Study On The Preparation Of Lead Oxide From Waste Lead Paste By Synchronous Reduction Sulfation-Desulfurization-Roasting

Lead-acid battery is a safe,reliable and low-cost energy storage device,which is widely used in important fields such as communication and transportation.As lead-acid batteries generally have an average life of only 2-5years,the number of waste lead-acid batteries is growing rapidly.Waste lead-acid batteries have both environmental pollution attributes and resource attributes.Therefore,the harmless treatment and resource reuse of waste lead-acid batteries are crucial in environmental protection and sustainable development.In this paper,the waste lead paste,the main component obtained from the manual disassembly of spent lead-acid batteries,was taken as the research object.In response to the characteristics that the Pb O₂ content in the waste lead paste is high and difficult to be converted,A new process of sulfation and roasting of spent lead paste after desulfurization to recover lead oxide was proposed.The waste lead paste with complex composition is converted into lead sulfate products,which makes the subsequent recycling process simpler and more efficient.Firstly,the waste lead paste was leached with sulfuric acid-oxalic acid system to reduce Pb O₂ to Pb O in the waste lead paste to realize the simultaneous reduction sulfurization of the waste lead paste,so that the vast majority of it was converted to Pb SO₄.The effects of sulfuric acid concentration,oxalic acid addition and reaction time on the simultaneous reduction and sulfation process of spent lead paste were investigated,the optimum technological conditions of simultaneous reduction and sulfation of spent lead paste were determined,and the synergistic mechanism of sulfuric acid and oxalic acid was analyzed.Then ammonium carbonate was used as desulfurizing agent to convert lead sulfate,the main component of acid leached paste,into lead carbonate precursor.The optimum desulfurization process conditions were explored by single factor experiments,and the kinetic mechanism of desulfurization reaction was analyzed.Finally,the desulfurization lead paste was roasted at low-temperature to recover lead oxide products,and the effects of roasting temperature and atmosphere on the roasted products were investigated,and the mechanism of thermal decomposition was analyzed.The main conclusions of this paper are as follows:（1）The composition and content of the spent lead paste were determined by chemical titration,and the main components and contents of spent lead paste were as follows:Pb SO₄（48.74 wt%）,Pb O₂（29.82 wt%）,Pb O（18.38wt%）and Pb（2.04 wt%）.（2）In the experiment of simultaneous reduction and sulfation of spent lead paste,sulfuric acid and oxalic acid have a good synergistic effect on the sulfation of spent lead paste.5 g of spent lead paste was reacted under the condition of 25 m L of sulfuric acid with 85%mass fraction and oxalic acid addition of 1.5 g for 2 hours at room temperature,and the effect of simultaneous reduction and sulfation was better.The content of Pb O₂ in the acid leached lead paste was obtained as 1.39 wt%,and the content of Pb SO₄reached 95.76 wt%.At the same time,some impurities in lead paste can be removed in the process of simultaneous reduction and sulfurization.（3）In the desulfurization experiment of acid leached lead paste,the optimum process conditions of desulfurization reaction were as follows:a C/S molar ratio of 1.2:1,a reaction temperature of 50℃,a stirring speed of500r/min,a liquid-solid ratio of 5:1 m L/g,and a reaction time of 30 min.Under this desulfurization process condition,the desulfurization rate of the acid leaching lead paste was 96.12%.Through analyzing the kinetics of the desulfurization reaction,it can be seen that the kinetic equation of desulfurization reaction of acid leached lead paste was 1﹣（2/3）α﹣（1﹣α）^2/3=exp（-2263.7+1.363/T）·t.The calculated apparent activation energy was18.82k J/mol.The reaction process between acid leaching lead paste with（NH₄）₂CO₃ was controlled by the internal diffusion step.（4）In the low-temperature roasting experiment of desulphurized lead paste,on the basis of differential thermal-thermogravimetric analysis of lead desulphurization paste,α-Pb O,β-Pb O and Pb₃O₄ products can be prepared by controlling roasting temperature and atmosphere conditions.The results showed thatα-Pb O with a purity of 97.72%could be obtained at a roasting temperature and time of 400°C and 1 hour,respectively,Pb₃O₄ can be obtained by roasting under air atmosphere and temperature of 450°C for 1hour,andβ-Pb O with a purity of more than 99%at 600°C for all products independent of the roasting atmosphere.