Investigations on the extraction of molybdenum and vanadium from ammonia leaching residue of spent catalyst

摘要

Extraction of molybdenum and vanadium from ammonia leaching residue (main chemical composition: 2.05 percent Mo, 0.42 percent V, 65.6 percent A1_2O_3 and 10.7 percent 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 percent of molybdenum and 90.1 percent of vanadium could be extracted when a charge containing a sodium carbonate to spent catalyst ratio of 0.15 was roasted at 750 deg C for 45 min and the roasted mass was leached with water (liquid to solid ratio of 2) at 80-90 deg C for 15 min. After the purification of leach liquor, an extraction solvent consisting of 20 vol.percent trialkylamine (N_(235), commercialized in China) and 10 vol. percent secondary octyl alcohol (phase modifier) dissolved in sulfonated kerosene was used to extract molybdenum and vanadium in leach liquor. 10 wt. percent ammonia water was used as stripping agent. Adding 30 g/1 NH_4NO_3 to the stripping solution and adjusting the pH to 7-8.5, over 99 percent of vanadium can be crystallized as ammonium metavanadate. Over 98 percent 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 deg C, the purity of MoO_3 and V_2O_5 was 99.08 percent and 98.06 percent respectively. In the whole process, 88.2 percent of molybdenum and 87.1 percent 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.