Selection of Microwave’s Local Position in Mineral Processing Circuit: Part I- Grindability of Copper Porphyry Ore

Improvement in materials’ grindabilities and energy consumptions using microwave pretreatment have been broadly reported in the literature. However, the impact of microwave’s local position in communition circuits has not been addressed yet. The present work aims to study the influence of microwave’s location (prior to jaw crusher (BC) and after the crusher (AC)), exposure time (15-150s) and grinding time (13, 15 and 17min) on particle size distribution (PSD), mineral liberation degree (LD) and energy consumption for a porphyry copper complex deposit. For this purpose, given samples (1kg) were pretreated under 900W with various time intervals. Semi-quantitative X-ray diffraction technique (SQ-XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and optic microscopic techniques were used for elemental, surface and mineralogical analyses. Comparative work index (RWI), standard Bond work index (Wi), and grindability index (GI) together with breakage and selection functions were utilized to assess the grinding efficiency and its kinetics. Thermal anomalies in the presence and absence of MW-heating were quantified by Testo portable thermal infrared imager. The results revealed that the microwave’s effect in lower grinding time (13min) was more evident while by increasing it to 15 and 17min, its impacts became relatively insignificant. It was also found that at 13min grinding time, the product size (P80) of MW-treated crushed sample for 150s had improvements of 27% and 17% compared to the un-microwaved and MW-treated uncrushed sample. The comparative GIs in the entire spectrum of fraction sizes were reasonably greater if the microwave was located at AC particularly for coarser sizes. The Wis were obtained 13.70, 13.04 and 10.86kWh/t for the untreated, MW-treated uncrushed and crushed samples, respectively. Chalcopyrite’s LD was examined in three fractions and the results showed a significant improvement in -150+74μm and -74+44μm fraction sizes and a reduction in -44μm. We found the interrelation between particle sizes, LDs and heat adsorptions inconsistence in the literature. Finally, it was concluded that MW-pretreatment of the samples before crushing stage could considerably improve the material’s grindability and its kinetics.