This volume is derived from the lectures on the principles on which hydrometallurgical processes are based, given as part of the undergraduate and MSc courses in hydrometallurgy which Professor A.R. Burkin gave from 1961 until he retired in 1988. It should be of interest to metallurgists and metallurgy students, inorganic chemists and environmental engineers. Professor Burkin is the author of The Chemistry of Hydrometallurgical Processes .