【作者】 董长勋；

【导师】 潘根兴；

【作者基本信息】 南京农业大学 ， 土壤学， 2007， 博士

【摘要】 土壤微团聚体是土壤最基本的物质和功能单元,其结构和组成特点对土壤环境的物理和化学过程起关键的控制作用。土壤中微团聚体与有机质和矿物质的结合方式不同,它们对植物养分的吸收和分布、对重金属和有机毒物的束缚能力以及生物有效性等方面存在一定的差异。因为微团聚体由较小的粘土矿物通过植物的细根和丛状菌根的菌丝进一步胶结形成的,因此部分强亲和力的位点被屏蔽或减弱。相反,实验室传统的风干磨细方法（即全土）使有机质和氧化铁等暴露在土壤表面而具有更多的吸附位点,对重金属的结合能力大大提高。所以过去以风干磨细的整体土壤作为对象,研究重金属吸附的结果,与田间实际情况下土壤对重金属的保持能力有一定的差异。本文以分离的微团聚体颗粒组为材料,研究其铜离子的吸附和解吸行为,讨论微团聚体颗粒组的铜吸附特性与本体土壤过程的联系与差别,以从微观尺度揭示田间微团聚体的物理化学过程,为认识野外土壤的微观过程和环境功能提供科学依据。本文选择太湖地区典型水稻土-黄泥土,采用低能量超声波分散和冷冻机干燥法提取不同粒径的微团聚体颗粒组样品,测定全土和微团聚体与重金属吸附有关的基本性质。采用平衡液吸附法和CaCl₂与HCl溶液连续解吸法,研究全土和微团聚体颗粒组对Cu²⁺的吸附与解吸特征以及铝的溶出和土壤溶液pH下降的特点;并研究土壤溶液pH和磷处理以及在磷共存条件下对铜吸附与解吸的影响;同时采用磁力搅拌法研究全土和微团聚体颗粒组对Cu²⁺吸附与解吸以及Cu²⁺吸附过程土壤溶液pH变化动力学。以平衡吸附法结合吸附动力学探讨土壤对重金属Cu²⁺的吸附与解吸的机理。主要结果和认识如下:一、黄泥土中有机质和铁、铝氧化物在微团聚体中的含量具有相同的趋势,即在粘粒级粒组中含量最高,而在粗粉砂级粒组中含量最低。有机质与游离氧化铁、铝在微团聚体中的分布显著相关,说明游离氧化铁、铝有利于有机质的固存。微团聚体中阳离子交换量和表面负电荷（包括可变负电荷、永久负电荷）的数量与其有机质和氧化铁、铝含量有正相关。而阴离子交换量与有机质含量负相关。二、全土对Cu²⁺的吸附更符合Langmuir吸附等温式,而微团聚体颗粒组对Cu²⁺的吸附更符合Freundlich吸附等温式。说明Cu²⁺在全土表面上主要可从单层吸附理解,而在微团聚体颗粒组表面上更多以多层吸附。全土和微团聚体颗粒组吸附量大小顺序为粘粒级＞砂粒级＞全土＞粉砂级＞粗粉砂级,这与其游离氧化铁、铝和有机质含量正相关。不同粒径微团聚体颗粒组的加和吸附总量小于全土,且各个粒径微团聚体颗粒组Cu²⁺吸附与解吸速率均较全土慢。Cu²⁺吸附分为快吸附与慢吸附两个阶段。快吸附阶段Cu²⁺以高亲和力专性吸附于高选择性的吸附位点,即专性吸附,该过程释放H⁺,土壤悬液pH迅速下降;慢吸附阶段Cu²⁺吸附于无选择性的吸附位点,即非专性吸附,该过程不释放H⁺,土壤悬液pH缓慢下降,然后略有缓慢上升,Al的溶出也发生在此阶段。温度升高增加快吸附速率,慢吸附速率随温度升高而降低。三、在外加Cu²⁺溶液浓度大于40 mg·L^-1条件下,全土和微团聚体颗粒组吸附Cu²⁺的过程发生Al的溶出,同时溶液pH显著下降。pH下降值与Cu²⁺吸附量和Al溶出量呈显著正相关,并且Al交换量与非专性吸附量呈极显著正相关。外加Cu²⁺溶液在pH2.0～6.5条件下,pH升高,Cu²⁺吸附量随之增加,Al溶出量随之减少。低pH条件下有利于非专性吸附,高pH条件下有利于专性吸附。四、全土和微团聚体颗粒组吸附P后,Cu²⁺吸附量显著增加,并且Cu²⁺吸附量与P的吸附量呈显著正相关,而Cu²⁺解吸率随P的吸附量增加逐渐减小。在P共存的土壤溶液中,在低P浓度时,P对Cu²⁺的吸附发生抑制作用,高P浓度时,发生促进作用,Cu²⁺吸附量随P浓度的变化呈波谷形变化。对于Cu²⁺的解吸,低P浓度时,P促进Cu²⁺的解吸,高P浓度时,P抑制Cu²⁺的解吸,Cu²⁺解吸率随P浓度的变化呈波蜂形变化。综上所述,平衡吸附法和动力学方法均证明了微团聚体的吸附特征不同于全土。在实验条件下,微团聚体颗粒组吸附总量小于全土,pH升高和P处理这种差异更为显著。微团聚体颗粒组中无机矿物表面被有机物质包被,而风干磨细的处理方法使有机质和氧化铁等暴露在土壤表面而具有更多的吸附位点,所以处理后的全土不仅增加了Cu²⁺吸附量,而且也增加了Cu²⁺吸附与解吸的速率。更多还原

【Abstract】 The micro-aggregated particles of soils are the fundamental materials and functional cell of the soils, and its structure and combination plays a key role in control the physical and chemical process of soil environment. The different combination mode exist between the soil micro-aggregates of different sizes and organic matter and minerals, which resulted in the diversity on the adsorption and distribution of plant nutrient, the constraint capability of the heavy metals and toxic organic pollutants, and biological effectiveness. The micro-aggregated particles are cemented by clay mineral through radicel and mycelium, some of the sites strong affinity are shielded or weakened. On the contrary, air-dried and milled soil（whole soil）in laboratory traditionarily, which made organic matter and ferric oxide exposing on the edaphic surface, are more adsorption sites, and the ability of combining with heavy metal enhances. So there is different heavy metal adsorption result between whole soil method and field soil. We study the adsorption and desorption of the copper ion in the micro-aggregated particles of soils, and find the relations between the adsorption and the properties of soils. From micro scales, we reveal the physical and chemical processes of micro-aggregate particles in soil environment. Our studies provide science evidences to recognize the microscopic process of field soil and environmental functions.In this paper, size fractions of micro-aggregates were separated from undisturbed paddy soil samples in Tai Lake region by using low energy ultrasonic dispersion and freeze-dry method. The adsorption and desorption of Cu²⁺ in the micro-aggregates and the original soils, the dissolution aluminum, and pH decrease in the soil solution were studied by using equilibrium adsorption method and continue desorption method of CaCl₂ and HC1 solution. The effects of soil solution pH, phosphorus treatment, and phosphorus coexistence on the adsorption and desorption of copper were investigated. The effects of the bulk soil and the micro-aggregate particles on the adsorption and desorption of Cu²⁺ and soil solution pH changes in Cu²⁺ adsorption process were also investigated by using magnetic stirring method. At the same time, the mechanism of effects of soil on the adsorption and desorption were investigated by the equilibrium adsorption method and adsorption kinetics.Our main results are :1. The organic matter, ferric oxide and alumina of micro-aggegates in yellow soil are all highest content in clay and low in sand. Organic matter is correlative evidently with ferric oxide and alumina in micro-aggegates, which means that ferric oxide and alumina are propitious to fix organic matter. The quantity of cation exchange capacity and superficial anion （including alterable anion and permanent anion） in micro-aggregates are correlative with organic matter, ferric oxide and alumina, while the anion exchange capacity is negative correlated with organic matter.2. The adsorption of Cu²⁺ by the bulk soil samples fits well to the Langmuir Isothermmodel and the adsorption of Cu²⁺ by micro-aggegates fits well to the Freundlich Isothermmodel. Its indicated that the Cu²⁺ in the surface of bulk soil belonged to the monolayeradsorption, while on the surface of micro-aggregate particles could be multilayer adsorption.The Cu²⁺ adsorption capacity was in the order: clay fraction > sand fraction > bulk soil >siltfraction >coarse silt fraction, which correlated well to the contents of free Fe/Al oxide andorganic matter within them. The total adsorption capacity of different size particles was lessthan the bulk soil, while the sequence of desorption rate was reversed. The adsorption ofCu²⁺ was divided into fast adsorption and slow adsorption. The Cu²⁺ adsorbed at highlyselective adsorption sites by high affinity at fast adsorption stage, which process belongedto rapid adsorption stage and releases H⁺ result in the decrease of pH in soil suspensions.Then, a slow adsorption stage followed, Cu²⁺ was adsorbed on the non-selective sites by theweak affinity adsorption, which process belonged to non-specific adsorption, and Cu²⁺exchange Al process also occurred in the course of this stage. The pH of soil suspensionsfirst slowly declined, then slightly increased to balance. The fast adsorption rate increasedas the temperature, while the slow adsorption rate decreased as the temperature increase.3. The Al exchanged and pH dropped significantly when the bulk soil and micro-aggregates particles adsorbed Cu²⁺ under the conditions of plus copper concentrations more than 40 mg-L^-1 . The amounts of adsorbed Cu²⁺ and the dissolution of aluminum were significantly correlated with the decrease of the pH. Al exchange capacities were significantly correlated and non-specific adsorption capacity. Cu²⁺ adsorption amounts increased and dissolution of aluminum decreased as the increase of pH when pH is at the range of 2.0～6.5. Low pH helped to non-specific adsorption and high pH helped to specific adsorption.4. Adsorption amount of Cu²⁺ increased significantly when bulk soil and micro-aggregates were previously treated with phosphate, and it correlated well to the adsorption contents phosphate, while the desorption rate of Cu²⁺ decreased as the increase of phosphate adsorption amount. At the P coexistence soil solution, Cu²⁺ adsorption was restrained by P at the low P concentration, while adsorption was accelerated at high P concentration. Hence fore, the adsorption amount of Cu²⁺ was generally characterized as valley-like curves with the change of P concentration. The desorption of Cu²⁺ was promoted by P at a low P concentration, while the desorption of Cu²⁺ was inhibited by P at a high P concentration. The desorption rate of Cu²⁺ was generally characterized as mountain-like curves with the change of P concentration.According to the above results, we can conclude that the characteristic of micro-aggregates is different to bulk soil, which can be obtained from both equilibrium adsorption and kinetic results. In experimental condition, adsorption amount of Cu²⁺ in micro-aggregates is less than bulk soil, which is more observable as pH increases and is treated with phosphate. Inorganic minerals wrapped with organic matter, and the air-dried and. milled soil made organic matter and ferric oxide exposing on the edaphic surface, are more adsorption sites, bulk soil can adsorb more Cu²⁺ and the velocity of adsorption and desorption of Cu²⁺ are more rapid.更多还原