Research On The Application Of Ionic Liquids In Chalcopyrite Hydrometallurgy

Copper hydrometallurgy has been an individual industrial system with a higher development rate than that of the overall copper industry since the 1970s as the technology of solvent extraction has made revolutionary change to copper hydrometallurgy. For many years, hydrometallurgists have been devoted to researching and developing the hydrometallurgical treatments of chalcopyrite, the leaching of which is the core of hydrometallurgy of copper sulphide, and many processes have been employed to recover copper from chalcopyrite including roast/leaching, pressure acid leaching, chloride leaching, ammonia leaching and bioleaching. The pressure acid leaching has been studied extensively but with limited industrial application. The procedures of chloride leaching are always complicated and most of them are in pilot or demonstration projects. Heap leaching is applied mainly to treat copper ores of low grade, which requires a longer operation cycle. Generally, many of the processes developed have not reached commercial-scale operation due to various drawbacks. Therefore, it is an urgent task for hydrometallurgists and relative workers to seek for new and green hydrometallurgical processes for the production of copper operated under ambient atmosphere and low temperature with low consumption of energy, acid and oxygen as well as free of pollutants release. The application of room temperature ionic liquids makes it possible to explore a green leaching process of chalcopyrite.This paper introduced systematically the exsited methods, processes and recent research development for chalcopyrite hydrometallurgy. Ionic liquids—new green solvents with a series of excellent properties and their promising application in hydrometallurgy was deeply analyzed. A Br(?)nsted acidic ionic liquid 1-butyl-3-methyl-imidazolium hydrogen sulphates ([bmim]HS04) was synthesized and used for the leaching of chalcopyrite concentrate at ambient pressure and low temperature. The redox potential (Eh) and pH of [bmim]HS04 and its aqueous solution were determined, which proved the feasibility to directly leach chalcopyrite with [bmim]HS04. The leaching of chalcopyrite with [bmim]HS04 and its aqueous solution was studied systematically. A high copper extraction of 95% was achieved by using pure [bmim]HS04 under the conditions: 90℃,oxygen partial pressure of 81 kPa, stirring speed of 800 rpm, concentrates of 74～65μm fraction, pulp density of 100 g/L, leaching time of 24 h. Compared to leaching of chalcopyrite in traditional H2SO4-Fe2(SO4)3 system, the copper extraction was increased by 3～4 times. Comparison was made for leaching chalcopyrite with ionic liquids of [bmim]HSO4, [hmim]HSO4 and[omim]HSO4, all of which showed the effectiveness of direct leaching.The Eh and pH value before and after leaching were determined, and the concentrations of cupric, ferric and ferrous ions as well as the composition of leaching residues were and analyzed. The chemistry and kinetics of the leaching process was disscussed. The leaching of chalcopyrite with ionic liquid and its aqueous solution were proved to be the process of consuming hydrogen ion and oxygen and the ionic liquid was able to release hydrogen ion acting as a acid. The main reaction for the leaching can be expressed as:Minishing the particle size of concentrate and increasing the stirring speed, temperature, ionic liquid concentration and oxygen partial pressure can increase the copper extraction. The dissolution of chalcopyrite in aqueous solution of ionic liquid was controlled by diffusion through the product layer of elemental sulfur with a apparent activation energy of 69.4 kJ/mol in the temperature range from 40～90℃, and the copper extraction increased markedly above 70℃. Compared with traditional aqueous solution, the ionic liquid could potentially prompt the transfer of dissolved oxygen to speed up the oxidative leaching process that seemed as a catalytic function. The relation between the kinetics constant and oxygen partial pressure was determined as following:It was found from the electrochemistry study that the direct anodic oxidation of chalcopyrite occurred obviously in the potential region of 600 to 800 mV (vs SHE) and the product of elemental sulfur could lead to passivation, consequently limiting the overall dissolution rate.