以低成本稻壳灰作为吸附剂, 使用FTIR, SEM, XPS, XRD, XRF等分析手段, 研究稻壳灰对Cr(Ⅵ)的去除机制。 FTIR研究表明酰胺Ⅱ带, Si—O—Si, O—Si—O等在Cr(Ⅵ)去除过程中有一定贡献。 由SEM图片清晰可见： 吸附Cr(Ⅵ)后, 稻壳灰表面分布有众多的光亮沉积物。 XPS图谱证明： 稻壳灰的主要组成元素为C, N, O, P和Si； C元素的存在状态以醛酮类为主, 含C官能团与Cr(Ⅵ)发生了配位反应； N元素以—NH2形态为主, Cr(Ⅵ)可能以静电作用与含N基团结合, 并以物理吸附为主； Si的存在以Si—O为主, 含Si官能团可能与Cr(Ⅵ)发生了配位反应。 XRD分析结果表明： 谱图中出现的峰是典型的SiO2特征峰； 稻壳灰的结晶度增加, 表明稻壳灰与Cr(Ⅵ)形成了具有晶体结构的金属化合物。 XRF研究发现, K, Na, Mg和Ca的元素含量在吸附前后有所变化, 另有两种新元素出现, 这说明吸附过程存在离子交换机制。 所有这些皆表明： 各种官能团在Cr(Ⅵ)去除过程中的角色各不相同, 无机微沉淀机制、 氧化还原机制、 表面络合机制、 离子交换机制等是稻壳灰去除Cr(Ⅵ)的主要途径。 这可以为吸附技术的实际应用提供理论支持。

Analyzing methods of Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction analysis (XRD) and X-ray fluorescence spectroscopy (XRF) were used to reveal the adsorption mechanism of Cr(Ⅵ) by low-cost adsorbent of rice husk ash. Results of FTIR showed that amide Ⅱ band, Si—O—Si, and O—Si—O were important for Cr(Ⅵ) removal. SEM micrographs suggested that series of needle-shaped precipitation appeared on cell surface, and inorganic precipitation mechanism and redox mechanism might work in the test. XPS spectra showed that main elements of rice husk ash were C, N, O, P and Si, existing state of C was mainly aldoketones groups, coordination reaction existed between C functional groups and Cr(Ⅵ); N element, —NH2 in chief, could remove Cr(Ⅵ) in the way of physical adsorption based on electrostatic interaction; Si—O might be useful in adsorption process. XRD data suggested representative characteristic adsorption band of SiO2, and the increasing crystallinity of rice husk ash showed metallic compound formed between Cr(Ⅵ) and rice husk ash. XRF results indicated that the content of K, Na, Mg and Ca changed, and two new elements were detected, the evidence of ion exchange mechanism. The functional groups played different roles in Cr(Ⅵ) adsorption process, and inorganic precipitation mechanism, redox mechanism, surf-complexation mechanism and ion exchange mechanism were important ways in Cr(Ⅵ) removal, which could provide theoretical support in further application.