论文标题:紫色土表面电荷性质的初步研究
Studies on Surface Charge Properties of Purple Soil
论文作者 杨兴伦
论文导师 李航；刘洪斌,论文学位 硕士,论文专业 土壤学
论文单位 西南农业大学,点击次数 102,论文页数 49页File Size1953k
2004-05-15论文网 http://www.lw23.com/lunwen_5270062/ 紫色土;表面电荷总量;表面电位;表面电荷密度
purple soil;surface charge quantity;surface potential;surface charge density
土壤最重要的性质是其表面带有电荷，该电荷深刻影响着土壤的其他性质以及发生在土壤中的物理、化学、生物化学过程。以土壤胶体表面的电荷性质，以及带电表面与土壤溶液中离子、电子、质子间的相互作用为核心的研究是土壤学20多年来研究的前沿。 研究表面电荷性质的传统方法因依赖比表面积的数据而导致表面电位、表面电荷密度和表面电场强度等参数测定的不可靠，并且不仅是甘油吸附法，目前几乎所有不同的方法所得结果之间差异都非常大。李航(2002年)提出了测定表面电位、表面电荷密度的另一种方法，其思路是，在测定平均电位的基础上，先计算表面电位值，再利用Gouy-Chapman公式计算表面电荷密度、表面电场强度，甚至还可以计算比表面积，摆脱了对不能准确测定的比表面积的依赖，从而在一定程度上弥补了传统方法存在的不足。 首先，本文采用流恒法对酸性、中性和石灰性紫色土表面电荷总量、表面电位、表面电荷密度、表面电场强度以及比表面积进行了测定和计算，与传统方法测定结果进行了比较；然后，研究了三种紫色土表面电荷性质随外部环境(电解质浓度、电解质类型、环境温度、陪伴阴离子类型、pH等)改变而变化的特点，同时，研究了紫色土表面电荷性质与土壤交换酸之间的关系；最后，研究了三种紫色土表面与重金属离子的相互作用以及该作用对表面电荷性质的影响。研究结果表明： 1)采用流动法在2：1型电解质体系中测定三种紫色土的表面电位分别约为-0.16～-0.18V、-0.17～-0.19V，-0.18～-0.19V；三种紫色土表面负电荷密度分别为-0.26～-0.44Cm~(-2)、-0.37～-0.59Cm~(-2)、-0.58～-0.67Cm~(-2)；表面电场强度在10~8Jm~(-1)C~(-1)以上；而比表面积分别约为26，45，41m~2g~(-1)。表面电荷总量、表面电位等参数的大小顺序基本满足酸性＜中性＜石灰性。层次上的差异不显著，与紫色土为初成土的特点吻合。流动法实验结果比传统方法测定值偏高，而这种差异可能主要来源于传统方法所测定的比表面积偏高。在2：1型电解质体系中，三种紫色土表面电位都明显低于在1：1型电解质体系中的测定值，前者约为后者的50％；而在两种电解质体系中表面电荷总量、表面电荷密度大致相当，这从一个侧面反映了紫色土表面电荷主西南农业大学硕士学位论文摘要-.口豆口.旦旦国里旦...口.祖目口户口口-皿要为恒电荷。 2)电荷总量、表面电荷密度随电解质浓度增加而呈增加趋势，但幅度并不大;而表面电位随电解质浓度的增加有所降低。所获得的酸性紫色土下极限和上极限表面电荷密度各约为刁.19 cm一，一26 c m-2;中性和石灰性紫色土约为众48 c m.2，一0.60 cm一和一0.64 cm一2，一0.70Cm一;由此推测三种紫色土的表面恒电荷约为总电荷的70叹尸90%。阴离子对三种紫色土表面电荷的影响非常小，只是HZPO4一处理导致平衡吸附量稍微有所增加，而表面电位、表面电荷密度基本没发生改变.pH对三种紫色土表面电荷性质的改变不显著，pH<5时三种紫色土表面电位表现出降低的趋势，降低了约o.lv，而表面电荷密度则出现稍微的增加:pH>5时表面电位、表面电荷密度基本保持不变。以上的结果表明恒电荷是三种紫色土的主要电荷类型，与其矿物主要为恒电荷矿物相吻合。随温度的升高，三种紫色土的表面电荷总量、表面电位、表面电荷密度都表现出减少的趋势。例如，温度从298K上升到3 13K时，表面电荷总量降低了50%左右，表面电位降低约加%，而三者的表面电荷密度降低30%左右，这可能由于温度升高导致了胶体凝聚以及离子在双电层中的分布的改变。 3)总体来讲，表面电荷密度的负值小的土样所含交换酸比表面电荷密度负值大的土样所含交换酸大。而其活性酸即pH的差异较小的事实表明，交换酸(H十、A13+)在紫色土双电层中的分布可能不同:交换性酸在表面电荷密度高的土壤表面双电层中的位置距离表面较远，而在表面电荷密度较低的土壤双电层中的位置距离表面相对较近，而环境中其他离子特别是caz+、Mgz+的数量和作用是造成交换性离子在双电层中分布的差异的主要原因. 4)在不同介质PH以及离子强度下，紫色土对重金属离子Pb2+、cu2+、zn2+吸附的研究表明，对重金属离子吸附强度大小依次都是石灰性紫色土>中性紫色土>酸性紫色土，该顺序与土壤的表面电荷密度的大小基本一致;而Pb2+与表面的吸附强度又明显强于其他两种重金属离子，并且zn2+吸附表现出比较明显的可逆性，这表明吸附强度又与重金属离子本性密切相关。结果同时也反映了三种紫色土表面与重金属离子之间除了存在静电吸附外还存在专性吸附.三种紫色土在吸附Pb2+、cu2+后表面电荷量、表面电位以及表面电荷密度都显著降低:表面电位下降约o.lv:表面电荷密度下降约3卜50%;并推测以静电作用方式吸附的重金属比例约50一70%，这和恒电荷占80一90%的结果存在差异，暗示重金属离子在带恒电荷的土壤胶体表面并非仅仅发生简单的电性吸附作用，还存在包括专性吸附在内的其他复杂过程。
The most important characteristics of soils is its charges on the surface. Because of its huge quantity of electric charges, its wide distribution and relatively long distance force action, the physical, chemical and biochemical processes concerned with ion, proton and electron exchanging and handing around should be deeply affected, the electro-chemistry has being the front of soil science since 3 decades before. The charge properties, the interaction between the surface and the ions, electron and protons are the focus of the study in soil electro-chemistry.The Theory of Double Layer is the basic theory of soil surface charge. In order to gain the number of potential and charge density in any place of the double layer, the formula of Gouy-Chapman should be used. But when using this formula to calculate those indexes, the surface potential and the surface charge density are needed. However, there is no satisfactory method to measure them. Li Hang presented a new method to measure the surface potential and the surface charge density. This method can get surface potential and surface charge density without the data of SSA and makes it more easy to measure the surface charge properties.The method has been used in this experimental study. Neutral purple soil, acid purple soil and calcareous purple soil were taken as the experimental materials. The charge quantity, the surface potential, the surface charge density, the surface electric field strength and SSA was measured. The experimental result has compared with the result measured by traditional method. The effect of electrolyte concentration, temperature, accompanying anion type, electrolyte type and pH on the surface charge properties was studied, too. The interaction between the surface and the heavy mental ions was also conducted. The experimental result as follows:Firstly, the surface potential of the acid purple soil, neutral purple soil and calcareous purple soil is -0.16- -0.18 V, -0.17- -0.19 V , -0.18- -0.19 V respectively; the surface charge density is -0.26--0.44 C m-2, -0.37- -0.59 C m-2, -0.58- -0.67 C m-2; the electric field strength is more than 108 J m-1 C-1; and the SSA is 26, 45. 41m2 g-1. The experimental result is higher than the one gained by the traditional method. The result of surface potential in 2:1 electrolyte type is lower than the one in 1:1 type, and the former is about 50% of the latter; but the charge quantity, surface charge density is almost same in both type.Secondly, with the increasing of electrolyte concentration, the charge quantity and the surface charge density increase a little; but the surface potential decreases. The up-limited surface charge density of acid, neutral and calcareous purple soils is -0.19 C m-2, -0.48 C m-2, -0.64 C m-2, and the down-limited surface charge density is -0.26 C m-2, -0.60 C m-2, -0.70 C m-2 .respectively. It can be speculated that the permanent charge accounts for 70%~90% of the total charge quantity; therefore, the permanent charge is the main type of the soil samples. The result is identical with the main mine in the soil samples. And the result is identical with the result gained by the method of Mehlich.Thirdly, the effect of accompanying anion on the surface charge is little. The effect of pH on the surface charge properties is not obvious. When pH < 5, the surface potential decreased about 0.1V, but the surface charge density increased a little; when pH > 5, there is no changed about the potential and the surface charge density. Those results ascribe to the fact that permanent charge is the main type of the soil sample. With the raise of temperature, the surface charge quantity, surface potential, surface charge density decrease sharply. For example, when the temperature changed from 298K to 313K, the charge quantity decreased about a half, the surface potential decreased 20 percent, and the surface charge density deceased 30 percent.Fourthly, the effect of pH and the ion strength on the adsorption of heavy mental ions (Pb2+, Cu2+) showed that there are static ad
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