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

该奖项由2009年《美国复苏和再投资法案》(公法111-5)资助。含金属矿石的开采和加工在位于加利福尼亚州南部的莫哈韦沙漠中北部的金、银和汞矿床上留下了受污染的矿山废物。除了在这些矿场开采的初级金属外，许多其他次要和潜在的有毒元素(如As、Cr、Pb、Sb)在这些矿石中天然富含并在采矿过程中释放，从而引入大量元素，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，矿山废物的风化和扩散会重新分配金属，并可能改变它们的化学形态(例如，通过氧化、溶解、吸附和二次矿化)，这可能进一步改变它们的潜在毒性。已知的一些研究系统地讨论了粒度对矿山废物中有毒金属的浓度、形态(化学组成)、分布和反应性的影响，尽管粒度分布是控制这些物质向周围地区运输的主导变量之一。我们假设，矿山废物中有毒金属的生物可获得性在很大程度上取决于与颗粒大小相关的特性，这些特性与浓度、形态和分布随颗粒大小的变化有关。因此，我们提出了一种系统的、综合的、多学科的方法来确定矿山废物的粒度与物化性质之间的关系，以便更好地预测采矿环境中有毒金属的分布和生物有效性。这种方法包括现场采样、按颗粒大小进行样品分离、选定粒度组分的化学和X射线光谱分析以及浸出提取试验，以评估选定粒度组分在水和模拟肺和胃液中的砷和汞的释放。智力优势：拟议的研究将揭示元素浓度、形态、相关性和生物可获得性随颗粒大小从2.783 mm到0.056 mm的函数而呈现的先前未表征的基本趋势。M.使用常规分析方法以及新的(微观)光谱技术来识别有毒金属(Loid)S(Loid)包括As和Hg的行为及其与不同粒度组分中其他元素的相对相关性，将产生与As和Hg作为原生矿石矿物、次生矿物、吸附相和/或矿物涂层存在的组合有关的新信息。由于形态形成被认为是评估污染样品中痕量金属的相对反应性和潜在毒性的关键组成部分，识别和量化颗粒大小对形态形成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有效性，对我们理解矿山废物的环境地球化学具有潜在的变革性贡献。广泛的影响：该项目涉及一个全面整合的研究和教育计划，通过为本科生创造独立研究和实地考察的机会，为本科生提供国家同步加速器研究设施的经验，并启动查普曼大学之间的合作伙伴关系，查普曼大学是一所主要是本科生的机构、政府机构和公立学校教育工作者。来自传统代表性不足群体的高中理科学生将被招募参加暑期研究实习，并通过海报演示和其他外联活动接触到拟议的研究，而学校教师将通过一个释放计划被带到查普曼，该计划为他们提供了解和参与新颖科学研究的机会。结果将传播给受矿场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.