1. Field of the Invention
The present invention relates to a process for the recovery of valuable metals, such as nickel, copper, zinc, manganese, cobalt, aluminium and magnesium, from sulfidic silicate-containing raw materials, and in particular from low-grade sulfidic, silicate-containing ores, by slurrying in water a finely-divided raw material which contains valuable metals, by subjecting the slurry to a selective leach under atmospheric conditions and in an acidic milieu, and by separating the valuable-metal bearing solution from the solid leach residue.
By the process according to the invention, it is possible to treat ores which contain nickel, copper, zinc, iron, sulfur, silicon, manganese, cobalt, aluminium, magnesium and calcium. By the process according to the invention it is possible to treat any sulfidic, silicate-containing ores, but concentrates of nickel, zinc and copper can also be treated by the process according to the invention.
Some of the requirements set on an industrially applicable hydrometallurgical leaching process for the recovery of valuable metals present in low-grade sulfidic, silicate-containing ores are that it must be applicable on a large scale, consume little energy, be suitable in the climate in which it is used, and be non-polluting, in addition to which the process must be economical and reliable.
2. Description of the Prior Art
The process according to the invention is highly suitable for the treatment of complex sulfidic silicate-containing ores which, owing to their complex structure, it has not been earlier possible to treat satisfactorily by froth-flotation without the yields remaining low and the consumption of reagents too high. It has also been suggested that chloride solutions be used for the recovery of valuable metals from sulfidic, silicate-containing raw materials, but the disadvantages of such processes include escape of chloride, a high consumption of reagents, and problems of corrosion. It has also been suggested that ammonium salts be used for the recovery of valuable metals from sulfidic, silicate-containing raw materials, but owing to the high sulfide content of the raw material the disadvantages of such processes have included environmental hazards and poor economy. It has also been proposed that valuable metals be recovered from sulfidic, silicate-containing raw materials by means of an acid which is cycled in the process. However, the finely-divided, readily reacting silicate constituent present in the raw material renders such an acid cycle system less economical. Silicates dissolve already at a pH of 2.0-2.5, and therefore too many aluminium(III) ions dissolve in the solution, and furthermore, silicates tend to precipitate on sulfide surfaces, thereby preventing the progress of the leach and further treatment.
Low-grade ores have also been processed by so-called bacterial leaching processes, in which the cycled solution consists of an acidic (pH 0.5-1.5) ferrisulfate solution to which carbon dioxide has been added. However, economically profitable results have not so far been obtained by these processes.