Reaction kinetics of the ferric chloride leaching of sphalerite—an experimental study

Abstract

Chloride leaching processes have significant potential for treating complex sulfides. One advantage of chloride leaching is fast dissolution rates for most sulfide minerals. This experimental study is concerned with ferric chloride leaching of sphalerite, a common component of many complex concentrates. The effects of stirring, temperature, ferric ion concentration, and particle size have been examined. In addition, reaction residues at various levels of zinc extraction were examined by SEM, and the products of reaction were identified by energy dispersive X-ray analysis and X-ray diffraction. These observations indicated that the dissolution reaction is topochemical. Moreover, the leaching results fit a surface reaction control model. The activation energy was calculated to be 58.4 kJ/mole which is reasonable for a rate limiting surface reaction. The order of the reaction was 0.5 with respect to Fe3+ at low concentrations and zero at high concentrations. The change in reaction order occurred at similar Fe3+ concentrations for various particle sizes. This is believed to be indicative of an electrochemical reaction mechanism at low Fe3+ and an adsorption mechanism at higher Fe3+. A kinetic model for the ferric chloride leaching of sphalerite was also obtained for the lower Fe3+ concentrations and is given by: (ie5-01) This model is in excellent agreement with the experimental results for fractions of zinc extracted up to 0.95.