Experimental Study About The Purification And Crystallization Of Lead Paste Pre-desulfurization By-prouduct Sodium Sulfate Solution

There remain many enterprises specialize in disposing the lead accumulator waste in China,where the major method adopted is the traditional dry desulfurization process,which may contribute to severe environmental pollution and resources waste and simultaneously the high cost of flue gas desulfurization,while environmental friendly wet desulfurization process is frequently employed abroad.<Secondary lead entry conditions>explicitly regulates that the screening resulted lead plaster must be desulfurization pretreated or can be deliveried to sulfation lead concentrate smelter to coordinately handle and the desulfurization mother solution must be disposed and recoveried.Therefore,the environmental friendly wet desulfurization process of lead plaste desulfurization pretreatment may be promotely employed in China.Processing 150000 tons of waste lead acid battery produces about 20000 tons of sodium sulfate every year.In this paper,experimental investigation of the process of crystallization and removal of the resulted desulfurization solidium sulfate solution is carried out.Firstly,iron-carbon microelectrolysis-coagulating sedimentation process was creatively adopted to remove the heavy metal ions(Pd²⁺,Cd²⁺ and Cu²⁺)and metal impurity ions(Fe²⁺/Fe³⁺)in the lead plaste desulfurization side products.In this study,three methods,that is,iron-carbon microelectrolysis process,coagulating sedimetation and iron-carbon microelectrolysis-coagulating sedimetation process might be employed to dispose the heavy metal ions and metal impurity ions and compared the removal efficiency.Futhermore,the focus of the section of iron-carbon microelectrolysis-coagulating sedimentation experiment was to investigate the effects of factors of residue time,iron-carbon alloy content,the initial concentration of metal impurity ions,pH and aeration rate on the removal of heavy metal ions and metal impurity ions.Under optimum operating conditions,the resulted removal efficiency of Pd²⁺,Cd²⁺,Cu²⁺ and Fe²⁺/Fe³⁺ is 99.2%,99.1%,97.9%,97.3%,respectively and the total content of heavy metal ions and metal impurity ions is lower than 5mg·L-1.Secondly,our research group introduced a method based on local cooling rapid precipitation to seperate sodium sulfate crystal from lead plaste desulfurization side products.This process adopted the thought of the rapidly decreasing temperature of cycle fluid by adding refrigerant to the by-pass of external cycle,instead of directly decreasing temperature of solution storage tank and thus prefectly precipitate.In this study,which measured the saturation crystallization point temperature by deccreasing the experimental temperature of different mass fraction of solidium sulfate solutions,explored the effects of different mass fraction of solidium sulfate solutions and the initial crystallization temperature on the rate and quality of resulted solidium sulfate crystal.Taken energy consumption and cost-efficiency into account,the minimum crystallization temperature was set to 5?.The results indicated that the process based on local cooling reapid precipitation had the characteristics of high energy usage,high productivity of crystal,successive operation and simple and reliable.Finally,the pilot scale test device based on iron-carbon electrolysis-coagulating sedimetation connecting with local cooling rapid precipitation was set up in spend lead accumulator recovery enterprises.In this test,taken the resulted solidium sulfate solution obtained from desulfurization pretreatment of lead paste as the research object whose mass fraction was 16%²5%,the treatment capacity reached up to 10m3/h and measured the efficiency of precipitation and removal of solidium sulfate crystal.The results indicated that the method of iron-carbon electrolysis-coagulating sedimetation connecting with local cooling rapid precipitation had the adaptive effect on crystallization and removal of solidium sulfate crystal and the quality of resulted solidium sulfate crystal meeted the I criteria of internation standard?GB/T2009-2014?.The resulted cooling water employed in process may be directly reused.