Research On The Recovery Of Lead Paste From Waste Lead-acid Batteries By Solid-phase Electrolysis

In recent years,with the declining reserves of lead ore resources,the increase in the scrap of lead-acid batteries and the serious environmental problems have brought great challenges to the recovery of waste lead-acid batteries.Among them,the treatment process of waste lead paste is the most important step and the most crucial step in the recycling process.Its cleaning feasibility and economic feasibility must be the focus of its development.At present,the recovery of waste lead paste by fire method is inevitably high temperature and lead dust problem,and the wet process has problems such as complicated process and large amount of chemical reagents.In this paper,a simple zero-emission electrochemical direct electrolysis strategy is used to recover metal lead from waste lead paste combined with desulfurization technology.In this process,the desulfurization and reduction of waste lead paste are carried out simultaneously at the cathode,which has a simple process and a short process.Features such as low reagent consumption.Firstly,the kinetic parameters of solid phase electroconversion of lead sulfate,the main component of waste lead paste,were calculated by electrochemical tests such as cathodic polarization curve and constant potential step.Then,the E-pH diagram made by HSC Chemistry 6.0 software thermodynamically proved the possibility of solid phase electrolytic reduction of waste lead paste under the sulfate system.Finally,the effects of electrolysis time,working temperature,current density and electrolyte composition on electrolysis were systematically studied by single factor conditional experiment.The phase composition of the electrolysis product was determined by XRD,XPS and chemical titration.The current efficiency was calculated.Changes in energy consumption,etc.The experimental results show that in the direct electrolysis process,the waste lead paste can be converted into metal lead by desulfurization and electrochemical reduction.The main findings are as follows:(1)The electrolytic reduction process of lead sulfate in 200 g·L-1(NH4)2SO4 solution at 40 C follows the three-dimensional instantaneous nucleation and growth mechanism under diffusion control,and the exchange current density is calculated to be 1.69×10-5 A·cm.-2,the apparent transfer coefficient is 0.1305,the lead-through potential is 0.733 V when the current density is 200 A/m2,and the apparent activation energy E is 8.23 KJ/mol at the potential potential of-1.3 V.At the same time,the temperature has a great influence on the reduction of lead sulfate.The higher the temperature,the lower the overpotential.(2)The solid phase electrolysis experiment of simulated lead sulfate in 200 g·L-1(NH4)2SO4 solution at a current density of 200 A·m-2 at 40? proved the feasibility of solid phase electrolytic reduction of lead sulfate.The content of lead in the electrolytic product accounts for 97.2%.Even if there is hydrogen evolution reaction in the late stage of reduction,the current efficiency can reach 85.57%,and the corresponding energy consumption per lead of solid phase electrolysis of lead sulfate is 609.6 kWh.(3)Thermodynamically,the E-pH diagram calculated by HSC Chemistry 6.0 software proves that the main components of waste lead paste,PbSO4,PbO2 and PbO,can be solid-phase reduced to metal lead in both acidic and basic sulfate systems..(4)The cathodic polarization curve indicates that lead dioxide is converted into metal lead by two-step reduction.(5)Solid phase electrolysis experiments of waste lead paste show that the solid phase electrolysis of waste lead paste is gradually carried out along the grid of the grid.The higher the temperature,the lower the energy consumption of electrolysis.The greater the current density,the greater the energy consumption.Under the optimum process parameters(200 A m-2 in 200g L-1(NH4)25O4 solution at 40?),the lead content in the electrolysis product is as high as 95.80%.Even if hydrogen evolution reaction occurs in the later stage of the reduction process,the current efficiency can still be maintained at 87.63%.The corresponding energy consumption in the direct electrolysis process is 597 kWh per ton of lead paste,and the recovery rate of metal lead is as high as 99.46%.In summary,the economic feasibility of recycling lead by solid phase electrolysis is demonstrated.As an important contribution to the circular economy,this method provides a viable alternative to metal lead in spent lead paste in lead-acid batteries,with a simple process and a clean production path.