Recovery and encapsulation of heavy metals on refinery spent hydrotreatingcatalyst

The experimental results indicate that spent hydrotreating catalyst (Co/Mo/ gamma Al2O3) 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 degreesC is an effective process fo r the removal of carbon and sulfur and generates oxide form of heavy metals . Optimum removal of these metals was achieved by two stage leaching proces s. 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/gamm a Al2O3. A TCLP leaching test confirmed that leaching treatment produced re sidue that was almost stabilised with respect to V but not for Co and Mo. E nhanced binder stabilization treatment generated a commercial value brick, with up to 30 wt. % spent catalyst in marine clay which proved to be an eff ective means of heavy metals stabilization.