Amax Incorporated

Raymond D Symens

Paul B Queneau

Eddie C Chou

Franklin F Clark

Antonio E Blandon

Nickel is selectively leached efficiently and rapidly from Ni-Cu-Fe-S matte under oxidizing conditions at ordinary pressure by controlling in combination the following variables: (1) the acid-to-copper mole ratio in the leaching solution, (2) the temperature, and (3) the sulfur content of the matte, whereby an enriched nickel solution is obtained low in copper and iron.

Leaching of Ni-Cu-Fe-S matte

A method is provided for leaching comminuted nickeliferous sulfide matte containing by weight about 20% to 75% nickel, about 5% to 50% copper, non-stoichiometric sulfur in the range of over 4% to about 20%, over 0.5% to about 15 or 20% iron, the sum of the nickel, copper and sulfur contents being at least about 80% of the matte composition, with the balance gangue or slag and incidental impurities. The matte, because of the iron content, is first granulated by quenching molten matte from a temperature at least about 10.degree.C above its solidus-liquidus temperature but below its boiling point, following which the matte is comminuted and subjected to atmospheric leaching to dissolve nickel selectively therefrom using a spent copper electrolyte solution containing sulfuric acid having a pH ranging up to about 2 while aerating said solution to cause the pH to rise to above 5 and effect substantial precipitation of copper and iron. Preferably, a two-stage atmospheric leaching is employed, the first stage in which the solution is aerated until the solution reaches a pH level of about 3.5 to 4.5 and a second stage atmospheric leaching step in which the aeration is replaced with a stronger oxidant, such as oxygen, in order to speed up the atmospheric leaching of the matte and to complete further said atmospheric leaching until the aqueous copper and iron are each reduced to less than 20 ppm as evidenced by a rise in pH to over about 5.

Atmospheric leaching of matte containing iron

A method is provided for removing trace amounts of selenium from acid leach solutions containing over 2 ppm of total selenium comprising either Se(IV) and/or Se(VI) obtained during the pressure oxidation leaching of metal sulfide concentrate comprising forming a slurry of said acid solution with comminuted metal sulfide concentrate, said slurry containing at least two grams of a metal ion as metal hydroxide per liter of solution and then subjecting said slurry to agitation at a temperature of at least about 185.degree.C at a pressure of a least about 160 psig, whereby to reduce the total selenium content of said solution to less than about 2 ppm.

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Arvada, CO, United States of America

Raymond D Symens