Strategy for extractant residual reduction: Experimental and computational investigation of fluorinated phosphate

Extractant residual in water phase is a destined and disgusted consequence after solvent extraction operation. In order to reduce extractant residual in aqueous phase, extractants modified by fluorination were probed. In this paper, tri-n-amylphosphate (TAP) was selected as model extractant along with its fluorinated analogue, tris (2,2,3,3,4,4,5,5-octafluoropentyl) phosphate (FTAP), to extract the salicylic acid from its aqueous solution to investigate residual and extraction behaviors by both experimental and computational methods. The experimental results obtained from multiple light scattering revealed that FTAP barely interacted with water and possessed high hydrophobicity. The solubility of FTAP in aqueous phase was less than 6.0×10−5 (w/w), and declined with increase of temperature, which was similar to the nature of nonionic surfactant. In acid solution with high concentration, the solubility of FTAP remained quite low. The one-step extraction efficiency of FTAP on salicylic acid was approximately 85%. The cycling experimental results showed that the durability of FTAP was overwhelmingly excellent compared with that of TAP, especially after the cycles more than 10 times. DFT calculation demonstrated the hydrophobicity and extraction behavior at molecular level. All results implied that fluorinated modification of extractant was a possible way to reduce its loss in aqueous phase.