Preparation of ferric oxide modified diatomite and its application in the remediation of As(III) species from solution

A new iron oxide–diatomite system was synthesized in one pot by mixing natural diatomite with a ferrous sulfate solution at room temperature. The characterization of the materials (Diatom–Fe) by XRD and chemical analysis revealed that iron (29% w/w) was crystallized under goethite phase (α-FeOOH). Analysis conducted by SEM further highlighted the preferential presence of goethite on the surface of diatomite, which involves hydrogen bonding between diatomite surface silanol groups and ion species. The mechanism of formation of goethite is suggested to occur through the precipitation of ferrous ions by hydroxyls ions followed by the oxidation of the iron species to yield first to lepidocrocite (γ-FeOOH) then goethite that is thermodynamically more stable. Within this mechanism, the contribution of calcium carbonate through its dissolution into hydroxyls species is evidenced by XRD and FTIR analyses. The remediation properties of Diatom–Fe towards arsenite species cations were investigated in batch jar tests for 24 h at auto-equilibrium pH. The materials showed a noticeable higher As (III) sorption capacity (16 mg/g) than the native diatomite (0.5 mg/g). These results can be explained by the strong affinity of arsenites to goethite which is further emphasized by the dispersion of the iron oxide crystals on diatomite surface.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Preparation of composite materials starting from diatomite and aqueous solution of iron(II) sulfate by an environmentally friendly process. ► Study of the mechanism of formation of lepidocrocite and goethite-diatomite composites. ► Application of the obtained composite for the removing of As(III) cations from water.