土壤化学英文.pptVIP

Soil processes and behaviour of metals金属的土壤过程与行为 Key soil properties 主要土壤属性 The soil reaction is the pre-eminent factor controlling the chemical behaviour of metals and many other important processes in the soil. 土壤反应是控制金属化学行为和其它重要的土壤过程决定因素。 The pH of a soil applies to the H+ ion concentration in the solution present in soil pores which is in dynamic equilibrium with the predominantly negatively charged surfaces of the soil particles. 土壤PH是指土壤孔隙溶液中的氢离子浓度，它与土壤颗粒以负电荷为主的表面达到动态平衡。 Hydrogen ions are strongly attracted to the surface negative charges, and they have the power to replace most other cations. 氢离子被吸附在表面负电荷,能够置换大多数阳离子. The diffuse layer close to a negatively charged surface has a higher concentration of H+ ions than the bulk soil solution. 接近负电荷层的扩散层具有比土壤溶液更高的氢离子浓度. When the soil solution is diluted, the diffuse layer expands, causing the pH of the bulk solution to increase. 当土壤溶液被稀释时,扩散层会扩大,导致土壤溶液的PH升高。 This has important implications for the measurement of soil pH in the laboratory. This normally involves mixing dry soil with 2-2.5 times its weight of water, shaking and then measuring the pH in the supernatant solution after 30 minutes. The pH value obtained is about 1 to 1.5 units higher than that of the soil solution near to the solid surfaces where the reactions take place. This dilution effect is usually overcome by measuring the pH in a suspension of soil in a solution of a neutral salt, such as CaCl2 or KCl. Normally, pH is measured in suspensions of soil with distilled water and with a dilute salt. It is usually assumed that the pH value given is for distilled water unless otherwise stated. Soil pH is affected by the changes in redox potential which occur in soils that become waterlogged periodically. Reducing conditions generally cause a pH increase, and oxidation brings about a decrease. Variations of up to 2 units can occur over a year in gley soils prone to waterlogging. Oxidation of pyrite (FeS2) in a soil parent materi