Preventing emulsification during rare earth solvent extraction by the addition of Span 80 to enhance the interfacial stability of the P507 oil droplets

Abstract

The demand for rare earth elements is increasing daily with rapid economic development, thereby increasing the requirements for its separation and purification technologies. The major method for purification and separation of rare earth in the industry is currently solvent extraction. In the actual production process, emulsification often occurs because of improper control of the organic phase, aqueous phase properties or operating conditions, and resulting in resource wastage and environmental pollution. This has become an issue that restricts the development of the rare earths industry. To prevent emulsification during rare earth solvent extraction, the organic structure of the P507-kerosene solution was regulated by the addition of Span 80 as a regulator. This study investigated the effects of Span 80 concentration, P507 concentration, saponification degree and the amount of pre-loading rare earth elements in the organic phase after adding Span 80 on the extraction efficiency of Er3+ and oil content in the raffinates. The results demonstrated that when the content of Span 80 was 6 %, the saponification degree of P507 in the organic phase was 10 %, the concentration of Er3+ in the aqueous phase was 0.5 g /L, the pH value in the aqueous phase was 3, the phase ratio (VO: VA) was 1:2, the extraction efficiency could still reach more than 99 %, and the oil content in the raffinates was 13.9 mg/L. The results demonstrated that the final extraction efficiency did not decrease; however, the extraction rate of rare earth elements did. Further, the oil content in the raffinates decreased greatly after the addition of Span 80. The mechanism was investigated using Fourier-transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM). The interfacial stability of P507 oil droplets was enhanced by the addition of Span 80. Emulsification was, thus, effectively prevented and the dissolution loss of the organic phase was greatly reduced. The results provide a novel method for preventing emulsification during rare earth extraction at the source, and a novel idea for preventing resource loss and protecting the ecological environment.