Effects of phosphate, silicate, humic acid, and calcium on the release of As(V) co-precipitated with Fe(III) and Fe(II) during aging.

The effects of phosphate (P), silicate (Si), humic acid (HA), and calcium (Ca) on the release of As(V) co-precipitated with Fe(III) and Fe(II) during aging were investigated. As(V) in synthetic groundwater could be efficiently removed by both Fe(III) and Fe(II) processes. The addition of P remarkably decreased As(V) removal efficiency while no obvious release of As(V) during aging was observed. Si and HA reduced As(V) removal to a less extent than P but caused notable As(V) release during aging. FTIR spectra and particle size of the precipitates before and after aging indicated that As(V) release in the presence of Si was due to the serious structural transformation and particle aggregation of the precipitates during aging. While for HA, As(V) release was caused by sorption of HA on the precipitates and dissolution of the precipitates by HA. The addition of Ca partially counteracted the adverse impacts of P, Si, and HA and promoted As(V) removal efficiency but had limited inhibitory effect on As(V) release as it induced more serious particle aggregation during aging. The results demonstrated that the release of As(V) caused by Si and HA should be considered when using Fe coagulation for in-situ treatment of As(V) contaminated groundwater.