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Microwave irradiation for
segregation roasting of nickeliferrous silicate laterites
J.
Ma and C.A. Pickles*
Department of Mining
Engineering, Queen’s University, Kingston, Ontario, Canada, K7L 3N6
Accepted 20 March 2005
ABSTRACT
In the conventional segregation process for nickeliferous silicate laterite
ores, charcoal and a chloridizing agent are added before reacting in the
range of 900 to 1200oC. Both nickel and iron segregate to the charcoal and
form ferronickel particles, which can be concentrated using standard mineral
processing techniques. The utilization of microwave radiation was
investigated as an energy source in the segregation process. The segregation
mixture was compacted into a briquette and then processed via microwave
irradiation. Variables such as processing time and power, type and amount of chloridizing agent, quantity of charcoal, sample size, additional moisture
and insulation were investigated for the recovery of nickel in the microwave
segregation process. The microwave results were compared to those obtained
by the conventional segregation process for the same ore.
The dielectric property measurements and the microwave heating behavior
studies demonstrated that segregation mixtures can be readily heated by
microwaves. This was attributed to the presence of charcoal in the
segregation mixture. In the microwave segregation experiments, the nickel
recovery in the concentrate increased with increasing power and processing
time for the ranges studied. Calcium chloride was found to be the most
effective chloridizing agent. The optimum amount of both calcium chloride
and charcoal was about six mass percent. The nickel recovery was higher when
hydrated calcium chloride was employed since this likely increased the water
vapor pressure within the briquette. The recovery increased with both
increasing sample size and insulation since these effects raised the
briquette temperature. The nickel recoveries in the microwave process were
much lower than those obtained in the conventional process. The nickel grade
of the ferronickel particles was lower in the center of the briquette than
at the outer surface. These effects were attributed to the non-uniform
heating characteristics associated with microwave processing. It is proposed
that more effective utilization of the microwaves can be achieved in a
hybrid process, which combines the advantages of both the conventional and
the microwave heating processes.
Keywords: Microwaves, Irradiation,
Laterites, Segregation roasting
* Corresponding author
E-mail :
pickles-c@mine.queensu.ca |
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