土壤中铬的形态及其转化

Forms and Transformation of Chromium Species in Soils.

通过土壤中不同结合态铬的逐级提取方法的研究，提出了以１ｍｏｌ／ＬＮＨ４Ａｃ、２ｍｏｌ／ＬＨＣｌ和５％Ｈ２Ｏ２－２ｍｏｌ／ＬＨＣｌ提取的铬分别为交换态铬、沉淀态铬和有机结合态铬。自然土壤中铬主要以沉淀态铬和残渣态铬形式存在。还原条件下，土壤中铬有向有机结合态铬转化的趋势。降低土壤ｐＨ，水溶态和代换态铬含量增加，沉淀态和残渣态铬含量降低，添加Ｃｒ（Ⅲ）能使土壤本身ｐＨ值下降，添加Ｃｒ（Ⅵ）使土壤ｐＨ值有所上升。

By developing a method for the fractional extractionof chromium species in various binding states in soil, it was found that the extractants of 1 mol/L NH4Ac,2 mol/L HCl and 5% H2O2--2mol/L HCl in use for a sequential extraction of chromium species from soil can give the exchangeable Cr species,precipitated Cr species, and organics-- bound Cr species ) respectively. The results show that in the natural soil the Cr spotes ace present dominantly in a precipitated or residual state. Under the reducing conditions,the Cr species in soil tend to be transformed into those in an organics--bound state.As the soil PH value was lowered,the levels of water soluble Cr species and exchangeable Cr species raised while the levels of Cr species in precipitated or residual state being reduced. The soil PH value can be lowered by adding Cr(Ⅲ) species and raised by adding Cr(Ⅵ)species.