Cu²⁺ Adsorption-desorption Of Tea Plantation Soil Aggregates With Low Molecular Weight Organic Acids

In order to investigate the effect of single organic acid（citric acid,malic acid and oxalic acid）and mixed organic acid on soil aggregate’adsorption-desorption of Cu²⁺,we collected the tea garden soil from Mingshan as the studied object in the present paper.By ultrasonic action and centrifuging methods,we collected the aggregate in soils successfully.Then through equilibrium liquid adsorption method and the NaNO₃ as desorbent’s desorption method,we can draw the conclusion and provide the scientific reference for effective management of soil.The main research showed that:（1）The Cu²⁺adsorption capacity of regular and of different-sized fractions of soil aggregates increased as Cu²⁺concentration increased.Factors such as surface area,ferric oxide availability,cation exchange capacity,and presence of organic matter influence Cu²⁺adsorption.Cu²⁺adsorption is also affected by soil aggregate size where in adsorption diminished as soil aggregate size increased:<0.002 mm>0.053⁰.002 mm>original soil>2⁰.25 mm>0.25⁰.053 mm.The isothermal adsorption process was fitted to three equations,namely,Langmuir,Freundlich,and Temkin.The equations were used to fit,resulting in a significant level,with the Langmuir equation showing the best fit.（2）Low molecular weight organic acids not only have a promoting effect but also an inhibitory effect on adsorption of Cu²⁺.Adsorption of Cu²⁺is promoted at a concentration of0–1 mmol/L for citric acid,malic acid,mixed organic acid.Adsorpition of Cu²⁺is also promoted at a concentration of oxalic acid at 0–0.1 mmol/L.However,at a concentration of citric acid,malic acid,mixed organic acid>1 mmol/L and>0.1 mmol/L for oxalic acid,adsorption of Cu²⁺is inhibited.The adsorption promotion of Cu²⁺reached a peak value at different concentrations by three organic acids.Adsorption capacity reached maximum when the concentration of oxalate was 0.1mmo/L,and adsorption capacity reached maximum when thethe concentration of citric acid,malic acid were 0.5 mmol/L.Different organic acids with different concentrations,as well as soil aggregate size,affect the Cu²⁺adsorption of soil aggregates.The amount of adsorption were ranking in the following order:（<0.002mm）>0.053⁰.002 mm>bulk soil>2⁰.25 mm>0.25⁰.053 mm.（3）Different concentrations of single and mixed organic acids promoted the desorption of Cu²⁺by soil aggregates,with the concentration of copper and low molecular weight organic acids increasing,desorption rate showed a upward trend.The difficult absorption rate is opposite to that,showing a downward trend.The easy desorption rate of soil aggregates with different concentration of organic acids from high to low is:0.25⁰.053 mm>2⁰.25mm>bulk soil>0.053⁰.002 mm>（<0.002 mm）.After adding different concentrations of single and mixed organic acids,the desorption of Cu²⁺from soil aggregate was promoted,the order was:citric acid<malic acid<oxalic acid,the promotion action of mixed organic acids ranged from large to small was:malic acid+oxalic acid>citric acid+oxalic acid>citric acid+malic acid.（4）After adding different concentrations of single and mixed organic acids,the adsorption of Cu²⁺on tea garden soil showed the trend of promoting in the low concentrations and inhibiting in the high concentration.The adsorption amount of soil aggregate under the action of single organic acid is citric acid>malic acid>oxalic acid,the amount of adsorption under mixed organic acids is:citric acid+malic acid>citric acid+oxalic acid>malic acid+oxalic acid,The amount of adsorption between a single organic acid and its mixed acid is citric acid>citric acid+malic acid>citric acid>citric acid+oxalic acid>oxalic acid malic acid>oxalic acid+malic acid>oxalic acid.