Magnetically recoverable nanoparticles for the simultaneous removal of Sb and As from water

•Iron-based nanocomposite for simultaneous As and Sb removal.•Magnetite enables the reduction of Sb(V) to Sb(III).•Iron oxy-hydroxide captures both Sb(III) and As(V).•Used nanoparticles are recovered by an online magnetic separator.•Efficient capture was optimized by theoretical calculations. This study examines the development of a nanocomposite consisting of iron oxy-hydroxides (FeOOH) embedded on magnetite (Fe3O4) nanocarriers, towards its application for the simultaneous uptake of As(V) and Sb(V) ionic forms at concentrations below drinking water regulation and its magnetically-assisted recovery at the end of the process. Considering Fe3O4 as the reductant, assisting the transformation of highly mobile Sb(V) to Sb(III), and the high affinity of FeOOH to adsorb both As(V) and Sb(III), adsorption experiments carried out at equilibrium pH 7 indicated that a FeOOH/Fe3O4 composition of 50%wt. is the optimum to establish a sufficient efficiency in the uptake of both pollutants. Particularly, the adsorption capacity for As(V) at residual concentration 10 μg/L is around 2.3 mg/g whereas around 0.4 mg/g of Sb(V) can be captured by the nanocomposite while keeping the residual concentration below 5 μg/L. Such efficiencies are preserved in the case of simultaneous adsorption of both pollutants without any appearance of cross-interference effects, at least for residual concentrations below 400 μg/L. The high magnetic response of Fe3O4 nanoparticles allows the application of the nanocomposite for water purification in an alternative setup, consisting of a contact stirring reactor and a magnetic separator constructed by permanent magnets. The dimensions and flowrates of the continuous-flow system were properly designed on the basis of theoretical calculations using the magnetization, adsorption efficiency and kinetics as input, to combine maximum purification and solid recovery. Suggestively, operation of the system using a natural water with pH 7 containing 50 μg/L As(V) and 10 μg/L Sb(V) showed successful decrease of residual concentrations below regulation limits for drinking water and 100% recovery of the solid when a nanocomposite's dose of 20 mg/L was added. [Display omitted]