Separation And Recycling Of Carbon And Electrolyte In Spent Potlining

With the increase of aluminum production capacity worldwide,the amount of waste related to this industry is also increasing.The spent pot lining is a major environmental issue in the primary aluminum industry.In the process of electrolytic aluminum production,the carbon cathode is eroded by fluoride and sodium ions,so it is discarded and resulting in a large amount of spent pot lining every year.The spent pot lining is a dangerous solid waste containing a variety of components.If it is handled improperly,it will cause serious environmental problems.The main purpose of this study is to seek methods and technological conditions for the recovery of valuable substances from the spent pot lining.At present,the technology of processing electrolytic aluminum the spent pot lining is not mature at home and abroad.In contrast,the flotation method is simple in operation,economical in cost,and easily realized in the process flow.What's more important is that it can make use of the differences in the hydrophobicity of carbon and electrolyte to achieve better separation of these two valuable components.However,the effect of flotation to recover the spent pot lining is not ideal.Therefore,further exploration is needed.Based on the relevant literature,this paper first explored the surface morphology and elemental composition of the spent pot lining,and then determined the flotation flow through flotation experiments.The effect of pulp density,sample size,the scraper speed,aeration rate,the stirring time before drug was added,the dosage of inhibitor and the spindle speed of the flotation machine on the flotation performance were studied by single factor experiment.Then,using the recovery rate of carbon as the evaluation index,the conditions of flotation were optimized and the carbon and electrolyte in the SPL can be separate and recovery by the Plackett-Burman design,steepest ascent experiment and the central composite design?CCD?of response surface methodology?RSM?.The optimum flotation conditions were determined to achieve the separation and recovery of carbon and electrolyte from the spent pot lining.The main conclusions are as follows:?1?There is an obvious interface between the electrolyte and the carbon block in the spent pot lining of this experiment,which can be separated by a certain physical treatment method.The main contents of spent pot lining are fluorine,carbon,oxygen,sodium,aluminum,silicon,potassium,calcium and iron,and the content of carbon is low,only20.455%,so the flotation is more difficult.?2?The basic flotation process was determined through experiments,which including rough selection,one sweep,one selection,second selection,and second sweep.?3?According to the single factor experiment,it is known that the seven factors affecting the flotation effect are the sample size,pulp density,spindle speed,aeration rate,the scraper speed,the time before adding the injection and the dosage of inhibitor water glass can influencing the results of flotation experiment.The sample size,pulp density,spindle speed,aeration rate and the scraper speed have a greater influence on the flotation effect.The time before adding the injection and the dosage of inhibitor water glass do not have a significant effect on flotation efficiency.?4?It can be known from orthogonal experiments that using the carbon grade and carbon recovery rate as evaluation indicators,the optimal flotation conditions were different.and the carbon recovery rate was 78.18%,which was better than that of any group in the orthogonal experimental group,indicating that the orthogonal experimental results are reliable.When the carbon recovery rate is used as the evaluation index,the influence degree of each factor on the flotation effect is:sample size>pulp density>aeration rate>scraper speed>spindle speed,the carbon grade is increased to 64.37%through the best flotation conditions.When the carbon recovery rate is used as the evaluation index,the influence degree of each factor on the flotation effect is:aeration rate>sample size>pulp density>spindle speed>scraper speed,and the carbon recovery is increased to 78.18%through the best flotation conditions.?5?According to the Plackett-Burman test,the steepest slope test and the response surface experiment,it can be seen that the aeration rate,sample size,and scraper speed are the key factors affecting flotation performance.The interaction among sample size,aeration rate and scraper speed is significant.Using the carbon recovery rate as evaluation indicators,the optimum conditions of the test are:the sample size was 120-140 mesh,the aeration rate was0.25m³/h,the scraper speed was 15r/min.?6?The calorific value of carbon was 607±11J/mol,the main phase composition of electrolytes were Na₃Al F₆,which accounted for 19.65%;followed by Na₃AlH₆?6.59%?,Na₃AlH₆?6.59%??Na₂Ca?CO₃?₂?5H₂O?6.55%??Ca₃AlF₇?12.28%??CaAl?F,OH?₅?H₂O?11.95%??NH₄HF₂?5.72%?and other phases.