Kinetic studies on the leaching reactions in the autoclave circuit of the Tati Hydrometallurgical Demonstration Plant

Until 2009, Tati Nickel Mining Company (TNMC) operated a hydrometallurgical demonstration plant (HDP) in Botswana using the Activox® leaching technology developed by LionOre Technology (now Norilsk Process Technology, NPT) to produce Ni and Cu cathodes and Co salt (mostly carbonate) (Western Minerals Technology, 2004). The Activox® leaching process combines fine milling, using a suitable power-efficient stirred mill, with low-temperature pressure oxidation. The mild operating conditions of temperature (about 105°C) and pressure (about 1 100 kPa) simplify the engineering requirements and reduce costs while maintaining the advantages of pressure oxidation compared to conventional pressure oxidative leaching (POX), which operates at temperatures over 200°C and pressures of over 2 200 kPa (Angove et al., 1993; Corrans et al., 1995; Johnson et al., 1993). The main purpose of the leach circuit is to selectively dissolve (leach) nickel, copper, and cobalt from the finely milled flotation concentrate. The resultant metal-rich liquor and oxidized solids are advanced to the rest of the Tati HDP, which employs the use of known downstream technologies such as partial neutralization (PN), countercurrent decantation (CCD), solvent extraction (SX), and electrowinning (EW) for Cu and Ni recovery (Western Minerals Technology, 2004; Nel and van den Berg, 2009 ). The autoclave circuit receives feed slurry from the concentrate preparation and milling circuits. The received slurry should have a feed size of P80 of around 10 μm after undergoing fine grinding in the milling circuit. This creates more surface area for oxidative attack in the autoclave, hence reducing the required retention time by increasing the rate of autoclave chemical reactions (Western Minerals Technology, 2004). The extraction of Ni, Cu, and Co in solution is achieved through the oxidation of the sulphide within a five-compartment autoclave operating at temperatures of 105°C to 110 °C and 1100 kPa pressure, by the addition of approximately 50 kg H2SO4 per ton, 10 kg NaCl per ton, and 1.21 kg O2 per kilogram S2-. The primary leaching of the base metals in the autoclave circuit can be represented as follows: Kinetic studies on the leaching reactions in the autoclave circuit of the Tati Hydrometallurgical Demonstration Plant