摘要
硅–铁氧化物共沉淀复合体在天然土壤和沉积物中普遍存在,然而关于复合体中Si对铁氧化物还原活性的影响还缺乏系统研究。本研究在pH值为3.0和7.5条件下,采用还原性溶解动力学实验和活性连续体(reactivecontinuum)模型,研究了不同Si/Fe摩尔比的Si-水铁矿(Si-Fh)复合体被抗坏血酸(AA)还原的动力学行为,并用表观速率常数k'和表观反应级数γ表征复合体的本征还原活性以及活性的非均匀度(即Fe还原过程中活性的变化)。结果表明, Si-Fh复合体中的Fe和Si均表现出非一致性溶解特征,但随Si/Fe摩尔比增大,更多的Si与Fe八面体聚合物的顶角结合或Fe被捕获进入无定形SiO_(2)中,该特征随之减弱。Si-Fh复合体的初始溶解速率随Si/Fe摩尔比增大呈增大趋势,表明Si的共沉淀以及Si含量增加可提高复合体中Fe的还原活性。由于复合体的粒度、结晶度和反应位密度等随Si/Fe摩尔比增大而发生变化,Si-Fh复合体还原活性的非均匀度随Si/Fe摩尔比增大表现出复杂的特征。本研究结果可为土壤和沉积物中Si-Fe共沉淀复合体的化学还原和微生物还原活性以及还原动力学过程提供重要信息。
Si-coprecipitated Fe oxides are ubiquitous in soils and sediments.However,the effect of Si on the reductive reactivity of Si-bearing iron oxides has not been well understood.Herein,reductive dissolution experiments and a reactive continuum model were combined to study the reduction kinetic behavior of Si-coprecipitated ferrihydrite(Si-Fh)complexes with various Si/Fe molar ratios using ascorbic acid as reductant at pH 3.0 and 7.5.Then,the obtained apparent rate constant(k')and apparent reaction order(g)were used to characterize the intrinsic reactivity and its heterogeneity,i.e.,the variation in reactivity as the Fe reduction proceeds.The results show that the release of Si and Fe exhibits incongruent dissolution,and the feature becomes weak with increasing Si/Fe molar ratios due to increasing Si complexation at the corner sites of the Fe octahedral polymer or the trapping of significant Fe in the amorphous silica phase.As indicated by the k¢,the initial reduction rate of Si-Fh complexes trended to increase with increasing Si/Fe ratio,suggesting that Si coprecipitation and an increase in Si content could enhance the reductive reactivity of the complexes.The heterogeneity of the reductive reactivity of the Si/Fh complexes,as characterized by thegvalues shows complicated patterns with increasing Si/Fe ratio,which can be attributed to the changes in multiple properties,including particle size,crystallinity,and reaction site density.The results of the present study provide important information for better understanding the reactivity and kinetics of Si-bearing Fe oxides during chemical and microbial reduction in soils and sediments.
作者
刘敏
李铁
朱茂旭
LIU Min;LI Tie;ZHU Maoxu(Key Laboratory of Marine Chemistry Theory and Technology,Ministry of Education,College of Chemistry and Chemical Engineering,Ocean University of China,Qingdao 266100,Shandong,China)
出处
《地球化学》
CAS
CSCD
北大核心
2024年第5期734-744,共11页
Geochimica
基金
国家自然科学基金项目(42176041、41776085)资助。
关键词
水铁矿
共沉淀Si
还原溶解
活性连续体
ferrihydrite
coprecipitated Si
reductive dissolution
reactive continuum
