Achieving sub-10 ppb arsenic levels with iron based biomass-silica gel composites

• Stable Iron based biomass-silica gel composites (IBC) have been synthesized.
• IBC can decrease arsenic in solution down to sub-10 ppb levels.
• IBC incorporates powdered fern that improves mechanical properties of raw silica gel.
• IBC can simultaneously remove arsenic and other heavy metals from solution.

This work reports results of the synthesis of new composites for arsenic uptake from solution. Initial screening of materials was done to adequately choose the components of composites. Keeping in mind arsenic affinity for (hydro)oxides of metal cations, particularly iron-based, As(V) sorption experiments were carried out using various biomaterials treated with iron (II) solutions. Binding equilibrium between two biomaterials (fern, Pteridium aquilinum, and Fucus vesiculosus) and Fe(II) was accurately described in terms of Langmuir–Freundlich model. An immobilization method with a silica gel matrix was developed in order to solve operational problems of biomass in aqueous solution. Therefore, composites synthesis was carried out in two steps: biomass immobilization by the sol–gel process and loading of gels with Fe(II) solutions of two different concentrations (200 and 400 mg L−1). Composites surface was characterized by SEM and EDS analysis. Batch experiments were done with composites to evaluate arsenic sorption capacity. Results showed the high capacity of the new materials for arsenic uptake, especially the composites with the higher content of Fe(II). Cadmium sorption experiments were also developed to prove the capacity of composites to uptake other metals after arsenic sorption, so suggesting an additional application for arsenic loaded sorbents before final disposal.

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