Coprecipitation of Pb and As in apatite and applications to environmental remediation

磷灰石族矿物(又称磷灰石)的晶体化学磷灰石)已被广泛研究。它们可以容纳许多取代基，包括阳离子、多阴离子和单阴离子。因此，它们在许多地球化学和环境过程中发挥着重要作用，如元素循环、营养物质的可获得性、污染物的迁移和归宿。磷灰石的形成作为一种污染物修复的手段，特别是对重金属铅、锌、镉、铜和镍的修复已被研究，并已被证明是有效的，因为它对这些金属的高亲和力和在地表条件下的低溶解度？S。因此，一旦在高度稳定的磷灰石结构中共沉淀，金属就不再容易分散或生物可用。然而，关于其他金属的封存和复合金属吸收的影响，仍有许多需要了解。一种具有巨大环境意义并具有通过磷灰石隔离修复的巨大潜力的金属是As。然而，关于砷在磷灰石中的共沉淀以及涉及这种金属的固溶体的性质的研究有限。此外，由于自然过程(如矿床的风化)和人类活动(如冶炼)，环境中经常同时存在铅和砷，而关于磷灰石中铅和砷同时共沉淀的工作更少，尽管存在天然的铅-砷磷灰石(假铅矿、斜铅矿)。这项建议的重点是：1)合成和阐明Ca-Pb-PO4-AsO4-OH-Cl体系中磷灰石族矿物的化学和物理性质，以评价其在As和Pb同时修复中的应用；2)测试Ca-PO4溶液通过磷灰石沉淀在受污染的沉积物中固定As和结合As和Pb的应用。PI将研究可能的固溶体程度、结晶反应的动力学、可能的形成途径、结构和晶体化学以及合成反应产物的热力学。他将在一家前冶炼厂进行一项特定地点的案例研究，当地沉积物受到砷和铅污染。还将对工程污染的沉积物进行调查，以帮助阐明在自然样品中发生的反应。这项研究的结果将极大地增加我们对一些最不了解的具有广泛地质意义的磷灰石族矿物的基础矿物学知识，例如研究矿床的岩石成因，以及砷和铅的一般地球化学循环。此外，这些结果可能导致这些矿物在环境修复中的有效应用。这项提议的更广泛影响是多方面的。这项工作具有广泛的环境影响(重金属的封存和稳定)，对社会具有极其重要的意义。这也可能带来一种更具成本效益的砷和铅的修复技术。拟议的研究将包括本科生和研究生的参与和教育。将通过在博物馆和业余协会的讲座以及在期刊上为不同的非专业受众出版出版物，促进公众的宣传和教育，特别是针对业余科学家和矿物爱好者群体。

The crystal chemistries of apatite group minerals (a.k.a. apatites) have been widely investigated. They can accommodate numerous substitutions, including cations, polyanions, and monoanions. Thus, they play a significant role in many geochemical and environmental processes such as elemental cycling, availability of nutrients, and contaminant transport and fate. Formation of apatites has been studied as a means for contaminant remediation, especially for heavy metals such as Pb, Zn, Cd, Cu, and Ni, through sequestration by sorption or coprecipitation, and has been shown to be effective due to its high affinity for these metals and its low solubility under earth?s surface conditions. Thus, once co-precipitated in the highly stable apatite structure metals are no longer easily dispersible or bioavailable. However, there is still a great deal to be learned about the sequestration of other metals and the effect of combined metal uptake. One metal of enormous environmental significance and with great potential to be remediated through apatite sequestration is As. However, there are a limited number of studies focused on coprecipitation of As in apatite and the properties of solid solutions involving this metal. Furthermore, Pb and As often occur together in the environment due to natural processes (e.g. weathering of ore deposits) and human activities (e.g. smelting), and even less work on the simultaneous coprecipitation of Pb and As in apatite exists, despite the fact that natural Pb-As apatites occur (mimetite, clinomimetite). This proposal focuses on I) synthesis and elucidation of the chemical and physical properties of apatite group minerals in the Ca-Pb-PO4-AsO4-OH-Cl system for evaluation of their application to simultaneous As and Pb remediation and II) testing the application of Ca-PO4 solutions for sequestration of As, and combined As and Pb, through apatite precipitation in contaminated sediments. PI will investigate the extent of possible solid solutions, the kinetics of crystallization reactions, the possible pathways of formation, the structure and crystal chemistry, and the thermodynamics of synthesis reaction products. He will conduct a site-specific case study at a former smelting facility with known As and Pb contamination of local sediments. Engineered contaminated sediments will also be investigated to help elucidate reactions taking place in the natural samples. The results of this study will greatly increase our knowledge of the fundamental mineralogy of some of the least understood apatite group minerals with wide geologic implications, for example the study of ore deposit petrogenesis, and the general geochemical cycling of As and Pb. Furthermore, the results may lead to the effective application of these minerals to environmental remediation. The broader impacts of this proposal are many. The work has broad environmental implications (heavy-metal sequestration and stabilization) that are of immense importance to society. It may also lead to a more cost effective remediation technology for As and Pb. The proposed research will include the participation and education of undergraduate and graduate students. Outreach and education of the general public, specifically targeting the amateur scientist and mineral enthusiast communities, will be facilitated through talks at museums and amateur societies, and publications in journals for a diverse non-professional audience.