ISEC2014 – International Solvent Extraction Conference September 7-11, 2014 Mechanism and thermodynamics of synergistic separation of V(IV) and Ni(II) from sulfate media using D2EHPA and Cyanex 272 S.M.M. Noori *,1 , F. Rashchi 1 , A. Babakhani 1 , E. Vahidi 2 Summary In this investigation a model was developed to predict the synergistic effect of Cyanex 272 and D2EHPA on co-extraction and separation of nickel and vanadium from sulfate leach liquors of power plant fly ash with the aim of increasing separation efficiency. The stoichiometric coefficient of vanadium was determined for sole D2EHPA and three different D2EHPA to Cyanex 272 ratios by applying the slope analysis method. The experimental data of vanadium extraction at pH range of 1 – 2.5, temperature of 25, 35, 45, and 55 °C and various proportions of organic solvents (D2EHPA and Cyanex 272) were used to propose correlations of distribution coefficient of vanadium by multiple linear regression. The extraction equilibrium constants, enthalpy change, and entropy change of the extraction reaction were also determined. Introduction Due to the wide applications of vanadium and nickel in the steel industry as alloying elements, ceaseless extraction of mineral resources of these two metals are becoming more and more insufficient to answer the rapid growing demands especially in industrialized countries. In recent years, mainly because of depleting in main sources of nickel and vanadium, researchers have been trying to recover and extract these metals from secondary sources such as fly ashes, crude oil, power plant residues, and spent catalysts [1, 2]. Fly ash generated by power plants is categorized as a special waste by US EPA. These residues from fossil fuel combustion are captured by pollution control equipment and disposed in special landfills [3]. In landfills, leaching of heavy metals such as nickel and vanadium from fly ash into ground water, soil, and/or surface water is the main potential environmental concern. Furthermore, due to the limited storage capacity of landfills, safe disposal becomes more and more costly. Based on the investigations by Tsai and Tsai [3] current consumption of heavy oil as fuel in power stations in Taiwan is approximately 15 million m 3 per year and the approximate production of fly ashes is 43000 tons per year. Therefore, from economical and environmental viewpoints, it is imperative to develop means of both diverting these types of wastes from the solid waste stream, and also recovering nickel and vanadium as valuable metals from fly ashes. Amer [4] leached boiler-ash with sulfuric acid to recover vanadium and nickel sulfate at temperature 200 °C, partial oxygen pressure 15 atm, and sulphuric acid concentration 60 g/l. The mentioned process requires high temperature and pressure that is not practical in industrial scale from the economic aspect. Lai et al studied metals (e.g. Al, Co, Cu, Fe, Mo, Pb, V, and Zn) recovery from spent Hydro Desulfurizarion Catalysts (HDS) by 2 types of strong acids for a leaching period of 0.5-2 h at 70 °C [5]. After finding the best condition, the metals recovery for Mo, Ni, V were 14, 60, and 65%, respectively which are not appropriate results for recovering those valuable metals. Other scientists have tried to develop processes for extracting and separating both nickel and vanadium from secondary sources, but most of the 1 School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, PO Box 11155/4563, Tehran, Iran, (rashchi@ut.ac.ir) 2 Department of Civil and Environmental Engineering, University of South Florida, Tampa, FL 33620, USA