Removal of tungsten and other impurities from spent HDS catalyst leach liquor by an adsorption route

Selective separation of Mo and W from Mo-rich leach liquor is always a difficult task. The SX route is more costly, and for better process economy an inorganic route is preferred in terms of impurity removal. Spent HDS catalyst leach liquor of composition (in g/L): 17.11 Mo, 0.583 W, 0.646 Ni, 0.052 Co, 0.005 V and 0.152 P was taken for the present study. Impurity removal was investigated by adsorption using Mn and ferric compounds. Adsorption of W and P on freshly precipitated hydrous ferric oxyhydroxide (HFO) at W/Fe ratio of 0.5 M, temperature 50 °C for 2 h was found to yield an optimum at ~ 90% efficiency, whereas Co and V become fully adsorbed. Adsorption kinetics of W onto HFO was determined and correlated with common equations; a good fit was found with Freundlich model, and it follows 1st order. Ni as an impurity remains almost untouched during adsorption; it was separated during precipitation of molybdenum as ammonium octamolybdate. The present approach may directly applied to remove impurities from Mo-rich leach liquor as per the proposed schematic flow sheet.