Pelleted Synthetic Siderite And Its Characteristics For Arsenic Adsorption

High Arsenic groundwater has become a serious environmental issue mainly due to its worldwide distribution and chronic health effects. Previous investigation has shown that synthetic siderite efficiently removes arsenic from groundwater. Siderite pelleting is essential for its actual application in removing arsenic from waters.This study mainly focused on pelleting processes and characteristics of arsenic adsorption on pelleted material. Results show that the best condition for pelleting was sintering for 90 min at 70℃. The equilibrium time was about 24 h. The adsorption process was well described by both pseudo-first-order and pseudo-second-order kinetics model for both As(III) and As(V). The data better fitted Freundlich isotherm in all temperatures (15℃, 25℃, 35℃, 45℃) than Langmuir isotherm for both As(III) and As(V). Higher adsorption capacity was observed at higher temperature. Both As(III) and As(V) adsorption were spontaneous. The presence of Cl-, SiO₃^2-, or PO₄^3- lowers As(III) adsorption on the pelleted material. The presence of SiO₃^2-, or PO₄^3- lowers As(V) adsorption on the pelleted material.For column experiments, the breakthrough time was 50 d, and the total flow is 106.3 L (initial As(V) concentration 1 mg/L, flow rate 2 mL/min). This study showed the effect of water chemistry, initial As concentration, flow rate and As species on breakthrough curves of arsenic removal by pelleted synthetic siderite. The results show that water chemistry affects As removal with the highest capacity for deionized water-synthesized As solution with coexisting anions, followed by deionized water-synthesized As solution and tap water synthesized As solution. Flow rate has influence on As removal with the highest removal efficiency at 3.5 mL/min, followed by 6 mL/min and flow rate 2 mL/min. Besides, As species also has effect on As removal with the highest removal efficiency for 1 mg/L As(III), followed by 0.5 mg/L As(III) and 0.5 mg/L As(V), and 1 mg/L As(V). The removal capacity for 1 mg/L As(V) was higher than that for 2 mg/L As(V) in breakthrough time.Pelleted synthetic siderite column was effectively regenerated after adsorption of arsenic when elution was applied with 0.1 mol/L NaOH solution. After 240 h, the elution proportion is 84.40%. HCl (pH=4) solution was used for regeneration. Regeneration efficiency is up to 50.6%.The data of XRD, SEM, XRF and XANES show that arsenic was removal by means of both chemical adsorption and coprecipitation.