| 针铁矿-高岭石复合体的表面性质和吸附氟的特性 |
| 摘要点击 1436 全文点击 1402 投稿时间：2009-11-17 修订日期：2009-12-28 |
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| 中文关键词 针铁矿 高岭石 复合体 表面性质 吸附 氟 |
| 英文关键词 goethite kaolinite association surface properties adsorption fluoride |
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| 中文摘要 |
| 采用X-射线衍射(XRD)、扫描电镜(SEM)、红外(FT-IR)光谱、质子电位滴定、比表面及微孔分析等方法对针铁矿、高岭石及其复合体的基本性质进行了表征；研究了供试样品对氟的吸附容量及吸附模型.结果表明，在悬浮液体系中，针铁矿可包被在高岭石表面形成二元复合体.复合体的孔径主要分布在0.42 nm和0.61 nm左右，BET表面积为34.08 m2/g，表面分形度 D=2.726，质子电荷零点(pHPZNPC)位于5.50～6.50间.初始pH=6.00时，针铁矿对氟的吸附容量(qmax)为4.506 mg/g，高岭石的吸附容量为0.608 mg/g，复合体的吸附容量为3.520 mg/g.用Langmuir和Freundlich方程拟合了针铁矿、高岭石及复合体对氟的等温吸附数据，其中Langmuir方程拟合的相关系数(R2)分别为0.964、 0.991和0.799，Freundlich方程拟合的相关系数分别为0.925、 0.886和0.995. 3种矿物吸附氟的主要机制有阴离子配体交换、表面配位和静电作用；此外，“F-键桥”对复合体吸附氟也有重要贡献.与2种单体的平均值比较，针铁矿-高岭石复合体的孔体积和孔径分布无明显变化，比表面积和表面分形度增加，表面羟基含量和质子电荷量减少，吸附氟的能力增强.针铁矿和高岭石单体对氟的吸附属于单层吸附模式，适合用Langmuir方程拟合；多层吸附模型Freundlich方程可很好地描述复合体对氟的吸附. |
| 英文摘要 |
| The basic properties of goethite, kaolinite and their association were characterized using X-ray diffraction (XRD), scanning electron microscopes (SEM), Fourier transform infrared spectroscopy (FT-IR), potentiometric titrations, specific surface area (SSA) and micropore analysis. Moreover, the adsorption capacity and adsorption models of fluoride by the investigated samples were studied. Results show that when kaolinite and goethite presented simultaneously in the same suspension system, goethite was apt to coat the surface of kaolinite and the interactions between them could occur rapidly. As a result, the binary association containing kaolinite and goethite was formed. The binary association possessed the pore diameter of 0.42 nm and 0.61 nm, specific surface area of 34.08 m2/g, surface fractal dimension of D=2.726 and the pHPZNPC (pH of point of zero net proton charge) in the range of 5.50-6.50. At the initial pH 6.00, the maximum adsorption capacity (qmax) of goethite, kaolinite and association was 4.506, 0.608 and 3.520 mg/g respectively. The adsorption of fluoride by the single kaolinite or goethite could ibe attributed to monolayer adsorption and the data of isotherm adsorption could be well fitted by Langmuir model (RM2=0.991 and R2=0.964 respectively). The Freundlich model was suitable for describing the adsorption of fluoride by the binary association (R2= 0.995), which indicated that the surface of the binary association is heterogeneous and is probably provided with multilayer adsorption sites. The adsorption mechanisms for fluoride by the investigated samples include anion ligand exchange, surface coordination and electrostatic attraction. In addition, F- acting as a bond bridge between the surfaces of kaolinite and goethite contributed to the adsorption of fluoride too. Compared to the single goethite or kaolinite, the binary association exhibited the higher specific surface area, surface fractal dimension and adsorption capacity for fluoride as well as the lower amount of hydroxyls and net proton charges on it’s surface, although no significant variation was found in the porosity structure of the association. |
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