Extraction of molybdenum and vanadium from ammonia leaching residue (main chemical composition: 2.05% Mo, 0.42% V, 65.6% Al(2)O(3) and 10.7% SiO(2)) of spent catalyst was investigated by roasting the residue with soda carbonate, followed by hydrometallurgical treatment of the roasted products. In the roasting process, over 91.3% of molybdenum and 90.1% of vanadium could be extracted when a charge containing a sodium carbonate to spent catalyst ratio of 0.15 was roasted at 750 degrees C for 45 min and the roasted mass was leached with water (liquid to solid ratio of 2) at 80-90 degrees C for 15 min. After the purification of leach liquor, an extraction solvent consisting of 20 vol.% trialkylamine (N(235), commercialized in China) and 10 vol.% secondary octyl alcohol (phase modifier) dissolved in sulfonated kerosene was used to extract molybdenum and vanadium in leach liquor. 10 wt.% ammonia water was used as stripping agent. Adding 30 g/l NH(4)NO(3) to the stripping solution and adjusting the pH to 7-8.5, over 99% of vanadium can be crystallized as ammonium metavanadate. Over 98% of molybdenum can be crystallized as ammonium polymolybdate when pH is between 1.5 and 2.5 (pH is adjusted by HNO(3)). Ammonium metavanadate and ammonium polymolybdate were calcinated at 500-550 degrees C, the purity Of MoO(3) and V(2)O(5) was 99.08% and 98.06% respectively. In the whole process, 88.2% of molybdenum and 87.1% of vanadium could be achieved. The proposed roasting, leaching and separation steps give a feasible alternative for the processing of ammonia leaching residue of spent catalyst and can be applied in the comprehensive utilization of low grade molybdenum ores. (c) 2005 Elsevier B.V. All rights reserved.