Extraction of molybdenum and vanadium from the spent diesel exhaust catalyst by ammonia leaching method

Molybdenum (Mo) and vanadium (V) were effectively extracted from the spent diesel exhaust catalyst (V2O5-MoO3/TiO2) by using an ammonia leaching method. Meanwhile, the structure of the spent catalyst carrier (TiO2) was not destroyed and might be reused. The effects of ammonia (NH3·H2O) concentration, leaching temperature and time, concentration of hydrogen peroxide (H2O2) and liquid to solid ratio on the extraction of Mo and V were systematically investigated. It is shown that the extraction efficiency of Mo increased from 68.68% to 96.45% while the extraction efficiency of V remained stable at 27% with increasing ammonia concentration from 2.95 to 7.38 mol/L, leaching temperature from 298.15 to 473.15 K, and reaction time from 1 to 8 h. With the concentration of H2O2 solution increasing from 1.0 to 2.5 mol/L, the extraction efficiency of V increased from 26.87% to 39.73%. Under the optimum conditions (the ammonia concentration of 4.5 mol/L, leaching temperature of 413.15 K, reaction time of 2 h, the H2O2 solution concentration of 1.0 mol/L and the liquid to solid ratio of 20/1 mL/g), the extraction efficiencies of Mo and V reached 95.13% and 46.25%. Moreover, the catalyst carrier TiO2 with anatase crystal phase was also obtained.