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.