| In this paper, Using wet sieving method,separation and centrifugal sedimentation to study the soil of tea garden soil in Mingshan (<0.002mm,0.053-0.002mm0.25-0.053mm,2-0.25mm), discussing the effects of low molecular organic acids in tea garden soil micro-aggregates of adsorption and desorption of Cd2+by the methods of equilibrium liquid adsorption isotherm and NH4OAC desorption. for effective prediction of Cd2+in the soil-plant system effectiveness, toxicity, migration and transformation, ease to provide scientific basis for environmental pollution of soil heavy metals and its regulation.The main conclusions are as follows:(1) In the tea garden,soil organic matter, free iron oxide, CEC in the soil and different particle size distribution of different particle size group with the same tendency,that (<0.002mm)>2-0.25mm>soil>0.053-0.002mm>0.25-0.053mm.Therefore, organic matter, free iron oxide and CEC in the distribution of different particle size fractions of all have the existence to the fine particle enrichment trend. Soil of tea garden soil,different particle fractions of particle group of CEC and the content of soil organic matter have the significant positive correlation. At the same time, the soil of tea garden soil and different particle fractions of microaggregates of free iron oxide particles and soil organic matter content show a significant positive correlation.(2) The soil of tea garden soil and the particle size of micro-aggregates on the adsorption quantity of Cd2+increases with the increase of initial Cd2+concentration, initial Cd2+concentration under the same condition, the soil of tea garden soil and different sizes of microaggregates with low molecular weight organic acids (citric acid, oxalic acid, malic acid and the mixed acid) increased adsorption concentration change in peak shape, trends, and greater adsorption capacity without acid under the conditions of Cd2+, the adsorption of low molecular weight organic acids promoted Cd2+at low concentrations, at high concentrations, adsorption and inhibition of Cd2+. The adsorption capacity of soil Cd2+of3kinds of organic acid was different:oxalic acid, citric acid, malic acid. Low molecular organic acids (citric acid, oxalic acid, malic acid) decreasing soil of tea garden soil and different particle size of different particle size fractions on the adsorption of Cd2+content in the following order:(<0.002mm)>2-0.25mm>soil>0.053-0.002mm>0.25-0.053mm, adsorption capacity of soil of tea garden soil and that the particle size of micelle dimer to the smallest particle size (<0.002mm) enrichment,as the same size with the original soil,different size of micro-aggregates particulate organic matter, CEC, free iron oxide content to sort.(3) The soil of tea garden soil and different sizes of microaggregates desorption of Cd2+increase with the increasing of the initial concentration of Cd2+, initial concentration of Cd2+under the same conditions, the soil of tea garden soil and different sizes of microaggregates with low molecular weight organic acids (citric acid, oxalic acid, malic acid and the mixed acid) concentration increase the desorption increase, low molecular organic acids (citric acid, oxalic acid, malic acid and their mixed acid) can promote desorption of soil Cd2+, and this effect is increased by the increasing concentration of low molecular organic acid. Soil and the microaggregate of Cd2+desorption decrease in following order:(<0.002mm)>2-0.25mm>soil>0.053-0.002mm>0.25-0.053mm.The desorption capacity of soil, soil of three kinds of organic acid are different:citric acid>oxalic acid> malic acid. The original soil and aggregation in Cd2+of NH4OAC desorption rate increase with the initial concentration of Cd2+increasing, according to the maximum desorption rate meter, the original soil and between different particle size aggregates NH4OAC desorption rate size relations:0.25-0.053mm>0.053-0.002mm> soil>2-0.25mm>(<0.002mm). Low molecular organic acids on yellow soil and different sizes of microaggregates of isothermal adsorption and desorption characteristics of Cd2+with Langmuir adsorption equation is the best, Freundlich, Temkin equation fitting effect times or less.(4) Citric acid, oxalic acid and two mixed effect on adsorption of Cd2+acid, in the initial concentration of Cd2+25,50,75,100mg· L-1, low concentration of oxalic acid, oxalic acid mixed with citric acid (<5mmol· L-1) and citric acid (<2.5mmol· L-1) promote the adsorption of Cd2+, high concentration of oxalic acid, oxalic acid is mixed with lemon acid (5-10.0mmol L-1) and citric acid (2-10.0mmol L-1) decrease the adsorption of Cd2+. The initial concentration of Cd2+25,50,75,100mg· L-1, in addition to the<0.002mm particle group, low molecular organic acids as1,2.5,5,7.5,10mg· kg-1other particle group Cd2+desorption, mixed acid citric acid>two oxalic acid, oxalic acid and two mixed acid on Cd2+desorption rather. Citric acid mixture of oxalic acid have antagonistic effects, which is lower than the desorption of citric acid, oxalic acid and below.(5) Citric acid, malic acid and the mixture of the two effects of adsorption amount of Cd2+acid, in the initial concentration of Cd2+25,50,75,100mg· L-1, low concentration of malic acid (<5mmol· L-1) or citric acid, malic acid, citric acid mixture (<2.5mmol· L-1) promote the adsorption of Cd2+, high concentrations of malic acid (5-10.0mmol· L-1) or citric acid, malic acid, citric acid mixture (2-10mmol· L-1) reduce the Cd2+adsorption. But comparing with the control group, high, low concentration of citric acid, malic acid and two mixed acid solution also increase the adsorption of Cd2+by soil. The initial concentration of Cd2+25,50,75,100mg· L-1, in addition to the<0.002mm particle group, low molecular organic acid concentration is2.5,5,7.5,10mg· kg-1, desorption of other particle group Cd2+, citric acid mixed acid and malic acid are higher than two; the initial concentration of Cd2+25,50,75,100mg· L-1, low molecular concentration of organic acid is2.5,5,7.5,10mg· kg-1in addition to<0.002mm,2-0.25mm, desorption of soil particle group Cd2+, mixed with citric acid malic acid than malic acid. Because the citric acid and malic acid have antagonistic effects, which is lower than the desorption of citric acid, malic acid and below.(6) Effect of oxalic acid, malic acid and two mixed adsorption amount of Cd2+acid, in the initial concentration of Cd2+25,50,75,100mg· L-1, low concentration of oxalic acid, malic acid malic acid mixed acid (<5mmol· L-1) promote the adsorption of Cd2+, high concentrations of malic acid, oxalic acid, malic acid, mixed acid (5.0-10.0mmol· L-1), decrease Cd2+adsorption, but comparing with the control group, high, low concentration of oxalic acid, malic acid and two mixed acid solution also increase the adsorption of Cd2+by soil. The initial concentration of Cd2+25,50,75,100mg· L-1, in addition to the<0.002mm particle group, low molecular organic acid concentration is2.5,5,7.5,10mg· kg-desorption of other particle group Cd2+, oxalic acid, malic acid are lower than the mixture of oxalic acid and malic acid, oxalic acid than malic acid on Cd2+desorption, but there are little differences. |
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