Process Intensification In Large Scale Gold Ore Roasters

Abstract:

The world's growing awareness of climate threat and pollution enhances the demand of new environmentally and economically superior processes and system concepts for the reduction of emissions in combination with increased efficiency even for raw material industries.Although fluidized bed processes are well established in the field of metal extraction, the use of plasma or microwave radiation, combined with an adjusted process control enables completely new perspective for process innovations.In a joined R&D-project Outotec together with InVerTec and the University of Bayreuth developed a pilot plant process for study of microwave and plasma assisted thermal treatment of ores under industrial conditions.Usually ores are extremely heterogeneous multi phase minerals with locally changing dielectric properties. In the paper the treatment of a carbon containing gold ore is discussed. The leachability of gold from the ore is mainly determined by the remaining content of Total Organic Carbon (TOC). The main objective of calcination is therefore removal of carbon to the minimum amount possible in large scale processes. The presence of carbon in the ore enables local overheating in a microwave field and oxidative removal of organic carbon at moderate macroscopic temperatures.The fluidised bed reactor is based on the Outotec Circoroast process for the calcination of ores in an annular fluidized bed. The modified 2 zone annular fluidized bed reactor enables microwave induced overheating of the organic carbon, while unwanted sintering and agglomeration of the ore particles are suppressed by a cyclic movement of the bed material between an area of high microwave field intensity and a colder annular zone.To realize the concept of roasting far from the thermal equilibrium in the technical scale, a special microwave feeding system has been developed.In the paper, the results of the test campaigns with a throughput of 5 kg of ore/h are discussed. Depending on the operating conditions, a substantial increase of gold leaching can be achieved. Since microwave energy compared to fossil fuel is expensive, the challenge is to minimize the microwave use without losing the positive effect of microwave treatment. The patent pending technical solution to resolve this conflict will be presented in the paper.

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