Metal recovery from end-of-life hydrotreating catalysts by selective precipitation: Laboratory tests and preliminary process analysis

Hydrotreating catalysts (HTCs) are a waste byproduct of the petroleum refining industry. The recovery of intrinsic and sorbed metals from spent catalysts is desirable for meeting environmental disposal regulations, as well as for the metal resell value. In this study, innovative process schemes for metal recovery from end-of-life (i.e., spent) HTCs were tested in laboratory experiments and compared by process analysis. Synthetic leach liquors containing Al, Mo, Ni, and V were prepared resembling both chemical leaching and bioleaching methods for metal extraction from spent catalysts. Subsequently, metals in the leach liquor were recovered individually according to two pH-dependent process schemes: (i) Mo and Ni were separated first and Al was removed last, and (ii) Al was removed first. The second metal separation process gave the best results in terms of selectivity, whereby 65% of Al was recovered by precipitation at pH 4.0, 87% of Mo was precipitated by sulfide addition at pH 0.5, 52% of Ni was precipitated by sulfide addition at pH 3.5, and 65% of V was recovered by hydroxide complexation at pH 6.0. Experimental data of metal precipitation were used to perform a process analysis comparing chemical leaching and bioleaching for different input flow rates and product depreciation in a simulated commercial scale plant. Simulation results indicate that chemical leaching is of superior performance over biological leaching in terms of metal recovery, which decrease the payback time for the capital investment to build the plant .