Development of gallium-aluminum ratios as a tracer of the Critical Zone behavior of Al

铝（Al）是常见原生和次生造岩矿物的主要成分，是主要土壤矿物和粘土的“骨干”。涉及铝的矿物转化是风化和土壤形成过程的基础。目前还不知道铝对生物体有什么有益作用，浓度升高时可能对水生生物有毒。铝可以抑制土壤中植物对养分的吸收，土壤中铝的高有效性已被证明会限制作物的生产力。铝在环境中的化学行为是复杂的，使其难以研究。地球化学家用来研究许多其他元素的行为的工具之一是使用自然发生的同位素的变化作为示踪剂，但铝只有一种同位素。相反，研究者建议开发镓（Ga）与铝的比例作为Al行为的示踪剂。Ga与ai具有相似的化学性质，并且表现出整体的一致行为。他可以使用Ga/Al比率来确定环境中Al的关键矿物来源和反应途径。此外，镓本身是一种具有关键技术应用的微量元素，用于蜂窝电话等普通消费产品的关键电子元件。因此，镓被美国能源部列为“战略金属”。例如，计划中的研究应该为将镓富集到铝土矿中可经济回收的水平的过程提供更多的见解。拟议的研究将与关键区天文台国家办公室（CZO-NO）一起工作，以创建与关键区科学相关的外展和教育材料。铝毒性和镓作为一种关键资源的应用方面为开发连接基础研究和社会影响的课程资源提供了极好的机会。研究者将与CZO-NO合作，为中学和本科科学课程开发课程资源，以支持下一代科学标准（NGSS, 2013）。他将继续通过工程和生物系促进与hbcu的联系，以展示关键地带科学的智力兴奋和社会影响。在hbcu建立联系对于建立地球科学多样性尤其重要，因为大多数hbcu没有地球科学系，因此没有传统的地球科学研究生项目管道。研究人员建议开发镓铝比（Ga/Al）作为关键带Al行为的有效地球化学示踪剂。总体目标是发展必要的基本理解，以支持使用Ga/Al作为关键区域及其他区域Al的质量平衡和示踪剂研究的有效工具；pseudo-isotope ?为了回答以下问题，他将重点研究控制关键带中Al分布并可能导致Ga/Al分馏的四个过程：1)风化过程中Ga/Al分馏是否由粘土矿物和氢氧化物的新形成引起？2) Ga和Al在临界区的分馏是由溶液化学（即水解或配体络合物的形成）驱动的吗？3)胶体中Ga和Al掺入量的差异是否导致了气流出口过程中Ga和Al的分离？他将结合实地研究和实验室研究，研究来自四个关键区域观测站（Calhoun、Boulder Creek、Catalina-Jemez和Luquillo）的花岗岩集水区的材料。他将分析岩石、土壤、植物和水样，以表征不同气候、风化和生物活动条件下Ga/Al比的行为。在地球化学模型的支持下，在实验室进行的矿物合成和土壤柱淋滤实验将了解Ga在氢氧化物中的分配以及有机配体对土壤中Ga和Al的影响。开发一种有效的环境中铝的示踪剂应该引起环境和地球科学界的广泛兴趣。铝在许多地球化学过程中起着核心作用，并与人类健康、水质和作物生产力等多个问题有关。作为一种战略金属，提高对镓地球化学的理解对社会也具有广泛的重要性。建议的工作将提供对矿物勘探界感兴趣的Ga地球化学的见解，特别是考虑到CZ过程是Ga铝土矿的主要经济来源的形成。

Aluminum (Al) is a major component of common primary and secondary rock-forming minerals, and forms the "backbone" of major soil minerals and clays. Mineral transformations involving aluminum are fundamental to weathering and soil formation processes. Aluminum is not known to perform any beneficial role in organisms, and can be toxic to aquatic life at elevated concentrations. Aluminum can inhibit plant uptake of nutrients in soils, and high Al availability in soils has been shown to limit crop productivity. The chemical behavior of aluminum in the environment is complex, making it difficult to investigate. One of the tools that geochemists have used to study the behavior of many other elements is to use variations in naturally occurring isotopes as tracers, but aluminum only has one isotope. Instead, the investigator proposes to develop the ratio of gallium (Ga) to aluminum as a tracer for Al behavior. Ga has similar chemistry to Al, and shows overall coherent behavior. He can use Ga/Al ratios to identify key mineral sources and reaction pathways for Al in the environment. Further, gallium itself is a trace element with critical technological applications, used in key electronic components in common consumer products such as cellular telephones. As such, gallium is classified as a "strategic metal" by the US Department of Energy. The planned research should provide additional insight into processes that can enrich Ga to levels that are economically recoverable in bauxite ores, for example. Proposed research will work in conjunction with the Critical Zone Observatories National Office (CZO-NO) to create outreach and educational materials related to Critical Zone science. The applied aspects of Al toxicity and Ga as a critical resource provide an excellent opportunity to develop curricular resources linking basic research and societal impacts. The investigator will work with the CZO-NO to develop curricular resources for secondary school and undergraduate science programs in support of Next Generation Science Standards (NGSS, 2013). He will continue fostering outreach to HBCUs via engineering and biology departments to demonstrate intellectual excitement and societal impacts of Critical Zone science. Building connections at HBCUs is especially important for building geoscience diversity since most do not have geoscience departments and thus do not have a traditional pipeline to Earth science graduate programs.The investigator proposes to develop gallium-aluminum ratios (Ga/Al) as an effective geochemical tracer for the behavior of Al in the Critical Zone. The overarching goal is to develop the necessary fundamental understanding to support the use of Ga/Al as an effective tool for mass balance and tracer studies of Al in the Critical Zone and beyond; a ?pseudo-isotope? for Al. He will focus on four of the processes that control the distribution of Al in the Critical Zone and may cause fractionation of Ga/Al in order to answer the following questions: 1) Is the neoformation of clay minerals and oxyhydroxides responsible for Ga/Al fractionation during weathering? 2) Is the fractionation of Ga and Al in the Critical Zone driven by solution chemistry (i.e. hydrolysis or ligand complex formation)? 3) Do differences in the incorporation of Ga and Al in colloids result in fractionation of Ga from Al during stream export? He will use a combination of field and laboratory-based studies on materials from granitoid catchments across four Critical Zone Observatories (Calhoun, Boulder Creek, Catalina-Jemez, and Luquillo). He will analyze rock, soil, plant, and water samples from each to characterize the behavior of Ga/Al ratio under different conditions of climate, weathering and biological activity. Mineral synthesis and soil column leaching experiments in the laboratory will provide understand partitioning of Ga in oxyhydroxides and the impact of organic ligands on Ga and Al in soils, supported by geochemical modeling. Development of an effective tracer for Al in the environment should be of broad interested to the environmental and geoscience community. Aluminum plays a central role in many geochemical processes and is associated with multiple issues in human health, water quality, and crop productivity. As a strategic metal, an improved understanding of gallium geochemistry is also of broad importance for society. The proposed work will provide insight into Ga geochemistry that will be of interest to the mineral exploration community, especially given that CZ processes are responsible for the formation of the main economic source of Ga, bauxites.