REAGENT RECOVERY IN CHLORIDE HYDROMETALLURGY - SOME MISSING LINKS

Chloride hydrometallurgy has great potential, which has not yet been fully realized. This is not only due to the corrosive nature of chloride solutions and the volatility of both HCl and Cl2. It is also due to three missing links in reagent regeneration. Leaching metal oxides with HCl yields metal chlorides (e.g. zinc, lead, copper, alkali. and alkaline earth) from which HCl often cannot be recovered, and leaching metal sulphides with Cl2 is only possible when combined with electrowinning. Nickel and cobalt treatment are examples of the latter. Other oxidative chloride leaching must be done with double valency metals, normally iron, for which HCl recovery (from ferrous chloride) is well established. but not the recovery of Cl2. Finally, limestone cannot be used as a neutralizing agent in chloride hydrometallurgy because calcium chloride conversion to HCl or Cl2 is not available as a technical option. This paper reviews three possibilities to supply the missing links, namely: (1) a new type of anode which regenerates HCl (plus oxygen) instead of Cl2; (2) the linking of ferrous chloride pyrohydrolysis with autoclave oxidation of ferrous iron to yield FeCl3; and (3) the pyrohydrolysis of CaCl2 in the presence of SiO2 to drive the reaction to completion while yielding calcium silicate.