Leaching kinetics of carbonatite and silicate based chalcopyrite minerals

Abstract

Copper (Cu) is a widely used metal with high thermal and electrical conductivities, which is primarily extracted from the low-grade Cu sulphide mineral, chalcopyrite. Hydrothermal extraction is the preferred process for leaching this mineral; however, recovery is typically low, as a passivation layer is formed on the mineral surface. This study investigated carbonate minerals from Phalaborwa, South Africa, and siliciclastic minerals from Katanga, Democratic Republic of Congo, by applying chemical leaching with ferric sulphate in a sulphuric acid medium, where pH evolution was allowed to occur. This was done in accordance with the aim of the study, which was the comparative evaluation of the leaching behaviour of various chalcopyrite minerals for Cu recovery determination. The objectives of the study were to evaluate the leaching behaviour of the minerals at different temperature conditions, and the effect of the mineral species formed; four temperatures were considered (25℃, 45℃, 65℃, 85℃). Magnetite was also investigated as a potential additive for enhancing leaching behaviour. To investigate the mineralogical and chemical compositions of the minerals, X-ray Diffraction and X-ray fluorescence were used, respectively. To predict the mineral species present in the aqueous solution of the observed minerals, PHREEQC simulation software with input parameters of pH, ORP, acidity, alkalinity, Cl- and SO42-, was used. The carbonatite associated with calcite-magnesium and dolomite displayed acid-consuming behaviour – rise in temperature was concurrent with rise in pH levels, thereby promoting alkaline conditions; retardation of the Cu recovery rate was observed under these alkaline conditions, likely due to the mineral’s surface being covered by a matrix mixture of gypsum and hematite, as well as ferric salts that restrict the transport of electrons from the mineral surface. The highest rates, albeit low, were observed at lower temperatures, were the formation of insoluble Cu species and the formation of gypsum reduced. Magnetite was identified as an effective additive during the mineral dissolution of both carbonatite minerals: 12.84% for run of mine and 20.94% for tails where achieved after 12 hours dissolution at 85℃; acidic conditions (pH 1-2) were promoted by the inclusion of magnetite, which promoted Cu solubility and, by extension, improved recovery behaviour. The silicate mineral associated with various silica species of quartz displayed characteristics of acid attack, which intensified with temperature increase, as pH was maintained at low levels (pH 1-2). Recovery of Cu was favoured under these conditions, as it allowed for the minimisation of ferric salt species (19.49% recovery at 85℃). The presence of pyrite also enhanced leaching through galvanic interactions with chalcopyrite. Cu extraction was not as effective (15.78%) when the silicate mineral was treated with magnetite, as low pH conditions (pH<1) favourable to ferric salt formation of jarosite was present, along with the formation of gypsum. With lower accumulation of pyrite, the effects of the Galvanox process was also reduced. It can be concluded that the recovery rate of copper from chalcopyrite host ores, in ferric sulphate solution, was enhanced at conditions where siliciclastic host ores, providing acidic conditions, were leached at high temperatures. The extraction behaviour of copper from the carbonate mineral was greatly affected by the host ores’ inability to naturally provide low pH levels, as a result of high concentration of alkaline earth species. Lastly, improved recovery from the carbonite dominant mineral could be achieved by the inclusion of magnetite as it was identified as a positively enhancing agent for the extraction of copper from the host ore with an intrinsic high-pH affinity.