Enhancing As(V) and As(III) adsorption performance of low alumina fly ash with ferric citrate modification: Role of FeSiO and monosodium citrate.

Fly ash and arsenic species have been regarded as contaminants that pollute the environment. Herein, low alumina fly ash (LAFA) was utilized to fabricate the As(V) and As(III) adsorbent via combining the routes of alkali fusion and incipient-wetness impregnation. The characterization results suggested that the grafted ferric citrate was coordinated to LAFA by substituting a Si to a Fe, and the compound monosodium citrate was observed. Based on the XPS analysis, the C-O and -COO groups of monosodium citrate played the significant role in uptaking As(V) and As(III) species by chemical complexation, the FeOOH adsorbed As(V) and As(III) species via ion-exchange, and the FeO oxidize As(III) into As(V). Additionally, it was observed that the As(V) removal performance by adsorbent prepared with different modifiers was in the order of FeCHO (ca. 93.7%) > CHO (84%) > HCl (73%). And then, the optimal adsorbent synthesis condition for As(V) uptake was explored at ferric citrate loaded LAFA with 1:1 mass ratio (fly ash to NaOH) under temperature 923 K. The maximum monolayer adsorption capacities of the optimal adsorbent were 2725.0 μgAs(V)/g and 2281.9 μgAs(III)/g, and the removal efficiency of As(V) and As(III) was near 100% for their initial concentrations below 500 ppb, where the residual arsenic concentration met the required standard in drinking water (lower than 10 ppb).