Abstract
M.Tech.
The Bushveld complex of South Africa contains the world`s largest resources of platinum-group elements and it occurs over an area of ~ 65,000 km2, and it includes the largest known terrestrial layered mafic intrusion. A broad group of deposits containing nickel, copper and platinum group elements (PGE) occur as sulphide concentrations associated with a variety of mafic and ultramafic magmatic rocks. In the current study the leaching behaviour of Ni-Cu was studied in an ammoniacal solution using the matte that was provided by Impala Platinum. To understand the leaching behavior of Ni – Cu matte the effect of the key leaching parameters were studied, i.e. temperature, solvent concentration, effect of oxygen as an oxidant and effect of stirring speed, and the end the kinetic model was used.
Leaching is basically making use of a hydrometallurgical process, that is chemical dissolution or leaching, metals can efficiently be extracted from sulphide concentrate/matte, leaving behind a residue of inert minerals originally present as well as insoluble decomposition products of the reacted minerals. Effect of the temperature was tested and it was found that Ni and Cu extraction increased when the temperature increased from 50- 60oC, and beyond 60oC no significant increment was observed. Ni was found to increase with the increase in solvent concentration, as concentration increased from 1.5 – 3 M, Ni increased from 3.93 – 32.88%. And with Cu the opposite was observed, 2 M NH3 solution and beyond 250 min the extraction of Cu metal began to decline. It was observed that between 10.43 – 10.37 pH more of the Ni and Cu were extracted, and below 10.37 the metal extraction started to decrease with decrease in the pH. The stirring speed was investigated between the range 320 – 560 rpm and it was observed that 45.5% of Cu and 34.7% of Ni were leached out from the Ni-Cu matte and as the speed increase beyond 410 rpm the percentage extraction of Ni and Cu started to decline, this behavior could be attributed to the disintegrate of the soft hydrated iron oxide residue particles and this determines the practical limit of
agitation, XRD results after leaching showed that the Ni3S2 phase transformed to NiS2 phase after 270 min of leaching, while Cu2S phase transformed to Cu1.8S phase. The results of using oxygen as an oxidant showed an increment in Ni and Cu extraction even though the increment was not that significant. After leaching the data obtained was modeled to determine whether the kinetic model follows diffusion controlled process, chemical controlled process or mixed controlled process and it was found that diffusion controlled process best describes the kinetic model at all temperatures.