Extraction of alkali metal salts from acidic solutions with crown ethers

Alkali metal ions have been extracted from aqueous solutions of mineral acids (HNO/sub 3/, HClO/sub 4/, and HCl) into the organic solvent dichloroethane (DCE) with the crown ether dicyclohexyl-18-crown-6 (DCH-6). A study was made of the distribution of the inorganic acids in a two-phase system using a solution of DCH-6 in DCE as the extractant. Under equilibrium conditions (T = 25/sup 0/C) the order of extractability of the acids in 0.1 M DCH-6 solution was HClO/sub 4/ 0.37 > HNO/sub 3/ (0.056) > HCl (0.003), in qualitative agreement with the hydration energies of the corresponding anions. The results for the extraction of alkali metal cations from nitric acid solutions as HNO/sub 3/ increases, the distribution coefficients of the alkali metal nitrates pass through a maximum and then decrease. The order of the cations by extractability characteristic of neutral and alkaline solutions is presented regardless of the acidity: K/sup +/ > Rb/sup +/ > Cs/sup +/ > Na/sup +/ > Li/sup +/. The observable maxima of the distribution coefficients of potassium nitrate and perchlorate correspond to the maximum extraction of nitric and perchloric acids by crown ethers. The maximum extraction of the perchlorates is observed for extraction from significantly less acidicmore » solutions. The results allow one to consider the crown ethers as effective extractants for the extraction and separation of alkali metals from acidic solutions of complex salt composition. 4 figures. (DP)« less