Hydrometallurgy

Abstract

Hydrometallurgy refers to the extraction of metals and production of inorganic substances from minerals through aqueous solutions. Although the entire amount of iron, lead, tin, and antimony and major production of copper and nickel come from the pyrometallurgical route, hydrometallurgy plays an important role in the extraction of reactive and rare metals and some common metals (e.g., aluminum, uranium, thorium, zinc, copper, nickel, tungsten, and molybdenum). There has been significant increase in hydrometallurgical processing of copper ores/minerals at the mine site [1] during the past few decades. In some cases, both methods are involved. For example, sphalerite and molybdenite concentrates are roasted to oxides (ZnO and MoO3) and dissolved in sulfuric acid and ammonia, respectively, and the resultant liquor after purification is electrolyzed and subjected to precipitation/reduction for production of zinc and molybdenum. On the other hand, gold from its ore is dissolved in alkali metal cyanide in the presence of oxygen and is cemented with zinc and finally treated at high temperature. In rare metal extraction, a combination of hydrometallurgy and pyrometallurgy is often adopted for the production of a suitable intermediate as well as the metal. In hydrometallurgy, there are two major steps for obtaining the metal value. The first step, known as leaching or lixiviation, is carried out with the objective of bringing the metal into aqueous solution. In the second step, the metal is recovered from the leach liquor by cementation or precipitation by controlling the operating conditions/variables. In addition, it is necessary to purify the leach liquor from the insoluble residues and suspended solid particles by adding steps like solid–liquid separation and purification before the metal recovery. Hydrometallurgy is comparatively a newer technique compared to pyrometallurgy which is being practiced from ancient times. The former offers the following advantages over the latter: © 2021, The Minerals, Metals & Materials Society.