Hydroxyl radicals(·OH)produced by the oxidation of structure Fe(Ⅱ)in clay mineral at the aerobic-anaerobic interface of soil and sediment play an important role in the transformation of organic matter.The reduction degree of structure Fe(Ⅲ)in the clay mineral of soil and sediment varies with environmental conditions.However,the effect of the reduction degree of iron-containing clay minerals[Fe(Ⅱ)/Fe total]on the formation of·OH and the mineralization of organic matter during the oxidation process is still unclear.Taking iron-rich nontronite(NAu-2)as the representative clay ore,the oxidation mechanism of NAu-2 with different reduction degrees(Fe(Ⅱ)/Fe total:15%,22%,39%,and 56%)to produce·OH and the difference of this process to natural DOM transformation were studied.The results demonstrated that when the concentration of structural Fe(Ⅱ)in NAu-2 suspension was 2.2 mmol·L-1,the reduction degree increased from 15%to 56%,cumulative concentration of·OH increased from 13.6 to 27.1 μmol·L-1 after 120 min of oxidation,and the conversion efficiency of unit O2 to·OH increased from 3.3%to 5.9%.The results of Fourier transform infrared spectroscopy(FTIR),Nitrotetrazolium blue chloride(NBT)deactivation experiments,and 2,2'-dipyridyl(BPY)edge reaction site passivation proved that the chlorite with 15%reduction degree mainly existed in dioctahedral Fe(Ⅱ)[Al-Fe(Ⅱ)],and it activated O2 at the edge site to produce·OH.In addition to octahedral Fe(Ⅱ),highly active trioctahedral Fe(Ⅱ)[Fe(Ⅱ)-Fe(Ⅱ)-Fe(Ⅱ)]were present in chlorite with a reduction degree of 56%.Both the basal and marginal sites could activate O2 to produce·OH,and the reduction efficiency of O2 to form·OH at the basal site was higher.The CO2content formed by·OH mineralized dissolved organic matter(DOM)increased with the increase of NAu-2 reduction degree.Therefore,compared with the low reduction degree of NAu-2(15%),the high reduction degree of NAu-2(56%)has a highly active trioctahedral and can form·OH from the bottom site,which improves the efficiency of·OH formation and further promotes the mineralization of DOM.
关键词
绿脱石/结构二价铁/还原程度/羟自由基(·OH)/天然DOM转化
Key words
nontronite/structural Fe(Ⅱ)/reduction extent/hydroxyl radicals(·OH)/natural DOM transformation
维普
万方数据