*Article* **Alkaline Leaching and Concurrent Cementation of Dissolved Pb and Zn from Zinc Plant Leach Residues**

**Marthias Silwamba 1,2,\* , Mayumi Ito <sup>3</sup> , Naoki Hiroyoshi <sup>3</sup> , Carlito Baltazar Tabelin <sup>4</sup> , Ryota Hashizume <sup>2</sup> , Tomoki Fukushima <sup>2</sup> , Ilhwan Park <sup>3</sup> , Sanghee Jeon <sup>3</sup> , Toshifumi Igarashi <sup>3</sup> , Tsutomu Sato <sup>3</sup> , Imasiku Nyambe <sup>5</sup> , Hokuto Nakata <sup>6</sup> , Shouta Nakayama 6,7 and Mayumi Ishizuka <sup>6</sup>**


**Abstract:** Zinc plant leach residues (ZPLRs), particularly those produced using old technologies, have both economic importance as secondary raw materials and have environmental impacts because they contain hazardous heavy metals that pose risks to human health and the environment. Therefore, the extraction and recovery of these metals from ZPLRs has both economic and environmental benefits. In this study, we investigated the removal of lead (Pb) and zinc (Zn) from ZPLRs by alkaline (NaOH) leaching and the concurrent cementation of dissolved Pb and Zn using aluminum (Al) metal powder. The effects of the leaching time, NaOH concentration, solid-to-liquid ratio (S/L), and dosage of Al metal powder on the extraction of Pb and Zn were investigated. Pb and Zn removal efficiencies increased with increasing NaOH concentrations and decreasing S/Ls. The Pb and Zn removal efficiencies were 62.2% and 27.1%, respectively, when 2.5 g/50 mL (S/L) of ZPLRs were leached in a 3 M NaOH solution for 30 min. The extraction of Pb and Zn could be attributed to the partitioning of these metals in relatively more mobile phases—water-soluble, exchangeable, and carbonate phases in ZPLRs. Around 100% of dissolved Pb and less than 2% of dissolved Zn were cemented in leaching pulp when Al metal powder was added. Minerals in the solid residues, particularly iron oxides minerals, were found to suppress the cementation of extracted Zn in leaching pulp, and when they were removed by filtration, Zn was recovered by Al metal powder via cementation.

**Keywords:** leaching; cementation; lead; zinc; Al metal powder; zinc plant leach residues
