Cr(VI)在Mg-Al型类水滑石上的吸附-脱附性研究I. 吸附性

研究了Cr(VI)在带结构正电荷的Mg-Al型类水滑石(HTlc)上的吸附性能, 考察了pH、无机电解质添加剂NaCl, NaNO₃, Na₂SO₄和Na₃PO₄及有机添加剂EDTA和柠檬酸等因素的影响, 并结合红外光谱和XRD实验结果探讨了吸附机理. 研究表明, Mg-Al型HTlc对Cr(VI)有很强的吸附能力, 其吸附动力学和吸附等温线分别符合准二级速率方程和Langmuir方程, 饱和吸附量达105 mg/g, 有望成为一种优良的含Cr(VI)污水处理剂和Cr(VI)污染土壤修复剂. 初始pH增大, 吸附量降低. 无机电解质和有机添加剂均能明显抑制Cr(VI)在HTlc上的吸附, 其抑制吸附作用的强弱顺序分别为Na₃PO₄≥Na₂SO₄≥NaCl>>NaNO₃和柠檬酸＞EDTA. Cr(VI)在HTlc上的吸附可分为层间的离子交换吸附和外表面的吸附, 其中外表面的吸附层在微观上又可分为因化学键合作用而形成的内络合层和因静电作用而形成的外络合层.

Adsorption-desorption of Chromium(VI) on Mg-Al Hydrotalcite-like Compounds Part I. Adsorption

Adsorption properties of Cr(VI) on Mg-Al hydrotalcite-like compounds (HTlc) were studied. The influences of initial solution pH, additives of inorganic electrolytes, NaCl, NaNO₃, Na₂SO₄ and Na₃PO₄, and organic ligands, EDTA and citric acid on the adsorption of Cr(VI) were investigated, and the adsorption mechanism was discussed in combination with the results of IR and XRD experiments. It was found that Mg-Al HTlc showed good adsorption ability for Cr(VI) from solution, indicating that the use of HTlc as a promising inorganic sorbent for the removal of Cr(VI) from wastewater is possible. The adsorption kinetics and the adsorption isotherms of Cr(VI) on the HTlc can be described by the pseudo-second order kinetic and Langmuir isotherm, respectively. With increasing pH, the adsorption amount decreased. The additives of inorganic electrolytes, NaCl, NaNO₃, Na₂SO₄ and Na₃PO₄, and organic ligands, EDTA and citric acid, could obviously restrain the adsorption of Cr(VI) on the HTlc, and the orders of the restraining ability on the adsorption are Na₃PO₄≥Na₂SO₄≥NaCl>>NaNO₃ and citric acid＞EDTA, respectively. The adsorption of Cr(VI) on the HTlc arose from the anion exchange in the interlayer space and the adsorption on the external surface, respectively. Furthermore, the adsorption layer of Cr(VI) on the external surface may be divided into two layers: the inner-sphere surface complexes arising from the chemical binding and the outer-sphere surface complexes arising from the electrostatic interaction.