Boliden Aktiebolag

Froystein Dyvik

Thomas K Mioen

The present invention relates to a method for manufacturing zinc hydrometallurgically from zinc-containing starting materials. The method comprises one or more leaching stages, one or more solution purifying stages and one or more electrowinning stages for recovering metallic zinc from the leaching solution obtained. The method is operating with a closed solution circuit. A predetermined part volume of the solution obtained in the electrowinning stage or stages is withdrawn and concentrated by evaporation so as to precipitate any magnesium and manganese present in the part volume in the form of metal salt crystals. The precipitated crystal mass is separated from the residual liquid phase. The liquid phase in this manner purified with respect to magnesium and manganese can be recycled to the leaching process or utilized for some other purpose. When the process is carried out in a sulphate environment, the solution obtained in the electrowinning stage or stages is concentrated to a sulphuric acid concentration of at least 60% by weight. The precipitated crystal mass, which has but a small volume, may be dumped to no disadvantage. In accordance with a preferred embodiment, the crystal mass is re-dissolved in a small quantity of water, thereby enabling practically all the zinc content to be recovered in metallic form, by electrowinning.

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Odda, Sweden

Froystein Dyvik