Abstract

D2EHP-] and 1-methyl-imidazolium di(2-ethylhexyl) phosphate [MIm+][D2EHP-] were synthesized and tested as extractants in the batch removal of mercury (II) from aqueous solution. The influence of contact time, aqueous to organic phase’s volume ratio, initial concentration of Hg (II), IL concentration, pH levels, ionic strength, and temperature was evaluated. The extraction equilibrium was established in 30 min for [MIm+][D2EHP-] and in 15 min for [BIm+][D2EHP-]. The maximum mercury extraction was obtained at pH 5.81. For the extraction of mercury, [([MIm+] [D2EHP-])5 (HgCl2)]org, [([MIm+][D2EHP-])5 (HgClOH)]org, [([BIm+][D2EHP-])3/2 (HgCl2)]org and [([BIm+][D2EHP-])3/2 (HgClOH)]org species were formed. Regarding the ionic strength for [MIm+][D2EHP-], the results show a significant improvement of the mercury extraction yield (100%) upon the addition of sodium acetate to the aqueous phase in a Na+/Hg2+ mass ratio ranging from 0.1 to 2.0. The relationship between the percentages of the extracted species and the extraction yield was established by calculations using CHEAQS V. L20.1 software. The results revealed a decrease in the extraction yield of Hg (II) with decreasing proportions of HgCl2aq from 65.15 to 40.31% and of HgClOHaq from 31.31 to 0.1%, when NaCl was added. The very important optimal sorption capacities for ([BIm+][D2EHP-]) and ([MIm+][D2EHP]) were 58.39 mg/g and 93.23 mg/g respectively. With a longer alkyl chain on the imidazolinic ring, the decreasing of extraction yield was observed.

Keywords: Mercury; Ionic liquid; Solvent extraction; Speciation