Journal
HYDROMETALLURGY
Volume 178, Issue -, Pages 137-145Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.hydromet.2018.04.011
Keywords
Tungsten; Spent SCR catalyst; CaWO4; Hydrometallurgy
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Funding
- R&D Center for Valuable Recycling (Global-Top Environmental Technology Development Program) - Ministry of Environment in Korea [GT-11-C-01-230-0]
- authorities of the Korea Institute of Geoscience and Mineral Resources (KIGAM) - Ministry of Science, ICT, and Future Planning of Korea
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This paper deals with the recovery of tungsten as synthetic CaWO4 from spent V2O5-WO3/TiO2 (selective catalytic reduction, SCR) catalyst. The newly developed process included the systematic experimental steps (roasting, decomposition (using HCl solution), leaching (using NaOH), and precipitation) to recover tungsten as CaWO4. The results revealed that the effect of roasting of spent SCR catalyst was significant for the extraction of tungsten. Furthermore, CaO addition in the roasting process promoted chemical equilibrium for the formation of CaWO4, and extraction efficiency of tungsten was increased simultaneously. Decomposition process revealed that 4 mol.L-1 of HCl solution was the best condition with considerable degree of removal (92.5%) of vanadium along with negligible loss of tungsten. The most appropriate concentration of NaOH (aq) to dissolve tungstic acid (H2WO4) from the decomposed sample was 1 mol L-1 (> 99% tungsten yield) in accordance with minimized concentration of foreign metals (Si, Al, Fe). The maximum amount of tungsten ( > 99%) was obtained from the sodium tungstate solution as synthetic CaWO4 using CaCl2 (molar ratio (CaCl2/WO3): 1). The best experimental conditions for the precipitation were under following conditions: temperature, 50 degrees C; equilibrium pH, 8-10; molar ratio (CaCl2/WO3), 1. The content of CaWO4 in the final product was 96.1 wt%. The overall yield of tungsten from the feedstock using the proposed process was 96.4%.
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