Computer technology in the past fifteen years has essentially rev olutionized engineering education. Complex systems involving coupled mass transport and flow have yielded to numerical analysis even for relatively complex geometries. The application of such technology together with advances in applied physical chemistry have justified a general updating of the field of heterogeneous kinetics in extractive metallurgy. This book is an attempt to cover significant areas of extrac tive metallurgy from the viewpoint of heterogeneous kinetics. Kinetic studies serve to elucidate fundamental mechanisms of reac tions and to provide data for engineering applications, including improved ability to scale processes up from bench to pilot plant. The general theme of this book is the latter-the scale-up. The practicing engineer is faced with problems of changes of order of magnitude in reactor size. We hope that the fundamentals of heterogeneous kinetics will provide increasing ability for such scale-up efforts. Although ther modynamics is important in defining potential reaction paths and the end products, kinetic limitations involving molecular reactions, mass trans port, or heat flow normally influence ultimate rates of production. For this reason, rate processes in the general field of extractive metallurgy have been emphasized in this book.