Organic acids modify the binding selectivity of crosslinked poly(ionic liquid) between Sb(III) and Sb(V)

Abstract

Antimony binding properties of a poly(ionic liquid), synthesised by crosslinking polymerisation of 1-butyl-3-vinyl-imidazolium bromide with N, N-methylene diacrylamide, in presence of complexing organic acids have been investigated. Sorption of Sb(V), Sb(III), and organic acids from their individual solutions and solutions containing antimony and organic acid by the crosslinked poly(ionic liquid) (P(BuVImBr-MDAA)) were studied at different pH conditions. The complexing organic acids, namely tartaric acid (TA), ascorbic acid (AA), citric acid (CA), EDTA and nitrilotriacetic acid (NTA), were shown to effect substantial changes in the antimony binding properties of P(BuVImBr-MDAA). Remarkable change in Sb(III) – Sb(V) selectivity of P(BuVImBr-MDAA) was observed in the presence of EDTA, NTA and CA. In the presence of EDTA, the selectivity could be toggled between Sb(III) and Sb(V) by varying the solution pH (initial). At pH 2.0 and 3.0, the uptake of Sb(V) was found to be higher than Sb(III) whereas at pH 4.0 there was about 40% reduction in Sb(III) uptake and no uptake of Sb(V). Citric acid and NTA, at pH 2.0 and pH 4.0 respectively, were found to be better choice for Sb(III) - Sb(V) separation using P(BuVImBr-MDAA) as there was negligible reduction in Sb(III) uptake and nil uptake of Sb(V). The pH dependent acid speciation and the nature of complexes influenced the selectivity. Tartaric acid was shown to be the most suitable organic acid for effective removal of antimony (both Sb(III) and Sb(V)) without compromising on the binding capacity.