Badruzzaman Mohammad, Westerhoff Paul, Knappe Detlef R U
Department of Civil and Environmental Engineering, Box 5306, Arizona State University, Tempe, AZ 85287-5306, USA.
Water Res. 2004 Nov;38(18):4002-12. doi: 10.1016/j.watres.2004.07.007.
Porous iron oxides are being evaluated and selected for arsenic removal in potable water systems. Granular ferric hydroxide, a typical porous iron adsorbent, is commercially available and frequently considered in evaluation of arsenic removal methods. GFH is a highly porous (micropore volume approximately 0.0394+/-0.0056 cm(3)g(-1), mesopore volume approximately 0.0995+/-0.0096 cm(3)g(-1)) adsorbent with a BET surface area of 235+/-8 m(2)g(-1). The purpose of this paper is to quantify arsenate adsorption kinetics on GFH and to determine if intraparticle diffusion is a rate-limiting step for arsenic removal in packed-bed treatment systems. Data from bottle-point isotherm and differential column batch reactor (DCBR) experiments were used to estimate Freundlich isotherm parameters (K and 1/n) as well as kinetic parameters describing mass transfer resistances due to film diffusion (k(f)) and intraparticle surface diffusion (D(s)). The pseudo-equilibrium (18 days of contact time) arsenate adsorption density at pH 7 was 8 microg As/mg dry GFH at a liquid phase arsenate concentration of 10 microg As/L. The homogeneous surface diffusion model (HSDM) was used to describe the DCBR data. A non-linear relationship (D(S)=3.0(-9) x R(p)(1.4)) was observed between D(s) and GFH particle radius (R(P)) with D(s) values ranging from 2.98 x 10(-12) cm(2)s(-1) for the smallest GFH mesh size (100 x 140) to 64 x 10(-11) cm(2)s(-1) for the largest GFH mesh size (10 x 30). The rate-limiting process of intraparticle surface diffusion for arsenate adsorption by porous iron oxides appears analogous to organic compound adsorption by activated carbon despite differences in adsorption mechanisms (inner-sphere complexes for As versus hydrophobic interactions for organic contaminants). The findings are discussed in the context of intraparticle surface diffusion affecting packed-bed treatment system design and application of rapid small-scale column tests (RSSCTs) to simulate the performance of pilot- or full-scale systems at the bench-scale.
多孔铁氧化物正在饮用水系统中进行评估和筛选，以用于去除砷。颗粒氢氧化铁是一种典型的多孔铁吸附剂，在市场上可以买到，并且在评估砷去除方法时经常被考虑。颗粒氢氧化铁是一种高度多孔的吸附剂（微孔体积约为0.0394±0.0056 cm³g⁻¹，中孔体积约为0.0995±0.0096 cm³g⁻¹），其BET表面积为235±8 m²g⁻¹。本文的目的是量化颗粒氢氧化铁对砷酸盐的吸附动力学，并确定在填充床处理系统中，颗粒内扩散是否是砷去除的限速步骤。来自瓶点等温线和微分柱间歇反应器（DCBR）实验的数据用于估计Freundlich等温线参数（K和1/n）以及描述由于膜扩散（k(f)）和颗粒内表面扩散（D(s)）引起的传质阻力的动力学参数。在pH值为7、液相砷酸盐浓度为10 μg As/L的条件下，经过18天接触时间后的准平衡砷酸盐吸附密度为8 μg As/mg干燥颗粒氢氧化铁。采用均相表面扩散模型（HSDM）来描述DCBR数据。观察到D(s)与颗粒氢氧化铁颗粒半径（R(P)）之间存在非线性关系（D(S)=3.0(-9) x R(p)(1.4)），D(s)值范围从最小颗粒氢氧化铁筛目尺寸（100×140）的2.98×10⁻¹² cm²s⁻¹到最大颗粒氢氧化铁筛目尺寸（10×30）的64×10⁻¹¹ cm²s⁻¹。尽管吸附机制有所不同（砷形成内球络合物，而有机污染物通过疏水相互作用），但多孔铁氧化物对砷酸盐吸附的颗粒内表面扩散限速过程似乎类似于活性炭对有机化合物的吸附。本文将结合颗粒内表面扩散对填充床处理系统设计的影响以及快速小规模柱试验（RSSCT）在实验室规模模拟中试或全尺寸系统性能的应用来讨论这些发现。
