膨润土改性及对水中Cr(Ⅵ)吸附性能的研究

Bentonite modification and adsorption capacity for Cr(Ⅵ) in water

【目的】提高膨润土对水中Cr(Ⅵ)的吸附性能。【方法】采用氢氧化钠和壳聚糖对膨润土进行改性,分别得到碱改性膨润土(B−NaOH)、壳化膨润土(B−CS)和壳化碱改性膨润土(B−NaOH−CS)。以钠基膨润土(B)为对照,利用红外光谱仪、扫描电镜和比表面积分析仪表征3种改性膨润土的理化性质,研究其对Cr(Ⅵ)的吸附性能。【结果】B−NaOH−CS中出现了强N—H吸收峰以及增强的C—H对称弯曲峰,同时B−NaOH−CS表面片状结构卷曲分散,层间孔隙增多,比表面积是其他膨润土的1.2倍以上。当Cr(Ⅵ)质量浓度为50 mg·L−1时,B−NaOH−CS对Cr(Ⅵ)的平衡吸附量为1.03 mg·g−1,分别是B−CS、B−NaOH的1.26、1.84倍。描述膨润土吸附Cr(Ⅵ)的动力学过程,准二级动力学模型优于准一级动力学模型;描述膨润土吸附Cr(Ⅵ)的热力学过程,Langmuir等温模型优于Freundlich等温模型。热力学参数△H>0、△G<0、△S>0,表明膨润土吸附Cr(Ⅵ)为吸热、自发、无序反应。B−NaOH在pH=7.0时对Cr(Ⅵ)的吸附量最大,B−CS、B−NaOH−CS在pH=3.0时对Cr(Ⅵ)的吸附量最大。【结论】B−NaOH−CS对Cr(Ⅵ)的吸附效果最好,改性膨润土对去除Cr(Ⅵ)污染有重要作用。

【Objective】To improve the adsorption capacity of bentonite for Cr(VI)in water.【Method】NaOH and chitosan were used for modifying bentonite.Alkali modified bentonite(B-NaOH),chitosan modified bentonite(B-CS)and chitosan-alkali modified bentonite(B-NaOH-CS)were obtained.Using sodium bentonite(B)as the control,we characterized physicochemical properties of three kinds of modified bentonite through infrared spectrometer,scanning electron microscope and specific surface area analyzer,and analyzed their adsorption capacities for Cr(VI).【Result】A strong N—H absorption peak and an enhanced C—H symmetric bending peak appeared in B-NaOH-CS.The surface sheet structure of B-NaOH-CS was curly dispersed,the interlayer pores increased,and the specific surface area was 1.2 times more than other bentonite.When the concentration of Cr(VI)was 50 mg·L−1,the equilibrium adsorption capacity of B-NaOH-CS for Cr(VI)was 1.03 mg·g−1,which was 1.84 and 1.26 times of B-NaOH and B-CS respectively.The quasi-second-order kinetic equation and Langmuir equation could more accurately describe adsorption process of bentonite for Cr(VI).Thermodynamic parameters of△H>0,△G<0 and△S>0 indicated the adsorption process of bentonite for Cr(VI)was endothermic,spontaneous and disordered.B-NaOH had the maximum adsorption capacity for Cr(VI)at pH=7.0,while B-CS and B-NaOH-CS at pH=3.0.【Conclusion】B-NaOH-CS has the best adsorption effect on Cr(VI).Modified bentonite plays an important role in Cr(VI)pollution remove.