The applications of microwave energy to improve grindability and extraction of gold ores.
Oxidation developed from the surfaces into the cores of the microwaved particles. Metallic
particles were also formed during microwave exposure.
Lihir gold ore, in which gold was finely disseminated in pyrite and marcasite, was an
extremely refractory gold ore. Without pretreatment, only 37-39% of the gold could be
extracted with sodium cyanide. However, this was improved after the head ores or floatation
concentrates were pretreated by microwave radiation. 74.581.2% of the gold was extracted
from the microwave treated head ore.
The hydrometallurgical pretreatment of pyrite and marcasite in a microwave field and a
conventional heating environment was also investigated.I,n a nitric acid solution, pyrite and
marcasite can be rapidly leached. Reaction temperature and the concentration of HNO3 had a
significant influence on decomposition rate. Marcasite had a substantially higher
decomposition rate than pyrite. Microwave heating could promote the dissociation of
marcasite and pyrite, compared with conventional heating. This was caused by special
volumetric heating during microwave exposure that may induce local overheating or
improve the interactions between the high dielectric loss minerals and the leaching solution.
Kinetic investigations show that the decomposition of both the minerals in a nitric acid
medium is controlled by chemical reactions on the surfaces of particles. The decomposition
is a second order reaction with respect to nitric acid concentration. Less than 5- 7% of the
decomposed sulphur was transformed into elemental sulphur during the leaching of both the