发布时间 : 星期一 文章三种土壤-钼吸附解吸的研究 - 图文更新完毕开始阅读38cbe1f8f5335a8103d22086
福建农林大学硕士学位论文 三种土壤钼吸附解吸的研究
2.2.3 影响因素试验 ............................................................................................... 20 2.2.4 等温吸附试验 ............................................................................................... 21
2.3 数据分析与处理 .............................................................................................................. 21
2.3.1 吸附动力学拟合方程 ................................................................................... 21 2.3.2 等温吸附模型拟合方程 ............................................................................... 21 2.3.3 吸附热力学分析 ........................................................................................... 22 2.3.4 数据处理 ....................................................................................................... 22
2.4 实验结果与讨论 .............................................................................................................. 23
2.4.1 红壤-钼吸附的影响因素.............................................................................. 24 2.4.2 三种土壤-钼吸附反应动力学 ...................................................................... 30 2.4.3 三种土壤-钼吸附等温线.............................................................................. 34 2.4.4 三种土壤热力学分析 ................................................................................... 39
2.5 小结 ................................................................................................................................. 40 3 土壤钼解吸研究 ......................................................................................................................... 42
3.1 材料与方法...................................................................................................................... 42 3.2 方法精密度...................................................................................................................... 43 3.3 实验结果与讨论 .............................................................................................................. 44 3.4 小结 ................................................................................................................................. 47 4 主要研究结论与展望 ................................................................................................................. 48
4.1 主要研究结论 .................................................................................................................. 48 4.2 研究展望.......................................................................................................................... 48 参考文献......................................................................................................................................... 50 附录 ................................................................................................................................................ 58 致谢 ................................................................................................................................................ 66
福建农林大学硕士学位论文 三种土壤钼吸附-解吸的研究
摘要
根据土壤钼主要为铁氧化物吸附的观点，本研究采集了三种含铁量较高的可变电荷土壤：红壤、紫色土和水稻土。通过吸附动力学试验，研究了不同条件下和不因素对土壤钼吸附过程的影响：包括不同初始钼酸根浓度和不同阴离子存在条件下，红壤钼的吸附过程；并根据三种土壤的理化性质，探讨了不同因素对土壤钼的吸附过程。另一方面，通过添加碳酸钙的方式研究不同pH下三种土壤钼的吸附情况。为了进一步了解土壤钼的吸附解吸情况，通过吸附动力学和等温吸附实验-传统吸附热力学分析，探讨了三种土壤钼吸附的主要机制和不同因素的影响情况。最后，采用三种溶液（NaNO3溶液、草酸溶液和Tamm溶液）解吸不同钼吸附量的土壤，分析了植物根系附近土壤钼吸附/解吸可能存在的主要行为。不同初始MoO42-离子浓度和不同竞争力子存在条件下，拟合红壤钼吸附过程发现：LJ方程和准一级吸附动力学方程均能较好地描述红壤对MoO42-离子的吸附，说明红壤中可变电荷胶粒（针铁矿等）和溶液MoO42-离子的吸附过程可能存在静电吸附和形成内层配合物的过程。等物质量浓度不同阴离子对红壤吸附MoO42离子-的影响顺序为：PO43- > SeO32- > SO42- > Cl- > SeO42- > NO3-。比较红壤、紫色土和水稻土的钼吸附过程，发现紫色土和水稻土对钼的吸附能力较差。通过添加CaCO3，土壤的钼吸附能力下降，水稻土对钼的吸附能力最差。由等温吸附试验发现：Freundlich方程能较好地描述土壤钼吸附过程；红壤对MoO42-的吸附能力最强，紫色土次之，水稻土最弱。通过四种热力学算法得到的热力学参数不尽相同，甚至违背热力学定律，传统热力学算法不适合描述土壤重金属吸附。通过草酸溶液、NaNO3溶液和Tamm溶液解吸三种土壤中的钼发现：Tamm溶液能解吸90%以上土壤外源添加钼，这可能进一步验证了铁氧化物对MoO42-离子的吸附是以静电吸附为基础的观点；对于红壤和紫色土而言，草酸解吸的土壤钼多于NaNO3溶液解吸的钼，水稻土反之。
关键词：吸附/解吸、碳酸钙、铁氧化物、模型、钼、土壤
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福建农林大学硕士学位论文 三种土壤钼吸附-解吸的研究
Abstract
This study collected three typical high-iron content soils that can adsorb molybdate (Mo), such as: red, purple and paddy rice soils. Adsorption kinetics experiment, analyzing under different experimental conditions affected Mo adsorption-process on the soils, including the initial concentration and competitive anions. According to different physical and chemical properties of the three soils, analyzing the influence of different factors on soil Mo adsorption-process. On the other hand, amendment of calcium carbonate to adjust different soil pH, studied their effect of Mo adsorbed by soils. The data of Mo adsorbed by soils fitted to kinetics, adsorption isotherm simulated equations and thermodynamical analysis, discussing the primary mechanism of soil Mo adsorption with three soils. Through three different soil desorption solutions (NaNO3, oxalic acid and Tamm solutions), analyzed Mo desorption quantities, discussing the most-possible major soil Mo adsorption/desorption behavior in the soils. In the different initial MoO42- ion concentrations and different competitive existence conditions, the fitting results of soil Mo adsorption process has found that both the LJ and the pseudo-first-order adsorption equations can well describe the MoO42- adsorption on the red-soil.which means Fe-oxide can attract MoO42- in solution and perhaps a chemical reaction. Anionic competitive adsorption with Mo following the order as: PO43- > SeO32- > SO42- > Cl- > SeO42- > NO3. Comparison of Mo adsorption process of red, purple and paddy rice soils, purple and paddy soil affected the adsorption process of Mo on Fe-oxide. Under the amendments of high CaCO3, purple soil adsorption ability on Mo is decreased. Paddy soil has low ability in adsorbing Mo. Isothermal adsorption experiment data of soil-Mo,
Freundlich equation can well fit the soil Mo adsorption process; the maximum adsorption capacity of red soil is greater than those of purple and paddy rice soil. According to the four kind algorithms of the thermodynamic parameters of data against the law of thermodynamics, conventional adsorption thermodynamic analysis is not applicable to the mixture of soil system. Using oxalic acid solution, NaNO3 and Tamm solutions to desorb soil-Mo, showed that Tamm solution can desorb above 90% exogenous-added Mo in the soils, which further demonstrate the view that the MoO42- adsorption on the Fe-oxide is based on static-ion exchange, however, red and purple soils, oxalic acid solution desorb more soil-Mo rather than NaNO3 solution.
Keywords：Adsorption/desorption, Calcium carbonate, Fe-oxide, Model, Molybdenum, Soils
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福建农林大学硕士学位论文 三种土壤钼吸附-解吸的研究
1 文献综述
1.1 土壤中的钼概况
随着人们的生活水平逐步提高，环境污染治理越来越受到国家的重视。污染土壤重金属治理是环境治理中的重要领域，与人们的生产生活息息相关。钼(Mo)作为动植物必须的微量元素[1]，土壤钼含量直接影响到人们的生产生活。
1.1.1 钼在我国土壤中的含量和分布
土壤中的钼主要来自于含钼矿石的风化和矿区尾矿的污染，含量较少。在我国，已探明的钼矿区共有222处（855万吨）[2~10]，分布于全国29个省、自治区、直辖市，集中分布在栾川（206万吨）、大黑山（109万吨）、金堆城（97万吨）、杨家杖子（16万吨）四个钼矿，占全国钼矿总储量的4/5[7~9]。
钼在地壳中的平均含量约为2.3 mg·kg-1[3]。随着矿石的风化和土壤类型的不同，土壤钼含量有较大的差异。我国土壤全钼含量的变化范围约为0.1 ~ 6 mg·kg-1，平均含量为1.7 mg·kg-1。据报道[11~17]，我国土壤全钼量，在东北森林土和白浆土中最丰富，约为1.3 ~ 6 mg·kg-1；草甸土、黑土、黑钙土和褐色土中约为0.2~5 mg·kg-1；碱土和盐土中约为0.5 ~ 2 mg·kg-1；栗钙土中约为0.1 ~ 1.2 mg·kg-1；砂土中钼含量最低，约为 0.1~0.7 mg·kg-1。其中，华中红壤中钼全量约为0.36 ~ 0.86 mg·kg-1；江苏南部黄棕壤和水稻土中约为0.27 ~ 1.83 mg·kg-1；白土中约为0.34 ~ 0.53 mg·kg-1(见图1)。
图 1. 我国土壤钼肥有效地点分布图（1982）[7]
Fig.1. Map of soil molybdenum fertilizer effective site in China
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