Ion-pair based liquid-liquid extraction of gold(III) from malonate media using 2-octylaminopyridine as an extractant: analysis of alloys, minerals, and drug samples

Authors: VISHAL SURYAVANSHI, ARJUN KOKARE, SUNIL ZANJE, ABHIJEET MULIK, RUPALI PAWAR, MAKRAND PATIL, ASHWINI GAIKWAD, MANSING ANUSE, GANPATRAO MULIK

Abstract: Liquid-liquid extraction of Au(III) from aqueous sodium malonate medium using 2-octylaminopyridine (2-OAP) as an extractant in xylene was achieved. The current work explored the influence of several experimental parameters such as pH, weak acid concentration, extractant concentration, equilibrium time, stripping agents, and aqueous:organic volume ratio on the extraction of Au(III). The experimental results showed that the Au(III) was quantitatively extracted to about 99.5% by 0.05 M 2-OAP in 0.05 M malonate at 5.0 pH. Ammonia solution was used to strip the gold-loaded organic phase and about 99.5% of Au(III) was reversibly extracted into the aqueous phase. Gold(III) was extracted into the organic phase via formation of ion-pair complex [2-OAPH$^{+}$.Au (C$_{3}$H$_{2}$O$_{4})_{2}^{-}$]. The stoichiometry of the extracted species was 1:2:1 (metal: acid: extractant) determined by slope analysis. The method affords the binary, ternary mixture separation as well as separation of Au(III) from synthetic mixtures and alloys. The method is applicable for the determination and separation of gold from ayurvedic samples and recovery of gold from e-wastes. A reproduction of the method was checked by finding relative standard deviation for n = 5, which was 0.29%, and the limit of detection was 1.08 $\mu $g/mL.

Keywords: Liquid-liquid extraction, gold(III), sodium malonate, 2-octylaminopyridine (2-OAP), e-wastes, ayurvedic samples

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