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 (PbCl 2 ) recovery from spent lead paste by using calcium chloride (CaCl 2 ) and silicon dioxide (SiO 2 ) as reagents. The process train includes pretreatment, simultaneous PbCl 2 production and sulfur fixation, and PbCl 2 volatilization. The pretreatment eliminated chlorine emission from direct chlorinating reaction of PbO 2 in the initial S-paste (PbSO 4 /PbO 2 /PbO/Pb). During the subsequent PbCl 2 production and sulfur fixation step, lead compounds in the P-paste (PbSO 4 /PbO) was converted to volatile PbCl 2, and sulfur was simultaneously fixed to the solid residues in the form of CaSO 4 to eliminate the emission of sulfur oxides. The final step, PbCl 2 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 PbCl 2 . This process offers a novel green lead recovery alternative for spent lead-acid batteries with environmental and economic benefits.