结冰过程对溶解性有机质典型组分还原Cr(Ⅵ)的影响

研究了结冰过程对溶解性有机质(DOM)的4种典型组分草酸、 酒石酸、 苹果酸和柠檬酸还原Cr(Ⅵ)的影响. 结果表明, 在低浓度下Cr(Ⅵ)在水溶液中不能被4种有机酸所还原; 而在冰中, 不同的有机酸对Cr(Ⅵ)的去除均有促进作用, 且去除效果随着有机酸浓度的增大逐渐增强. 4种有机酸的作用效果强弱顺序为草酸>酒石酸>苹果酸>柠檬酸. 通过使用不同浓度的无机盐和无机酸可以改变冰表面上类似液体层的厚度来抑制Cr(Ⅵ)的还原, 作用效果与无机盐种类无关. 溶液的初始pH值和有机酸结构是影响Cr(Ⅵ)还原的重要因素. 实验条件下冷冻浓缩效应的富集倍数至少可达10³, 对冰中草酸去除Cr(Ⅵ)有明显的促进作用.

Influences of Freezing on the Reduction of Cr(Ⅵ) by Typical Components of Dissolved Organic Matter†

The influences of freezing on the reduction of Cr(Ⅵ) by four typical components of dissolved organic matter(DOM), namely oxalic acid, tartaric acid, malic acid and citric acid, were investigated. The results show that under the condition of a low concentration in the experiments, Cr(Ⅵ) in the aqueous solution cannot be reduced by those four organic acids. However, in the ice, the four organic acids all facilitate to remove Cr(Ⅵ). Moreover, the removing effects gradually strengthens with the increasing concentration of organic acids. And the effects of these four organic acids rank as oxalic acid>tartaric acid>malic acid>citric acid. The concentration of inorganic salts and inorganic acid can inhibit the reduction of Cr(Ⅵ) by changing the thickness of liquid-like layers in the ice surface, but the inhibiting effect is independent of the kinds of inorganic salts. It is the initial pH of the solution and the structure of the organic acid that greatly influence the reduction of Cr(Ⅵ). Upon the experiment condition, the concentration factor of the freeze-concentration effect can reach 10³ at least, which apparently facilitates the oxalic acid to remove Cr(Ⅵ) in the ice.