Bi-functional organophosphorus extractants and computational modeling for copper(II) and zinc(II) extraction

Novel bi-functional extractants, which possess two phosphonic groups on both sides of the extractants, have been synthesized for the separation of Zn(II) and Cu(II). The separation properties and extractability of the novel extractants were investigated using the liquid-liquid extraction technique. These bi-functional extractants provide a high selectivity towards Zn(II) over Cu(II) compared to that of monoacidic phosphorus extractant as an analog. We discussed the extraction behavior of the bi-functional extractants with a computational modeling by means of semi-empirical molecular orbital methods. The calculation suggests that the length of the spacer is one of the decisive factors to enhance the selectivity in the bi-functional extractants. The high separation ability for the bi-functional extractants was related to the high energy difference in the heat of formation calculated by computational modeling. The computational simulation was found to be very useful for the design of novel extractants and prediction of their separation performance.