| The pollution of heavy metals in soil has become a normalcy of soil in China due to sewage irrigation,heavy metal atmospheric sedimentation,pesticide fertilizer use and industrial sludge and municipal solid waste composting and other human producing activity.The bioavailability and toxicity of heavy metals in the soil are not only related to the total amount,but more to the species of heavy metals in the soil.In this study,the multi-surface model was used to predict the labile heavy metals speciations in the soil,and the concentration of free heavy metals in the soil which was measured by Donnan Membrane Technique(DMT)for testing the accuracy of model prediction.By the model optimization,several heavy metal forms in the red soil were predicted,and the applicability of the Multi-surface model to the soils with high iron content in southern China was improved.The main results are as follows:1.The contents of p H,organic matter,CEC,free iron and amorphous iron and clay minerals in dryland soil of Tiezhuang and Liangqiao were analyzed.The range of p H value is 4.05~5.12,the range of organic matter is 15 g/kg~29 g/kg,and the CEC value ranged from 5.9/cmol/kg to 13.1 cmol/kg.The mass percentage of clay minerals which is <2 ?m in the soil is 15.9% ~ 48.9%,and the texture of the soil is sandy and sandy loam,and the free iron and amorphous iron content of 94.1 g Fe/kg~116 g Fe/kg,1.1 g Fe/kg~2.2 g Fe/kg,respectively.While the contents of free iron and amorphous iron in Liangqiao soil is 36.5 g Fe/kg~40.2 g Fe/Kg,2 g Fe/kg,respectively.The type of clay mineral of soil samples are similar,mainly kaolinite,water mica and 1.4 nm minerals,of which Tieshiling soil samples relative content are 41%~43%,33%~38% and 19% ~ 26%,respectively.The relative contents of three types of clay in Liangqiao soil samples were 34% ~ 35%,53% ~ 56% and 10% ~ 12% respectively.2.The prediction results of the Multi-surface model using default parameters are consistent with the actual measured values of free Zn,Cu and Cd in the soil solution,while the predicted value of free lead is different from the measured value.The mean deviation between the predicted value and the measured value is 0.12 log Mfor Zn,0.34 log M for Cu and 0.05 log M for Cd,respectively.The average deviation between the predicted value and the measured value is 0.81 log M for free Pb.The results of the Multi-surface model have been improved by optimizing the n,log KPb values in the NICA-Donnan model and considering the contribution of manganese oxide.The optimizing value of n has little effect on the predicted value of the free Pb concentration,and the predicted value of the model is only shifted by about 0.01 log M.And optimizing the log KPb value,the correction of the Liangqiao soil sample effect is more obvious.The predicted values of free Pb concentration of Liangqiao soil samples were shifted by 0.28~0.41 log M and 0.34~0.41 log M after optimizing log KPb1 and log KPb2.While the optimization of log KPb has little effect on the prediction of the Tieshiling soil.3.Considering the adsorption of Pb on manganese in the framework of the model,the model predicts further improvement of the free Pb,and the deviation between the predicted and measured values of the free Pb is in the range of 0.05 log M to 0.29 log M with an average deviation of 0.21 log M.The average deviation of Zn,copper and Cd was 0.18 log M,0.36 log M and 0.08 log M,respectively Considering the adsorption of Pb on manganese oxides in the framework of the model,the model predicts further improvement of the free Pb,and the deviation between the predicted and measured values of the free Pb is in the range of 0.05 to 0.29 log M with an average deviation of 0.21 log M.The average deviation of Zn,copper and Cd was 0.18 log M,0.36 log M and 0.08 log M,respectively.4.Multi-surface model can further predict the dissolved heavy metals in soil.The predicted range of the dissolved Zn,Pb,Cu and Cd was 0.14 log M ~0.36 log M,0.01 log M ~0.46 log M,0.07 log M~0.25 log M,0 log M~0.24 log M,the corresponding mean deviation was 0.28 log M,0.13 Log M,0.17 log M,0.09 log M.In the model,0.1% ~ 0.4% Zn,0.9%~4% Pb,4.7%~13.8%Cd,2.9%~4%Cu were complexed with dissolved organic matter.According to the model,0.1%~0.4% Zn,0.9%~4% Pb,4.7%~13.8% Cd and 2.9%~4% Cu were complexed with dissolved organic matter.5.The predicting results of Multi-surface model show that the soil organic matter and crystalline iron oxides in the soil play the important role for adsorping Zn,Cu and Cd,while the content of manganese oxide in soil has a great influence on the adsorption of Pb.The relative contribution of crystalline iron to Zn is more than 80%,followed by the contribution of organic matter to zinc adsorption of 0.4%~13.3%,the contribution of other adsorbate is smaller.Organic matter is the main adsorbent of copper(19%~47%)and the relative contribution of crystalline iron minerals(52%~81%).The adsorption of Cd on organic matter is also obvious(4.1%~71%)and the relative contribution of crystalline iron and clay minerals is 87%~40% and 35%~69%,respectively.The relative contribution of organic matter was higher(17%~89%)for Pb in the lower soil samples,while in the high p H value,the contribution of iron(14%~43%)more significant,manganese oxide for the contribution of Pb adsorption accounted for 3% to 80% 6.The sensitivity of different heavy metals to p H value is: Pb> Cu> Zn> Cd... |
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