LEACHING

The chapter examines slurry-based leaching processes for fine and ultrafine mineral particles, with emphasis on their chemistry and behavior in leach reactors. It restricts consideration to agitation and pressure leaching of slurries, excluding vat, dump, and solution mining. Four main research and design areas are identified: generation of fine particles, heterogeneous leaching kinetics, solution chemistry, and engineering design and control of flow reactors. Detailed discussion is given to how particle size and surface area, controlled by grinding methods such as ball, attrition, and vibratory milling, affect leaching rates and energy costs. Experimental data for chalcopyrite and other concentrates show the practical size limits of different mills, the trade-off between energy input and extraction efficiency, and the benefits of ultrafine grinding in certain high-value feeds. The chapter also develops basic rate expressions for leaching, contrasts surface-reaction versus diffusion-controlled behavior, and notes the role of electrochemical mechanisms in sulfide and oxide dissolution.