Year 1996
Janne Antero Karonen

Direct leaching of nickel concentrates

In the first part of this work various leaching methods of nickel sulphide concentrates are reviewed. Special attention is paid to acidic oxidative leaching (H2So4/O2). At the end of the first part control principles of leaching systems are reviewed with reference to nickel matte leaching at Outokumpu Harjavalta Metals.

In the experimental part of this work the leaching behaviour of two different kind of concentrates were examined. The variables used were leaching temperature, oxygen pressure, solids content and the initial pH of slurry.

The leaching of nickel from Forrestania concentrate was found to be relatively easy, i.e. nickel was transferred to solution quite quickly even at very mild conditions (80o C, 4 h, yield of Ni 80 %). With a rising temperature the selectivity of nickel leaching over iron was greatly reduced due to increased reactivity of pyrite in higher temperatures.

The leaching of nickel from Hitura concentrate was found to be dependent on temperature, solids content and the initial pH of slurry while the recovery of elemental sulphur depended on temperature, oxygen pressure and solids content. In addition a very strong interaction between temperature and oxygen pressure was discovered. Above the melting point of the elemental sulphur its passivation effect was found to be very severe. Furthermore foam over slurry collected significant amounts of sulphides.

The most important difference between the two concentrates is the recovery of elemental sulphur as temperature rises. Temperature has much greater effect on recovery of elemental sulphur in the leaching of Forrestania concentrate than Hitura concentrate. This is evidently due to the fact that the formation of elemental sulphur from pentlandite and violarite is more sensitive to temperature than form pyrrhotite.

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