The experimental results indicate that spent hydrotreating catalyst (Co/Mo/γAl2O3) contains carbon (C), sulfur (S), molybdenum (Mo), cobalt (CO) and vanadium (V) at levels of 16 wt.%, 7.3 wt.%, 10.9 wt.%, 4.0 wt.% and 4.6 wt.% respectively. Calcination at 500°C is an effective process for the removal of carbon and sulfur and generates oxide form of heavy metals. Optimum removal of these metals was achieved by two stage leaching process. The first stage using concentrated ammonia was successful in removing 83 w/v % Mo. In a second stage with 10% v/v% sulfuric acid, it was found that 77% w/v% Co together with 4 w/v% Mo were removed from the spent Co/Mo/γAl2O3. A TCLP leaching test confirmed that leaching treatment produced residue that was almost stabilised with respect to V but not for Co and Mo. Enhanced binder stabilization treatment generated a commercial value brick, with up to 30 wt.% spent catalyst in marine clay which proved to be an effective means of heavy metals stabilization.

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