Department of Civil and Environmental Engineering, University of California-Davis, Davis, California 95616, United States of America.
Environ Sci Technol. 2011 Jan 15;45(2):561-8. doi: 10.1021/es1026745. Epub 2010 Dec 15.
Interest in the development of oxide-based materials for arsenate removal has led to a variety of experimental methods and conditions for determining arsenate adsorption isotherms, which hinders comparative evaluation of their adsorptive capacities. Here, we systematically investigate the effects of buffer (HEPES or carbonate), adsorbent dose, and solution pH on arsenate and phosphate adsorption isotherms for a previously well characterized goethite-based adsorbent (Bayoxide E33 (E33)). All adsorption isotherms obtained at different adsorbate/adsorbent concentrations were identical when 1 mM of HEPES (96 mg C/L) was used as a buffer. At low aqueous arsenate and phosphate concentration (∼1.3 μM), however, adsorption isotherms obtained using 10 mM of NaHCO(3) buffer, which is a reasonable carbonate concentration in groundwater, are significantly different from those obtained without buffer or with HEPES. The carbonate competitive effects were analyzed using the extended triple layer model (ETLM) with the adsorption equilibrium constant of carbonate calibrated using independent published carbonate adsorption data for pure goethite taking into consideration the different surface properties. The successful ETLM calculations of arsenate adsorption isotherms for E33 under various conditions allowed quantitative comparison of the arsenate adsorption capacity between E33 and other major adsorbents initially tested under varied experimental conditions in the literature.
人们对开发基于氧化物的砷酸盐去除材料产生了浓厚的兴趣，这导致了各种用于确定砷酸盐吸附等温线的实验方法和条件，从而阻碍了对它们吸附能力的比较评估。在这里，我们系统地研究了缓冲液（HEPES 或碳酸盐）、吸附剂剂量和溶液 pH 值对先前经过充分表征的针铁矿基吸附剂（Bayoxide E33（E33））吸附砷酸盐和磷酸盐的影响。当使用 1mM 的 HEPES（96mg C/L）作为缓冲液时，在不同吸附剂/吸附剂浓度下获得的所有吸附等温线都是相同的。然而，在低水相砷酸盐和磷酸盐浓度（约 1.3μM）下，使用 10mM 的 NaHCO3 缓冲液（地下水中碳酸盐的合理浓度）获得的吸附等温线与没有缓冲液或使用 HEPES 获得的吸附等温线有很大的不同。使用扩展三层模型（ETLM）分析了碳酸盐的竞争效应，该模型使用经过独立发表的纯针铁矿碳酸盐吸附数据校准的碳酸盐吸附平衡常数进行了计算，同时考虑了不同的表面性质。在各种条件下，成功使用 ETLM 计算了 E33 的砷酸盐吸附等温线，这使得可以根据文献中在不同实验条件下最初测试的其他主要吸附剂，对 E33 的砷酸盐吸附能力进行定量比较。
