Study on antimony and arsenic cycling, transformation and contrasting mobility in river-type reservoir

Antimony (Sb) and arsenic (As) are toxic heavy metals of the same group on the periodic table of elements. They have similar but different properties, and their migration processes in water affect the ecological environment. A river-type reservoir polluted by Sb mining was selected as the study object. Water and sediment samples were collected. Sb, As, Fe and Mn concentrations in water were determined. Sb and As forms in sediment were also analysed. Using geochemical theories and PHREEQC software, it was found that there was an obvious deposition and reductive release process of Fe in the reservoir, and the environmental behaviour of Sb and As in it was influenced by this cycle. The dissolved Sb could be purified through adsorption by suspended particles especially in the bottom layer where the removal rate could reach above 40%. Sb and As enriched in sediment could distribute in equilibrium among different forms including acid soluble, reducible, oxidizable, and residual, and were mainly found in residual form. Both of their concentrations in porewater had significantly positive correlations with the content of the reducible form. The concentration of As showed a positive correlation with the concentration of Fe in pore water, whereas Sb showed the opposite. In addition, Sb and As could influence the overlying water quality through continuous diffusion, although the fluxes were low. This will provide a basis for the scientific management of such polluted reservoirs. [Display omitted] •Difference of migration and transformation process of antimony and arsenic in reservoir.•Relationship between secondary distribution and form of antimony and arsenic in sediment.•Effect of iron cycle in reservoir on geochemical behaviour of antimony and arsenic.