Chalcopyrite hydrometallurgy at atmospheric pressure: 2. Review of acidic chloride process options

• High chloride, temperature and surface area facilitate rapid Cu extraction from CuFeS2.
• Reagent recycle and/or regeneration key to economics
• Seawater is an effective solvent in heaps when freshwater is limited or not available.
• Salt-tolerant microorganisms make bioleaching a future possibility in seawater heaps.

Hydrometallurgical process developments for the extraction of copper from chalcopyrite tend to target complex concentrates, dirty concentrates that would incur penalties if smelted or low-grade ores that are thus far an uneconomic source of copper. Perceived advantages of chloride systems are the higher solubilities of copper and iron, the ease of ferrous ion oxidation and faster leaching kinetics of chalcopyrite compared with ferric sulfate systems, and the generation of sulfur rather than sulfate as the product of sulfide oxidation. Process developments for concentrates employ acidic, oxidising leach media containing sodium or other chloride salts and temperatures up to the boiling points of the high-concentration solutions. In those processes, chloride ion is thought to be an active agent in the dissolution mechanism. Leaching conditions fall into two groups, those targeting Cu(II) and those targeting Cu(I) in pregnant leach solutions. For low grade ores, usually processed in heaps, the use of seawater or other naturally saline water in leaching operations may be an ‘economic’ choice to overcome the scarcity and/or cost of freshwater. Few studies have been published describing the advantages and disadvantages of seawater substitution for freshwater in leaching processes but, from the sparse information available, seawater appears to be as efficient a solvent and carrier of acid and oxidant as freshwater. The recent descriptions of some iron(II)- and sulfur-oxidising, salt-tolerant acidophilic microorganisms indicate that a diverse group of microorganisms that could function in sulfide heaps irrigated with seawater await discovery. With regard to processing using seawater instead of freshwater, the salt content in seawater would impact directly on solution transport costs to and round a mine (through increased solution viscosity and specific gravity) and could adversely affect product and by-product purity.