Mechanisms of Mineral Dissolution: Time-Resolved Synchrotron X-ray Diffraction of Fe-and Mn-oxides with Dissolved Organic Ligands

矿物溶解机制：溶解有机配体的铁氧化物和锰氧化物的时间分辨同步加速器 X 射线衍射

• 批准号: 1147728
• 负责人: Peter Heaney
• 金额: $ 35.03万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-03-15 至 2016-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1147728&HistoricalAwards=false
• 关键词: Mechanisms; Mineral; Dissolution; Time; Resolved

Technical Description. This project will explore the dissolution of iron and manganese oxides by siderophores using real-time, in situ X-ray diffraction to determine mechanisms and rate laws for these important soil reactions. Our preliminary results reveal that the siderophore desferrioxamine-B (DFOB) at concentrations ranging from 0.1 to 10 mM will induce complete dissolution of the layered Mn oxide birnessite within hours. Moreover, Rietveld analysis of our time-resolved synchrotron XRD data have revealed that Mn(III) is selectively removed from the birnessite structure relative to Mn(IV). Removal of 20 mol% Mn(III) induces a critical instability in triclinic birnessite, and the structure collapses when vacancy concentrations increase beyond this value.These observations lead us to hypothesize that the mechanism by which siderophores dissolve minerals depends on the heterogeneity of metal valence state. In mixed-valence metal (hydr)oxides, siderophore-mediated dissolution occurs by a structural collapse after a critical 3-dimensional vacancy concentration is achieved. In contrast, homovalent metal (hydr)oxides dissolve by the more conventional mode of 2-dimensional surface depletion. We will test these ideas by applying TR-XRD techniques to DFOB-assisted dissolution of a variety of heterovalent oxides (e.g., magnetite [Fe3+ (Fe2+,3+)2O4], hausmannite [Mn3+(Mn2+,3+)2O4], riebeckite [Na2Fe2+3Fe3+2(Si8O22)(OH)2] and homovalent oxides (e.g., hematite [Fe3+2O3], goethite [Fe3+O(OH)]), in the presence and absence of light.Broader Impacts. Mineral dissolution mechanisms are foundational to a range of societally important issues, including soil fertility and the cycling of metals in the critical zone, contaminant transport, the sequestration of CO2, and the chemistry of Earth?s surface waters. Most prior studies of the rates by which minerals dissolve in aqueous solutions have monitored reaction progress through changes in fluid chemistry. Here we propose a novel and complementary strategy that correlates the chemical evolution of the fluid with structural changes in the reacting solid. By this approach, we can rigorously couple the chemical kinetics of the fluid with structural mineral transitions, greatly expanding our understanding of the underlying reaction mechanisms.The work described in this proposal will help reveal the factors that control the mechanisms and rates by which siderophores can extract insoluble metals to sustain healthy metabolic activity in soil and marine environments. Siderophores are low-weight, biogenic compounds that occur ubiquitously in micromolar concentrations in soil and marine waters, and they are produced by a wide variety of microbes, fungi, and grasses to gain a selective advantage in severely Fe-limited conditions. Siderophores can extract Fe(III) and Mn(III) from nearly insoluble Fe(III) and Mn(III,IV) oxides with extremely high specificity, transporting the cations to parent organisms to satisfy nutritive or redox metabolic needs. Insights gained from this work may lead to a better understanding of methods to increase metal bioavailability in iron-deficient agricultural regions, and they will improve our understanding of mineral weathering, a major means of atmospheric CO2 drawdown.

技术说明。 该项目将利用实时、原位X射线衍射来探索铁载体对铁和锰氧化物的溶解，以确定这些重要土壤反应的机制和速率规律。 我们的初步结果表明，铁载体desferrioxamine-B（DFOB）在浓度范围从0.1至10 mM将诱导完全溶解的层状锰氧化物水钠锰矿在数小时内。 此外，Rietveld分析我们的时间分辨同步XRD数据显示，Mn（III）被选择性地从水钠锰矿结构相对于Mn（IV）。 去除20摩尔%的Mn（III）诱导的临界不稳定性的三斜水钠锰矿，和结构崩溃时，空位浓度增加超过此value.These观察导致我们假设，铁载体溶解矿物的机制取决于金属价态的异质性。在混合价金属（氢）氧化物，铁载体介导的溶解发生后，达到临界三维空位浓度的结构崩溃。相比之下，同价金属（氢）氧化物溶解的二维表面耗尽的更传统的模式。 我们将通过将TR-XRD技术应用于DFOB辅助溶解各种杂价氧化物（例如，磁铁矿[Fe 3+（Fe 2+，3+）2 O 4]、黑锰矿[Mn 3+（Mn 2+，3+）2 O 4]、钠闪石[Na 2Fe 2 + 3Fe 3 +2（Si 8 O22）（OH）2]和同价氧化物（例如，赤铁矿[Fe 3 + 2 O3]、针铁矿[Fe 3 +O（OH）]）。更广泛的影响。矿物溶解机制是一系列社会重要问题的基础，包括土壤肥力和金属在临界区的循环，污染物的运输，二氧化碳的封存，和地球的化学？S的表面沃茨。 大多数先前的研究，矿物溶解在水溶液中的速度监测反应的进展，通过流体化学的变化。 在这里，我们提出了一种新的和互补的策略，相关的化学演变的流体中的反应固体的结构变化。 通过这种方法，我们可以严格耦合流体的化学动力学与结构矿物的转变，大大扩展了我们的理解的潜在的反应mechanism.The工作中描述的建议将有助于揭示的因素，控制的机制和速率，铁载体可以提取不溶性金属，以维持健康的代谢活动在土壤和海洋环境。铁载体是一种低分子量的生物源化合物，广泛存在于土壤和海洋沃茨中，由多种微生物、真菌和草类产生，在铁含量严重不足的条件下具有选择性优势。 铁载体可以从几乎不溶的Fe（III）和Mn（III，IV）氧化物中提取Fe（III）和Mn（III），具有极高的特异性，将阳离子运输到母体生物体以满足营养或氧化还原代谢需要。 从这项工作中获得的见解可能会导致更好地理解在缺铁农业地区提高金属生物利用度的方法，并将提高我们对矿物风化的理解，这是大气CO2下降的主要手段。