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。在加利福尼亚南部莫哈韦沙漠中北部的金矿、银矿和汞矿中，含金属矿石的开采和加工留下了被污染的矿渣。除了在这些地点开采的原生金属外，许多其他次要和潜在有毒元素（如砷、铬、铅、锑）在这些矿石中自然富集，并在开采过程中释放出来，引入了大量元素，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使金属重新分布，并可改变其化学形态（例如通过氧化、溶解、吸附和二次矿化），这可能进一步改变其潜在毒性。很少有已知的研究系统地讨论了颗粒大小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，尽管尺寸分布是控制这些物质向周围地区运输的控制变量之一。我们假设，矿山废弃物中有毒金属的生物可及性在很大程度上取决于与颗粒大小相关的浓度、形态和分布的变化。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料的粒度与物理和化学性质之间的关系，以便更好地预测有毒金属在采矿环境中的分布和生物利用度。该方法包括现场取样、按粒径分离样品、选定粒径组分的化学和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中的选定粒径组分中砷和汞的释放情况。智力优势：拟议的研究将揭示元素浓度，物种形成，相关性和生物可及性作为粒径范围从2.783毫米到0.056毫米的函数的先前未表征的基本趋势。利用传统的分析方法和新的（微）光谱技术来鉴定包括as和Hg在内的有毒金属（样金属）的行为以及它们与不同尺寸分数中其他元素的相对相关性，将产生关于as和Hg与它们作为原生矿物、次生矿物、吸附相和/或矿物涂层相容的关联的新信息。由于物种形成尤其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关键组成部分，确定和量化颗粒大小对物种形成的影响，并利用它们更好地预测自然系统中痕量金属的生物可利用性，这对我们了解矿山废物的环境地球化学具有潜在的变革性贡献。更广泛的影响：该项目通过为本科生提供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，并在查普曼大学，主要的本科机构，政府机构和公立学校教育工作者之间发起合作伙伴关系，涉及研究和教育的全面整合计划。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外展活动接触到拟议的研究，而学校教师将通过一个释放项目被带到查普曼，为他们提供学习和参与新科学研究的机会。研究结果将分发给受矿区影响的利益攸关方，也可能直接导致在重金属污染引起环境关注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.