Selective separation and enrichment of neodymium and gadolinium by emulsion liquid membrane using a novel extractant CYANEX® 572

In present study, the novel commercial extractant, CYANEX (R) 572, was applied for selective separation and enrichment of neodymium and gadolinium through an emulsion liquid membrane. Response surface methodology (RSM) based on central composite design (CCD) is carried out to explore the relationships between process variables namely, carrier concentration, initial pH of feed phase, surfactant concentration and mixing speed, and their interactions. The contours and 3D response surfaces of selective extraction of Gd(III) were achieved and significance of four important variables and their interactions on extraction efficiency of Gd(III) and Nd(III) and separation factor were found out. Also, three regression models for them were developed. A multiple optimization was performed to evaluate the best possible goals for the responses, simultaneously. Results indicated that the maximum separation factor of Gd(III) over Nd(III) was achieved using 0.75 M CYANEX (R) 572 as minimum concentration of carrier, initial feed pH of 1.56, surfactant concentration of 4% (v/v) and mixing speed of 135 rpm. Under the optimum condition, the extraction percentage of Gd(III) was maximum (67.45%), while the extraction percentages of Nd(III) was minimum (28.98) and the separation factor was found to be 3.78. Under the optimized condition, further experiments were conducted to investigate the effect of hydrochloric acid as internal stripping phase on the stripping efficiencies and enrichment factors were examined. At the internal concentration of 0.5 M, the stripping efficiency and enrichment factor reached the maximum of 89.04% and 12.01 for Gd(III), and 19.45% and 1.13 for Nd(III).