Thermodynamics Behavior of Germanium During Equilibrium Reactions between FeO x -CaO-SiO 2 -MgO Slag and Molten Copper
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The distribution ratio of germanium (Ge), LGe during equilibrium reactions between magnesia-saturated FeOx-CaO-SiO2 (FCS) slag and molten copper has been measured under oxygen partial pressures from 1010 to 107 atm and at temperatures 1473 to 1623 K (1200 to 1350 C). It was observed that the Ge distribution ratio increases with increasing oxygen partial pressure, and with decreasing temperature. It was also observed that the distribution ratio is strongly dependent on slag basicity. The distribution ratio was observed to increase with increasing optical basicity. At fixed CaO concentration in the slag, the distribution ratio was s=m found to increase with increasing Fe/SiO2 ratio, tending to a plateau at LGe = 0.8. This behavior is consistent with the assessment of ionic bond fraction carried out in this study, and suggested the acidic nature of germanium oxide (GeO2) in the slag system studied. The characterisation results of the quenched slag suggested that Ge is present in the FeOx-CaO-SiO2-MgO slag predominantly as GeO2. At 1573 K (1300 C) and pO2 = 108 atm, the activity coefficient of GeO2 in the slag was calculated to be in the range of 0.24 to 1.50. The results from the current study suggested that less-basic slag, high operating temperature, and low oxygen partial pressure promote a low Ge distribution ratio. These conditions are desired for maximizing Ge recovery, for example, during pyrometallurgical processing of Ge-containing e-waste through secondary copper smelting. Overall, the thermodynamics data generated from this study can be used for process modeling purposes for improving recovery of Ge in primary and secondary copper smelting processes. DOI: 10.1007/s11663-016-0759-x The Minerals, Metals & Materials Society and ASM International 2016
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INTRODUCTION
GERMANIUM (Ge) is a lustrous, grayish-white, brittle, and scarce metalloid with a concentration in the earth’s crust of about 1.6 ppm.[1–3] The average concentration of Ge in sphalerite ((Zn,Fe)S) ores is up to 0.3 mass pct. The main route for Ge production is through refining process of zinc, where Ge is recovered from zinc residue as a by-product.[4] This is mostly carried out in Belgium and Canada. Fly ash and flue dust produced from the combustion of certain coal can also be a source for Ge, with the highest concentration found from Hartley coal ash at Northumberland, U.K., i.e., about 1.6 mass pct Ge.[2] There are a number of producers in China which recover Ge from coal fly ash and zinc ore. Russia has been increasing their Ge
M.A.H. SHUVA, PhD Student, M.A. RHAMDHANI, Associate Professor, G.A. BROOKS, and S. MASOOD, Professors, are with the Department of Mechanical and Product Design Engineering, Swinburne University of Technology, Melbourne, VIC 3122, Australia, as well as with the Wealth from Waste Research Cluster, Melbourne, VIC 3122, Australia. Contact Email: [email protected] M.A. REUTER, Professor, is with the Helmholtz Institute Freiberg for Resource Technology (HZDR), Freiberg, 09599, Germany. Manuscript submitted March 22
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