土壤胶体和土壤吸收特性.课件.ppt

1、 The soil contains minute particles called soil colloids. They are smaller than one hundredth-thousand of a millimeter. Soil colloids are thin and disc-like. There are mineral as well as organic soil colloids. Mineral colloids are usually found to be fine particles of clay minerals. （一）胶体的概念（一）胶体的概念

2、一种或数种物质的微小颗粒均匀地分散于另一种物质中，便构成一种或数种物质的微小颗粒均匀地分散于另一种物质中，便构成分散体系。均匀分散的颗粒称为分散相颗粒。分散体系。均匀分散的颗粒称为分散相颗粒。分散相颗粒的粒径在分散相颗粒的粒径在1-100nm（毫微米）范围的分散相体系，称（毫微米）范围的分散相体系，称为胶体分散体系，其中的分散相颗粒就是胶体颗粒。为胶体分散体系，其中的分散相颗粒就是胶体颗粒。MicaHumic AcidKaolinite(kandite)Montmorillonite(smectite)Tarbuck and Lutgens, 2003Tarbuck and Lutgens,

3、2003Tarbuck and Lutgens, 2003Tarbuck and Lutgens, 2003There are three main groups of clay minerals: Kaolinite - also includes dickite and nacrite; formed by the decomposition of orthoclase feldspar (e.g. in granite); kaolin is the principal constituent in china clay. Illite - also includes glauconit

4、e (a green clay sand) and are the commonest clay minerals; formed by the decomposition of some micas and feldspars; predominant in marine clays and shales.Smectites or montmorillonites - also includes bentonite and vermiculite; formed by the alteration of mafic igneous rocks rich in Ca and Mg; weak

5、linkage by cations (e.g. Na+, Ca+) results in high swelling/shrinking potentialAll have layers of Si tetrahedraand layers of Al, Fe, Mg octahedra, similar to gibbsite or bruciteSEM view of claySi tetrahedral and Al octahedral sheets formed by sharing oxygen moleculesThe kaolinite clays are 1:1 phyll

6、osilicatesThe montmorillonite and illite clays are 2:1 phyllosilicates1:1 silicate clay (kandite)2:1 silicate clay (smectite & vermiculite)Kaolinite clays have long been used in the ceramic industry, especially in fine porcelains, because they can be easily molded, have a fine texture, and are white

7、 when fired. These clays are also used as a filler in making paper. In the United States, deposits are found primarily in Georgia, North Carolina, and Pennsylvania; china clay is also mined in England (Cornwall) and France. Kaolinite is the purest of clays, meaning that it varies little in compositi

8、on. It also does not absorb water and does not expand when it comes in contact with water. Thus, kaolinite is the preferred type of clay for the ceramic industry. Illite is similar to muscovite and is the most common clay mineral, often composing more than 50 percent of the clay-mineral suite in the

9、 deep sea. They are characteristic of weathering in temperate climates or in high altitudes in the tropics, and typically reach the ocean via rivers and wind transport. Relict zircon in illiteThe Illite clays have a structure similar to that of muscovite, but is typically deficient in alkalies, with

10、 less Al substitution for Si. Thus, the general formula for the illites is:KyAl4(Si8-y,Aly)O20(OH)4 , usually with 1 y 1.5, but always with y 2.Because of possible charge imbalance, Ca and Mg can also sometimes substitute for K.The K, Ca, or Mg interlayer cations prevent the entrance of H2O into the

11、 structure. Thus, the illite clays are non-expanding clays. Illite type clays are formed from weathering of K and Al-rich rocks under high pH conditions. Thus, they form by alteration of minerals like muscovite and feldspar. Illite clays are the main constituent of shales. Montmorillonite or smectit

12、e is family of expansible 2:1 phyllosilicate clays having permanent layer charge because of the isomorphous substitution in either the octahedral sheet (typically from the substitution of low charge species such as Mg2+ , Fe2+, or Mn2+ for Al3+)The most common smectite is Montmorillinite, with a gen

13、eral chemical formula : (12Ca,Na)(Al,Mg,Fe)4(Si,Al)8O20(OH)4.nH2OMontmorillinite is the main constituent of bentonite, derived by weathering of volcanic ash. Montmorillinite can expand by several times its original volume when it comes in contact with water. This makes it useful as a drilling mud (t

14、o keep drill holes open), and to plug leaks in soil, rocks, and dams. Montmorillinite, however, is a dangerous type of clay to encounter if it is found in tunnels or road cuts. Because of its expandable nature, it can lead to serious slope or wall failures. From Yucca Mountain, NV三.胶体双电层构造（ Electric

15、al Double Layer）决定电位离子决定电位离子potential determining ion扩散双电层扩散双电层diffused double layer双电层模型双电层模型 Electrical Double Layer胶核决定电位离子层（-）固定层（+） 可动层胶粒反离子层胶团结构 电位电位电位反离子层呈大气式分布反离子层呈大气式分布MontmorilloniteKaolinite Permanent ChargeVariable ChargeAlOSi4+SiOOOOONo net chargeAlOAl3+SiOOOOONet negative chargeSoil de

16、velopment-Mg2+Clay structure magnified 1,600 timesOLow pHHOHH+NO3-Anion Exchange CapacityO-Mg2+AlOSi4+SiOOOOONo net chargeAlOAl3+SiOOOOONet negative chargeSoil development-Mg2+Cation Exchange Capacity = Ability to hold (retain) cations and is an important part of soil fertility（ Ions are atoms with

17、an electrical charge）Can be dependent on permanent charge or pH dependant chargeNegatively charged colloids (organic matter and clay) attract and hold cationsCationsCa2+, Mg2+Na+, K+AnionsSO42-, PO43-Cl-, NO3- Ability of a soil to hold and exchange cationsIons are atoms with an electrical chargeNega

18、tively charged colloids (organic matter and clay) attract and hold cationsIons are atoms with an electrical charge Organic Matter Content Clay Content Type of ClayMontmorillonite high CECIllite mod. CECKaolinite low CEC Most soils are negatively charged and hold cations. Cations held on exchange sit

19、es may move into the soil solution & be taken up by roots. Anions are not held on soil and are subject to leaching (P is exception).SOIL COLLOIDN SN SS NN SLike poles (charges) repelOpposite poles (charges) attractCa2+K+Na+Mg2+SO42-NO3-Cl-Cations in Soil SolutionNO3-NH4+Ca2+K+K+K+Mg2+Ca2+H+K+H+H+Ca2

20、+Mg2+Cation Exchange CapacitySandSandClayOrganic Matter-Cations Held on Exchange SitesCommon CEC RangeHeavy ClaySandCEC 25More Clay, More Positions to Hold CationsCEC 5Less Clay, Fewer Positions to Hold CationsH+Ca2+Mg2+NH4+Na+K+H+H+H+K+SandClay1.作为土壤保肥性能的评价指标 阳离子交换量是评价土壤肥力的一个指标。它直接反应土壤可以提供速效养分的数量，也能表示土壤保肥能力、缓冲能力的大小。2.作为制定施肥计划的参考CEC高的土壤，稳肥，耐肥性好，可以少次多量；CEC低的土壤，性燥，耐肥性差，可以少量多次1.1.土壤胶体有何特性？简述其对土壤肥力的影响？土壤胶体有何特性？简述其对土壤肥力的影响？2.2.影响土壤保肥性和供肥性的因素主要有哪些？如何影响土壤保肥性和供肥性的因素主要有哪些？如何调节？调节？3.3.试比较高岭石与蒙脱石晶层构造上的差异。试比较高岭石与蒙脱石晶层构造上的差异。