Department of Earth Science and Engineering, Imperial College London, London, United Kingdom.
Water Res. 2010 Nov;44(19):5673-83. doi: 10.1016/j.watres.2010.05.056. Epub 2010 Jun 9.
This study reports the adsorption of arsenate, As(V), on goethite (α-FeO(OH)) and oil-coated goethite at experimental conditions chosen to mimic settings of wastewater from oil fields being released into marine and freshwater bodies. Similarities are evident between the As(V)-goethite and As(V)-oil-goethite systems: i) Adsorption is fast and saturation is achieved within 180 min, ii) Reaction rates approximate to a pseudo second order rate expression and range between 6.5 and 52.3 × 10(-4)g/μmol/min, iii) Adsorption mechanisms are best described with a Langmuir model, and iv) Adsorption capacity rises with decreasing pH reflecting the increase of positive charges on the goethite surface. A difference is discernable in that the adsorption of As(V) is reduced significantly when the goethite is coated with oil. The similar experimental macroscopic observations for both systems, i.e., Langmuir model fits, reaction rates, and the effect of pH and ionic strength (I), suggest that the oil reduces the effective and/or reactive surface area. The zeta potential (ζ) indicates that the oil coating also changes the surface charge of the goethite, shifting the pH point of zero charge from 9.8 to about 3, thus contributing to the reduced As(V) adsorption. FTIR spectra show that As(V) interacts with the carbonyl functional groups of the oil. Our results suggest that oil-covered goethite significantly reduces the adsorption of As(V) and this points to a potentially significant indirect effect of oil on the cycling of As(V) and other oxyanions in oil polluted waters.
本研究报告了砷酸盐（As(V)）在针铁矿（α-FeO(OH)）和油涂覆针铁矿上的吸附，实验条件的选择旨在模拟油田废水排放到海洋和淡水中的情况。As(V)-针铁矿和 As(V)-油涂覆针铁矿系统之间存在明显的相似之处：i）吸附速度快，在 180 分钟内达到饱和，ii）反应速率接近伪二级速率表达式，范围在 6.5 到 52.3×10(-4)g/μmol/min 之间，iii）吸附机制最好用朗缪尔模型描述，iv）吸附容量随 pH 值降低而升高，反映出针铁矿表面正电荷的增加。一个区别是，当针铁矿被油覆盖时，As(V)的吸附显著减少。两个系统的实验宏观观察结果相似，即朗缪尔模型拟合、反应速率以及 pH 值和离子强度 (I) 的影响，表明油降低了有效和/或反应表面积。Zeta 电位 (ζ) 表明油涂层还改变了针铁矿的表面电荷，将 pH 零电荷点从 9.8 转移到约 3，从而导致 As(V)吸附减少。傅里叶变换红外光谱 (FTIR) 显示 As(V)与油的羰基官能团相互作用。我们的结果表明，油覆盖的针铁矿显著减少了 As(V)的吸附，这表明油对 As(V)和其他含氧阴离子在油污染水中循环的潜在间接影响很大。
