An Emission-Free Vacuum Chlorinating Process for Simultaneous Sulfur Fixation and Lead Recovery from Spent Lead-Acid Batteries

Spent lead-acid battery recycling by using conventional technologies is usually accompanied by releases of lead-containing wastewater as well as emissions of sulfur oxides and lead particulates that may potentially cause secondary pollution. This study developed a vacuum chlorinating process for simultaneous sulfur fixation and high-purity lead chloride (PbCl₂) recovery from spent lead paste by using calcium chloride (CaCl₂) and silicon dioxide (SiO₂) as reagents. The process train includes pretreatment, simultaneous PbCl₂ production and sulfur fixation, and PbCl₂ volatilization. The pretreatment eliminated chlorine emission from direct chlorinating reaction of PbO₂ in the initial S-paste (PbSO₄/PbO₂/PbO/Pb). During the subsequent PbCl₂ production and sulfur fixation step, lead compounds in the P-paste (PbSO₄/PbO) was converted to volatile PbCl₂, and sulfur was simultaneously fixed to the solid residues in the form of CaSO₄ to eliminate the emission of sulfur oxides. The final step, PbCl₂ volatilization under vacuum, is a physical phase-transformation process of ionic crystals, following a zeroth-order kinetic model. A cost estimate indicates a profit of USD $ 8.50/kg PbCl₂. This process offers a novel green lead recovery alternative for spent lead-acid batteries with environmental and economic benefits.