Effect of liquid and air flowrates on the efficiency of a two-stage air-assisted solvent extraction system in pilot scale

Air-assisted solvent extraction (AASX) in continuous-mode is a new development in the solvent extraction process for the extraction of valuable metals from dilute solutions. The main aim of this research was to investigate the effect of the flowrate of liquid and air phases on Cu recovery and organic phase recycling in a two-stage AASX system at pilot scale. The experiments were carried out in continuous-mode and the effect of the flowrates of liquid (18–30 L/min) and air (5–15 L/min for the first stage and 20–40 L/min for the second stage) were evaluated. Response surface methodology was used for designing the experiments, and results were analyzed by the analysis of variance (ANOVA). It was found that increasing the liquid flowrate reduced the Cu recovery in both stages by decreasing the retention time. While, enhancing the air flowrate in the first column increased the Cu recovery and organic phase recycling probably due to the adsorption of uncoated portion of the organic phase and collection of the smaller coated bubbles. Maximum Cu recovery (85%) and organic phase recycling (84%) were achieved at liquid flowrate of 18 L/min, first column aeration of 15 L/min, and second column aeration of 30 L/min for a solution containing 150 mg/L copper. Moreover, 98 and 94% Cu recoveries were obtained for 50 and 100 mg/L Cu solutions, respectively. The results indicated that using the newly developed AASX process, the application of the solvent extraction process could be extended to treat dilute metal-bearing solutions such as acid mine drainage.