Development of a hydrometallurgical process for the recovery of calcium molybdate and cobalt oxalate powders from spent hydrodesulphurization (HDS) catalyst.

Abstract

In order to recover molybdenum and cobalt from spent hydrodesulphurization (HDS) catalysts, a hydrometallurgical process consisting of leaching, solvent extraction and precipitation was developed. The Mo and Co in the spent HDS catalysts were leached in HCl solution. Mo was first separated by solvent extraction with TBP and the Mo free raffinate was then contacted with TEHA to separate Co. Stripping of Mo and Co from the loaded organic phases was carried out using dilute HCl solution and distilled water. The extraction and stripping isotherms were constructed to get the required number of multi-stages. 99.8% of Mo and 99.4% of Co were recovered by solvent extraction and the purity of Mo and Co stripping solutions was found to be 99.99%. CaMoO₄ powders with uniform morphology were obtained by adding calcium chloride to the Mo stripping solution at pH 5.0 and 90 °C. The optimum conditions for the formation of uniform rod-like CoC₂O₄ particles by adding oxalic acid were at pH 5.0 and 60 °C. The overall recovery of Mo and Co from spent HDS catalyst was 96% and 93%.