An investigation on dichromate leaching of copper converter slag

ABSTRACT MASTER THESIS AN INVESTIGATION ON DICHROMATE LEACHING OF COPPER CONVERTER SLAG Mustafa BOYRAZLI Fırat University Graduate School of Natural and Applied Sciences Department of Metallurgy and Material Engineering 2001, Page: 97 The converter slags usually discarded during the pyrometallurgicall copper production from sulphuric minerals contain significant amounts of some valuable metals such as copper, cobalt and zinc. The evaluation of converter slag for the recovery of these metals is important. The hydrometallurgical extraction processes are usually employed for this purpose. The aim of this study is to investigate the extraction characteristics of metals from converter slag by dichromate leaching. For this purposes, first, converter slag samples obtained from Ergani (EBİ) and Karadeniz (KBİ) Copper Plants were characterized chemically and mineralogically. Then, the effects of various parameters such as KîCraO? and H2SO4 concentrations, temperature, time, particle size and slag dosage on the extraction of metals from these slags were investigated. Also, experimental data obtained for Cu extraction were applied to various kinetic models in order to explain the leaching mechanism. The experimental results indicated that the Y^CriOj ve H2SO4 concentrations have large influences on the extraction of metals. It was observed that the metal extraction yields increase by increasing of H2SO4 concentration. On the other hand, while the Cu extraction yield increases by increasing of K2&2O7 concentration, Co, ZnVI and Fe extraction yields decrease significantly probably due to some hydrolyzing, precipitation and adsorption phenomenon. Also, it is said that the extraction yields of all metals increase by increasing of temperature and time and by decreasing of particle size. It was concluded that a high degree of copper extraction can be achieved in this process. The extraction yields of Cu, Co, Zn and Fe from EBİ converter slag were 99.66 %, 42.09 %, 49.86 % and 27.59 %, respectively, under the conditions of -200 mesh of particle size fraction, 10 gA of slag dosage, 70 °C of leaching temperature, 120 min of leaching time, 0.1 M of K^G^O? and 0.25 M of H2SO4 concentrations. Under the same conditions, extraction yields of Cu, Zn and Fe from KBİ slag were 74.69 %, 39.76 % and 27.58 %, respectively. The kinetic study showed that the extraction of copper from the both converter slags is well represented by a shrinking core model controlled by diffusion through a porous layer, l-3(l-X)2/3+2(l-X)=kt. The Arhenius equation and observed rate constants obtained at various temperatures have been used to determine activation energies for extraction of copper. The activation energies for Cu extractions from EBİ and KBİ converter slags were calculated as 33.66 and 28.18 kj/mol, respectively for the temperature range 25 to 70 °C. Finally, it was found that dependence of the leaching rate of Cu from EBİ and KBİ converter slags on the initial concentration of the K^C^O? are first and zero orders, respectively. Key Words: Copper converter slag; Dichromate leaching; Metal recovery; Leaching kinetics