First Principle Simulations and Thermodynamic Models of Aqueous Aluminum Chemistry for Geochemical and Environmental Applications

提出了在Al、Na、K、H、OH、Cl、SO4、SiO2、H2O体系中高温、高浓度下铝的分子和热力学分析的相关研究项目。该体系中的铝化学——酸/碱反应、单核和多核水解产物的形成、与二氧化硅和硫酸盐的相互作用、铝硅酸盐矿物的形成——控制着许多重要的地球化学和环境过程（例如，铝硅酸盐矿物形成的演变、酸雨对土壤形成的影响以及铝硅酸盐相互作用对铝对植物和动物群落的毒性的影响）。该研究计划的一个目标是开发一个适合该综合系统混合特性的热力学模型，该模型可以正确预测这些过程在高盐，Al和Si(OH)4浓度下的平衡化学反应。另一种方法是使用第一性原理分子模拟方法（ab-initio分子动力学，AIMD），这是无参数的，以及实验结构研究（NMR， EXAFS（关于Ga）等），以提供关于Al相互作用的分子化学的可靠信息，这些相互作用由于可用的实验数据有限而难以建模，以定义溶液形态。智力优势：将开展三个相关的研究项目，这将对自然水/矿物化学的解释做出重大贡献。(1)我们将构建一个热力学模型（模型#1），结合水溶液自由能的Pitzer表示，以准确预测Al， Na， K， H， OH, Cl, SO4, SiO2， H2O体系中溶剂和物种活性，物种分布和矿物溶解度作为pH对高溶液浓度和温度（T = 250℃）的函数。由于数据限制，该模型将只包括单核Al相互作用，适用于通常在天然流体中遇到的流体成分和低浓度Al和Si。我们将处理环境问题所需的广泛pH值（例如，酸性矿山排水，pH = -3）。硫酸盐对于分析低Ph环境是必不可少的，因为H2SO4是酸性水的常见成分。(2)专注于低pH值和高pH值溶液，其中数据可用于定义物种形成，我们将扩展模型#1来处理富硅水中的Al- si相互作用，这可能具有重要的环境后果（例如，土壤流体中Al浓度升高；保护水生物种免受铝毒性）。AIMD模拟将提供有关水相二氧化硅形态和Al-Si相互作用的分子水平信息，既有助于模型的发展，又提供了该系统化学的急需的分子水平解释。(3)在Al浓度较高的溶液中，羟基多离子（如Al13O4(OH)247+）占主导地位。这些物种已在土壤水体中被发现，可能比单核铝物种对植物和动物的毒性更大。AIMD模拟将提供在没有实验数据的地区多核铝形态形成的温度依赖性信息。利用这些结果和其他结构数据（例如，核磁共振，具有类似水解化学的金属的EXAFS研究）以及电位测量数据，我们将开发与模型1一致的Al羟基聚合物热力学模型。更广泛的影响：拟议的研究活动具有广泛的影响（例如，热液储层和相关流体的演化、土壤形成、铝生产、酸雨对土壤流体和自然水体中铝动员的影响、废物隔离场地的完整性、沸石形成、多离子分子设计以开发新的高性能材料）。UCSD的研究团队在热力学模型和AIMD模拟的开发和应用方面有着丰富的经验。我们将使用的模拟软件是由Weare和合作者Marat Valiev和Eric Bylaska（太平洋西北实验室，PNNL）开发的，是PNNL分发的NWChem软件包的一部分。合作者John Fulton （PNNL）正在计划EXAFS实验（在Ga3+系统上），这将提供新的高TP结构数据。根据大学政策，在计划中开发的热力学模型将在我们的网站（geotherm.ucsd.edu）上实施，模拟代码将纳入NWchem软件包。因此，我们的研究产品将可供其他研究人员广泛应用于地球化学，材料科学，环境化学和其他领域。该项目的研究生将分享热力学模型和模拟软件开发的各个方面，以及这些方法在地球化学和环境问题上的应用。

EAR-0545811Nancy MOLLERInterrelated research activities projects are proposed that analyze the chemistry of aluminum in the Al, Na, K, H, OH, Cl, SO4, SiO2, H2O system to high temperature and concentration at the molecular and thermodynamic level. Aluminum chemistry in this system - acid/base reactions, formation of mononuclear and polynuclear hydrolysis products, interactions with silica and sulfate, aluminosilicate mineral formation - controls many important geochemical and environmental processes (e.g., the evolution of aluminosilicate mineral formations, acid rain effects on soil formation and the effects of aluminum-silicate interactions on Al toxicity to plant and animal communities). One objective of this research program is to develop a thermodynamic model tailored to the mixing properties of this comprehensive system that can correctly predict the equilibrium chemistry of these processes to high salt, Al and Si(OH)4 concentration. Another, is to use first principles molecular simulation methods (ab-initio molecular dynamics, AIMD), which are parameter-free, and experimental structural studies (NMR, EXAFS (on Ga), etc.) to provide reliable information about the molecular chemistry of Al interactions that are difficult to model because of the limited experimental data available to define solution speciation.INTELLECTUAL MERIT: Three related research projects will be carried out that will significantly contribute to the interpretation of natural water/mineral chemistry. (1) We will construct a thermodynamic model (model #1), incorporating the Pitzer representation of the aqueous solution free energy, to accurately predict solvent and species activities, species distributions and mineral solubilities in the Al, Na, K, H, OH, Cl, SO4, SiO2, H2O system as a function of pH to high solution concentration and temperature (T = 250 degrees C). This model, which will include only mononuclear Al interactions due to data limitations, is applicable to the fluid compositions and low concentrations of Al and Si usually encountered in natural fluids. We will treat the wide range of pH values required for environmental problems (e.g., acid mine drainage water, pH = -3). Sulfate is essential for the analysis of low Ph environments because H2SO4 is a common component of acid waters. (2) Focusing on low and high pH solutions, where data are available to define speciation, we will expand model #1 to treat Al-Si interactions in silica rich waters, which can have important environmental consequences (e.g., elevated Al concentrations in soil fluids; protection of aquatic species against aluminum toxicity). AIMD simulation will provide molecular level information about aqueous silica speciation and Al-Si interactions, both contributing to the development of the model and providing a much needed molecular level interpretation of the chemistry of this system. (3) In solutions with higher Al concentrations, hydroxyl polyions (e.g. Al13O4(OH)247+) dominate. These species have been identified in soil waters and may be more toxic to plants and animals than mononuclear Al species. AIMD simulation will provide information about the temperature dependence of polynuclear Al speciation in regions where experimental data are not available. Using these results and other structural data (e.g., NMR, EXAFS studies of metals with similar hydrolysis chemistry) along with potentiometric data, we will develop a thermodynamic model for Al hydroxyl polymers that is consistent with model #1.BROADER IMPACTS: The proposed research activities have broad impacts (e.g., studies of the evolution of hydrothermal reservoirs and associated fluids, soil formation, aluminum production, acid rain effects on Al mobilization in soil fluids and natural waters, the integrity of waste isolation sites, zeolite formation, design of polyion molecules to develop new high performance materials). The UCSD research team has considerable experience in the development and application of thermodynamic models and AIMD simulations. The simulation software we will use has been developed by Weare and collaborators, Marat Valiev and Eric Bylaska, (Pacific Northwest Laboratories, PNNL) and is part of the NWChem software package distributed by PNNL. Collaborator John Fulton (PNNL) is planning EXAFS experiments (on the Ga3+ system) that will provide new high TP structural data. In accordance with University policy, thermodynamic models developed in the proposed program will be implemented on our web site (geotherm.ucsd.edu) and simulation codes will be incorporated in the NWchem software package. Therefore, our research products will be available for use by other researchers for a wide range of applications in geochemistry, materials science, environmental chemistry and other areas. The graduate students in this program will share in all aspects of thermodynamic model and simulation software development as well as the application of these methods to geochemical and environmental problems.