【作者】 周红艳；

【导师】 兰叶青；

【作者基本信息】 南京农业大学 ， 环境工程， 2008， 硕士

【摘要】 由于铬（Cr）的特殊物理和化学性质,铬及其化合物在冶金、电镀、制革、颜料、油漆、印染和化工等行业中得到广泛应用。在这些行业的生成过程中产生的大量含铬废渣、废气和废水因不能有效地控制或不合理的排放,导致了我国许多地区存在着严重的土壤铬污染问题。土壤中广泛存在小分子有机酸和腐殖酸等有机物,它们均可直接将土壤中的Cr（Ⅵ）还原为Cr（Ⅲ）,从而降低Cr（Ⅵ）在土壤中的迁移性和生物的可利用性,达到减轻铬污染的危害。铁是土壤中含量较高的金属元素,占土壤含量的3.8%,土壤中锰的含量尽管远少于铁,但同铁一样,对于铬在土壤中的化学行为有重要影响。研究锰和铁对小分子有机酸和腐殖酸还原六价铬的影响,对进一步了解土壤中六价铬的化学行为具有重要的意义。本试验主要研究了高岭石和蒙脱石表面吸附态的Mn²⁺和Fe³⁺对草酸、柠檬酸和酒石酸还原六价铬的影响以及水溶态的Mn²⁺和Fe³⁺对腐殖酸还原六价铬的影响。主要研究结果如下:通过批式试验着重研究了高岭石表面吸附态Mn²⁺对草酸、柠檬酸和酒石酸还原Cr（Ⅵ）速率的影响。结果表明,高岭石表面吸附态Mn²⁺对3种有机酸还原Cr（Ⅵ）均展示出良好的催化作用,其效果为:草酸＞柠檬酸经＞＞酒石酸。酒石酸为还原剂,初始浓度≤2.0 mmol·L^-1时,高岭石表面吸附态Mn²⁺对酒石酸还原Cr（Ⅵ）的催化作用不显著,但其催化作用随酒石酸初始浓度的增加而明显提高。温度和pH对高岭石表面吸附态Mn²⁺催化草酸和柠檬酸还原Cr（Ⅵ）有显著影响,温度越高,反应速率越快;pH=3.5-4.5范围内,草酸对Cr（Ⅵ）的还原反应随pH的降低而显著升高;然而,柠檬酸对Cr（Ⅵ）的还原作用却在pH=4.0时为最快。通过批式试验研究高岭石表面吸附态Fe³⁺对草酸、柠檬酸和酒石酸还原Cr（Ⅵ）速率的影响。结果表明,高岭石表面吸附态Fe³⁺对3种有机酸还原Cr（Ⅵ）均展示出良好的催化作用,其效果为:酒石酸＞草酸＞柠檬酸。本试验条件下草酸、柠檬酸和酒石酸3种有机酸自身光解的速度比较慢,因此该三种有机酸自身光解产生的还原性自由基对Cr（Ⅵ）的还原作用不占主导地位。Fe³⁺光催化还原Cr（Ⅵ）的速率与有机酸分子中羧基的数量并不存在线性相关。pH对高岭石表面吸附态Fe³⁺催化草酸还原Cr（Ⅵ）有显著影响,pH=3.5-4.5范围内,草酸对Cr（Ⅵ）的还原反应随pH的降低而显著升高。然而草酸浓度在2mmol·L^-1-10mmol·L^-1范围内,对于该反应无明显影响。25℃和pH=2.0-6.0条件下,研究了外加的Mn²⁺和Fe³⁺对腐殖酸还原六价铬的影响。结果表明,pH对腐殖酸还原Cr（Ⅵ）有较大的影响,在2.0-6.0范围内,随pH的降低反应速率得到提高。Mn²⁺对腐殖酸与Cr（Ⅵ）之间的氧化还原反应并无明显影响。光照下腐殖酸还原Cr（Ⅵ）的速率比无光照情况下要大一些,而光照条件下,外加的Fe³⁺对腐殖酸还原六价铬的反应影响不显著。更多还原

【Abstract】 With its special physical and chemical properties,chromium and its compounds are widely used in dustries such as the production of stainless steel,galvanization,tanning of leather,pigment,corrosion prevention,dyeing and chemical industry.The wide distribution of chromium contaminants in soil in China is from the unproper disposal of wastes containing chromium from these industries.The organic matters in soil such as low-molecular weght organic acids and humic acid can reduce Cr（Ⅵ）to Cr（Ⅲ） to allay chromium contamination.Fe as a metal element with high content is about 3.8%in soil. Althought Mn content in soil is far less than that of Fe,it has important effect on the chemical activity of chromium like Fe.Study on the influence of Mn²⁺ and Fe³⁺ on reduction of Cr（Ⅵ） by low-molecular weght organic acids and humic acid has important meaning on knowing more about the chemical activity of chromium in soil.These experiments focus on studying the influence of Mn²⁺ and Fe³⁺ adsorbed by kaolinite and montmorillinite on reduction of Cr（Ⅵ） by oxalate,citrate and tartaric acids, and the influence of Mn²⁺ and Fe³⁺ on the reaction between humic acid and Cr（Ⅵ）.The main results in the study are as follows:The influence of Mn²⁺ adsorbed by kaolinite on the reduction of Cr（Ⅵ） by oxalate, citrate and tartaric acids is studied through batch experiments.The results show that Mn²⁺ adsorbed by kaolinite accelerates the reduction of Cr（Ⅵ） by the three organic acids,and the catalysis is in the order:oxalate＞citrate＞＞tartaric.When tartaric concentration is lower than 2.0 mmol·L^-1,the catalysis of adsorbed Mn²⁺ is not obviously observed,but it becomes manifest with a higher concentration.The temperature and pH exert a great impact on the reduction of Cr（Ⅵ） by oxalate and citrate acid,the reaction rates increase with temperature. When pH ranges from 3.5-4.5,the reduction of Cr（Ⅵ） by oxalate acid increases with pH decreasing.However,the reduction of Cr（Ⅵ） by citrate acid is fastest at pH=4.0.The influence of Fe³⁺ adsorbed by kaolinite on the reduction of Cr（Ⅵ） by oxalate, citrate and tartaric acids is studied through batch experiments.The results show that Fe³⁺ adsorbed by kaolinite accelerates the reduction of Cr（Ⅵ） by the three organic acids,and the catalysis is in the order:tartaric＞oxalate＞citrate.In the absence of Fe³⁺,the photolysis of oxalate,citrate and tartaric acids is slight,so the reduction of Cr（Ⅵ） by photoreaction products generated from oxalate,citrate and tartaric acids are not the main reason for degradation of Cr（Ⅵ）.Fe³⁺ photocatalytic does not exhibit a good linear correlation with the number of carboxylic groups in a molecule,pH values exert great impact on the reduction of Cr（Ⅵ） by oxalate acid,when pH ranges from 3.5-4.5,the reaction rates increase with pH decreasing.The concentration of oxalate acid has no manifest impact on the reaction.The influence of Mn²⁺ and Fe³⁺ on the reduction of Cr（Ⅵ） by humic acid is studied at 25℃and pH=2.0-6.0.The results show that pH value exerts great impact on the reduction of Cr（Ⅵ） by humic acid from black soils,the reaction rates increase with pH decreasing, when pH ranges from 2.0-6.0.Mn²⁺ has no effect on the reaction between humic acid from black soils or yellow-brown soils and Cr（Ⅵ）.The rate of reaction between humic acid from black soils or yellow-brown soils and Cr（Ⅵ）with light is higher than that without light,and Fe³⁺ does not increase the rate of reaction between humic acid from black soils or yellow-brown soils and Cr（Ⅵ）with light.While,the rate of reaction between humic acid from zijinshan soils and Cr（Ⅵ）is much higher than that of reaction between humic acid from black soils and Cr（Ⅵ）.The reason may be the difference on the structure of humic acid from different soils.更多还原