Influence Of Redox Change Of Structural Iron In Clay Minerals On Peservation And Degradation Of Organic Matters

Iron redox cycle is an important geochemistry process,which influences element cycle,energy flows and migration and transformation of organic matters.Clay minerals are common iron-bearing minerals in terrestrial environment.Previous studies have shown that clay minerals are closely associated with organic matters.Redox state of structural iron in clay minerals greatly influencestheir mineral structures,binding state with organic matter and organic matter transformation.The interaction between an model organic matter,12-aminododecanoic acid(ALA),and an iron-rich smectite nontronite was studied.We found that ALA could enter the interlayer region of nontronite through cation exchange,forming organo-clay mineral complexes.Afterwards we compare the different impact between biological and chemical driven iron redox cycle on the complexes.The results showed that at the beginning stage of bioreduction,microbes preferentially reduced Fe(III)from the edges of nontronite.They also preferred toreduce and dissolve small and poorly crystalline particles and release the associated ALA,resulting in a positive correlation between ALA release and iron reduction extent(<12%).The subsequent bioreduction(reduction extent ranged from 12~30%)and complete air re-oxidation showed no further effect on ALA release.These results suggest that released ALA was largely from the edges of clay and small and poorly crystalline NAu-2 particles.In contrast to bioreduction,chemical reduction did not exhibit any selectivity in reducingALA-NAu-2 particles,and a considerable amount of reductive dissolution was responsible fora large amount of ALA release.Because bacteria are the principal agent for mediating redox process in natural environments,our results demonstrated that the structural interlayer of smectite can serve as a potential shelter to protect organic matter from oxidation.On the other hand,we found that structural Fe(II)in various iron-bearing minerals can produce hydroxyl radicals(·OH)through oxygenation under circumneutral pH and dark condition.Due to the high oxidation state of ·OH,it can effectively degrade a newly-emerging contaminant,1,-4 dioxane.The amount of 1,4-dioxane degradation was positively correlated with the amount of ·OH and consumption of Fe(II).The major degradation product of 1,4-dioxane is formate.Different clay mineral types,initial Fe(II)concentration,and buffer composition all affected·OH production and 1,4-dioxane degradation efficiency.Nontronite,an iron-rich smectite,was a reusable and effective material for sustainableproduction of ·OH and 1,4-dioxane degradation,through regeneration of Fe(II)either biologically or chemically.The results proved that iron-bearing clay minerals can produce abundant ·OH under redox fluctuating environment,which can effectively degrade dissolved organic matters/organic pollutants such as 1,4-dioxane.Iron-bearing clay mineral can serve as an promising materials for in-situ environmental remediation.It also provide valuable enlightenment for organic matter transformation and migration in nature environment.