Lead removal in zinc leach residues from Kabwe, Zambia by carrier-in-pulp method using zero-valent iron

Zinc leach residues (ZLRs) are hazardous materials because they contain toxic heavy metals such as lead (Pb) and pose serious risks to the ecosystem and people living nearby. This study investigated Pb removal from ZLRs collected from Kabwe (Zambia), one of the most Pb-polluted towns in the world, using carrier-in-pulp method. ZLRs and zero-valent iron (ZVI), which was used as the carrier, were simultaneously mixed in NaCl solution. Pb was extracted from ZRLs and formed Pb-chloride complexes, which was reductively precipitated as Pb0 on ZVI. The Pb-loaded ZVI was then separated from the leach pulp by magnetic separation. Pb removal was evaluated under various conditions such as leaching time, ZVI dosage and solution composition. The maximum Pb removal from ZLRs (about 78 wt% Pb) was collated with Pb bound to acid leachable solid phases determined by sequential extraction. Comparing Pb removal when ZLRs were leached with and without the addition of ZVI, it was found that the addition of ZVI significantly improved the removal of Pb at low concentrations of NaCl.