Abstract- An attempt to determine the various phenomena at play and leaching mechanism of chalcopyrite dissolution, was conducted on a chalcopyrite concentrate. The study was performed at atmospheric conditions (room temperature) in a stirred Erlenmeyer flask with 10% solid at free pH in acidic sulphate system. It appears that, the mineral dissolution is to some extent dependent on the pH. The Cu dissolution curve was characterized at the early stage by a rapid withdrawal of both copper and solid residue. Leachate solid residue characterization results, obtained from the X-ray diffraction revealed the presence of intermediate minerals phases including bornite, covelite and chalcocite. Thermodynamic calculations predict that the dissolution of bornite and chalcocite would be spontaneous while covelite was found to be refractory. In addition to that, sulfur and gangue related mineral were identified as the dissolution reaction products. Keywords: Chalcopyrite, dissolution, mechanism, mineral phases I. INTRODUCTION Approximately 70-80% of metallic copper (Cu) is produced from the chalcopyrite mineral, the major copper sulfide mineral in nature used for copper production [1, 2] and the most refractory copper sulfide towards hydrometallurgy [3]. An Manuscript received October 03, 2018. This work was supported and sponsored by the North-West University in South Africa Kolela J Nyembwe is with the Water Pollution Monitoring and Remediation Initiatives Research Group, School of Chemical and Minerals Engineering, Faculty of Engineering, North-West University, South Africa. Elvis Fosso-Kankeu is with the Water Pollution Monitoring and Remediation Initiatives Research Group, School of Chemical and Minerals Engineering, Faculty of Engineering, North-West University, South Africa, Frans Wanders is with the Water Pollution Monitoring and Remediation Initiatives Research Group, School of Chemical and Minerals Engineering, Faculty of Engineering, North-West University, South Africa, Edward Ntumba Malenga is with the Mineral Processing and Technology Research Centre, Department of Metallurgy, School of Mining, Metallurgy and Chemical Engineering, Faculty of Engineering and the Built Environment, University of Johannesburg, estimation of 85 % of the copper production worldwide is obtained via the pyrometallugical route [4]. Efforts made over the past three decades in order to promote copper extraction through the hydrometallurgical method continue to be vain due to the controversy surrounding the mechanism of the dissolution and the incomplete copper recovery [5]. This, has resulted in several leaching processes in which the ferric sulphate system possess many advantages including a simple chemistry, low capital and operation cost, environment [6-15] and it is convenient for the recovery of copper by solvent extraction and electrowining [16, 17]. The hindered dissolution and slow dissolution kinetic is believed to be caused by the formation of a passive layer, building up on the mineral surface. The nature, characters (composition) and its formation mechanism are subject to controversy [18, 19]. There are four main hypotheses explaining the structure of the impermeable passive layer. According to the first hypothesis, the elemental sulphur formed as the reaction product to prevent further diffusion of reactant to unleached chalcopyrite [20, 21]. The second theory and the commonly cited [22] suggests the formation of the copper rich polysulfide which takes place as a result of solid state transformation through the preferential iron dissolution. This theory is referred to as the metal-deficient sulfide. The third theory holds responsible iron precipitates compounds, which act as a barrier hindering the dissolution. The candidates for this last theory include jarosite, jarosite like and goethite. These phases are usually formed due to the hydrolysis of iron [23]. To the authors knowledge most of the dissolution studies conducted on the chalcopyrite mineral focus mainly on the mechanistic, electrochemical, morphological. In these investigation the kinetic information with regards to the Cu dissolution were obtain from the leachate characterization after periodic withdrawal of a small solution portion. While, the residue characterization are usually assessed at the study time resolved. The purpose of this work is to present the kinetics in regards to Cu dissolution and simultaneously using the diffraction analysis to present the mineralogical changes taking place during the leaching of chalcopyrite. Lastly, to use thermodynamic prediction, in order to explain the dissolution and mineralogical observations. Mineralogical Observation Made During the Kinetic Dissolution Study of Chalcopyrite Mineral in Sulphate Media under Free pH at Room Temperature Kolela J Nyembwe, Elvis Fosso-Kankeu*, Frans Wanders and Edward Ntumba Malenga 10th Int'l Conference on Advances in Science, Engineering, Technology & Healthcare (ASETH-18) Nov. 19-20, 2018 Cape Town (South Africa) https://doi.org/10.17758/EARES4.EAP1118240 148