Synthesis of iron composites on nano-pore substrates: Identification and its application to removal of cyanide

Abstract

Two types of nano-pore substrates, waste-reclaimed (WR) and soil mineral (SM) with the relatively low density, were modified by the reaction with irons (i.e. Fe(II):Fe(III) = 1:2) and the applicability of the modified substrates (i.e. Fe-WR and Fe-SM) on cyanide removal was investigated. Modification (i.e. Fe immobilization on substrate) decreased the BET surface area and PZC of the original substrates while it increased the pore diameter and the cation exchange capacity (CEC) of them. XRD analysis identified that maghemite (γ-Fe2O3) and iron silicate composite ((Mg, Fe)SiO3) existed on Fe-WR, while clinoferrosilite (FeSiO3) was identified on Fe-SM. Cyanide adsorption showed that WR adsorbed cyanide more favorably than SM. The adsorption ability of both original substrates was enhanced by the modification, which increased the negative charges of the surfaces. Without the pH adjustment, cyanide was removed as much as 97% by the only application of Fe-WR, but the undesirable transfer to hydrogen cyanide was possible because the pH was dropped to around 7.5. With a constant pH of 12, only 54% of cyanide was adsorbed on Fe-WR. On the other hand, the pH was kept as 12 without adjustment in Fe-WR/H2O2 system and cyanide was effectively removed by not only adsorption but also the catalytic oxidation. The observed first-order rate constant (kobs) for cyanide removal were 0.49 (±0.081) h−1. Moreover, the more cyanate production with the modified substrates indicated the iron composites, especially maghemite, on substrates had the catalytic property to increase the reactivity of H2O2.