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环境化学  2015 

有机酸溶解砖红壤过程中Mn(Ⅱ)的释放规律

Keywords: 砖红壤,有机酸,Mn(Ⅱ)释放

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Abstract:

研究土壤Mn(Ⅱ)释放规律对揭示锰氧化物的形成机制和了解酸性土壤锰毒效应大小具有重要意义.结果表明,柠檬酸溶解砖红壤过程中,Mn(Ⅱ)的释放速率在前4h比较迅速,其释放数量可达24h反应时间内总释放量的59.5%,但随后释放速率逐渐减缓.快速阶段被认为是土壤表面交换态Mn(Ⅱ)的释放,而慢速阶段则与土壤锰氧化物的缓慢溶解密切相关.低pH条件有利于Mn(Ⅱ)释放,其释放机制包含柠檬酸对土壤锰氧化物的还原-溶解.Al(Ⅲ)对Mn(Ⅱ)的释放有抑制作用,而Fe(Ⅲ)则有促进作用.有机酸的解离性质及官能团活性对Mn(Ⅱ)的释放有重要影响.在所研究的pH范围内,Mn(Ⅱ)释放数量按柠檬酸>丙酮酸>酒石酸>苹果酸≈乳酸的顺序下降.此外,就草酸和柠檬酸比较而言,当pH值小于4.25,草酸体系中Mn(Ⅱ)释放数量大于后者,但随着pH升高,则表现出相反的规律.

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