Green and efficient removal of cadmium from rice flour using natural deep eutectic solvents

•NADESs are used for the first time for cadmium (Cd) removal from rice flour.•Synergistic effect of NADESs and 1% saponin solution was observed on Cd removal.•>99% Cd was removed using NADES ChSor −1% saponin aqueous mixtures.•Adsorption is one of the mechanisms of Cd removal by NADES in presence of saponin.

Natural deep eutectic solvents (NADESs) constitute a novel class of biodegradable and inexpensive solvents. In this study, twenty choline chloride- and glycerol-based NADESs were prepared and investigated as washing agents in the removal of cadmium (Cd) from rice flour for the first time. Choline chloride-based NADESs demonstrated good Cd removal (51%-96%). A natural, biodegradable surfactant, saponin, was mixed with the NADESs to enhance their efficiency. No increase in Cd removal was observed when glycerol-based NADESs were combined with 1% saponin; however, synergistic effects between saponin and choline chloride-based NADESs were observed during the washing process and >99% Cd was removed using NADES-saponin mixtures. Moreover, NADESs washing process did not affect the main chemical components or structure of rice flour. The mechanism of Cd removal by NADESs and regeneration of Cd-contaminated NADESs were also explored. The study presents a green and efficient way of removing Cd from contaminated rice.