Soil Heavy Metal Adsorption Characteristic Under Different Types Of Forests Or Soil Main Component

Cu²⁺ adsorption of 24 soil samples gathered out of 4 soil layers (0～10,10～20,20～40,40～60cm) of 6 different types of forests in Anji, Zhejiang were determined to explore relationship of Cu²⁺ adsorption with organic matter content, CEC, pH and particle composition. A batch experiment was conducted to study the adsorption of copper, lead, cadmium and nickel by bentonite, humic acid and hydration manganese oxide in single component and binary systems. The result shows that:(1) In terms of Cu²⁺ adsorption the six types of forests are in the order of broadleaved deciduous forest＞shrubbery＞tea grove＞broadleaved evergreen forest＞bamboo grove＞pine forest. Cu²⁺ adsorption decreases with the depth of the profile.(2) Organic matter content and CEC are the two major factors affecting soil Cu²⁺ adsorption. Based on the findings, a model is established to illuminate the relationship of Cu²⁺ adsorption with organic matter content and CEC: Y (Cu²⁺ adsorption)=39.65+1.57X₁(organie matter)+3.65 X₂(CEC)(3) Adsorption capacity of copper and lead are higher than that for cadmium and nickel by bentonite. The order of adsorption capacity was as follows: Pb²⁺＞Cu²⁺＞Ni²⁺＞Cd²⁺. Adsorption of Pb²⁺ is decuple of Cd²⁺. The single ion equilibrium data were fitted to Langmuir, Freundlich and Temkin isotherms. Temkin isotherms is best for Pb²⁺, Cu²⁺, and Cd²⁺ and the best for Ni²⁺ is Freundlich isotherms.(4) Adsorption capacity of Cu²⁺ by humic acid was higher than Pb²⁺ and Cd²⁺. The order of adsorption capacity was as follows: Cu²⁺＞Pb²⁺＞Cd²⁺. Equilibrium data of Pb²⁺ and Cd²⁺ were fitted to Langmuir, Freundlich and Temkin isotherms, and Freundlich isotherm is the best. Langmuir isotherm is best for Cu²⁺, than Freundlich isotherm, but Temkin isotherm is not fitted very well.(5) The results of infrared spectrum show that humic acid and Pb²⁺ link mainly on phenolic hydroxyl group. Humic acid and Cd²⁺ link on carboxyl of aromatic ring. Humic acid and Cu⁺ link both on phenolic hydroxyl group and carboxyl of aromatic ring.(6) Adsorption capacity of Pb²⁺ byδ-MnO₂ is higher than non-crystal MnO₂. This is because the crystalline grain of isδ-MnO₂ smaller, crystallinity is weaker, specific surface is larger; contain more carboxyl and crystal water of unit cell. These characterstics ofδ-MnO₂ result in more absorption site than non-crystal MnO₂.(7) Adsorption capacity of Pb²⁺ is higher than that for Cu²⁺ and Cd²⁺ byδ-MnO₂. The order of adsorption capacity was as follows: Pb²⁺＞＞Cu²⁺≥Cd²⁺. The equilibrium data of Pb²⁺ is fitted to Langmuir, Freundlich and Temkin isotherms, and Temkin is the best. Freundlich isotherm is better than. Temkin for Cu²⁺, but Langmuir isotherm is not fitted very well. Langmuir isotherm for Cd²⁺ is best, but Freundlich and Temkin isotherms are not fitted very well.(8) The affects of pH to adsorption of metal ion by bentonite, humic acid andδ-MnO₂ are similar. The lower pH is not good for adsorption of metal ion. Along with the increasing of pH, both the adsorption capacity and adsorption rate increase.(9) The adsorption isotherms in binary-component systems showed that there were competition among copper, lead and cadmium byδ-MnO₂, humic acid and bentonite. Adsorption of one metal ion was depressed by the presence of other metal ion in the adsorption solution. Althoug the detail data of competition adsorption are different by virous sorbents, adsorption of Pb²⁺ is higher than other metal ion.(10) Unit adsorption capacity of different sorbents to the same metal ion is different. Adsorption capacity of metal ion byδ-MnO₂ is higher than humic acid and bentonite. This is becauseδ-MnO₂ absorbs metal ion not only by its surface but also by crystal interior site. The further mechanism will be studied later.(11) Equilibrium data for the binary adsorption of Pb²⁺ and Cu²⁺ by bentonite were analyzed by using Ideal-Adsorption-Solution (IAS) and Langmuir-Competitive-Adsorption models, but these equations weren't fitted to data for the mixed solutions. The Modified LCA model fits the binary adsorption equilibrium data satisfactorily and adequately. Finally, binary-component competitive adsorption of copper and lead was simulated by Modified LCA model in computer.