Potential Leaching of Heavy Metals from Pristine and Accelerated Weathered Slag from Recycling of Automobile Lead-Acid Batteries

Abstract

Recycling of automotive lead-acid batteries generates large qualities of potentially toxic slag. The current study investigated heavy metal leaching and partitioning in spent lead-acid battery slag (LaBS) as a function of pH, liquid/solid (L/S) ratio, and pore volume. LaBS was highly alkaline (pH: 12.22) and contained high total concentrations (mg/kg) of Pb (101,300), Cu (2508), Cr (1238), Zn (589), Cd (515) and Ni (110), indicating poor metal recovery in the recycling processes. pH-dependent leaching results showed that maximum leaching of Pb, Cu, Cr, Zn, Cd and Ni occurred under acidic conditions (pH 2–6), but dropped under neutral and alkaline conditions (pH 7–13) due to precipitation as insoluble compounds. Heavy metal leaching at high L/S (5–10) was significantly higher (p < 0.05) than those at low L/S ratios (0.5–2.0), suggesting that the greatest risk of release of these heavy metals occurs in the long-term following disposal into the environment. Heavy metal breakthrough curves exhibited washout behaviour of highly soluble fractions, generally characterized by an initial rapid release of heavy metals within the first pore volumes, followed by a drop in concentration. Accelerated weathering of LaBS significantly reduced heavy metal leaching in both batch and column experiments except in very few cases. Heavy metal partitioning showed that total cumulative leaching in column experiments was very low, accounting for just 0.1–7.7%, while 92.3–99.9% occurred as the residual fraction. Despite high total concentrations of heavy metals in LaBS, the risk of heavy metal leaching under neutral-to-alkaline conditions or natural pH of the LaBS was very low, but could be high if the material is exposed to acidic conditions.