Selective extraction of Mo by Cyanex-272 and tributyl phosphate (TBP) was investigated from the leach liquor of a low grade Ni-Mo ore, which contains mainly Mo(VI), Fe(III), Ni(II) and a small quantity of other impurities. The elements in the leach liquor were divided into four groups based on the extraction mechanism of acid phosphorus extractants, and the behavior of four elements (Mo, Fe, As and V) was investigated. The separation factors of Mo to Fe, As and V were calculated separately using di-2-ethylhexylphosphoric acid, 2-ethylhexyl phosphonic acid mono-2-ethylhexyl ester and bis(2,4,4-trimethylpentyl)phosphine acid (Cyanex-272) under the same conditions. Cyanex-272 was found to be the optimum extractant. The synergistic coefficients of Cyanex-272 and co-solvents (secondary caprylic alcohol and TBP) were calculated separately for the extraction of Mo, Fe, As and V and TBP was found to be the better choice. Several operational factors such as initial leach liquor pH, extractant concentration, co-solvent concentration and stripping reagent concentration were examined to establish suitable conditions for the effective extraction and stripping of Mo. The separation factors, beta(Mo/Fe) = 1803.61, beta(Mo/As) = 480.09 and beta(Mo/V) = 103.22, were obtained under the optimum experimental conditions of 15%(v/v) Cyanex-272, 15%(v/v) TBP, initial leach liquor pH of 0.0 and organic/aqueous (O/A) phase ratio of 1.0. The theoretical number of stages required for extraction and stripping was determined from the McCabe-Thiele diagrams. Molybdenum (11.62 g/L) was extracted in five stages with an O/A ratio of 1.0, yielding a raffinate with only 0.30 g/L Mo. Three stripping stages yielded a 98.0% Mo stripping efficiency from 11.23 g/L Mo loaded organic phase, producing an enriched 55.05 g/L Mo solution that contained 0.058 g/L As and 0.023 g/L V. A high purity final MoO3 product (99%) was obtained by re-crystallization from the stripped Mo solution. (C) 2012 Elsevier B.V. All rights reserved.