EFFECT OF SODIUM, CALCIUM, MAGNESIUM, AND CHLORIDE-IONS ON THE SOLVENT-EXTRACTION OF BORON FROM AQUEOUS-SOLUTIONS

The effect of Na+, Ca2+, Mg2+ and Cl- ions upon the solvent extraction of boron from aqueous solutions has been studied. The extraction of Na+, Ca2+, Mg2+ and Cl- ions singly and in various mixtures into 2-ethyl-1,3-hexanediol(EHD), 2-chloro-4-(1,1,3,3-tetramethylbutyl)-6-methylolphenol (CTMP) and 1:1 mixture of the two is considered here. The results show that in the absence of berates each of the solvent systems will extract a small amount of dissolved Na+, Mg2+ and Ca2+ cations, presumably as solvated ion pairs, and the order of extraction is generally CTMP > CTMP/EHD > EHD and Ca2+ > Mg2+ > Na+ (all exhibiting considerable increase with pH). A maximum is achieved for calcium with CTMP at pH 11. These observations are consistent with larger bulk shielding effect of CTMP in ion-pair formation and also with its (likely) stronger acidity. The same general trends are observable in the extraction of the same cations in the presence of boron, but the effects are much greater. However, the extent of the extraction of boron is little affected by the presence of the cations. These results can be rationalized if it is assumed that any of the species H+, Na2+, Mg2+, or Ca2+ can act as counter ions in the formation and extraction of borate-cation complex ion pairs.