Coordination extraction for separating vanadium and impurities from black shale HCl leachate at low pH using D2EHPA and EHEHPA mixture

Comprehensive study on the coordination behavior of vanadium ions and extractants is an important guide to the establishment of new efficient extraction systems. In this study, the synergistic effect and mechanism of D2EHPA and EHEHPA as combined extractants for separating vanadium and impurity ions were investigated in detail. The optimal extraction conditions were D2EHPA:EHEHPA ratio 7:3, feed solution pH 1.4, extractant concentration 20%, stirring time 8 min, and phase ratio (O/A) 1:2. Under these optimal conditions, the extraction percentages of V, Fe, Al, and Zn were 79.22%, 16.6%, 2.61%, and 4.29%, respectively. Under the optimal conditions of three-stage extraction and two-stage stripping, V2O5 product with 98.62% purity could be obtained after ammonia precipitation. FTIR spectroscopy and ESI-MS analysis results indicated that D2EHPA and EHEHPA could form HA center dot HB dimer under the action of hydrogen bonding, and this dimer exhibited excellent extraction performance and selectivity. The solution chemistry and quantum chemistry results showed the dissociation process of the coordination bond between chloride ions and VO2+ at the extraction interface; however, only VO2+ ions entered the organic phase to react with the extractant, and the final extractant appeared as VOA(2)center dot HB.

Automated summary

Comprehensive study on the coordination behavior of vanadium ions and extractants is crucial for establishing new efficient extraction systems. This study investigated the synergistic effect and mechanism of D2EHPA and EHEHPA as combined extractants for separating vanadium and impurity ions. The results showed that under the optimal conditions, high purity V2O5 product could be obtained.