Recovery of heavy metals and stabilization of spent hydrotreating catalystusing a glass-ceramic matrix

Chemical analysis of spent Co/Mo/gamma Al2O3 catalyst revealed the presence of carbon, molybdenum, sulfur, vanadium and cobalt at levels of 16.0, 10.9 , 7.3, 4.6 and 4.0 wt.%, respectively. It was found that calcination at 500 degreesC provides an effective solution for the removal of carbon and sulf ur and this generates the oxide form of the heavy metals. The removal of th ese heavy metals can be achieved through a two-stage leaching process. Duri ng the first stage, in which concentrated ammonia is used and it has been f ound that this process can be successful in removing as much as 83% (w/v) M o. In a second stage, it was found that using 10% (v/v) of sulfuric acid, i t was possible to account for up to 77% (w/v) Co and 4% (w/v) Mo removal. L eaching test results indicated that the vanadium present in the heated spen t catalyst was almost stabilized but the molybdenum and cobalt were not. Th e combination of two solid wastes, ladle furnace slag (LFS) and treated res idue of spent catalyst, could be used for making a high value-added anorthi te glass-ceramic materials. Further leaching tests showed that ceramic glas s materials provided a very effective method of Co, Mo and V heavy metals s tabilization resulting in a product with a possible commercial value. (C) 2 001 Elsevier Science B.V. Ail rights reserved.