Study On The Effect Of Particle Size On Chalcocite Dissolution Kinetics Under Controlled Eh In Chemical And Bacterial Leaching

Chalcocite(Cu2S)is one of the most common secondary copper sulfide mineral and important copper resources which can be treated by hydrometallurgical method such as heap bioleaching.Since the 1980s,the bio-heap leaching process for low-grade chalcocite ore has been used worldwide due to its environmental and economic benefits.Although this method has been widely used in industry,there are some limitations such as slow leaching kinetics,low recoveries,longer extraction time,and high operation cost due to acid consumption.The particle size is one of the most important parameters as the particle size affects the copper recovery rate and excessive crushing affects cost and leaching process.Although many studies have reported on the leaching kinetics of chalcocite in acidic Fe2(SO4)3 media,there is a lack of research on the influence of particle size on the kinetics of chalcocite column leaching under controlled potential conditions.In order to identify the effect of particle size on the leaching rate and production cost during the bio-heap leaching of chalcocite,the kinetics analysis on the first stage and second stage of chalcocite of different particle sizes have been conducted.This research can give the helpful information for optimizing the engineering practice for heap bioleaching of chalcocite.In this study,natural high-grade chalcocite samples were leached in columns under controlled Eh,constant temperature and solution pH to investigate the effect of particle size.Moreover,low-grade ore of larger size fraction was leached in the column using raffinate from the industrial heap as an irrigation solution to simulate the real heap conditions.This study aimed to investigate the effect of particle size and identify the rate-controlling steps for leaching of different particle sizes(0.054-200 mm)using shrinking core model.The experimental results showed that the particle size has a significant effect on the first stage kinetics of the chalcocite dissolution.However,the particle size has slight effect on the leaching rate in the second stage due to the hindrance of the sulfur layer.X-ray CT and SEM-EDS results showed that pores and cracks increased significantly after leaching of chalcocite.The kinetic analysis of second stage showed that the leaching of small particles(0.054-31 mm)was controlled by both chemical reaction and product layer diffusion while the leaching of large particles(31-200 mm)was mainly controlled by the diffusion process.In addition to the influence of particle size on the leaching kinetics of chalcocite,the role of microorganisms in enhancing the leaching of chalcocite is further clarified.Maintaining the solution potential and acidophilic iron oxidizing bacteria are more importantly played in increasing the driving force for diffusion of Fe3+ and Fe2+.The main role of sulfur oxidizing bacteria is to oxidize the S0 layer for reducing diffusion barriers.This paper provides basic information for selecting a reasonable particle size used for the heap bioleaching and provides a reference for optimizing the industrial practice.