P. C. Chaubal

Thermodynamics of copper matte converting: Part III. Steady-state volatilization of Au, Ag, Pb, Zn, Ni, Se, Te, Bi, Sb, and As from slag, matte, and metallic copper

A comprehensive compilation of various thermodynamic data required for a complete analysis of copper matte converting reactions is presented. The data comprise estimated free energies of formation for such gases as SeO, SeS, TeO, TeS, BiO, BiS, SbO, SbS, AsO, and AsS, as well as activity coefficients in dilute copper alloys and vapor pressures of various elements and compounds. The volatilization of minor elements in steady-state reactors comprising gas and several condensed phases is mathematically formulated, and a parameter which governs the volatilization in such reactors is defined and named volatilization constant. The vapor pressures of various volatile species are calculated thermodynamically for the Noranda Process reactor by assuming equilibrium conditions. The volatilization constants of various minor elements are expressed explicitly as functions of oxygen and sulfur activities.

Intrinsic kinetics of the oxidation of chalcopyrite particles under isothermal and nonisothermal conditions

The overall kinetics of oxidation of chalcopyrite in the absence of heat- and mass-transfer effects were studied for temperatures up to 1150 K. Experiments were conducted using a nonisothermal technique. Below 873 K, the pore-blocking model was applicable with an activation energy of 71 kJ/mol in the temperature range 754 to 873 K and 215 kJ/mol below 754 K. Above 873 K, the rate of sulfur vaporization dominates the kinetics of oxidation in the initial stage. The oxidation of the decomposition product above 873 K is described by power-law kinetics. The kinetics of sulfur vaporization were found to follow the power-law kinetics with an activation energy of 208 kJ/mol. The results indicate that the oxidation rate is first order with respect to oxygen concentration and inversely proportional to the square of the particle size over the entire range of temperatures studied. Predominance area diagrams were constructed at various temperatures and used in conjunction with X-ray analyses of partially oxidized samples to determine the intermediate phases formed during the reaction. This analysis also provides a justification for the kinetic models used.

Volatilization of bismuth in copper matte converting — computer simulation

A computer model has been developed to simulate the behavior of bismuth in copper matte converting at 1100 to 1300 °. The rate equation is integrated numerically by dividing a continuous process of matte converting into a great number of microsteps, in each of which the volatilization of Bi-bearing gases is thermodynamically calculated by assuming a steady state. The bubbles of offgas consisting of SO2 and N2 are assumed to be saturated with the vapors of BiS, Bi, BiO, and Bi2. However, the partial pressures of BiO and Bi2 are found to remain negligible at all stages of converting. BiS is the most volatile species over the slag-making stage with low grade mattes, but its volatility decreases markedly, becoming negligibly low over white metal. When the copper content of the initial matte is known together with the weight of matte, converting temperature and blowing rate of tuyere air, the present computer model can predict the Bi contents in all the phases involved (gas, slag, matte, copper) at any given time. The predictions by the present computer model are compared with the known commercial data from various smelters around the world. The agreements between the computer predictions and the commercial data are excellent in all cases, so that the present computer model can be used to monitor and optimize the bismuth elimination in the actual industrial operations of copper matte converting.

Thermodynamics of copper matte converting: Part IV. A priori predictions of the behavior of Au, Ag, Pb, Zn, Ni, Se, Te, Bi, Sb, and As in the noranda process reactor

The general formulae are derived which allow calculation of the weight of each molten phase (copper, matte, slag) in the Noranda Process reactor as a function of matte grade and suspension indices. These expressions and the volatilization constants are then inserted in the steady-state volatilization equation (derived in the Part III) to calculate the overall distribution of minor elements and their concentrations in all the reactor productsi.e., copper, matte, slag, and offgas) in the Noranda Process. The overall distribution of ten minor elements can be predicted for any set of controllable process parameters such as feed composition, temperature, degree of oxygen enrichment, slag composition (or magnetite activity), and matte grade. The computer predictions are in good agreement with the commercially observed values with the exception of selenium.