Transforming mining residues to valuable products

Purpose and goal:

One of the environmental challenges in the mining and metallurgical industry is the pyrite tailings and gypsum, which its poor management could lead to acid mine drainage. The project aim was to develop and validate a novel recycling process for simultaneous treatment of gypsum and pyrite residues which are two major residues in the mining industry.

The project at the same time leads to production of valuable products, such as lime, sulfur, sulfur dioxide and metallic iron through which the project generates additional commodity from mining residues. Expected results and effects:

A recycling process included the decomposition of pyrite (FeS2) under inert atmosphere to obtain pyrrhotite (Fe1-xS) and elemental sulfur (S) is studied. The produced pyrrhotite was reduced by bio-carbon in the presence of lime to produce metallic iron (Fe), calcium sulfide (CaS) and carbon monoxide gas (CO). The Product mixture is separated by magnetic separation to a magnetic fraction which is rich in metallic iron and non-magnetic fraction which is rich in CaS.

The separated CaS is then recycled by reaction with gypsum (CaSO4.2H2O) to produce CaO and sulfur dioxide (SO2) gas Approach and implementation:

The obtained results should strengthen the Swedish mining and metallurgical industry, by providing improved management of the residues. The results are not constrained to Swedish mining industry but implementation in extraction of base metals from sulfidic ore is beneficial. Mining, hydrometallurgy and water treatment are not the only industries, which generate pyrite and gypsum residues.

Chemical manufacturing industry, coal cleaning and flue-gas desulfurization processes produce millions of tons of gypsum and pyrite wastes annually in the coal-related energy industry.