我国土壤资源的现状及特点 (54).ppt

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1、8.5 土壤胶体的基本性质8.5 The Fundamental Properties of Soil ColloidsThe specific surface areaThe surface area per unit mass of an object with the unit of m2/g.Definition Take a cube for example:Assume that the soil particles are ideally spherical：Soil particles(Diameter mm)Specific surface area(cm2/g)Soil p

2、articles(Diameter mm)Specific surface area(cm2/g)Medium sand(0.1)226Clay(0.0005)500 nm45,200Fine sand(0.01)2,260Colloidal particle(0.0001)100 nm226,000Clay(0.001)22,600Colloidal particle(0.00005)50 nm452,000The surface of soil clay mineral is divided into internal surface and external surface.Soil c

3、lay mineralInternal surface area(m2/g)External surface area(m2/g)Total specific surface area(m2/g)Montmorillonite70075015150700850Vermiculite400750150400800Hydromica059015090150Kaolinite0540540The specific surface areaTypes of surface charges1Permanent charges：they originate from the isomorphous sub

4、stitution of clay minerals and are not affected by the external environmental conditions,such as pH and electrolyte concentration.2Variable charges:they change with the change of solution pH,and come from the protonation and deprotonation of functional groups on the surface of minerals.Soil colloidH

5、ydromicaMontmorilloniteKaoliniteGibbsiteFerric hydroxideHumic acidsVariable chargePermanent chargeSurface charges of soil colloidsPermanent charges are developed from the isomorphous substitution.The isomorphous substitution of 2:1 type clay mineral-MontmorilloniteSi4+O2O2Al3+OHMg2+0.066 nm0.051 nm0

6、.039 nmThe permanent chargesThe sign and amount of variable charges change with the solution pH.Si-OH Silanol groupsAl-OH Aluminol groups1:1 type clay mineral-KaoliniteAl3+Si4+O2O2O2GoethiteFe-OH Ferrol groupsLow pHHigh pHM-OH+M-OHM-OThe variable chargesCOOHROHCOOROHCOOROpH 8pH 810Dissociation of ca

7、rboxyl and phenolic hydroxyl groups on the humus surface:The variable chargesThe sign and amount of variable charges change with the solution pH.The state of colloidal suspensionSoil colloidSol Gel CoagulateDisperseFactors affecting colloid coagulationElectrolyte concentration and electrolyte typeThe coagulation ability of cations:Fe3+Al3+Ca2+Mg2+NH4+K+Na+Coagulation and dispersion of soil colloids谢谢THANK YOU