Study On The Recovery Process Of Monomeric Lead From Lead Paste By Suspension Electrolysis

More than 80%of refined lead is used to produce lead batteries globally every year,and the dismantled lead paste from waste lead batteries becomes the main raw material for lead recycling.More than 60%of lead paste is lead sulfate,and its physicochemical properties such as non-water soluble,non-conductive and high melting point lead to high energy consumption in the pyrometallurgical recovery process and great limitation in traditional electrochemical technology,which requires pre-desulfurization treatment and has disadvantages such as complicated operation,excessive chemical reagent consumption and long process.In this study,according to the insoluble nature of lead sulfate in lead paste,the lead paste is directly treated by suspension electrolysis in the cathode area using sulfuric acid as the electrolyte.The recovery of lead paste by suspension electrolysis technology significantly shortens the process and is easy to operate.The thermodynamic and electrochemical kinetic analysis demonstrated the feasibility of lead paste recovery by suspension electrolysis in the sulfuric acid system.XRD,SEM,FIB-SEM and electrochemical analyses of the cathode deposited products were carried out.It was found that the spatial structure of the cathode products greatly influenced the reduction effect based on the morphological changes and component changes,electrochemical properties and the reduction rate of monomeric lead.By improving the spatial structure of the cathode product and increasing the conductive path through physical compaction without changing the chemical components of the cathode product,a large amount of monomeric lead can be reduced by direct electrolysis.The main research results are as follows.（1）By thermodynamic analysis（E-p H diagram）,Pb is the main equilibrium species in the whole p H region when E is below-0.2V.Depending on the p H and potential values,it is observed that interconversion can be achieved between all phases such as Pb O₂,Pb SO₄,Pb O,Pb²⁺and metallic Pb.From the thermodynamic point of view,the precipitation of monomeric lead from Pb O₂ and Pb SO₄ is more favourable under acidic conditions.According to the polarization curves obtained from the electrolysis of the original Pb paste in the sulfuric acid system,the reduction potential of each component of Pb paste is significantly more negative than the reduction potential compared with the hydrogen precipitation potential,which indicates that the reduction of the original Pb paste in the sulfuric acid electrolyte is easier than the hydrogen precipitation reaction.In summary,from the viewpoint of thermodynamics and electrochemical kinetics,the electrolysis of raw lead paste in the sulfuric acid electrolyte is feasible for the recovery of monomeric lead.（2）The morphological changes of lead compounds in the cathode products during the suspended electrolysis process were summarized,and at the beginning of electrolysis,the cathode plate surface was first deposited with flower cake Pb O₂ crystals.As the electrolysis process proceeds,Pb O₂ is gradually reduced to Pb O_x（1<x<2）,forming a layer of lamellar Pb O_x substrate.One part of the lamellar Pb O_x crystals was reduced to Pb O and then reacted rapidly with the H₂SO₄ electrolyte to form Pb SO₄.flower cake Pb O₂ crystals continued to be generated on the surface of the lamellar crystals and were gradually reduced to a solid layer of Pb O to wrap the newly generated Pb SO₄,forming a（Pb O）_xPb SO₄ amorphous mesh structure.Another part of the lamellar Pb O_x crystal surface is attached by the Pb SO₄ bulk crystals in the suspended particulate matter and produces flower cake Pb O₂ crystals on its surface,and finally,a Pb O solid layer is formed on the surface of the Pb SO₄ bulk crystals to form the（Pb O）_xPb SO₄amorphous mesh structure.（3）The poor conductivity of the amorphous mesh structure of the suspended electrolytic cathode product limits the reduction rate of monomeric lead.With the accumulation of electrolysis time,the current efficiency decreased from 32%to 12%,while the reduction rate of monolithic Pb only increased from 0.6%to 1.3%,indicating that the spatial structure of the cathode product is the key factor affecting the reduction of monolithic Pb by suspension electrolysis.（4）The cathode product obtained from suspension electrolysis increased its conductive path by compaction,attached to the cathode plate,and electrolyzed directly in the sulfuric acid electrolyte.As a control experiment,the original lead paste was also compacted into sheets for direct electrolysis.It was found that the samples treated by suspension electrolysis avoided the electron competition from Pb⁴⁺in Pb O₂ during the compaction electrolysis and finally obtained smooth molten lead monoliths.Comparing the energy consumption of the two experiments,the energy consumption of the new process was 1.91 W-h/g,while the energy consumption of the direct compacted lead paste electrolysis process was 3.71 W-h/g,which proved the feasibility and economy of the new process.In summary,this method lays a certain theoretical foundation for the electrochemical deposition technology of suspension systems and provides technical support for the recycling of lead paste,which is a"green"recycling method.