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


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