Thermodynamic and kinetic analysis of the polymetallic copper concentrate oxidation process

Abstract

This paper presents the experimental investigation results of the polymetallic copper concentrate oxidation process with the oxygen from the air. Concentrate characterization included chemical analysis, X-ray diffraction (XRD), energy dispersive X-ray fluorescence (EDXRF), and light microscopy. Chemical analysis and EDXRF results showed that the investigated copper concentrate consisted mainly of copper, iron and sulphur, with small amounts of zinc, lead, arsenic and other minor elements. XRD analysis showed that metals were bonded to sulphur in sulphide minerals: chalcopyrite, pyrite, luzonite, sphalerite and enargite. Those minerals were mutually bonded into aggregates, confirmed by light microscopy. The results of DTA/TG analysis were used for determining the mechanism of the oxidation process. Comparison between experimental data obtained by XRD, DTA/TG and data obtained from the phase stability diagrams, implied that the oxidation process of the investigated concentrate can be divided in two stages: the first stage consisted of sulphide oxidation reactions with the characteristic exothermal effects below 973 K while forming sulphates and oxysulphates, and the second stage, which consisted of sulphates and oxysulphates decomposition reactions and forming copper and iron oxides, with endothermal effects above 973 K. Kinetic studies were carried out in isothermal conditions in the temperature range (573-873) K. Calculations were done according to Sharp's method of reduced half-time reaction. Calculated values for the activation energies were 82 kJ mol(-1) for the initial stage of the oxidation process (up to 723 K), and 42 kJ mol(-1) for the stage of the process where desulphurization degree reached 68-86 % for the oxidation temperatures 748 K and higher. Calculated activation energy values indicated that the reaction of oxidation is a chemically controlled reaction.