喀斯特生态系统土壤表面电化学特征及其影响因子

以西南喀斯特典型石漠化生态系统土壤为研究对象,采用空间替代时间的方法,研究石漠化演替过程中土壤表面电化学特征演变规律及其与土壤理化性质的相关性。采用物质表面联合分析法对不同石漠化等级土壤表面电化学属性进行测定。结果表明,土壤表面电荷密度、表面电场强度、比表面、表面电荷数量随石漠化强度的增加而下降,其变化范围分别为0.34 C·m^(-2)~0.42 C·m^(-2)、4.85×10^(8)V·m^(-1)~5.86×10^(8)V·m^(-1)、47.11 m^(2)·g^(-1)~53.16 m^(2)·g^(-1)、16.86 cmol·kg^(-1)~22.82 cmol·kg^(-1),土壤表面电位随石漠化强度的增加而上升,其变化范围为-113.74 mV~-115.10 mV;研究区黏土矿物组成为伊利石、高岭石、绿泥石、伊蒙混层、绿蒙混层,且以绿蒙混层为主;土壤黏粒、砂粒、非晶质氧化铝、胡敏酸是影响喀斯特石漠化地区土壤表面电化学属性变化的主要因素,解释率分别为48.3%、38.1%、13.0%、12.0%;土壤粒径组成、有机质组分和金属氧化物对土壤表面电化学特征影响由强到弱依次分别为:土壤黏粒>砂粒>粉粒,胡敏酸>有机碳>富里酸,非晶质氧化铝>游离氧化铁>非晶质氧化铁。本研究对中国西南喀斯特石漠化土壤管理与调控、退化植被恢复重建具有重要意义。

测量模拟土体zeta电位的简易流动电位装置及其使用方法

本文展示了一款可应用于土壤学领域研究的简易流动电位测量装置。为验证该装置的可行性,采用石英砂和包铁石英砂模拟土体所具有的多孔结构和表面电荷特征,基于流动电位法测量了石英砂在不同浓度(0.01、0.05、0.1、0.5、1.0、2.0和5.0 mmol·L^(-1))NaCl溶液中的zeta电位和石英砂与包铁石英砂在不同pH(4.4、5.2、6.1、6.6、6.9、7.7和8.0)电解质溶液中的zeta电位。同时采用电泳法测量了石英砂胶体在不同pH电解质溶液的zeta电位以作比较。结果表明:在考虑表面电导时,流动电位法测得石英砂在不同浓度NaCl溶液中的zeta电位随溶液浓度的升高逐渐往正值方向移动。这是由于随着离子强度增加,石英砂的双电层厚度受到压缩,zeta电位的绝对值逐渐降低;相同离子强度下,随溶液pH升高,石英砂和包铁石英砂表面官能团发生去质子化作用,流动电位法测得石英砂和包铁石英砂的zeta电位均随pH升高而逐渐降低;由于电荷屏蔽作用,在带负电荷的石英砂表面包被带正电荷的氢氧化铁后,流动电位法测得包铁石英砂的等电点pH(IEP)介于石英砂和氢氧化铁的IEP。此外,流动电位法测得的石英砂颗粒在不同pH电解质溶液中的zeta电位与电泳法测得的石英砂胶体在不同pH电解质溶液中的zeta电位具有较好的一致性。可见采用自制流动电位装置所获结果均与理论预测及常规电泳法测定结果相符,准确度较高。自制流动电位装置结构简单、操作方便、加工制造容易。该装置可被土壤学领域的研究者借鉴参考,以望为土壤电化学研究工作做出贡献。

Relationship Between Iron Oxides and Surface Charge Characteristics in Soils

The relationship between iron oxides and surface charge characteristics in variable charge soils ( latosol and red earth ) was studied in following three ways. ( 1 ) Remove free iron oxides ( Fed ) and amorphous iron oxides ( Feo ) from the soils with sodium dithionite and acid ammonium oxalate solution respectively. ( 2 ) Add 2% glucose ( on the basis of air-dry soil weight ) to soils and incubate under submerged condition to activate iron oxides, and then the mixtures are dehydrated and air-dried to age iron oxides. ( 3 ) Precipitate various crystalline forms of iron oxides onto kaolinite. The results showed that free iron oxides ( Fed ) were the chief carrier of variable positive charges. Of which crystalline iron oxides ( Fed-Feo ) presented mainly as discrete particles in the soils and could only play a role of the carrier of positive charges, and did little influence on negative charges. Whereas the amorphous iron oxides ( Feo ) , which presented mainly as a coating with a large specific surface area, not only had positive charges, but also blocked the negative charge sites in soils. Submerged incubation activated iron oxides in the soils, and increased the amount of amorphous iron oxides and the degree of activation of iron oxide, which resulted in the increase of positive and negative charges of soils. Dehydration and air-dry aged iron oxides in soils and decreased the amount of amorphous iron oxides and the degree of activation of iron oxide, and also led to the decrease of positive and negative charges. Both the submerged incubation and the dehydration and air-dry had no significant influence on net charges. Precipitation of iron oxides onto kaolinite markedly increased positive charges and decreased negative charges. Amorphous iron oxide having a larger surface area contributed more positive charge sites and blocked more negative charge sites in kaolinite than crystalline goethite.