Extraction of molybdenum from a spent HDS catalyst using alkali leaching reagent

Abstract

This research investigated extraction of molybdenum from spent hydrodesulfurization (HDS) catalyst used in petroleum refinery. The spent HDS catalyst still however contains significant amounts of valuable metals such as molybdenum and nickel for example, thereby recovery of such metals are of great interest. Pyro-hydrometallurgical process was utilized in this research to selectively extract molybdenum from the spent HDS catalyst using alkali leaching reagent. The process start from calcination of spent HDS catalyst, alkali leaching using sodium carbonate, purification by carbon adsorption-desorption, precipitation of ammonium molybdate and finally calcination to give molybdenum trioxide (MoO3) as the final recycling product. Effects of calcination temperature (450℃ to 650℃) together with alkali concentration (1 M to 3 M Na2CO3), solid to liquid ratio (100 g×L-1 to 300 g×L-1) and leaching time (30 min to180 min) have been investigated. Calcination at 450℃ has shown to give the highest leaching efficiency. The optimum leaching condition, giving 97% leaching efficiency was determined to be 40 g×L-1 sodium carbonate concentration, 2 h-leaching time, 100 g×L-1 solid to liquid ratio and 90℃ leaching temperature, by controlling the temperature at 90℃ and the pH at 2, ammonium molybdate then precipitated. Calcination at 450℃ finally converted the obtained precipitate to molybdenum trioxide as the final recycling product of 99.5% purity.