Effect of the particle size and microstructure characteristics of the sample from HPGR on column bioleaching of agglomerated copper ore

High-pressure grinding rolls (HPGR) technology is a valuable way to improve the extraction efficiency of valuable minerals; however, the excessively fine particles of the HPGR products affect the heap permeability and limit its application in heap leaching. This study aims at investigating whether the HPGR products can still be leached efficiently after agglomeration to provide new guidance for the application of HPGR in heap leaching. In this study, the copper grain exposure of ores with different particle sizes was tested by X-ray microtomography (XMT), and the microstructure characteristics of the ore under different crushing methods were analyzed by stereomicroscope, scanning electron microscope (SEM), and nuclear magnetic resonance (NMR). The column bioleaching tests were carried out on the ores with different particle sizes and the agglomerates composed of fine-grained ores from different crushing methods. XMT, SEM, and NMR test results showed that copper grain exposure increases with decreasing particle size, and HPGR produces particles with more micro-cracks and higher porosity. The column bioleaching tests indicated that the copper extraction increased with the decrease of particle size, but excessive fine particles affected the heap's permeability in the column. After 66 days of column bioleaching, the copper extractions of agglomerates composed of fine-grained ores from HPGR and jaw crusher were 55.82% and 44.16%, respectively, while the copper extraction of 20-30 mm coarse-grained ores was only 28.54%. These results demonstrated that the increased copper grain exposure caused by the reduced particle size and the richer micro-cracks and higher porosity of the HPGR products could still significantly improve the leaching efficiency of copper ore after agglomeration.