Halide based leaching and electrowinning
Note that of the processes shown in Table 1, those with halide are generally performed at lower temperature (near ambient conditions) than those with sulfate. Halide based leaching is generally much faster than sulfate leaching at ambient temperature. Chloride salts such as sodium chloride are readily available and inexpensive, and in some locations seawater brines are used out of necessity in arid coastal areas. In addition, halides can in some cases be directly integrated with gold leaching. Thus, the halide based methods are among those most likely to be used in a heap leaching scenario for chalcopyrite ore. Metal recovery experiments using integrated leaching-electrowinning [23,24], have also been performed for recovery of metals such as Cu, Ag, Pd, Sn, and Pb from electronic scrap in halide media. Copper recovery from IPC (Inco Pressure Carbonyl) process has been reported, where multistage leaching was utilized in order to produce copper without solvent extraction. However, most of these experiments were performed for metal rich residue leaching. Other methods, such as many of those in Table 1, can be effective in concentrate leaching scenarios, but are
not likely to be utilized in commercial heap leach environments due to reagent costs, heating costs, capital costs, and a variety of other reasons.