Comparison Studies On Ion Adsorption In Differently Developed Variably Charged Soils

Large areas of variable charge soils are distributed in the tropical and subtropical regions in south China,which are the important soil resources for sustainable agriculture in these areas.The mineral compositions and electrochemical properties of these soils are different from those of constant charge soil evolution.Variable charge soils carry both negative and positive charges and can adsorb both cations and anions.Although surface chemical properties of these soils have been investigated extensively,only few reports are available on the comparison of the surface chemical properties of variable charge soils on different pedogenic stage.Ultisols derived from Quaternary red earth were respectively collected from LANG Xl,CHANG SHA and LIU ZHOU。Effect of degree of soil development on adsorption of Cu(II) and Cd(II) and adsorption mechanisms of heavy metal ions on the surface of rea soil were investigated,which could provide reference on prevention and restotation for heavy metal pollution. Results showed that the amount of Cu(II) and Cd(II) absorbed by three Ultisols decreased with the increase in degree of soil development and the decrease in cation exchange capacity.The order is:the Ultisol from Anhui> the Ultisol from Hunan> the Ultisol from Guangxi.Under the same conditions, the amount of Cu(II) sbsorbed by three Ultisols were higher than Cd II).The amount of Cu(II) sbsorbed by Ultisol from Guangxi decreased with the increase in ionic strength,which indicated that adsorption mechanisms of heavy metal on the surface of Ultisol changed with the chang of ambient conditions.Physicochemical properties, mineral compositions, adsorption and desorption of Cu(II) and Cd(II) of Latosols derived from basalts aged 10,1330,2290kiloyears(ky) from Hainan were investigated.The effect of removal of organic matter on adsorption and desorption of Cu(II) and Cd(II) was also studied. X-ray diffraction analysis indicated that the clay minerals were dominated by smectite,halloysite, and kaolinite mixed with montmorillonite in the soil derived from 10 ky-basalt and by kaolinite, halloysite,and gibbsite in the soils derived from 1,330 and 2,290ky-basalt.The content of 2:1 minerals decreased with their parent rock,whereas the kaolinite and gibbsite showed an opposite trend.Results of removal of organic matter and results of adsorption and desorption of heavy metals indicated that physicochemical properties were closely related to soil development age.Higher soil development age caused lower CEC and higher the content of free iron..The order of adsorption and desorption by soils with different development ages was:0.01Ma>1.33Ma>2.29Ma.The amount of adsorption of Cu(II) and Cd(II) showed positive relationship with CEC and negative relaionship with freee iron.The proportion of specific adsorption of (II) was larger than that of Cd(Ⅱ).The content of organic matter was the main factor that affected the specific adsorption of Cu(),while it had little impact on Cd(Ⅱ).Results of adsorption and desorption of CrO42-,PO43- by Ultisol from Hainan showed that: adsorption of two anions was mainly specific adsorption, the adsorption amount of PO43- was larger than CrO42-.With the change of soil development age, the order of the adsorption and desorption amount of two ions was:0.01Ma<2.29Ma<1.33Ma.Desorption degree of PO43- by different strippants followed the order:deionized water>0.1mol/L NaNO3>0.1mol/L KNO3.Zeta potential curves of PO43- absorbed by 2.29Ma soil in different ion strengths crossed at a point(IEP).When pH>IEP, zeta potential was negative and absolute value decreased with the increase in ion strength.When pH