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研究报告

摘要：重金属Cr在环境中存在Cr（Ⅵ）和Cr（Ⅲ）两种氧化态，Cr（Ⅲ）的稳定性强，是人体必需的微量元素，而Cr（Ⅵ）具有强氧化性和高迁移性，是公认的致癌物质.总Cr含量不能完全反映其环境毒性效应，进行Cr（Ⅲ/Ⅵ）的形态分离对评价其环境行为具有重要意义.本研究以天然白云石粉末（80~100目）为吸附分离材料，研究在pH=4~10的水体中Cr（Ⅲ）与Cr（Ⅵ）的吸附，发现其对Cr（Ⅲ）的吸附率在99%以上，而对Cr（Ⅵ）的吸附不到10%，可用于Cr（Ⅲ/Ⅵ）的分离.Cr（Ⅲ）在白云石上的吸附符合Freundlich模型，最大吸附容量为0.3 mg·g^-1.环境中主要共存物质如Mg²⁺、Ca²⁺和腐殖酸对白云石吸附Cr（Ⅲ）无明显的影响，而高浓度（>0.05 mol·L^-1）的CO₃^2-、醋酸和柠檬酸会降低白云石对Cr（Ⅲ）的吸附率.在环境水样（自来水、井水、河水、电镀废水和铬渣提取液）的Cr（Ⅲ/Ⅵ）分离实验中，Cr（Ⅲ）的回收率在80.7%~113.0%之间，Cr（Ⅵ）的回收率在103.4%~121.9%之间.结果表明，利用天然白云石分离Cr（Ⅵ）和Cr（Ⅲ）高效易行，该研究为现场的Cr形态分离提供了一种简便快捷的方法.

Abstract：Chromium exists as Cr(Ⅲ) and Cr(Ⅵ) in the environment. Cr(Ⅲ) is an essential trace element to human, whereas Cr(Ⅵ) is highly toxic. Total chromium concentration cannot be utilized to accurately evaluate its environmental toxicology. Therefore, separating Cr(Ⅲ/Ⅵ) is a foremost requirement in analyzing environmental samples. In the present work, dolomite in a size range of 80~100 mesh was used as sorbent to separate Cr(Ⅲ) and Cr(Ⅵ) in water. More than 99% of Cr(Ⅲ) but less than 10% of Cr(Ⅵ) were adsorbed by dolomite during pH 4~10. The Cr(Ⅲ) adsorption capacity of dolomite was 0.3 mg·g^-1 as determined by Freundlich isotherm. Common coexisting molecules such as Mg²⁺, Ca²⁺, and humic acid have no effect on the sorption of Cr(Ⅲ) on dolomite. However, high concentrations of CO₃^2- and acetic acid could moderately reduce Cr(Ⅲ) sorption, and citric acid could markedly decrease Cr(Ⅲ) sorption. The separation of Cr(Ⅲ/Ⅵ) was tested in five environmental matrices including tap water, well water, river water, electro plating wastewater and TCLP leachate. The recovery rates were 80.7%~113.0% for Cr(Ⅲ) and 103.4%~121.9% for Cr(Ⅵ). The results indicate that dolomite is an effective and convenient material for the field separation of Cr(Ⅲ) and Cr(Ⅵ).