EXTRACTION FOR ECONOMIC UTILIZATION OF INDIGENOUS COPPER ORES BY USING HYDROMETALLURGICALTECHNIQUES

Abstract

The present study based on extraction of copper from indigenous sources in Darosh area Chitral Khyber Pukhtun Khwa (KPK) and copper concentrate from Saindak (Bluchistan) of Pakistan was conducted by using hydrometallurgical techniques. The convenient representative sampling involved collection of high grade ores selected by hand sorting for studies. The samples were tested by different techniques involving chemical analyses, roasting with and without oxidants/ additives prior to leaching. The chemical analyses have shown that on an average these ore samples contained 20 percent Copper, 2.01 percent Iron, 1.54 percent Zinc, 0.074 percent Lead, 2.35 ppm Silver, 1.0 ppm Gold and 20 percent Sulfur. The XRD analysis of the samples has shown the presence of dominant Chalcopyrite and subordinate amount of Chalcocite, Azurite, Tetrahedrite, Malachite as other copper minerals. The dominant accessory/ gangue minerals are muscovite and other carbonates, silicates. A suitable and cheap method to process the sulfide copper containing chalcopyrite ore was investigated by thermo-chemical processes. The higher amount of copper leaching was 70 to 75 percent achieved by prior roasting at 650oC. The effect of various oxidants to increase copper leaching was also investigated during roasting of sulfide ores sample at 5000C to 6500C. The oxidants used for the purpose were sodium per sulfate, sodium chlorate, potassium chlorate, sodium nitrate, and sodium nitrite. The copper leaching was only 70 percent achieved by roasting with sodium per sulfate at 5000C. The new method was developed for economic utilization of copper indigenous ores. The research introducing a series of novel additives used first time in such roasting. The 23 additives have properties of ions and vapors such as nitrate, chlorate, sulfate, phosphate, acetate, oxalate, carbonate, and ammonia. Some of these ionic species were used only in aqueous medium as reported in literature. The additive’s dissociation products in the form of gas or vapors were investigated during roasting in dry and solid medium in present study. The novel processes developed envisaged that the vapor-solid metallurgy of complex copper sulfide ores changes the mineralogy into leachable minerals. The additive roast leach processes gave about 85 percent to 98 percent copper leaching with low range of roasting temperature and roasting time. The XRD analysis of additive roasted sample has shown the formation of sulfur rich mineral of copper as Cubanite. It is prove that the additive roast leach processes have friendly environment by reducing sulfur dioxide emission. The combined effect of additives in two - stage roasting at lower range of temperatures gave better results with reducing roasting time. The best combination of additive’s products found was chloride – sulfate of ammonium. This combination is also better in aqueous medium of direct leach processes as reported in literature. The additive roast leach processes gave higher percentage of copper leaching with 2.5 percent sulfuric acid in 1:5 solid liquid ratio within very short time. The kinetics of roasting processes was studied. The roasting results were compared with the help of kinetic models of Sharp (1966) to investigate the mechanism of reactions. It was found the reactions mechanism during the roasting ranges from boundary phase reaction to diffusion reaction. It was found that roasting with additives has decreased the activation energy in order to chloride > chloride-sulfate > nitrate > sulfate.