CAREER: Effects of particle size on physical and chemical properties of mine wastes

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。含金属矿石的开采和加工在位于加州南部的中北部莫哈韦沙漠的金、银和汞矿床中留下了受污染的矿山废物。除了在这些地点开采的原生金属外，许多其他微量和潜在有毒元素（如砷、铬、铅、锑）自然富集在这些矿石中，并在开采过程中释放出来，造成大量元素流动，对人类健康以及矿山周围的当地和区域环境构成威胁。此外，矿山废物的风化和分散会使金属重新分布，并改变其化学形态很少有已知的研究系统地讨论了颗粒大小对浓度、形态和二次矿化的影响，（化学组成）、分布和矿山废物中有毒金属的反应性，尽管事实上尺寸分布是控制这些材料向周围区域运输的控制变量之一。我们假设，矿山废料中的有毒金属的生物可及性在很大程度上取决于粒度相关的浓度，形态和分布的变化作为粒度的函数的属性。因此，我们提出了一个系统的，综合的，多学科的方法来确定粒度和矿山废物的物理和化学性质之间的关系，以更好地预测有毒金属在采矿环境中的分布和生物利用度。 这一方法结合了实地取样、按颗粒大小进行样品分离、对选定的颗粒级进行化学和X射线光谱分析以及浸出提取试验，以评估暴露于水和模拟肺液和胃液的选定颗粒级中砷和汞的释放情况。拟议中的研究将揭示元素浓度、物种形成、相关性、和作为粒径的函数的生物可利用性，粒径范围从2.783 mm下降到0.056& μ m。使用传统的分析方法，以及新的（微）光谱技术，以确定有毒金属（类）的行为，包括砷和汞和它们的相对相关性与其他元素在不同的尺寸级分，新的信息将产生关于协会的砷和汞兼容的存在，作为原生矿物，次生矿物，吸附相，和/或矿物涂层。由于形态分析被认为是评估受污染样品中痕量金属的相对反应性和潜在毒性的一个关键组成部分，因此确定和量化粒度对形态分析的影响，并利用它们更好地预测自然系统中痕量金属的生物利用度，对我们理解矿山废料的环境地球化学具有潜在的变革性贡献。该项目涉及研究和教育的一个完全整合的计划，通过产生独立的研究和实地考察的机会，本科生，提供在国家同步加速器研究设施的经验，并启动查普曼大学，主要是本科院校，政府机构和公立学校教育工作者之间的合作伙伴关系。来自传统上代表性不足的群体的高中理科学生将被招募参加暑期研究实习，并通过海报展示和其他推广活动接触拟议的研究，而学校教师将通过一个发布计划被带到查普曼，为他们提供了解和参与新颖科学研究的机会。研究结果将分发给受矿区影响的相关利益攸关方，并可能直接导致在重金属污染引起环境关切的地区制定补救战略。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).The mining and processing of metal-bearing ores has left a legacy of contaminated mine wastes across the gold, silver, and mercury deposits of the north-central Mojave Desert located in southern California. In addition to the primary metals being mined at these sites, a host of other minor and potentially toxic elements (e.g. As, Cr, Pb, Sb) is naturally enriched in these ores and released during the mining process, introducing significant fluxes of elements that pose threats to human health as well as the local and regional environments surrounding the mines. Furthermore, weathering and dispersal of mine wastes redistributes metals and can change their chemical forms (e.g. through oxidation, dissolution, sorption, and secondary mineralization), which may further alter their potential toxicity.Few known studies have systematically addressed the effects of particle size on the concentration, speciation (chemical makeup), distribution, and reactivity of toxic metals in mine wastes, despite the fact that size distribution is one of the governing variables controlling the transport of such materials to surrounding regions. We hypothesize that the bioaccessibility of toxic metals in mine waste materials is largely dependent on particle size-dependent properties related to changes in concentration, speciation and distribution as a function of particle size. We therefore propose a systematic, integrated, multidisciplinary approach to determine the relationships between particle size and the physical and chemical properties of mine waste materials in order to better predict the distribution and bioavailability of toxic metals in mining environments. This approach involves a combination of field sampling, sample separation by particle size, chemical and X-ray spectroscopic analysis of selected size fractions, and leach extraction tests to assess the release of As and Hg in selected size fractions exposed to water and simulated lung and gastric fluids.Intellectual Merit: The proposed research will reveal previously uncharacterized yet fundamental trends in elemental concentrations, speciation, correlations, and bioaccessibility as a function of particle size ranging from 2.783 mm down to 0.056 m. Using both conventional analytical methods as well as novel (micro)spectroscopic techniques to identify the behavior of toxic metal(loid)s including As and Hg and their relative correlations with other elements in different size fractions, new information will be generated regarding associations of As and Hg compatible with their presence as primary ore minerals, secondary minerals, sorbed phases, and/or mineral coatings. Since speciation in particular is recognized as a critical component of assessing the relative reactivity and potential toxicity of trace metals in contaminated samples, identifying and quantifying the effects of particle size on speciation and using them to better predict trace metal bioavailability in natural systems represents a potentially transformative contribution to our understanding of the environmental geochemistry of mine waste materials.Broader Impacts: This project involves a fully integrated plan of research and education by generating opportunities for independent research and fieldwork to undergraduate students, providing undergraduates with experience at national synchrotron research facilities, and initiating collaborative partnerships between Chapman University, a primarily undergraduate institution, governmental agencies, and public school educators. High school science students from traditionally underrepresented groups will be recruited for summer research internships and exposed to the proposed research through poster presentations and other outreach activities, while schoolteachers will be brought to Chapman through a release program that provides them with the opportunity to learn about and participate in novel scientific research. Results will be disseminated to relevant stakeholders impacted by the mine sites and may also lead directly to the development of remediation strategies in areas where heavy metal contamination is cause for environmental concern.