Process for upgrading an ore or concentrate

A process for upgrading an ore or concentrate that contains metal sulphur minerals and gangue material, the process including the stages of:

• a) selectively leaching the ore or concentrate using an ammoniacal solution containing ammonium carbonate that forms soluble metal ammine complexes;
• b) separating the solid and liquid phases formed in stage a) with the liquid phase forming a solution including soluble metal ammine complexes and the solid phase including at least in part the gangue material;
• c) removing ammonia and carbon dioxide from the liquid phase formed in step b) under conditions that are selected to facilitate the precipitation of valuable metal(s) and minimise the sulphur content in the valuable metal(s) precipitated;
• and
• d) separating the solid and liquid phases formed in stage c) with the solid phase forming a more-concentrated source of valuable metal.

A plant for upgrading an ore or concentrate that contains metal(s) sulphur minerals and gangue material, the plant including:

• a first stage in which an ammoniacal solution containing ammonium carbonate can selectively leach metal(s) and metal compounds from the ore or concentrate to form soluble metal ammine complexes;
• a separator for separating the solid and liquid phases formed, in which, the liquid phase includes soluble metal ammine complexes and the solid phase includes at least in part gangue material;
• a second stage that is supplied with the liquid phase formed in the separator and from which ammonia and carbon dioxide are removed under conditions that are selected to facilitate the precipitation of valuable metal(s) and minimize the sulphur content in the valuable metal(s) precipitate;
• and
• a further separator for separating the solid and liquid phases formed in the second stage whereby the solid phase forms a more-concentrate source of valuable metal(s).