Electrochemical aspects in hydrometallurgy

Hydrometallurgy is concerned with extraction of metal values from ore miner als through aqueous processing. This is usually achieved in two steps, name ly (i) solubilising the specific metal value into the aqueous phase and (ii ) subsequently taking it out of the solution. These are heterogenous proces ses involving solid and liquid phases. Quite often a gaseous phase is also involved. These steps may be chemical or electrochemical in nature. The ele ctrochemical phenomena, if present will depend on the electrical properties of the solid material and redox characteristics of the solution. The prese nt paper discusses some electrochemical aspects of hydrometallurgical opera tions and describes a useful electrochemical method for studying reactions. The method is based on the study of polarization data of individual half c ell reactions. Five examples are cited to discuss the following phenomena : (i) corrosion coupling, (ii) galvanic coupling, (iii) dissolution via cycl ic action of a redox couple, (iv) displacement or cementation reaction and (v) precipitation under reducing conditions.