Impregnation of activated carbon by iron oxyhydroxide and its effect on arsenate removal

Abstract

AbstractBackgroundImpregnation of activated carbon or oxidized activated carbon was carried out using iron(III) nitrate as starting solution and ammonia as the precipitating agent, intending the removal from aqueous solution of arsenates – a priority pollutant. The high affinity of iron oxyhydroxide nanocrystals toward inorganic arsenic species is known. Activated carbon, on the other hand, can provide a high surface area for adsorption. The initial materials and those after adsorption of arsenate were characterized, in order to explain the adsorption enhancing effect found, when using this precipitating agent.ResultsThe role of carbon surface chemistry and structural heterogeneity on iron oxyhydroxide and thus, on the adsorption of arsenate were investigated. The study of the materials was carried out by adsorption of nitrogen, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS) and thermal analysis. In this paper, it is suggested that a meso/microporous carbon surface possibly contributed to changes of arsenic, via reduction of As(V) to As (III). This might be visible in the increased degree of carbon oxidation. The adsorption capacity found was 32.86 mg of arsenic per gram of carbon, which is higher than the capacities of the other adsorbents reported in the literature.ConclusionOxidation of the carbon support increased the dispersion of iron oxyhydroxide species on the surface and thus, enhanced the efficiency of arsenate immobilization in the carbon pore system. These species react with arsenate‐forming salts. Moreover, iron impregnation (or doping) of activated carbon combined by ammonia precipitation, especially on oxidized carbon support, led to ammonium moieties capable of attracting by electrostatic forces arsenate anionic species, resulting in enhanced adsorption capacity.