{"id":{"repo_id":"unsw","oai_identifier":"oai:unsworks.library.unsw.edu.au:1959.4/100500"},"canonical_url":"https://search.dev.ndltd.org/etd/unsw/oai:unsworks.library.unsw.edu.au:1959.4/100500","repository":{"repo_id":"unsw","name":"University of New South Wales","base_url":"https://unsworks.unsw.edu.au/oai/provider"},"display":{"title":"The Chemodenitrification of Nitrate by Green Rust and Mackinawite and its Geochemical Implications","abstract":"Soil minerals that can participate in the redox cycling of Fe(II)/Fe(III) have received a significant amount of attention over recent decades in terms of their capability to reduce contaminants. Although evidence has demonstrated that the biogeochemical coupling of Fe and N redox cycles has potentially important capabilities, the relevance of abiotic Fe and N redox transformations remain unclear. Therefore, in this thesis, aspects around abiotic nitrate (NO3-) reduction under environmentally relevant conditions has been undertaken to shed further insight into NO3- chemodenitrification driven by Fe(II)/Fe(III)-bearing minerals. The kinetics of NO3- chemodenitrification in Fe(II)/Fe(III) (oxy)(hydr)oxide heterogeneous systems were investigated at neutral pH (i.e. pH 6.5 to 7.5). Of the suite of minerals examined, NO3- chemodenitrification was only relevant in the presence of green rust (GR), a layered double hydroxide Fe(II)/Fe(III) mineral. High anion (SO42-/Cl-) concentrations could arrest chemodenitrification, most likely through competition for sorption, and hence electron transfer, sites. Stable N and O isotope studies indicated that 15ε and 18ε values produced from NO3- chemodenitrification, principally to ammonium (NH4+), by GR(SO42-) (37.9‰ and 14.4‰) and GR(Cl-) (12.9‰ and 4.5‰) were unique, suggesting the possibility of distinguishing between NO3- chemodenitrification induced by these two minerals as well as from microbial NO3- denitrification. Electron transfer from aqueous Fe(II) to structural Fe(III) in montmorillonite has recently been discovered to be a pathway to GR formation at circumneutral pH. In contrast to the observations described above, the kinetics of NO3- chemodenitrification by these GR minerals were found to be extremely slow. It was demonstrated that the reduction potentials induced by the GR minerals formed through this unique pathway (~ -110 to -210 mV) were much higher than those obtained for GR minerals prepared in the absence of montmorillonite (~ -300 mV). As such, the driving force for electron transfer was decreased to the point that GRs formed through this unique pathway will no longer provide a competitive process to microbial NO3- denitrification reactions. Although iron sulfides are known to facilitate NO3- chemodenitrification, there are still fundamental knowledge gaps on reaction mechanisms and stable N and O isotope dynamics. Here, studies were conducted to examine aspects around NO3- chemodenitrification by mackinawite (FeS). Although it was observed that NO3- chemodenitrification kinetics were faster at acid pH values, in disagreement with thermodynamics, this observation most likely resulted from the higher reactivity of a soluble reductant or possibly FeS oxidation products precipitating at higher pH values passivating redox-active surfaces. These oxidation products included greigite (Fe3S4), elemental sulfur (S0), thiosulfate (S2O32-) and sulfate (SO42-), suggesting that both Fe and S participated in the reduction of NO3-. In this case, the major reduced N species was N2(g), and not NH4+. No N and O stable isotope fractionation was observed for the first electron transfer step in the reduction of NO3- indicating that it is a reversible reaction and, as a result, this reaction will introduce variability to the kinetic isotope effects produced by other concurrent NO3- (chemo)denitrification reactions. Overall, this thesis has significantly advanced knowledge on NO3- chemodenitrification reactions, mechanisms and methods for distinguishing chemical and microbial denitrification pathways.","abstract_html":"Soil minerals that can participate in the redox cycling of Fe(II)/Fe(III) have received a significant amount of attention over recent decades in terms of their capability to reduce contaminants. Although evidence has demonstrated that the biogeochemical coupling of Fe and N redox cycles has potentially important capabilities, the relevance of abiotic Fe and N redox transformations remain unclear. Therefore, in this thesis, aspects around abiotic nitrate (NO3-) reduction under environmentally relevant conditions has been undertaken to shed further insight into NO3- chemodenitrification driven by Fe(II)/Fe(III)-bearing minerals. The kinetics of NO3- chemodenitrification in Fe(II)/Fe(III) (oxy)(hydr)oxide heterogeneous systems were investigated at neutral pH (i.e. pH 6.5 to 7.5). Of the suite of minerals examined, NO3- chemodenitrification was only relevant in the presence of green rust (GR), a layered double hydroxide Fe(II)/Fe(III) mineral. High anion (SO42-/Cl-) concentrations could arrest chemodenitrification, most likely through competition for sorption, and hence electron transfer, sites. Stable N and O isotope studies indicated that 15ε and 18ε values produced from NO3- chemodenitrification, principally to ammonium (NH4+), by GR(SO42-) (37.9‰ and 14.4‰) and GR(Cl-) (12.9‰ and 4.5‰) were unique, suggesting the possibility of distinguishing between NO3- chemodenitrification induced by these two minerals as well as from microbial NO3- denitrification. Electron transfer from aqueous Fe(II) to structural Fe(III) in montmorillonite has recently been discovered to be a pathway to GR formation at circumneutral pH. In contrast to the observations described above, the kinetics of NO3- chemodenitrification by these GR minerals were found to be extremely slow. It was demonstrated that the reduction potentials induced by the GR minerals formed through this unique pathway (~ -110 to -210 mV) were much higher than those obtained for GR minerals prepared in the absence of montmorillonite (~ -300 mV). As such, the driving force for electron transfer was decreased to the point that GRs formed through this unique pathway will no longer provide a competitive process to microbial NO3- denitrification reactions. Although iron sulfides are known to facilitate NO3- chemodenitrification, there are still fundamental knowledge gaps on reaction mechanisms and stable N and O isotope dynamics. Here, studies were conducted to examine aspects around NO3- chemodenitrification by mackinawite (FeS). Although it was observed that NO3- chemodenitrification kinetics were faster at acid pH values, in disagreement with thermodynamics, this observation most likely resulted from the higher reactivity of a soluble reductant or possibly FeS oxidation products precipitating at higher pH values passivating redox-active surfaces. These oxidation products included greigite (Fe3S4), elemental sulfur (S0), thiosulfate (S2O32-) and sulfate (SO42-), suggesting that both Fe and S participated in the reduction of NO3-. In this case, the major reduced N species was N2(g), and not NH4+. No N and O stable isotope fractionation was observed for the first electron transfer step in the reduction of NO3- indicating that it is a reversible reaction and, as a result, this reaction will introduce variability to the kinetic isotope effects produced by other concurrent NO3- (chemo)denitrification reactions. Overall, this thesis has significantly advanced knowledge on NO3- chemodenitrification reactions, mechanisms and methods for distinguishing chemical and microbial denitrification pathways.","abstract_has_math":false,"creators":["Wang, Xin"],"institution":"UNSW, Sydney","degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2022,"date_issued":"2022","date_published":"2022","updated_at":"2026-07-24T05:32:00Z","subjects":["Acid sulfate soils","Green Rust","Mackinawite","Montmorillonite","Chemodenitrification","Abiotic nitrate reduction to ammonium","Fe(II)-catalyzed ferrihydrite transformation","Stable N and O isotope fractionation of abiotic nitrate reduction to ammonium","Iron (oxy)(hydr)oxides","anzsrc-for: 41 ENVIRONMENTAL SCIENCES","anzsrc-for: 410503 Groundwater quality processes and contaminated land assessment","anzsrc-for: 370303 Isotope geochemistry","anzsrc-for: 3402 Inorganic chemistry"],"languages":["en"],"rights":["open access","CC BY 4.0","free_to_read"],"rights_urls":["https://purl.org/coar/access_right/c_abf2","https://creativecommons.org/licenses/by/4.0/"],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["https://doi.org/10.26190/unsworks/24207"],"render_values":[{"text":"https://doi.org/10.26190/unsworks/24207","href":"https://doi.org/10.26190/unsworks/24207","code":true}]}]},"links":{"outbound_url":"http://hdl.handle.net/1959.4/100500","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:creator","label":"Author","values":["Wang, Xin"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2022"]},{"key":"dc:publisher","label":"Institution","values":["UNSW, Sydney"]},{"key":"dc:type","label":"Dc Type","values":["doctoral thesis","http://purl.org/coar/resource_type/c_db06"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Acid sulfate soils","Green Rust","Mackinawite","Montmorillonite","Chemodenitrification","Abiotic nitrate reduction to ammonium","Fe(II)-catalyzed ferrihydrite transformation","Stable N and O isotope fractionation of abiotic nitrate reduction to ammonium","Iron (oxy)(hydr)oxides","anzsrc-for: 41 ENVIRONMENTAL SCIENCES","anzsrc-for: 410503 Groundwater quality processes and contaminated land assessment","anzsrc-for: 370303 Isotope geochemistry","anzsrc-for: 3402 Inorganic chemistry"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["open access","https://purl.org/coar/access_right/c_abf2","CC BY 4.0","https://creativecommons.org/licenses/by/4.0/","free_to_read"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["http://hdl.handle.net/1959.4/100500","https://unsworks.unsw.edu.au/bitstreams/f2fd3d20-9e40-4893-bade-779849c7595a/download","https://doi.org/10.26190/unsworks/24207"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Soil minerals that can participate in the redox cycling of Fe(II)/Fe(III) have received a significant amount of attention over recent decades in terms of their capability to reduce contaminants. Although evidence has demonstrated that the biogeochemical coupling of Fe and N redox cycles has potentially important capabilities, the relevance of abiotic Fe and N redox transformations remain unclear. Therefore, in this thesis, aspects around abiotic nitrate (NO3-) reduction under environmentally relevant conditions has been undertaken to shed further insight into NO3- chemodenitrification driven by Fe(II)/Fe(III)-bearing minerals. The kinetics of NO3- chemodenitrification in Fe(II)/Fe(III) (oxy)(hydr)oxide heterogeneous systems were investigated at neutral pH (i.e. pH 6.5 to 7.5). Of the suite of minerals examined, NO3- chemodenitrification was only relevant in the presence of green rust (GR), a layered double hydroxide Fe(II)/Fe(III) mineral. High anion (SO42-/Cl-) concentrations could arrest chemodenitrification, most likely through competition for sorption, and hence electron transfer, sites. Stable N and O isotope studies indicated that 15ε and 18ε values produced from NO3- chemodenitrification, principally to ammonium (NH4+), by GR(SO42-) (37.9‰ and 14.4‰) and GR(Cl-) (12.9‰ and 4.5‰) were unique, suggesting the possibility of distinguishing between NO3- chemodenitrification induced by these two minerals as well as from microbial NO3- denitrification. Electron transfer from aqueous Fe(II) to structural Fe(III) in montmorillonite has recently been discovered to be a pathway to GR formation at circumneutral pH. In contrast to the observations described above, the kinetics of NO3- chemodenitrification by these GR minerals were found to be extremely slow. It was demonstrated that the reduction potentials induced by the GR minerals formed through this unique pathway (~ -110 to -210 mV) were much higher than those obtained for GR minerals prepared in the absence of montmorillonite (~ -300 mV). As such, the driving force for electron transfer was decreased to the point that GRs formed through this unique pathway will no longer provide a competitive process to microbial NO3- denitrification reactions. Although iron sulfides are known to facilitate NO3- chemodenitrification, there are still fundamental knowledge gaps on reaction mechanisms and stable N and O isotope dynamics. Here, studies were conducted to examine aspects around NO3- chemodenitrification by mackinawite (FeS). Although it was observed that NO3- chemodenitrification kinetics were faster at acid pH values, in disagreement with thermodynamics, this observation most likely resulted from the higher reactivity of a soluble reductant or possibly FeS oxidation products precipitating at higher pH values passivating redox-active surfaces. These oxidation products included greigite (Fe3S4), elemental sulfur (S0), thiosulfate (S2O32-) and sulfate (SO42-), suggesting that both Fe and S participated in the reduction of NO3-. In this case, the major reduced N species was N2(g), and not NH4+. No N and O stable isotope fractionation was observed for the first electron transfer step in the reduction of NO3- indicating that it is a reversible reaction and, as a result, this reaction will introduce variability to the kinetic isotope effects produced by other concurrent NO3- (chemo)denitrification reactions. Overall, this thesis has significantly advanced knowledge on NO3- chemodenitrification reactions, mechanisms and methods for distinguishing chemical and microbial denitrification pathways."]},{"key":"dc:format","label":"Dc Format","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["The Chemodenitrification of Nitrate by Green Rust and Mackinawite and its Geochemical Implications"]}]}],"canonical_facts":{"dc:creator":["Wang, Xin"],"dc:date":["2022"],"dc:description":["Soil minerals that can participate in the redox cycling of Fe(II)/Fe(III) have received a significant amount of attention over recent decades in terms of their capability to reduce contaminants. Although evidence has demonstrated that the biogeochemical coupling of Fe and N redox cycles has potentially important capabilities, the relevance of abiotic Fe and N redox transformations remain unclear. Therefore, in this thesis, aspects around abiotic nitrate (NO3-) reduction under environmentally relevant conditions has been undertaken to shed further insight into NO3- chemodenitrification driven by Fe(II)/Fe(III)-bearing minerals. The kinetics of NO3- chemodenitrification in Fe(II)/Fe(III) (oxy)(hydr)oxide heterogeneous systems were investigated at neutral pH (i.e. pH 6.5 to 7.5). Of the suite of minerals examined, NO3- chemodenitrification was only relevant in the presence of green rust (GR), a layered double hydroxide Fe(II)/Fe(III) mineral. High anion (SO42-/Cl-) concentrations could arrest chemodenitrification, most likely through competition for sorption, and hence electron transfer, sites. Stable N and O isotope studies indicated that 15ε and 18ε values produced from NO3- chemodenitrification, principally to ammonium (NH4+), by GR(SO42-) (37.9‰ and 14.4‰) and GR(Cl-) (12.9‰ and 4.5‰) were unique, suggesting the possibility of distinguishing between NO3- chemodenitrification induced by these two minerals as well as from microbial NO3- denitrification. Electron transfer from aqueous Fe(II) to structural Fe(III) in montmorillonite has recently been discovered to be a pathway to GR formation at circumneutral pH. In contrast to the observations described above, the kinetics of NO3- chemodenitrification by these GR minerals were found to be extremely slow. It was demonstrated that the reduction potentials induced by the GR minerals formed through this unique pathway (~ -110 to -210 mV) were much higher than those obtained for GR minerals prepared in the absence of montmorillonite (~ -300 mV). As such, the driving force for electron transfer was decreased to the point that GRs formed through this unique pathway will no longer provide a competitive process to microbial NO3- denitrification reactions. Although iron sulfides are known to facilitate NO3- chemodenitrification, there are still fundamental knowledge gaps on reaction mechanisms and stable N and O isotope dynamics. Here, studies were conducted to examine aspects around NO3- chemodenitrification by mackinawite (FeS). Although it was observed that NO3- chemodenitrification kinetics were faster at acid pH values, in disagreement with thermodynamics, this observation most likely resulted from the higher reactivity of a soluble reductant or possibly FeS oxidation products precipitating at higher pH values passivating redox-active surfaces. These oxidation products included greigite (Fe3S4), elemental sulfur (S0), thiosulfate (S2O32-) and sulfate (SO42-), suggesting that both Fe and S participated in the reduction of NO3-. In this case, the major reduced N species was N2(g), and not NH4+. No N and O stable isotope fractionation was observed for the first electron transfer step in the reduction of NO3- indicating that it is a reversible reaction and, as a result, this reaction will introduce variability to the kinetic isotope effects produced by other concurrent NO3- (chemo)denitrification reactions. Overall, this thesis has significantly advanced knowledge on NO3- chemodenitrification reactions, mechanisms and methods for distinguishing chemical and microbial denitrification pathways."],"dc:format":["application/pdf"],"dc:identifier":["http://hdl.handle.net/1959.4/100500","https://unsworks.unsw.edu.au/bitstreams/f2fd3d20-9e40-4893-bade-779849c7595a/download","https://doi.org/10.26190/unsworks/24207"],"dc:language":["en"],"dc:publisher":["UNSW, Sydney"],"dc:rights":["open access","https://purl.org/coar/access_right/c_abf2","CC BY 4.0","https://creativecommons.org/licenses/by/4.0/","free_to_read"],"dc:subject":["Acid sulfate soils","Green Rust","Mackinawite","Montmorillonite","Chemodenitrification","Abiotic nitrate reduction to ammonium","Fe(II)-catalyzed ferrihydrite transformation","Stable N and O isotope fractionation of abiotic nitrate reduction to ammonium","Iron (oxy)(hydr)oxides","anzsrc-for: 41 ENVIRONMENTAL SCIENCES","anzsrc-for: 410503 Groundwater quality processes and contaminated land assessment","anzsrc-for: 370303 Isotope geochemistry","anzsrc-for: 3402 Inorganic chemistry"],"dc:title":["The Chemodenitrification of Nitrate by Green Rust and Mackinawite and its Geochemical Implications"],"dc:type":["doctoral thesis","http://purl.org/coar/resource_type/c_db06"]},"updated_at":"2026-07-24T05:32:00Z"}