Abstract:The recovery of tungsten (W) from a honeycomb-type spent selective catalytic reduction (SCR) catalyst using an alkaline leaching-ion exchange method was investigated. Spent SCR catalyst mainly consists of TiO 2 and other oxides (6.37% W, 1.57% vanadium (V), and 2.81% silicon (Si), etc.). The ground catalyst was leached at the optimal conditions, as follows: NaOH concentration of 0.3 kg/kg of catalyst, pulp density of 3%, leaching temperature of 70 • C, particle size of −74 µm, and leaching time of 30 min. In this study, the leaching rate values of V and W under the above conditions were 87 wt %, and 91 wt %, respectively. The pregnant solution was then passed through a strong base anion exchange resin (Amberlite IRA900). At high pH conditions, the use of strong base anion exchange resin led to selective loading of divalent WO 4 2− from the solution, because the fraction of two adjacent positively-charged sites on the IRA900 resin was higher and separate from the coexisting VO 4 3− . The adsorbed W could then be eluted with 1 M NaCl + 0.5 M NaOH. The final concentrated W solution had 8.4 g/L of W with 98% purity. The application of this process in industry is expected to have an important impact on the recovery of W from secondary sources of these metals.

The recovery of gallium (Ga) from gallium arsenide (GaAs) scrap using a leaching-ion exchange method was investigated. The ground GaAs scrap was leached, using 2.0 N nitric acid at 30 °C for 1.0 h, and the dissolution of Ga and arsenic (As) reached 98%. The pregnant solution with a 1/20 dilution ratio was then passed through a weak acid chelating resin Diaion CR-11. Highly charged Ga3+ has the ability to form complexes with the chelating resin and separate from the coexisting H3AsO4 in the leachate with very low pH. The loaded column was eluted with 0.1 M H2SO4, and the final concentrated solution had 4.5 g/L of Ga with 99.3% purity. The effluent from the column was further processed to remove As by ferric arsenicate precipitation, and reused continuously as the dilution water for raw leachate.

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