School of Water Resources and Environment, China University of Geosciences, Xueyuan Road 29, Haidian District, Beijing 100083, PR China.
J Hazard Mater. 2011 Feb 28;186(2-3):1847-54. doi: 10.1016/j.jhazmat.2010.12.078. Epub 2010 Dec 23.
Synthetic siderite has been used as adsorbent for As(III) removal in this study. Effects of contact time, temperature, pH, co-existing anions on As(III) adsorption were intensively investigated. Adsorption mechanisms were also studied using the X-ray absorption technique. Results show that the maximum adsorption capacity is up to 9.98 mg g(-1) at 25°C at a siderite dosage of 2 g L(-1). Adsorption kinetics agrees with the Lagergren pseudo-second order model. Arsenic(III) adsorption can be better described by Langmuir isotherm model for As(III) adsorption at 55°C, indicating that the coverage of the adsorption sites is in the form of monolayer, although Freundlich isotherm yields a better fit to the experimental data at 25, 35 and 45°C. Thermodynamic study indicates that As(III) adsorption on the synthetic siderite is spontaneous and endothermic in nature. The adsorption capacity is enhanced with the increase in reaction temperature. The adsorption is independent on solution pH between 3.0 and 9.6. The presence of NO(3)(-), SO(4)(2-), PO(4)(3-) or SiO(3)(2-) with element concentrations less than 20 mg L(-1) does not have adverse effect on As(III) adsorption. XANES spectra indicate that As mainly occurs as As(V) in the As adsorbed-materials, and the fraction of oxidized As(III) increases with the decrease in As(III) concentration. The formation of Fe hydroxide minerals (such as lepidocrocite and goethite) followed by As(III) oxidation and adsorption is shown to be the main mechanism of As(III) removal by the synthetic siderite.
在这项研究中，合成菱铁矿被用作吸附剂来去除 As(III)。详细考察了接触时间、温度、pH 值、共存阴离子对 As(III)吸附的影响。还使用 X 射线吸收技术研究了吸附机制。结果表明，在 25°C 下，菱铁矿用量为 2 g/L 时，最大吸附容量高达 9.98mg/g。吸附动力学符合 Lagergren 拟二级动力学模型。在 55°C 下，As(III)吸附更符合 Langmuir 等温吸附模型，表明吸附位点的覆盖度以单层形式存在，尽管 Freundlich 等温吸附模型在 25、35 和 45°C 下更能拟合实验数据。热力学研究表明，As(III)在合成菱铁矿上的吸附是自发的、吸热的。吸附容量随反应温度的升高而增强。吸附在 3.0 至 9.6 的溶液 pH 值范围内是独立的。当 NO(3)(-)、SO(4)(2-)、PO(4)(3-)或 SiO(3)(2-)的元素浓度低于 20mg/L 时，它们的存在对 As(III)吸附没有不利影响。XANES 谱表明，吸附材料中 As 主要以 As(V)的形式存在，氧化的 As(III)比例随 As(III)浓度的降低而增加。菱铁矿去除 As(III)的主要机制是形成 Fe 氢氧化物矿物（如纤铁矿和针铁矿），随后进行 As(III)氧化和吸附。
