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An Investigation into the Effect of Temperature on the Leaching of Copper-Matte

A study was carried out to determine the influence of the temperature and the reaction involved on the leaching of copper- matte. Copper (Cu) bearing matte from Impala Refinery (Pty) Ltd was used in the investigation. The experiments were conducted in a leaching cell submerged in a water bath, with ammonia concentrations (leaching solution) of 3.0M, temperature of 50˚C, 60˚C and 70˚C, pH of 11 and for a time period of 130 minutes. Leaching tests indicated that Cu recovery increased in the temperature range 50˚C - 60˚C, however at a temperature of 70˚C Cu recovery decreases because of cementation process as nickel displace copper. The shrinking core model was used to determine if the leaching process was diffusion controlled, or chemical controlled, or even mixed controlled. It was found that the leaching process could not be determined using the shrinking core model due to the cementation process of Cu. It was concluded that an increase in temperature results in an increase in the Cu recovery however the temperature should not be too high as cementation process increase with increasing temperature. HE extraction of copper metals from matte (mixture of metal sulphides and precious metals) has been a critical process in the refining of precious metals. Matte is produced from the smelting of sulphide ores to separate the valuable metals from the gangue (waste material). Base (copper) metals are normally recovered from the precious metals by leaching leaving behind a solid residue rich in precious metals and producing a base metal rich liquor. Leaching is the extraction of a soluble constituent from a solid by means of a solvent (1). Generally the leaching process can be considered by the change of phase of solute as it dissolves in the solvent, diffusion of the solute through the solvent in the pores of the solute to the outside of the particles and the transfer of the solute from the solution in contact with the particles to the main bulk of the solution. An active chemical solution known as a lixiviant or leaching solution is brought into contact with the ore (or concentrate). The transfer of a metal from ore to lixiviant constitutes a transfer from a solid to a liquid phase. Because the dissolution is selective, most of the unwanted components in the ore are unaffected by the leaching process and remain in the solid state. Consequently, the metal is separated from them when the solids are separated from the solution after the leach process has been completed. The solution that is produced is termed a pregnant solution or leach liquor. The solid product is termed the residue or tailings. II. LEACHING AGENT Ammonia as an effective leaching agent has been widely used in a number of Hydrometallurgical processes. The main advantage is that the basic leach solution alleviates corrosion problems encountered in the acid systems. Ammonia is also advantageous in that ammonia and ammonium ion constitute a pH buffer solution. However, it has the disadvantage of operating at relatively high temperature and pressure. Extraction of copper using ammonia solutions proceeds in an analogous way as that of using acid solutions. However, it is necessary to consider metal complexing by ammonia molecules: +