土壤腐殖质氧化还原电位及其相应电子转移能力分布

Distribution of soil humic acids redox potentials and corresponding electron transfer amounts

本实验以土壤提纯腐殖酸及国际标准腐殖酸(Pahokee Peat Humic Acid,PPHA)为研究对象,测定腐殖酸与3种不同氧化还原Eh的铁矿物(水铁矿(Ferrihydrite)Eh0'=0 m V,赤铁矿(Fe2O3)Eh0'=-287 m V,磁铁矿(Fe3O4)Eh0'=-314 m V及溶解性铁铁氰化钾Eh0'(Ferricyanide=+430 m V)的氧化还原反应,结合Eh-p H计的实验体系,分析腐殖质分子氧化还原官能团的分布规律.磁铁矿同时拥有二价和三价铁离子,具有与腐殖质发生氧化或者还原反应的条件.不同土壤腐殖酸与磁铁矿反应表现的还原/氧化能力不同,这是由于腐殖酸的不同Eh引起,在此基础上测量显示原态下腐殖酸Eh值大约为245 m V,H2还原后,Eh值降低至-620 m V,表明腐殖酸的氧化还原Eh是不同种类和数量的氧化还原官能团Eh叠加值.分析标准腐殖酸在不同氧化还原Eh下的氧化/还原能力显示原态下标准腐殖酸的氧化还原Eh分布比较均匀,还原态腐殖酸在Eh>0范围存在易于被氢气还原的官能团,具有显著的还原能力.

Humic substances （HS） can be reduced by microorganisms and oxidized by electron acceptors such as Fe（Ⅲ） due to their redox properties. They can stimulate the series reactions and therefore have effects on the fate of redox active compounds under different conditions. The extent of redox reaction depended on the difference of redox potentials between iron and HS. However, because of the complicated structures of HS and unknown information about their redox potentials, it is still not available to clearly estimate and measure their redox potentials and the corresponding electron transfer amounts of redox functional groups. In order to understand the distribution of redox functional groups based the values of redox potentials, extracted soil humic acids （HA） and Pahokee Peat Humic Acid （PPHA） were conducted to react with iron compounds with different redox potentials, e.g. ferrihydrite Eh^0＇（Ferrihydrite）=0 mV,hemitate Eh^0＇（Fe2O3） =-287 mV, magneitite Eh^0＇（Fe3O4） =-314 mV and dissolved ferricyanide Eh^0＇ （K3[Fe（CN）6]]）=＋430 mV. Measurements of Eh values by using Eh-pH meter showed that native and reduced HA had Eh of 245 mV and-620 mV, respectively, and that all of the HA studied had comparable Eh, suggesting that the measured Eh represent a combination of different redox potentials of various redox functional groups.