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: 1226554
• 负责人: Donald Sparks
• 金额: $ 23.62万
• 依托单位: University of Delaware
• 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=1226554&HistoricalAwards=false
• 关键词: Collaborative; Research; role; layered; Fe; 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.

技术描述。在地球化学环境中铁的生物地球化学循环与碳，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金属的溶解度和形态。此处提出的研究重点是河岸土壤中的Fe和痕量金属循环，这些河岸土壤位于旱地栖息地和水生环境之间的界面上，并在养分和水生生态系统之间的养分和污染物的转移中起关键作用。我们观察到在淹没土壤共有的地球化学条件下，在水性Fe（II）与Al-氧化物和粘土矿物底物的反应过程中，层状Fe（II）-AL（III） - 氢氧化物矿物质的形成。我们假设这些先前未识别的Fe（II）阶段在河岸环境中Fe和Trace金属的生物地球化学循环中起着关键作用。这些二级矿物质很快形成（在模型系统中的时间范围内，在用湿地土壤进行的几天内进行的几天内），因此有望在Fe（III） - 氧化物还原性溶解期间释放出Fe（II）的主要水槽。此外，由于粒径小，分层结构和高铁（II）含量，这些Fe（II）矿物可能对氧化还原活性污染物（例如Cr（VI））具有高反应性，并且可以通过吸附和互动反应来控制ni（ii）和Zn（II）等二线金属的保留。我们假设Fe（II）-AL（III） - 氢氧化物相在Fe（II）与AL-BAIREARED底物的初始反应期间形成的是可稳态的过渡阶段，随着时间的流逝，它们会衰老成更结晶的Fe吸附产物，其反应性降低，对痕量金属（LOID）s。我们将研究这些新型Fe（II）阶段形成的热力学，动力学和机械方面，并在几秒钟到几年的时间内表征它们的结构和反应性。一套最先进的光谱技术，包括Q-XAS，Bulk Xas和Mossbauer分析，将用于解决这些问题。该项目将填补我们对减少和河岸环境中Fe骑自行车的了解的重大空白，并将提高我们对这些动态系统中污染物命运和运输的理解。BROADER的意义和重要性。地球地面的4-6％是间歇性地或永久淹没的。土壤洪水会导致土壤孔隙水的化学变化，主要由微生物活性驱动，因为土壤微生物被迫从使用氧气转向替代电子受体来呼吸有机碳。在微生物呼吸中使用Fe（III） - 氧化物矿物质会导致这些矿物质的还原性溶解，从而导致溶解的Fe（II）的高水性浓度堆积，并释放与Fe（III） - 氧化物矿物质相关的有毒金属（LOID）杂质。该研究探讨了Fe（II）和金属污染物在洪水期间释放到解决方案的命运。我们已经确定了一种先前未知的降水机制，该机制可能会重新释放Fe（II），并痕量金属回到固相。通过溶解的Fe（II）与含Al的土壤矿物质的反应激活降水过程，从而导致继发性Fe（II）-AL（III） - 羟基矿物质的沉淀。这些新的FE（II）阶段的沉淀在典型的洪水泛滥的条件下迅速而广泛地发生，因此很可能是管理这些系统中释放的Fe（II）命运的重要过程。 Fe（II）矿物质的形成可去除溶液中的有毒金属，并将金属掺入结构或吸附到新阶段的表面上。此处提出的研究将表征控制这些Fe（II）阶段在洪水泛滥的土壤中的形成和反应性的主要地球化学参数，并提供定量的热力学数据，允许预测其在自然系统中的发生。该项目的结果将填补我们对河岸系统中控制土壤和水质的地球化学过程的重大空白，其中包括像极地沼泽和芬斯，热带沼泽，沿海和淡水湿地，稻田和洪泛区土壤一样多样化的环境。这项工作对于评估以前的湿地的恢复（通过重新建立河岸条件）是一种管理洪水控制和恢复生物多样性的管理选择，这一点很重要，在该地点（重新）动员先前积累的污染物是一个问题。我们的工作还预计，对于涉及金属还原微生物种群的生物刺激以固定地下污染物的补救策略具有重要意义。