface oxide film.When the aluminum ions in solution reaches a certain concentration,it will affect the surface quality of the film-forming material,it needs to clear some of the electrolyte tank discharge,a large amount of aluminum ions and sulfate-containing waste,on the surrounding environment caused serious pollution.In this paper,a two-step process of leaching soluble fluoride with water and leaching insoluble electrolyte with aluminum anodizing wastewater was adopted to deal with the spent cathode pot-lining.The effects of stirring speed,ratio of solid to liquid and temperature on the leaching rate of electrolyte were examined.And the corresponding reaction kinetics was also analyzed.Leachate is treated recovering valuable components,the final recovery carbonaceous powder and wherein the electrolyte,not only cost savings leaching agents and wastewater treatment,reached by Waste and comprehensive recovery of value purposes,Through the experimental research,the main conclusions are as followed:1)The constituents of the spent pot lining are mainly C,Na₃AlF₆,NaF,Ca_F2,in which the carbon content is up to 68.58%and others are the electrolyte.The fluoride are mainly Na₃AlF₆,CaF₂,NaF,and most of NaF can be solubled at room temperature.2)Spent pot-lining by crushing into 150 mesh powder,with conditions of liquid to solid ratio 4:1,stirring speed 300r/min at room temperature,dissolution 180min,most of NaF dissolution by flooding,residue after aqueous are mainly water-insoluble cryolite,continue to use anodizing waste treatment SPL,by leaching of the remaining insoluble electrolyte with the aluminum ions and the acid in wastewater.3)Treatment SPL were investigated with the conditions of stirring rate,liquid-solid ratio,leaching temperature,leaching time on leaching insoluble electrolyte,the results show that within a certain range,increase the stirring speed,solid-liquid ratio,leaching time,leaching temperature can enhance the leaching rate,determined by single factor experiments of waste cathode optimum leaching parameters:leaching temperature 80?,stirring rate 300 r/min,liquid to solid ratio of 8:1,leaching time 180 min.after two-step leaching,carbon purity can be increased to 95%4)Aqueous extracts and wastewater leaching solution by mixed toghther,the effect of different pH on precipitation was investigated,determined by adjusting the pH of 9 to precipitate cryolite,subsequently investigated the effects of different temperature and F/Al ratio of the amount of precipitation,the results prove that improve F/Al ratio can increase the amount of precipitated cryolite,when the F/Al ratio of 6:1,50m L solution can be recovered 3.14g cryolite and aluminum fluoride ion in solution ions recoveries were more than 95%,by raising the reaction temperature to reach steady-state time can be shortened,the filtered solution was adjusted to neutral and evaporated to get 1.24g sodium sulfate.5)The leaching process in wastewater applies to unreacted core model,by applying stirring 300r/min,By applying 300r min stirring/,you can basically eliminate the influence of external diffusion of electrolyte leaching rate.The effects of different ratio,leaching temperature,reactant liquid-solid particle impact over time on the leaching rate was investigated,different kinetic equation for the relevant fitting,different kinetic equation for the relevant fitting proof waste cathode material in the electrolyte during leaching waste oxidation reaction control links to internal diffusion control,apparent activation energy E is 12.71 kJ/mol,the relationship of kinetic equationswith leaching rate X,time t,liquid to solid ratio L/S,particle diameter D and temperature T is followed:1+2(1-X)-3(1-X)^2/3=5.52×10^-4×(L/S)^0.802×D^-1.014×exp(1.5292×10³/T)t.