Separation of molybdenum and cobalt from spent catalyst using Cyanex 272 and Cyanex 301

• Extraction of Mo and Co with Cyanex 272 and Cyanex 301, respectively.
• Mo extraction in 3 stages at A:O = 2:1 and stripping in 2 stages at A:O = 1:2.
• Co extraction in 2 stages at A:O = 1 and stripping in 3 stages at A:O = 1:2.
• MoO3 and Co3O4 prepared by crystallization/precipitation and thermal decomposition.

Separation of molybdenum and cobalt from a spent catalyst leach liquor bearing 12.52 g/l Mo, 1.74 g/l Co and 9.98 g/l Al was investigated using solvent extraction technique followed by preparation of metal oxides. Cyanex 272 (bis(2,4,4-trimethylpentyl)phosphinic acid) and Cyanex 301 (bis(2,4,4-trimethylpentyl)dithiophosphinic acid) were used as extractants for molybdenum and cobalt, respectively. The effects of various parameters such as pH, concentration of extractant, A/O ratio and temperature on extraction of Mo and Co were studied. The number of stages required for extraction and stripping were determined from the McCabe–Thiele diagram and confirmed by counter current simulation study. The extracted species for Mo and Co were found to be MoO2A2.H2A2 and CoA2.H2A2, respectively. The thermodynamic parameters such as ΔH, ΔS and ΔG were calculated for molybdenum and cobalt. The enthalpy change (ΔH) values for extraction of molybdenum and cobalt were positive indicating the extraction processes were endothermic. The oxides of molybdenum and cobalt were prepared from the strip solutions of molybdenum and cobalt by crystallization followed by thermal decomposition and the products were characterized by XRD and RAMAN spectra.