Use of Cyanex 572 as an effective extractant for the recovery of Mo(VI) and V(V) from HDS spent catalyst leach liquor

Abstract

In this study, the extraction of Mo(VI) and V(V) from the simulated leach liquor of hydrodesulfurization spent catalyst was studied. The commercial extractant Cyanex 572 was used for the extraction of both Mo(VI) and V (V). At the low pH region, the extraction of Mo(VI) was higher than that of V(V). At higher pH, the extraction of V (V) was more but, the co-extraction of Mo, Fe and Al was also more. By increasing H2SO4 concentration in the feed solution from 0.25 to 5.0 mol/L, molybdenum extraction decreased from 96% to 70% and remained constant after 1 mol/L H2SO4. The extraction of V(V) was less than that of Mo(VI). With increasing Cyanex 572 concentration from 1 to 10%, Mo(VI) extraction increased from 20.1% to 97.6%, whereas V(V) extraction increased to 9.1% only. The co-extraction of Al, Ni, Fe and Co was not observed. From the slope analysis data, it was observed that two moles of H+ were released during the extraction of Mo(VI) and one mole of H+ was released during the extraction of V(V). Similarly, two and three moles of Cyanex 572 were associated with the extraction of Mo(VI) and V(V), respectively. The extracted species of Mo(VI) and V(V) were MoO2.A(2).H(2)A(2) and VO(2)A.5HA, respectively. The McCabe-Thiele diagram for Mo(VI) showed three stages at A:O ratio of 2:1 for quantitative extraction of Mo(VI). From the loaded organic V(V) was removed by scrubbing with 0.3 g/L Mo solution followed by Mo stripping with (NH4)(2)CO3. After that, V(V) extraction was carried out with the same extractant at pH 2.0 in three counter-current stages at A:O ratio of 1:1, and from the loaded organic, V was selectively stripped with (NH4)(2)CO3. The thermodynamic parameters such as Delta H degrees, Delta S degrees and Delta G degrees were also determined.