Extraction of metals from spent hydrotreating catalysts: Physico-mechanical pre-treatments and leaching stage

► In this paper we studied pre-treatments of spent hydrotreating catalysts before hydrometallurgical processes aimed at the recovery of valuable metals (Ni, Co, V, and Mo). ► Pre-treatments, usually used in mining industry, are: attrition, flotation, and grain size separation. ► Influence of other pre-treatments were evaluated: preliminary grinding and roasting stage. ► Extraction of metals was tested using alkaline and acid leaching. ► Tests demonstrated that some pre-treatments are not able to concentrate metals, but others can improve the extraction of them in the leaching stage.