阳极氧化硫酸铅膜的固相电解还原机理探讨

铅酸电池废旧铅膏的回收问题一直是当前科学工作者关注的重要问题,同时废旧铅膏中硫酸铅作为最难处理的成分之一,其具体的固相电解还原过程可行性和作用机理尚不明确。从废旧铅膏的固相电解还原为出发点,着重研究硫酸铅的固相电解还原机理和实际可行性。采用循环伏安曲线在铅电极表面阳极氧化形成硫酸铅膜,利用线性扫描伏安和恒电位阶跃方法研究硫酸铅膜在40℃、200g/L的(NH_4)_2SO_4溶液中的阴极还原过程。结果表明,硫酸铅电解还原过程遵循扩散控制下的三维瞬时形核与生长机理,计算得到对应的交换电流密度为2.753×10~(-9) A/cm~2,表观传递系数为0.314 7。模拟硫酸铅在200A/m~2电流密度下的固相电解试验。结果表明电解产物中铅元素质量分数占比为97.2%。即使在还原后期有析氢反应发生,电流效率仍可达到85.57%,对应的每吨硫酸铅固相电解能耗为609.6kW·h。

Discussion on Solid-Phase Electrolytic Reduction Mechanism of Anodized Lead Sulfate Film

The recovery of waste lead paste (WLP) from lead-acid battery has always been an important issue for scientists at present, where lead sulfate is the most difficult component to deal with in WLP at the same time. With the solid-phase electrolysis reduction of WLP as the starting pointing, this paper mainly focuses on the solid-phase electrolytic reduction mechanism and practical feasibility of WLP. First, anodic oxidation lead sulfate film is prepared on lead surface, and the features are determined by cyclic voltammetry and X-ray diffraction techniques. Then, the cathodic reduction process of lead sulfate film in 200 g.L-1 (NH4)2SO4 solution is studied by linear sweep voltammetry and potentiostatic step method. Finally, the experimental results reveal that the electrolytic reduction process of lead sulfate follows the three-dimensional instantaneous nucleation and growth mechanism with diffusion control, where the corresponding exchange current density is calculated to be 2.753×10-9A·cm-2 with the apparent transfer coefficient 0.3147. The solid-phase electrolysis experiment of lead sulfate at a current density of 200 A·m-2 is simulated. The content of lead in the electrolysis product accounts for 97.2%. Even hydrogen evolution reaction occurs in the late stage of reduction process, the current efficiency could still reach 85.57%, and the corresponding energy consumption solid phase electrolysis is 609.6 kWh per ton lead sulfate.