Temperature and frequency dependencies of the permittivities of nickeliferous silicate laterite ores and reaction mixtures

Abstract

The global demand for nickel metal continues to grow, while the resource base for nickel is transitioning from the nickel sulphide ores to the nickeliferous laterite oxide ores. Considerable research is being performed on developing innovative processes for extracting the nickel from the oxide ores. One potential new energy source for these processes could be microwave radiation. The interaction of microwaves with a given material is mainly determined by the permittivities. In the present research, the permittivities of a nickeliferous silicate laterite ore and both activated charcoal-ore and segregation reaction mixtures were measured as a function of both temperature and frequency using the cavity perturbation technique. In general, the ore permittivities increased slowly at low temperatures and more rapidly at higher temperatures. For the reaction mixtures, the rapid rise in the permittivities occurred at a temperature lower than for the ore and there was a characteristic peak in the permittivities. In order to understand the behaviours of the mixtures, the relevant thermodynamic literature was reviewed and also reaction simulations were performed using HSC Chemistry® 7.1. The initial rapid rise in the permittivities was attributed to the presence of the charcoal. For the activated charcoal-ore mixtures, at high temperatures the amounts of carbon and iron oxide decreased as a result of the reduction reactions and thus the permittivities decreased. Similarly, for the segregation mixture, the carbon was consumed due to the water-gas reaction and once more the iron oxide decreased. The permittivity information can be utilized to better understand the heating behaviours of the mixtures and also can be employed in numerical modelling for process development.