Removal of arsenic from contaminated soils by combining tartaric acid with dithionite: An efficient composite washing agent

In the context of the increasing global problem of arsenic (As) contamination in soils, an efficient remediation method is urgently needed to alleviate it. In this study, a composite washing agent consisting of 0.2 mol L-1 dithionite and 0.05 mol L-1 tartaric acid (TA) in a 1:1 mixing volume ratio was prepared and used in the remediation of arsenic-contaminated soils. The results showed that the removal efficiency of arsenic was 62.47% in soil 1 at a concentration of 134 mg kg-1 and 70.08% in soil 2 at a concentration of 70 mg kg-1. Dithionite achieved greater release of the arsenic associated with amorphous hydrous oxides of iron and aluminium (F3) and arsenic associated with crystalline hydrous oxides of iron and aluminium (F4) forms of arsenic by the reductive dissolution of iron oxides, while also reducing Fe3+. TA released some arsenic in the specifically adsorbed (F2) and F3 forms through acidic effects. The mechanism of arsenic removal from the composite washing agent was found to be a synergistic effect between dithionite and TA. The TA complexation formed Fe -TA complexes with Fe2+ in solution, preventing the formation of new iron mineral phases and reducing the readsorption or precipitation of arsenic to the soil surface. Meanwhile, the formation of Fe-TA complexes kept the iron oxides dissolved, allowing more iron oxide-bound arsenic (F3 +F4) to be released. This study showed that combining TA with dithionite is a promising technology for remediating arsenic-contaminated soils because of its high efficiency.