Investigating the pressure leaching of chalcopyrite in the presence of effective oxidazing agents

Copper production from sulphide ores and concentrates, to a large extent, have been accomplished by using pyrometallurgical techniques consists of smelting processes carried out at high temperatures. Besides the various economical factors, since there has been growing environmental sensation, alternative copper production techniques are investigated continuously. Hydrometallurgical techniques including leaching processes carried out in the aqueous media are most important routes among the investigated alternative methods. Commercial hydrometallurgical processes developed for copper extraction from sulphide copper concentrates are present and these processes need some segments having high cost such as mechanical activation, effective oxidative leaching stage and treatment of pregnant solution obtained after leaching. Most important problems observed during the hydrometallurgical treatment of complex sulphide copper concentrates are low extraction yield and high iron content of pregnant solutions. Most important reason of low extraction yield is passivation effect on the particle surface stemming from, to a great extent, oxidation of sulphide sulphur to elemental sulphur during the oxidative leach process. On the other hand, passing the iron to the solution in significant amounts during the leaching process carried out under the acidic conditions is unavoidable situation. Most suitable way for the eliminating these problems is to fulfil the leaching process under the effective oxidation conditions provided by using high temperature and pressure.In this study, it has been investigated that the application possibilities of some soluble oxidation agents in aqueous media having extremely high oxidation ability such as hydrogen peroxide and persulphates instead of oxygen. For this purpose, oxidative leaching experiments were performed to extract copper from two different chalcopyrite concentrates (Küre and Ergani) by using some persulphate salts, hydrogen peroxide and oxygen in a pressure leaching system-reactor under different conditions. Since the Ergani concentrate plant recently finished the production activities, the basic experiments have been focused on Küre chalcopyrite concentrate. Experimental study consists of three main sections which are preliminary experiments, design experiments aimed optimization by using Response Surface Method (RSM) and experiments focused on increasing the copper extraction yield. Also, to interpret the extraction mechanisms of metals, various instrumental investigations have been carried out such as mineralogical phase analyses, particle size distribution measurements and surface analyses after and before the leachingThe experimental studies showed that the best results can be obtained by using ammonium persulphate among the leaching agents. Copper and iron extraction yields from Küre chalcopyrite concentrate have been determined as 63.50 % and 24.04 %, respectively under the conditions (Leaching temperature of 105 ?C; APS concentration of 308 g/l; reactor load factor of 0.78; liquid/solid ratio of 11; leaching time of 180 min; mixing speed of 500 rpm) optimized by using response surface method (RSM) and central composite design (CCD) model.In the studies aimed to increase the copper extraction yields, it was determined that the copper extraction yield could be increased to 86.65 % by using a mechanical activation performed by fine grinding before ammonium persulphate leaching. It was determined that 34.12 % of iron passed into solution under these conditions. Also, in another study aimed to increase the copper extraction yields, the possibilities of ammonia usage together with ammonium persulphate have been investigated. It was determined that about the 93 % of copper could be extracted without a mechanical activation under the experimental conditions using high ammonia ratio as 22.5 % (w/w) in the leach solution. Under these conditions, it was determined that the concentrations of iron passed into the solution were below the detection limits.Keywords:Copper, Chalcopyrite concentrate, Pressure leaching, Persulphates, Hydrogen Peroxide, Oxidation