Thermodynamics on Dissolution Behavior of Indium in FeO-SiO2-Al2O3-5CaO-MgOsat slag system

Abstract

Indium (In) represents a minor percentage of the earth’s crust and its concentration is comparable to that of silver, which is about 0.1 mass ppm, and ranges from 50 to 200 ppb in the earth’s crust. Indium is usually produced as a minor by-product in the lead and zinc smelting and refining processes and is commonly used for indium tin oxide (ITO) sputtering targets, LCD screens, and other sources. Because the demand for indium in increasing, an interest in recycling In-containing materials has developed. So, pyrometallurgical recycling of In-containing materials has been issued in view of 'Urban Mining' due to the high cost and scarcity of indium. However, Indium dissolution behavior in FeO-bearing metallurgical slags has not been fully understood yet. Therefore, in the present study, indium solubility in the FeO-SiO2-Al2O3-CaO-MgOsat slag system was measured at 1573 K (1300 oC) under P_(O_2 )=〖10〗^(-12) 〖~10〗^(-11) atm using a CO-CO2 gas mixture over a wide range of compositions to determine the dissolution mechanism of indium in FeO-bearing slags. The pure indium(99.99%) contained in a MgO crucible was equilibrated with a purified CO-CO2 gas mixture in the mullite reaction tube which was heated by MoSi2 heating element. The oxygen potential was controlled by CO2/CO equilibrium. The equilibration time was determined to 12hours at 1573K through pre-experiment. After equilibrating for 12hours, the samples were quenched by dipping the crucible into the brine and crushed for chemical analysis. The content of indium was analyzed by ICP-AES and the of slag components was analyzed by XRF spectroscopy. The indium solubility in FeO-bearing slags increased with increasing oxygen partial pressure and decreased with increasing basicity which is in proportion to the activity of FeO. Relationship between indium capacity and sulfide capacity in FeO-SiO2-Al2O3-CaO-MgOsat slag system is discussed. And the effect of slag composition and temperature on the indium solubility is also discussed. Finally, comparison between CaO-bearing and FeO-bearing slag system is discussed on the indium solubility.