Hydrogen reduction of single pellet nickel oxide under microwave irradiation

Microwave technology has potential applications in the field of mineral processing and extractive metallurgy. The use of microwave energy to the extractive metallurgy is relatively new. This potential is being explored wide range for oxide ores, ranging from drying to the segregation process to electric arc furnace dust recycling, and reduction of composite pellets over the last two decades. For the present study, the fundamental thermal response of metal oxides such as hematite, nickel oxide etc., and reagents were heated under microwaves to understand their independent heating behaviours. The microwaves were generated with the microwave power supply of 800W and at a frequency of 2.54 GHz. The samples heated rapidly to ^300°C within 20 seconds of microwave irradiation. Oxides of iron and nickel showed clear increase in temperature. However, CaO and SiO₂, were found to be transparent to microwaves as they did not show significant rise in temperature even after a microwave irradiation of 300 seconds. Based on these preliminary experimental results, the present study was extended to gas-solid reactions under microwave heating. For the gas-solid reaction study, nickel oxide reduction by hydrogen was chosen since it has a good microwave absorbing property and single step reaction system and yield only two products: nickel and water vapour. The experimental results of microwave heating are compared with conventional heating. Results show that microwave heating appears to be superior to the conventional one.