Predicting the Loading Ratio and Optimum Extractant Concentration for Solvent Extraction

Abstract The loading ratio of a solvent extraction process is the ratio of moles of metal extracted to moles of extractant fed. Since the efficiency has several limitations, it is recommended to quantify a metal-extraction system in terms of its loading ratio in addition to its efficiency or extraction rate coefficient. In this study, the loading ratio was compared to the efficiency and equations relating the two metrics were derived. It was shown that due to competing effects of the extractant concentration on the loading ratio, an optimum extractant concentration exists for nearly all metal-extraction systems. This optimum is dependent solely on the equilibrium data and the phase ratio. A method to predict the optimum extractant concentration and the loading ratio at any extractant concentration was presented. The method was validated by comparing the predicted loading ratios to the observed loading ratios for previous metal-extraction studies. The advantages of quantifying a process by its loading ratio and targeting the optimum extractant concentration to maximize the loading ratio were discussed.