Removal of arsenic in freshwater wetland waters using fly ash modified with zirconium-manganese binary oxides

Abstract

A new alternative supporting matrix for constructed wetlands was explored using fly ash modified with Zr-Mn binary oxides (Zr-Mn/FA) and examined its performance in the control of arsenic pollution in wetland waters. The prepared matrix was characterized by SEM, XRD and EDS. Batch experiments were performed to investigate the effects of various conditions for the adsorption of arsenic onto Zr-Mn/FA including pH, contact time, concentration, temperature,loading amount of Zr-Mn and co-existing ions. The results showed that Zr-Mn oxides on the surface of Zr-Mn/FA dominated the reaction force between arsenic and adsorbent. The phosphate anion could reduce the adsorption process of arsenite (As(Ⅲ))and arsenate (As(Ⅴ)) when its concentration exceeds 1.0 mg·L⁻¹. The experimental data of both As(Ⅲ) and As(Ⅴ) adsorption on Zr-Mn/FA were well fitted with pseudo-second order kinetic model as well as Langmuir adsorption isotherm model with the maximum adsorption capacities of 70.13 mg·g⁻¹ for As(Ⅲ) and 43.19 mg·g⁻¹ for As(Ⅴ), respectively. The thermodynamic study suggested that the adsorption of As(Ⅲ) and As(Ⅴ) were both endothermic. However, the adsorption of As(Ⅴ) was spontaneous while the opposite conclusion was obtained for As(Ⅲ). The prepared material (Zr-Mn/FA) was then successfully applied in the real water samples from wetland which indicated that Zr-Mn/FA composite could be a promising matrix for constructed wetland to effectively remove inorganic arsenic from water.