Extraction of chromium from contaminated wastewater with deep eutectic solvent

Extraction with deep eutectic solvent (DES) is a new separation process by liquid–liquid
microextraction using green solvent. Cr(III) and Cr(VI) were extracted from synthetic wastewater and
analyzed by flame atomic absorption spectrometry. A deep eutectic solvent was prepared by mixing choline
chloride as the hydrogen acceptor and urea as the hydrogen donor. The Cr(III) and Cr(VI) concentrations of
100 mg/L were prepared in the synthetic wastewater and used 1.0 mL in the experiments. The studied
parameters of extraction consisted of pH values (2-8), molar ratios of DES comprising choline chloride and
urea (1:1, 1:2, 1:3, 1:4 and 1:5), volumes of DES (0.2-0.8 mL), volumes of 0.1% (w/v) ammonium pyrrolidine
dithiocarbamate (APDC) (0.2–1.2 mL) and 0.4 mL of tetrahydrofuran (THF). The suitable conditions of
Cr(III) and Cr(VI) extraction by DES were pH values of 8 and 2 for Cr(III) and Cr(VI), respectively, molar
ratios of choline chloride and urea of 1:2, volume of DES of 0.4 mL and volume of 0.1% (w/v) APDC of 0.6
mL and 1.0 mL for Cr(III) and Cr(VI), respectively, which resulted 90-103 % of Cr recovery. The extraction
of Cr by DES was interested because of high percentage recovery and environmentally friendly solvent.