外源Cl-添加对不同母质土壤溶液Cd2+浓度的影响

土壤镉(Cd)的环境行为与其在土壤溶液中的存在形态以及陪伴离子有关,然而外源Cl~-与土壤溶液中Cd~(2+)的关系以及不同母质土壤对Cd~(2+)的环境行为的影响并没有明确的结论.选取2种水稻土(第四纪红色黏土母质发育的红黄泥、紫色砂页岩母质发育的紫泥田)为研究对象,添加离子态外源Cd~(2+)(0、1、2.5、5 mg·kg~(-1)),平衡老化后添加外源Cl~-(0、0.6、1.2 mg·kg~(-1)),在保持水分恒定的情况下进行模拟培养试验,研究外源Cl~-添加对土壤溶液Cd~(2+)浓度的影响.结果表明,随着外源Cd~(2+)的增加,土壤溶液Cd~(2+)的浓度提高,红黄泥土壤溶液Cd~(2+)的浓度显著高于紫泥田;添加Cl~-会使土壤溶液中Cd~(2+)浓度升高,且Cd~(2+)浓度与外源Cl~-呈显著正相关,红黄泥和紫泥田土壤溶液中Cd~(2+)的平均浓度比不添加Cl~-时Cd~(2+)的平均浓度分别增加了12.74%、51.49%;土壤对Cd~(2+)的吸附关系符合Freundlich等温吸附方程,紫泥田对Cd~(2+)的吸附量显著高于红黄泥,添加Cl~-对红黄泥Cd~(2+)的吸附影响很小,而对紫泥田的影响显著.Cl~-存在下,红黄泥和紫泥田的解吸率分别为12.50%～19.25%、14.76%～24.99%,外源Cl~-添加对Cd~(2+)解吸影响小.综合分析认为,Cl~-对不同土壤Cd~(2+)的吸附解吸行为影响有较大的差异.

Effects of exogenous Cl- on Cd2+ concentrations in soil solutions of different soil types

Environmental behaviors of cadmium (Cd) in soil are related to its chemical forms and the co-existed ions in soil solutions. However, there are no clear conclusions for the relationship between exogenous Cl^- and soil solution Cd²⁺ and for the effects of soils with various parent materials on the environmental behaviors of Cd²⁺. In this research, two kinds of paddy soils (reddish clayey soil developed from quaternary red clay parent materials and purple paddy soil developed from purple sandy shale parent materials) were selected as the research objects, the effects of exogenous Cl^- on Cd²⁺ concentrations in soil solutions were studied by simulated culture experiments. Different amounts of exogenous Cl^- (0, 0.6, 1.2 mg·kg^-1) were introduced to the cultural paddy soils with Cd²⁺ contents of 0, 1, 2.5, 5 mg·kg^-1 and with a constant water content. The results showed that Cd²⁺ concentrations in soil solutions were increased with increasing in amounts of exogenous Cl^-, and Cd²⁺ concentrations in reddish clayey soil solutions were significantly higher than those in purple paddy soil solutions. Exogenous Cl^- enhanced Cd²⁺ concentrations in soil solutions, and a significant positive correlation between exogenous Cl^- and solution Cd²⁺ was observed. Compared to the treatment with no exogenous Cl^- addition, Cd²⁺ concentrations increased averagely by 12.74% in reddish clayey soil solutions and 51.49% in purple paddy soil solutions, respectively. Cd²⁺ adsorption on these two soils accorded with the Freundlich isotherm adsorption equation, and the adsorption amount of Cd²⁺ on purple paddy soil was significantly higher than that on reddish clayey soil. It was clear that exogenous Cl^- had little effects on Cd²⁺ adsorption on reddish clayey soil, but had obvious effects on Cd²⁺ adsorption on purple paddy soil. In the presence of Cl^-, Cd²⁺ desorption rates were 12.50%~19.25% from reddish clayey soil and were 14.76%~24.99% from purple paddy soil, respectively, showing that exogenous Cl^- addition had only a little effects on Cd²⁺ desorption from the tested soils. In summary, the effects of exogenous Cl^- on the adsorption and desorption behaviors of Cd²⁺ in different soils were quite different.