【作者】 肖莉莉；

【导师】 马伟；

【作者基本信息】 大连理工大学 ， 无机化学， 2011， 硕士

【摘要】 本文以硝酸镁、硝酸铝、硝酸铁、氢氧化钠、碳酸钠为主要原料,采用液相共沉淀法合成了Mg/Al及Mg/Al/Fe纳米级水滑石材料,并采用热分解法在500℃焙烧制得本实验所需吸附剂-煅烧水滑石材料(CH-Mg/Al, CH-Mg/Al/Fe)。三价铁的加入对CH-Mg/Al去除铬的影响主要从结构特性、吸附性能及去除机理三方面来考察。结构特性主要通过X射线衍射图谱、透射电镜观察、热重-差热分析、红外光谱分析等手段对吸附剂的晶体结构、形貌形态、热稳定性等方面进行表征；吸附性能的影响主要从溶液pH、初始铬浓度、吸附剂投加量、接触时间、温度及竞争离子等方面的影响来考虑；另外还通过吸附剂前后红外谱图对比、不同接触时间的XRD分析从吸附机理方面研究了Fe3+的加入对CH-Mg/Al吸附铬的影响。通过表征得知：三价铁的加入对其结构几乎没有本质影响,只是降低了水滑石前驱体的结晶度和层间距,增加了粒子的分散性能。吸附性能表明：CH-Mg/Al及CH-Mg/Al/Fe对溶液中Cr (Ⅵ)的吸附均在pH=3.0时达到最好,通过各种影响因素的考查发现：尽管吸附过程都是吸热、自发的熵增过程,但是Fe3+的加入不利于溶液中Cr (Ⅵ)的去除,Langmuir等温线拟合出的最大饱和吸附量显示Fe3+的引入使其平均吸附量降低了10.2 mg/g左右。不同接触时间的XRD谱图分析得知：CH-Mg/Al及CH-Mg/Al/Fe对铬的去除机理不仅涉及煅烧水滑石的插层作用,而且还有层状结构恢复后的外表面吸附及层间阴离子的离子交换作用。吸附比例结果显示无论是CH-Mg/Al还是CH-Mg/Al/Fe,去除过程中插层作用都占很大比例,而且CH-Mg/Al中加入三价铁之后,使得层间阴离子的离子交换作用变得更加难以进行。更多还原

【Abstract】 The calcined hydrotalcites (CH-Mg/Al and CH-Mg/Al/Fe) were obtained by thermal decomposition of their corresponding precursors at 500℃. The precursors were synthesized by co-precipitation method using Mg(NO3)2·6H2O, Al(NO3)3·9H2O, Fe(NO3)3·9H2O, NaOH and NaCO3. The influence of ferric iron in calcined nano-Mg/Al hydrotalcite on removal of Cr (VI) from aqueous solution was studied from aspects of structure characteristics, adsorption properties and mechanism discussions. The structure characteristics of the adsorbents were analyzed by means of XRD, TEM, TG-DTA, pHPZC and FTIR. The adsorption properties were studied as a function of pH, initial chromium concentration, sorbent dose, contact time, temperature and coexisting ions. Additionally, the removal mechanism was also discussed by comparing the analysis of FTIR before and after adsorption and the XRD patterns of adsorbents at different contact times during reconstruction process. The structure characteristics showed that replacing Al3+ with Fe3+ has almost not changed the structure of CH-Mg/Al but reducing the crystallinity and interlayer spacing. The removal of Cr (VI) gets the maximum at pH 3.0 for both CH-Mg/Al and CH-Mg/Al/Fe. The isotherms indicated that the adsorption both fitted better to Langmuir model, but the theoretical saturated adsorption capacity reduces by 10.2 mg/g by addition of Fe3+. Although thermodynamic parameter values revealed the adsorption natures on CH-Mg/Al and CH-Mg/Al/Fe are endothermic and spontaneous processes, the value changes indicated the addition of Fe3+ in CH-Mg/Al goes against the adsorption process. The removal mechanism involved not only intercalation but also adsorption on external surface of the layers and interlayer anion exchange for both CH-Mg/Al and CH-Mg/Al/Fe. Furthermore, it also indicated that intercalation accounts for a large proportion during the removal process whatever for CH-Mg/Al, or for CH-Mg/Al/Fe. Additionally, the replacement of Al3+ by Fe3+ in hydrotalcite led to the interlayer anion exchange more difficult.更多还原