【作者】 梁斌；

【导师】 兰叶青；

【作者基本信息】 南京农业大学 ， 环境科学， 2007， 硕士

【摘要】 工业上得到广泛应用的重金属元素铬（Cr）在电镀、鞣革、颜料、油漆、合金、印染、胶印等方面扮演着重要的角色，但它对人和动植物也存在有严重的危害。在人类对环境问题和自身健康问题日益关注下，如何在继续发挥铬在国民经济建设中的重要作用的同时控制和减少铬对环境的污染，受到环境科学研究者和环境保护倡导者们的普遍重视。铬主要以六价铬和三价铬两种形态存在于自然环境中，其中Cr⁶⁺有强氧化性，在环境中的溶解性、迁移性大，具有高毒性；然而Cr³⁺却具有迁移性小和低毒性的特性。目前在其他生物和物理方法还难以有效控制铬污染的现状下，多数情况是采用化学还原法，即将Cr⁶⁺还原为Cr³⁺。本文主要是在水溶液单相体系和矿物多相悬浮液中研究一些土壤和水中经常存在的有机质包括生物生命活动过程中产生并滞留在其中的一些有机酸类物质还原Cr⁶⁺的反应动力学机理和及其影响因素，力求探索一些基本的反应规律和影响条件。本论文共分三部分：第一部分：在不同温度和pH条件下，通过批式试验研究了纤维素、葡萄糖还原Cr⁶⁺的作用以及Mn²⁺对反应的影响。结果表明在有无Mn²⁺存在时，纤维素、葡萄糖与Cr⁶⁺的还原反应速率差别不大，都进行得十分缓慢，所测定的时间内Cr⁶⁺浓度无明显变化。整个反应阶段，总的反应速率逐渐趋于稳定，没有意味着存在某种反应中间产物对反应速率有更大的催化加速作用的表征出现。第二部分：在25℃、35℃、45℃和pH=4.0、5.0、6.0条件下，研究了均相体系中苦杏仁酸，苹果酸，乳酸还原Cr⁶⁺的反应速率。结果表明，在总体上三种有机酸还原Cr⁶⁺的能力表现为：苦杏仁酸＞苹果酸＞乳酸。苦杏仁酸受pH变化的影响较大，乳酸受温度变化的影响较大。同时研究了25℃、pH=4.0条件下Mn²⁺对反应的催化作用。试验表明Mn²⁺对三种有机酸还原Cr⁶⁺均有一定的催化作用，其中苦杏仁酸表现更为明显。且受温度和pH条件变化影响的趋势与无Mn²⁺参与的情况保持一致。这表明不同的α-OH有机酸因所连接的基团不同造成还原Cr⁶⁺的能力有较大差异，同时矿物表面的Mn²⁺与土壤中的有机酸形成配合物是导致反应加速的先决条件。Mn²⁺-有机酸配合物的形成可能提高了这三种酸都具有的α-OH的活性，使其更易与Cr⁶⁺结合并形成Cr⁶⁺-α-OH有机酸-Mn²⁺配合物，从而导致Cr⁶⁺的快速还原。第三部分：在25℃、35℃、45℃和pH=4.0、5.0、6.0条件下，研究了伊利石、蒙脱石、高岭石存在条件下苦杏仁酸，苹果酸还原Cr⁶⁺的反应速率。结果表明，总体上两种有机酸还原Cr⁶⁺的能力与前述实验保持一致，即苦杏仁酸＞苹果酸。三种矿物对苦杏仁酸和苹果酸还原Cr⁶⁺均有一定的催化作用。三种矿物的催化作用为：伊利石＞蒙脱石＞高岭石。矿物的催化作用与其表面吸附交换性的Mn²⁺含量保持一致。表面交换性的Fe³⁺对有机酸还原Cr⁶⁺同样也有催化作用，但其作用小于Mn²⁺。结合第二部分的研究可以表明矿物表面的Mn²⁺和Fe³⁺与有机酸形成配合物应该是导致反应加速的先决条件。Mn²⁺-有机酸酸配合物的形成可能提高了有机酸结构中a-OH的活性，使其更易与Cr⁶⁺-有机酸-Mn²⁺形成三元配合物，从而导致Cr⁶⁺的快速还原。同时经过研究和分析证明矿物比表面积的大小并不是导致土壤中有机酸快速还原Cr⁶⁺的主要因素。更多还原

【Abstract】 Chromium （Cr） is widely used in industries, such as steel production, leather tanning,corrosion prevention, dye, tannery industry and galvanic. As a result of unproper disposalof the wastes containing chromium, chromium danger to human, animal and plants hasbecome one of the most serious environmental contaminants. How to reduce the danger andmake chromium play the more important role has been the problem which the environmentprotectors care.Chromium mainly exsits in two forms in natural environments: Cr⁶⁺ and Cr³⁺. Thesetwo forms exhibit completely different mobility and toxicity. Cr⁶⁺ is high toxicity andsolubility. However, Cr³⁺ is much less toxic and has a strong affinity for soil particlesurfaces, displaying immobility. So, Cr⁶⁺ is often reduced to Cr³⁺ by chemical reductionagents to control chromium contaminatnts. In the paper, kinetics of the reduction of Cr⁶⁺ byorganic acids and its impact factors were studied in the homogenious and heterogeneoussystem.This thesis contains three chapters:In chapter I The Cr⁶⁺ reduction by cellulose and glucose was studied through batchexperiments at different temperatures and pH values. Then the effects of Mn²⁺ on thereaction were also studied.Results showed that reduction of Cr⁶⁺ by cellulose and glucosewas so slowly. Through the reaction, there is not any indication showing that Mn²⁺ had thecatalysis effects.In chapterⅡThe reduction of Cr⁶⁺ by mandelic, malic and lactic acid was conductedat 25℃、35℃、45℃and a pH range of 4.0 to 6.0.The results showed that the ability in thereduction of Cr⁶⁺ by these organic acid was generally in the order: mandelic＞malic＞lactic. The influence of pH is the largeset to mandelic, but lactic is too easily effected bytemperature. We still conducted the catalysis of Mn²⁺ on the reduction of Cr⁶⁺ by the threekinds of acids at 25℃and pH=4.0. The results showed that Mn²⁺ catalyzed all the reaction,especially for mandelic acid. This proves that the different radicals make the differentability of the organic acid on the reduction of Cr⁶⁺. It indicates that the complex formation of Mn²⁺ with organic acid was the prerequisite.Complex of Mn²⁺with organic acidincreased the activity ofα-OH, resulting in the complex formation of Mn²⁺-α-OHorganic acid -Cr⁶⁺ and then accelerating Cr⁶⁺ reduction.In chapterⅢThe catalysis of minerals on the reduction of Cr⁶⁺ by mandelic acid andmanlic acid was conducted at 25℃,35℃, 45℃and a pH range of 4.0 to 6.0. The resultsshowed that these minerals all had some catalysis effects on the reaction. The role ofminerals in accelerating the reduction of Cr⁶⁺ by mandelic acid and mamlic acids was in theorder: illite＞montmorillonitc＞＞kaolinte, which was agreement with the amounts ofexchangeable Mn²⁺ on the mineral surfaces. Exchangable Fe³⁺ on mineral surfaces alsoaccclerated the reduction of Cr⁶⁺ by citrate remarkably, but its catalytic role was less thanthat of Mn²⁺. Complex of Mn²⁺ with mandelic acid and manlic acid increased the activity ofa-OH of citrate, resulting in the complex formation of Mn²⁺-citrate-Cr⁶⁺ and thenaccelerating Cr⁶⁺ reduction. The study further pointed surface area of minerals was not thekey to catalyzing the reduction of Cr⁶⁺ by organic acids in soils.更多还原