Collaborative Research: The role of layered Fe(II)-Al(III)-hydroxides in the biogeochemical cycling of iron and trace metals in riparian environments

合作研究：层状 Fe(II)-Al(III)-氢氧化物在河岸环境中铁和微量金属生物地球化学循环中的作用

• 批准号: 1226581
• 负责人: Evert Elzinga
• 金额: $ 26.1万
• 依托单位: Rutgers University Newark
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-09-01 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1226581&HistoricalAwards=false
• 关键词: Collaborative; Research; role; layered; Fe

Technical description.The biogeochemical cycling of iron in aqueous geochemical environments is intimately linked to the cycling of carbon, nitrogen, phosphorus and sulfur, and strongly impacts the solubility and speciation of trace metals and metalloids in these systems. The research proposed here focuses on coupled Fe and trace metal cycling in riparian soils, which are located at the interface between dryland habitats and aquatic environments and play a key role in the transfer of nutrients and contaminants between upland and aquatic ecosystems. We observe the formation of layered Fe(II)-Al(III)-hydroxide minerals during reaction of aqueous Fe(II) with Al-oxide and clay mineral substrates under geochemical conditions common to submerged soils. We hypothesize that these previously unrecognized Fe(II) phases play a critical role in the biogeochemical cycling of Fe and trace metals in riparian environments. These secondary minerals form fast (on a time scale of hours in model systems, and within several days in experiments performed with wetland soil) and are therefore expected to be a major sink for Fe(II) released during reductive dissolution of Fe(III)-oxides. In addition, owing to small particle size, layered structure, and high Fe(II) content, these Fe(II) minerals are likely to be highly reactive towards redox-active contaminants such as Cr(VI) and may control retention of divalent metals such as Ni(II) and Zn(II) through adsorption and coprecipitation reactions. We hypothesize that the Fe(II)-Al(III)-hydroxide phases formed during initial reaction of Fe(II) with Al-bearing substrates are metastable transitional phases which over time will age into more crystalline Fe sorption products with reduced reactivity towards trace metal(loid)s. We will study the thermodynamic, kinetic and mechanistic aspects involved in the formation of these novel Fe(II) phases, and to characterize their structure and reactivity over a time span ranging from seconds to years. A suite of state-of-the-art spectroscopic techniques, including Q-XAS, bulk XAS, and Mossbauer analyses, will be used to address these issues. This project will fill a major gap in our knowledge of Fe cycling in reducing and riparian environments, and will improve our understanding of contaminant fate and transport in these dynamic systems.Broader significance and importance.About 4-6% of the Earth's land surface is intermittently or permanently submerged. Soil flooding causes drastic changes in the chemistry of soil pore waters, driven mostly by microbial activity as soil microbes are forced to switch from using oxygen to alternative electron acceptors for respiration of organic carbon. Use of Fe(III)-oxide minerals in microbial respiration causes reductive dissolution of these minerals, which leads to the build-up of high aqueous concentrations of dissolved Fe(II) and release of toxic metal(loid) impurities associated with the Fe(III)-oxide minerals. The research addresses the fate of Fe(II) and metalloid pollutants released to solution during flooding. We have identified a previously unknown precipitation mechanism which may repartition released Fe(II) and trace metals back to the solid phase. The precipitation process is activated by reaction of dissolved Fe(II) with Al-bearing soil minerals causing precipitation of secondary Fe(II)-Al(III)-hydroxide minerals. Precipitation of these new Fe(II) phases occurs rapidly and extensively under conditions typical of flooded soils, and is therefore likely to be an important process governing the fate of released Fe(II) in these systems. Formation of the Fe(II) minerals removes toxic metals from solution as well as metals are incorporated into the structure or adsorb onto the surface of the new phases. The research proposed here will characterize the main geochemical parameters controlling the formation and reactivity of these Fe(II) phases in flooded soils, and provide quantitative thermodynamic data allowing for prediction of their occurrence in natural systems. The results of this project will fill a major gap in our understanding of the geochemical processes controlling soil and water quality in riparian systems, which includes environments as diverse as polar bogs and fens, tropical swamps, coastal and freshwater wetlands, paddy rice fields, and floodplain soils. The work is of importance in assessing the restoration of former wetlands (through re-establishment of riparian conditions) as a management option for floodwater control and restoration of biodiversity at sites where (re)mobilization of previously accumulated pollutants is a concern. Our work is also expected to be of major significance to remediation strategies involving biostimulation of metal-reducing microbial populations to immobilize subsurface contaminants.

技术说明.水地球化学环境中铁的地球化学循环与碳、氮、磷和硫的循环密切相关，并强烈影响这些系统中痕量金属和准金属的溶解度和形态。本文提出的研究重点是河岸土壤中铁和微量金属的耦合循环，河岸土壤位于旱地栖息地和水生环境之间的界面，在高地和水生生态系统之间营养物质和污染物的转移中发挥着关键作用。我们观察到形成层状Fe（II）-Al（III）-氢氧化物矿物的反应过程中的水溶液Fe（II）与Al-氧化物和粘土矿物基质的地球化学条件下常见的淹没土壤。我们推测，这些以前未被识别的Fe（II）相在河岸环境中的Fe和痕量金属的地球化学循环中发挥着至关重要的作用。这些次生矿物形成快（在模型系统中的时间尺度为几个小时，在湿地土壤进行的实验中为几天），因此预计将是Fe（III）氧化物还原溶解过程中释放的Fe（II）的主要汇。此外，由于小颗粒尺寸、层状结构和高Fe（II）含量，这些Fe（II）矿物可能对氧化还原活性污染物如Cr（VI）具有高反应性，并且可以通过吸附和共沉淀反应控制二价金属如Ni（II）和Zn（II）的保留。我们假设在Fe（II）与含Al基质的初始反应期间形成的Fe（II）-Al（III）-氢氧化物相是亚稳过渡相，其随着时间的推移将老化成更结晶的Fe吸附产物，其对痕量金属（类）的反应性降低。我们将研究这些新的Fe（II）相的形成所涉及的热力学，动力学和机械方面，并在几秒钟到几年的时间跨度内表征其结构和反应性。一套国家的最先进的光谱技术，包括Q-XAS，散装XAS和穆斯堡尔分析，将用于解决这些问题。该项目将填补我们在还原和河岸环境中铁循环知识的一个主要空白，并将提高我们对这些动态系统中污染物归宿和运输的理解。更广泛的意义和重要性。大约4-6%的地球陆地表面间歇性或永久性地被淹没。土壤淹水导致土壤孔隙沃茨的化学性质发生剧烈变化，这主要是由微生物活动驱动的，因为土壤微生物被迫从使用氧气转换为替代电子受体来呼吸有机碳。在微生物呼吸中使用Fe（III）-氧化物矿物导致这些矿物的还原溶解，这导致高水溶液浓度的溶解Fe（II）的积累和与Fe（III）-氧化物矿物相关的有毒金属（类）杂质的释放。这项研究解决了洪水期间释放到溶液中的Fe（II）和非金属污染物的命运。我们已经确定了一个以前未知的沉淀机制，可能重新分配释放的Fe（II）和痕量金属回到固相。通过溶解的Fe（II）与含Al土壤矿物的反应激活沉淀过程，从而导致次生Fe（II）-Al（III）-氢氧化物矿物的沉淀。这些新的Fe（II）相的沉淀发生迅速和广泛的条件下，典型的淹水土壤，因此可能是一个重要的过程，在这些系统中释放的Fe（II）的命运。Fe（II）矿物的形成从溶液中除去有毒金属，并且金属被并入结构中或吸附到新相的表面上。这里提出的研究将表征的主要地球化学参数控制这些Fe（II）相的形成和反应性在淹水的土壤，并提供定量的热力学数据，允许预测其发生在自然系统中。该项目的结果将填补我们对控制河岸系统土壤和水质的地球化学过程的理解中的一个主要空白，河岸系统包括极地沼泽和沼泽，热带沼泽，沿海和淡水湿地，稻田和洪泛平原土壤等多种环境。这项工作在评估恢复前湿地（通过重建河岸条件）作为洪水控制和恢复以前积累的污染物（重新）动员令人关切的地点的生物多样性的管理选择方面具有重要意义。我们的工作也预计将具有重大意义的修复策略，涉及生物刺激的金属还原微生物种群，以修复地下污染物。