Study On Recovery Process Of Carbon And Sodium Fluoride In Aluminum Electrolytic Spent Pot Lining

In 2019,China's aluminum electrolytic production capacity reached 35.7 million tons.Based on the calculation of 30 kg of spent pot lining produced per ton of electrolytic aluminum,1.071 million tons of spent pot lining were produced in 2019 alone.Because the content of sodium fluoride in the spent pot lining is more than 30%,if it is stacked randomly,its soluble fluorine will cause great harm to the soil and groundwater.In 2016,spent pot lining were included in the "National Hazardous Waste List",waste code 321-023-48,and the hazardous characteristic was "T"(toxic).With the country's emphasis on environmental protection,the recycling of spent pot lining has become got hot.This study aimed at the recovery of carbon and sodium fluoride in spent pot lining,and carried out the following studies:(1)Crush the spent pot lining to a particle size of less than 170 mesh,under the conditions of time 50 min,temperature 80°C,and liquid-solid ratio 20:1,the experiment of removing sodium fluoride with water was carried out,and the solution was separated by filtration.After processing,a filter cake with a carbon purity of 57.34% was obtained.The filtrate was evaporated and crystallized to obtain sodium fluoride with a purity of 96.42%,and the recovery rate was 94.50%.(2)The alkali-eluting silicon experiment was performed on the filter cake with a carbon content of 57.34% after washing.The experimental conditions were: time 100 min,temperature 140°C,mass fraction 50%,and liquid-solid ratio 5:1,the desiliconization rate was 92.76%.After filtration and separation,a filter cake with a carbon purity of 74.73% can be obtained,and the alkaline washing waste liquid is used for future use.(3)An experiment of removing calcium hydroxide by aciding a filter cake having a carbon content of 74.73% after alkaline washing.The experimental conditions are: temperature 70°C,mass fraction 15%,time 80 min,and liquid-solid ratio 5:1.Carry out the experiment and separate by filtration to obtain 97.27% carbon.The acid washing filtrate is mixed with the alkali washing filtrate to generate calcium hydroxide removed by the acid washing process,and the filtrate is separated.The filtrate is adjusted to pH =9 by hydrochloric acid to obtain cryolite,filtered and separated.The filtrate is evaporated and crystallized to obtain the main substance as chloride Sodium salt.To sum up: 10.00 g of spent pot lining is put into this process.After the process,4.14 g of sodium fluoride with a purity of 96.42% and 3.45 g of carbon powder with a purity of 97.27% can be obtained.This process has no secondary pollution and achieves the goal of recovering carbon and sodium fluoride.Therefore,the water washing-alkali washing-acid washing process developed in this research provides a method for the recycling of spent pot lining.