Predicting The Partition Equilibrium And The Kinetic Reactions Of Heavy Metals In Soil Components

The increasing serious pollution of heavy metals in soil is accompanied by the rapid development of the economy,and the research on the environmental behavior of heavy metals in soil has been gradually focused on.The reactive components in soil can be classified as soil organic matter,metal oxides and clay minerals.These soil reactive components can have reactions with heavy metal elements,such as complexation and oxidization,and control their reactivity and bioavailability in soils.In this study,the environmental behavior of heavy metals in soil was investigated from the equilibrium partition and kinetic reaction two aspects.For the equilibrium partition of heavy metals,we specifically investigated how soil components and SOM binding sites control metal partition at various chemistry conditions in soil.We used the Windermere Humic Aqueous Model?WHAM?7 to predict the solid-solution partition and speciation of Cd,Cu,Ni,Pb,and Zn based on compiled literature data including98 soil samples from five continents.Based on the root-mean-square-error?RMSE?values of logarithm of dissolved metal concentrations between model predictions and experimental results,WHAM 7 reasonably predicted metal partition equilibrium over a wide range of reaction conditions,with RMSE less than 0.5 for Cd and Zn,and less than 1.0 for the other three metals.Soil organic matter dominated metal binding at most acidic to neutral pH,clay minerals were significant at low pH,and iron oxides might effectively compete with SOM for metal binding when pH was high.For the complexations between all five heavy metals and SOM,WHAM 7 predicted the bidentate bindings were the dominant form of metal complexes.The formation of monodentate complexes and electrostatic outer-sphere complexes was significant at low pH,while tridentate complexes were only significant at high pH values.The modeling results help to accurately predict the environmental behavior of heavy metals in pH3 to 7 soil environments.For the kinetic reactions between Sb and MnO₂,we developed a quantitative model for assessing the coupling between Sb???oxidation and Sb???/Sb???adsorption/desorption kinetics and the role of each individual reaction process in controlling the overall reaction rates.Antimony?Sb?pollution has become a severe environmental problem around Sb mining sites and has posed risks to human health.Understanding the kinetic reactions of antimony?Sb?at the MnO₂–water interface is essential for predicting the dynamic behavior of Sb in soil environments.Based on our modeling results,Sb???oxidation rates were very fast at the early stages of the reactions and may significantly slow down with time,and Sb???and Sb???showed different adsorption behavior ond-MnO₂.Our kinetics model provides a general modeling framework for predicting Sb kinetic behavior at the MnO₂–water interface.