An overview of metals extraction and recovery from industrial wastewater sludge.

Industrial wastewater sludge is one of the vital sources of metals, including heavy metals, valuable metals, and precise metals. Apart from metals' necessity and economic value, some are toxic and harmful to the environment. This review explores the technologies currently applied for extracting and recovering heavy metals from industrial wastewater sludge. The technologies have been explained, and the merits and demerits of methods, as reported in past investigations, have been highlighted. The salient findings of this review are that the hydrometallurgical processes using acid leaching (H2SO4, HNO3, HCl, etc.) have been considered for the metal extraction process. Metal dissolution, concentration/purification, and recovery are the main stages of hydrometallurgical processes. The selection of successive metal recovery methods depends on the concentration of metals and chemical characteristics of industrial wastewater sludge. Different metal purification and concentrations were reported, including adsorption, ion exchange solvent extraction, and so forth, while precipitation and electrodeposition were mainly applied for metal recovery from industrial wastewater sludge. In this review, the cost and economic viability of the metal recovery process are also evaluated by previous reported studies. This review may be considered a valuable source of information for environmentally friendly and cost‐effective methods for metal recovery from industrial wastewater sludge. [ABSTRACT FROM AUTHOR]