The influence of microwaves on the leaching kinetics of chalcopyrite
The influence of microwave heating on the leaching kinetics of chalcopyrite has been investigated. Microwave-assisted leaching has been investigated in an attempt to improve the yields of extracted metal and reduce processing time. This is especially pertinent in view of the increased demand for more environmentally friendly processes. The data from both microwave and standard leaching tests were best fitted by a shrinking core model in which, the surface reaction controlled the rate. It was found that the activation energy calculated for microwave leaching (76.5 kJ/mole) as calculated from the data was slightly lower than that for standard leaching (79.5 kJ/mole): however, the difference lies within the limits of experimental error. Enhanced recovery of copper was noted for samples leached within the microwave field. Previous work has suggested that this may be due to a "microwave effect". For the first time this work proves that higher recoveries in microwave systems occur as a result of selective heating of the mineral particle over the solution. It is postulated that the reaction interface has a higher temperature than that of the bulk solution, leading to a higher reaction rate. In addition, it is suggested that high loss leaching solutions will develop a superheated layer close to the periphery of the reaction vessel (due to the small penetration depth) which creates localised heating compared with the measured bulk solution temperature. If leaching takes place within this layer, an apparent rate increase will be noted with respect to the measured bulk temperature. © 2005 Elsevier Ltd. All rights reserved.