SOLVENT-EXTRACTION OF ANIONIC SILVER(I) THIOCYANATE COMPLEX AS ION-PAIRS WITH TETRABUTYLAMMONIUM IONS INTO CHLOROFORM AND 4-METHYL-2-PENTANONE

Solvent extraction of silver(I) from aqueous 1 moldm(-3) Na(SCN, NO3) solutions, where the thiocyanate ion concentration was higher than 1x1 0(-3) moldm(-3) and pH was 3, into chloroform and into 4-methyl-2-pent anone (MIBK) was studied in the presence of tetrabutylammonium ions (t ba(+)) at 298 K. The extraction equilibria of the ion-pairs, tba(+)SCN (-) and tba(+)NO(3)(-) into these solvents were also determined. The e xperimental data were well explained by extraction of tba(+)Ag(SCN)(2) (-) into chloroform and both tba(+)Ag(SCN)(2)(-) and Na+Ag(SCN)(2)(-) into MIRK and by formation of Ag(SCN)(n)(1-n), where n was 2 to 4 in t he aqueous phase. More than half of the initial amount of tba(+) in th e aqueous phase was extracted as tba(+)SCN(-) and tba(+)NO(3)(-). The analysis of the extraction data of silver(I) should be made by taking the decrease in the tba(+) concentration due to these extractions into account. No dissociation of the ion-pairs was found in chloroform but the extracted ion-pairs were partially dissociated in MIBK. In the pr esence of 1x10(-3) moldm(-3) tba(+) in the initial aqueous phase, the extraction of silver(I) was much better into MIBK than into chloroform under otherwise identical conditions. The extraction and dissociation constants of the above species and the stability constants of the ani onic thiocyanate complexes of silver(I) in the aqueous phase were calc ulated.