Abstract:
This work reports a fundamental study into the influence of microwave energy on the dissolution of sulphide minerals. Chalcopyrite
and sphalerite were chosen as model materials due to their economic importance and the diversity of their heating behaviour in a
microwave field. Leaching of both chalcopyrite and sphalerite in ferric sulphate under microwave conditions has shown enhanced
recoveries of metal values compared to that produced conventionally. The enhanced copper recovery from chalcopyrite during
microwave treatment is believed to be as a result of the selective heating of the mineral particles over the solution and also due to the
superheated layer of the leaching solution close to the periphery of the reaction vesselwhich creates higher temperatures compared to the
bulk solution temperature. The enhanced recovery of zinc from sphalerite seems to occur as a result of only the presence of the
superheated layer. If leaching takes place within this layer, an apparent rate increase will be noted with respect to the measured bulk
temperature. Negligible differences between the activation energy values under microwave and conventional conditions for both
chalcopyrite and sphalerite. Furthermore, measurements of the dielectric properties of the leaching solutions have shown that such
solutions are highly lossy and characterised by a penetration depth of an order of about 3 mm suggesting that most microwave power
dissipate within the thin outer layer of the reactor. Finally, numerical electromagnetic simulations showed that chalcopyrite particles
could be heated selectively when microwaved within highly lossy leaching solutions due to their high conductivity.
It is concluded that the dielectric properties of both the solid and liquid phases, the dimensions of the reactor and the position of
solid particles within the reactor determine the leaching outcome. More importantly, it is likely that the enhanced recoveries
observed are not likely to be as a