Solvent Extraction of Anionic Silver(I) Thiocyanate Complex as Ion-Pairs with Tetrabutylammonium Ions into Chloroform and 4-Methyl-2-pentanone

Abstract

Abstract Solvent extraction of silver(I) from aqueous 1 mol dm−3 Na(SCN, NO3) solutions, where the thiocyanate ion concentration was higher than 1 × 10−3 mol dm−3 and pH was 3, into chloroform and into 4-methyl-2-pentanone (MIBK) was studied in the presence of tetrabutylammonium ions (tba+) at 298 K. The extraction equilibria of the ion-pairs, tba+SCN− and tba+NO3− into these solvents were also determined. The experimental 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 MIBK and by formation of Ag(SCN)n1−n, where n was 2 to 4 in the aqueous phase. More than half of the initial amount of tba+ in the aqueous phase was extracted as tba+SCN− and tba+NO3−. 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 presence of 1 × 10−3 mol dm−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 anionic thiocyanate complexes of silver(I) in the aqueous phase were calculated.