Air-assisted solvent extraction (AASX) has been introduced as a new method for the selective extraction of metals from dilute solutions in order to overcome the economic and technical problems of the conventional processes. Producing organic coated bubbles in AASX can increase the specific surface area which reduces the organic phase consumption and enhances the floatability of the organic phase. The main objective of this research is to identify the mechanisms of Cu extraction from dilute solutions in AASX process. For this purpose, the effect of chemical and operational parameters on Cu recovery, organic phase recycling, as well as the size and distributions of the bubbles in a continuous AASX process were investigated at a pilot scale. Furthermore, the selectivity of Cu extraction from the pregnant leach solution (PLS) of the heap and the raffinate stream of solvent extraction plant of the Sarcheshmeh copper complex was studied. A response surface methodology was used to investigate the influence of aqueous phase flowrate, extractant concentration and silicone oil dosage in the organic phase, organic phase level in the organic coating cylinder (OCC), and Cu concentration in the aqueous phase as independent variables. The results showed that increasing OCC level and silicone oil dosage reduced the aqueous to organic phase ratio (A/O). This reduction occurred as a result of reducing the surface tension of the organic phase in the presence of silicone oil, increasing the coating degree of bubbles, and reducing the coalescence of coated bubbles. Moreover, increasing the extractant concentration and the silicone oil dosage improved the Cu recovery. Increasing the organic phase loading capacity and coating degree could be mentioned as the main reasons for this behavior. The optimized results revealed that 78% of Cu recovery and 38% of organic phase recycling could be achieved from 50 mg/L of Cu solution at A/O phase ratio of 83. The surface phenomena of AASX process were examined in the presence of various additives including frothers, salts, and silicone oil. The results indicated that the surface tension of the aqueous phase has been reduced strongly by a rise in the frother dosage, where the most and least effective frothers were Dowfax-2A1 and Flomin-F742, respectively. Besides, the reduction of organic phase surface tension in the presence of silicone oil led to the reduction in A/O phase ratio. The size and distributions of bubbles were enhanced by increasing the silicone oil dosage. In the optimized condition (using 50 mg/L of pine oil and silicone oil), 61% Cu recovery and 72% organic phase recycling were attained through synthetic leach solution (150 mg/L Cu). Subsequently, a second column was added to AASX apparatus to improve the Cu recovery and organic phase recycling. The effects of liquid and air flowrates on the efficiency of the developed AASX apparatus were studied. The organic phase recycling has been significantly improved through the rise in retention time of the fluids in the columns (i.e. reduction in the liquid flowrates), collecting the small coated bubbles, and reducing the portion of uncoated organic phase which is resulted in enhancing the air flowrates. At the optimum conditions, 98% of Cu and 83% of organic phase were recovered from 50 mg/L of Cu solution. Furthermore, the Cu recovery values from the solutions with 100 and 150 mg/L concentrations were obtained 94% and 84.7%, respectively. Moreover, the selectivity of the AASX process was examined for Cu extraction from raffinate of SX plant and PLS of the heap-leaching of the Sarcheshmeh copper complex. Treatment of raffinate solution (contained 47 mg/L of Cu) and PLS (~890 mg/L of Cu) showed that ~90 and 95% of Cu could be recovered in AASX process. High A/O phase ratio, high efficiency, and continuous operation could be mentioned as the advantages of AASX process. Besides, this method has a high potential for selective extraction of valuable metals from dilute solutions such as acid mine drainage and leach solutions of low-grade and complex ores.