Tham khảo tài liệu 'asm metals handbook - desk edition (asm_ 1998) ww part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Leaching Processes Leaching is a separation process that uses aqueous solutions. A suitable aqueous environment is selected which can decompose the mineral containing the valuable metal. The objectives of leaching are Production of a compound for further processing by pyrometallurgical techniques Production of a metal from impure metal or metal compounds that have been prepared by a pyrometallurgical process Direct production of a metal from an ore or concentrate Selection of a particular objective depends on economic factors and the involved thermodynamic and kinetic conditions of the system. The theoretical possibility is limited by thermodynamic constraints whereas kinetic constraints relate to the overall time required and affect the reactor size and design. The thermodynamics of leaching are concerned with the ability to decompose a particular compound so that it will selectively dissolve and become stable in the aqueous solution used for leaching. Proper calculations can predict the maximum amount of mineral that can be leached until the system reaches equilibrium. The rate of dissociation and dissolution is kinetically controlled. Figures 9 and 10 are schematic diagrams of a mineral water interface on a microscopic scale. The concentration of the active chemical in the bulk of the solution is greater than the concentration near the surface of the mineral. This occurs because the active chemical is removed from solution by reaction at the mineral surface. Figure 9 shows that the rate at which the reaction or decomposition of the mineral will occur is determined by 1 the diffusion of reactant R from the bulk of the solution to the surface of the mineral 2 the reaction of the reagent with the surface to form a soluble species and finally 3 the diffusion of the product metal species M away from the surface. In Fig. 10 diffusion of R through the porous product layer and diffusion of M through the product layer are also possible Ref 15 . Fig. 9 Schematic diagram .
