Optimization of continuous air-assisted solvent extraction for treating dilute Cu leach solutions using response surface methodology

A newly designed air-assisted solvent extraction (AASX) system was used to extract Cu from dilute solutions in a continuous-mode at pilot scale. The effects of some operational and chemical parameters including aqueous phase flowrate, extractant concentration, organic phase level in an organic coating cylinder (OCC level), Cu concentration, and silicone oil dosage on the efficiency of AASX process were investigated using a response surface methodology. The main and interaction effects of the variables on Cu recovery (26–85%), organic phase recycling (the portion of entered organic phase transferred to the column overflow for stripping, 7–56%), and aqueous/organic phase ratio (A/O, 59–435) were evaluated by the analysis of variance (ANOVA). The results showed that the addition of silicone oil increased Cu recovery and reduced organic phase recycling. Also, increasing OCC level caused to reduce A/O ratio and increase Cu recovery. Increasing extractant concentration and reducing the Cu concentration increased Cu recovery. The results were interpreted by their effects on bubble size, organic coating of air bubbles and A/O ratio. Varying the aqueous phase flowrate changed the A/O ratio in a curved mode which was related to the venturi tube suction force. Results showed that maximum efficiency of the AASX process (78% Cu recovery and 38% organic phase recycling, predicted by the ANOVA model), occurred at the aqueous flowrate of 24 L/min, extractant concentration of 40%, OCC level of 28 cm, Cu concentration of 50 mg/L without using silicone oil with an A/O ratio of 83. It can be concluded that AASX process could be used as an efficient and promising method for treating dilute solutions such as AMDs and wastewaters.