Research On The Treatment Of Spent Potlining Of Aluminum Electrolysis Cell By NaOH Sub-molten Salt

nnually,there is a large amount of spent potlining of aluminum electrolysis cell produced by aluminum electrolysis industry and the amount is still growing in the future.If the valuable components of spent potlining of aluminum electrolysis could be recovered effectively and harmful substances could be treated properly,the environment will be protected and resources will be saved.In view of the phase composition in the spent potlining of aluminum electrolysis cell and the characteristics of the sub-molten salt,a new method of treating the spent potlining of aluminum electrolysis cell with NaOH sub-molten salt was given and analyzed in the present study.Under the guidance of related thermodynamic calculation,the effects of NaOH sub-molten salt leaching conditions on the carbon content and aluminum content of the leached solid product were researched.The kinetics of the leaching process was also studied,and then the reaction rate limiting process in the leaching process was analyzed.Finally,the degree of graphitization of the carbon material in the leached solid product is characterized by Raman spectroscopy.First of all,the elemental and phase composition of spent potlining of electrolysis cell from an aluminum electrolysis plant were analyzed.The results have shown that the main phase components in the samples are C,Na3AlF6,NaF,CaF2,Al2O3,NaA111O17 and NaAlSiO4 and the content of them are 67.4%,4.01%,19.45%,1.91%,1.69%,2.83%and 1.29%,respectively.Based on the above analysis,a series of reactions of NaOH sub-molten leaching spent potlining were calculated thermodynamically.Secondly,single factor experiments were designed to study the influence of different experimental conditions on the carbon content and aluminum content of the leached solid product.Meanwhile,the dynamics of the leaching process was analyzed.The experimental results show that increasing the mass fraction of NaOH in the sub-molten salt has the greatest effect on the carbon content and aluminum content of the leached solid product.Increasing the leaching temperature,leaching time and stirring rate can also improve the leaching effect,but the effect is not as effective as increasing the NaOH mass fraction of sub-molten salt.While increasing the partial pressure of oxygen has the least effect on the leaching effect.The leaching process is controlled by interfacial chemical reaction and diffusion,and the activation energy of the reaction is 17.05 kJ/mol.Leached solid product had the highest carbon content of 92.37%under the condition of leaching time of 6 hours,leaching temperature of 240?and stirring rate of 1500r·min-1.If the leached solid product was treated with 1mol/L HCl,the final product had a carbon content of 95.69%.Finally,the degree of graphitization of the carbon material in the leached solid product is characterized by Raman spectroscopy.The experimental results show that the mass fraction of NaOH of the sub-molten salt,the leaching temperature and the leaching pressure have no effect on the graphitization degree of the carbon material in the leached solid product.Increasing the stirring rate in the leaching process can increase the graphitization degree,and the graphite defect density of the carbon material in the leached solid product decreases with increasing stirring rate,showing a certain linear relationship.Extending the stirring time in the leaching process is also beneficial to increase the graphitization degree,and the graphite defect density decreases with the increase of the stirring time.