Kinetics of Hydrogen Reduction of Chalcopyrite Concentrate

Abstract

A Ghatshila chalcopyrite concentrate (average particle size, 50 lm) containing primarily CuFeS 2 and SiO 2 (Cu 16 pct) was reduced by a stream of hydrogen in a thermogravimetric analyzer (TGA) at selected temperatures [1173 K to 1323 K (900°C to 1050°C)], hydrogen flow rates, partial pressures of hydrogen (0.33 9 101.3 to 101.3 kPa), and sample bed heights. The product was a mixture of Cu (26 pct), SiO 2 , CuFeO 2 , and Fe. The rate equations for the three typical controlling mechanisms, namely, gas film diffusion (mass transfer), pore diffusion, and interfacial reaction, have been derived for the system geometry under study and applied to identify the rate-controlling steps. The first stage of the reduction, which extended up to the first 13 minutes, was rate controlled by the interfacial reaction. The last stage, which spanned over the last 60 to 120 minutes and accounted for a small percentage of reduction, was controlled by pore diffusion through the built-up Cu (and Fe) layer. The activation energy in the first stage was 101 kJ mol À1 and that in the second stage was 76 kJ mol À1 . Subsequent acid leaching with 1 M HCl solution of the reduction product removed all soluble species, leaving a Cu (53.3 pct) + SiO 2 mixture, with a small concentration (2.7 pct) of Cu 2 O in it. This result compares well with the predicted final mixture of Cu (59 pct)-SiO 2 based on a mass balance on the starting concentrate. A follow-up heating at 1523 K (1250°C) produced a sintered Cu-SiO 2 composite with spherical copper particles of 400 lm diameter embedded in a silica matrix. Elemental chemical analyses were carried out by energy-dispersive X-ray spectroscopy/atomic absorption spectroscopy. The phase identification and microstructural characterization of CuSiO 2 mixtures were carried out by X-ray powder diffraction and optical microscopy.

Theoretical description of the motion of a particle in rotary dryer

“…The analytical expression of the position of the particle on the lifter is now completely determined as a function of time. To find the time t 2 for which the particle reaches the end of the lifter (corresponding also to the time when the fall starts) we write (19) as x(t 2 ) = 0. Thus we obtain:…”

“…During recent years, a large number of correlations have been published using additional parameters other than diameter, length, rotation speed and slope of the drum. [12][13][14]19,20] These new parameters are the shape and number of lifters, particle diameter, density, and filling rate. Among the numerous parameters that control the efficiency of the process, particle trajectories and mean residence time of the material in the dryer seem to be important.…”