Sequential Precipitation of Iron, Copper, and Zinc from Wastewater for Metal Recovery

Abstract

Hydroxide precipitation is the most widely used heavy metal wastewater treatment method. However, the metal hydroxide sludge produced must be treated concurrently. In this paper, an integrated treatment procedure, which modifies hydroxide precipitation with oxidation treatment and sulfide precipitation, is proposed to sequentially precipitate Fe, Cu, and Zn from wastewater for metal recovery. An industrial wastewater specimen containing Cu (290±6.25 mg/L), Fe (2,092±12.3 mg/L), and Zn (4,648±15.4 mg/L) was used. First, hydroxide precipitation using lime was applied to study the precipitation characteristics of Cu, Fe, and Zn, following which H2O2 oxidation treatment and NaHS sulfide precipitation were conducted and integrated with hydroxide precipitation to selectively precipitate Cu, Fe, and Zn from the wastewater specimen. The Fe, Cu, and Zn were sequentially removed from the wastewater by introducing 0.1% (v/v) H2O2, altering the pH of the wastewater to pH 3.5–4.0 using lime, adding 1 g/L NaHS, and subsequently altering the pH to 9.0. The Fe, Cu, and Zn were subsequently separated as individual precipitates with recoveries of 99.8±0.1, 94.0±0.3, and 96.1±0.7%, respectively, which can facilitate metal recovery and render sludge disposal unnecessary.