纳米金在黄铁矿及掺杂黄铁矿表面吸附的实验研究

The mechanism of adsorption of nanoparticles as adsorbates on the surface of minerals may play a key role in developing basic theory of nanogeosciences and understanding relevant environmental problems and geological phenomena. Gold nanoparticles have been widely found in environmental media, pyrite and elements doped pyrite in many gold deposits. The adsorption of gold nanoparticles on the surface of minerals, especially on pyrite and elements doped pyrite, is essential to the migration, fate as well as associated ecological toxicity in the environment, and it may significantly contribute to the formation of gold deposits. However, to date, the adsorption mechanisms of gold nanoparticles on the surface of pyrite and elements doped pyrite have not been well understood due to the lack of targeted systematic experimental studies and the limits of research methods as well as analytic technique. The project is aimed to experimentally investigate the adsorption of gold nanoparticles on the surfaces of pyrite and elements doped pyrite on the basis of the theory and technology of nanogeochemistry, colloidal probe technique, and spectroscopic analysis. The effects of several possibly intertwining experimental variables (including temperature, pH, dissolved oxygen concentration, organic matter type and concentration, type and concentration of doped elements in pyrite, surface chemical properties of doped pyrite) on the adsorption behavior would also be systematically studied to reveal the microscopic mechanism of interactions. The microscopic theoretical model, which could be used to elucidate the adsorption mechanisms of gold nanoparticles on the surface of pyrite and elements doped pyrite, would be established based on the experimental results. The accomplishment of this project would facilitate the understanding of the microcosmic mechanism of formation, migration, fate, and exposure pathways of gold nanoparticles in environments as well as ore deposits, and provide reliable experimental data and theoretical basis for the environmental protection and resources exploration.

纳米颗粒在矿物表面的吸附对丰富和发展纳米地球科学基础理论以及理解相关环境问题和地质现象有重要意义。纳米金在环境介质及金矿中黄铁矿(尤其是含砷等杂质元素的黄铁矿)中已被大量发现，其在黄铁矿等矿物表面的吸附对其在环境中的迁移归趋及在矿床中的成因及赋存状态具有重要制约作用，但目前有针对性及系统性的实验研究工作还非常有限，掺杂元素对吸附的影响以及微观吸附机制也尚不清楚。本项目拟开展纳米金在黄铁矿及掺杂黄铁矿表面的吸附实验研究，并结合胶体探针等微区-原位观察及光谱分析等技术，系统考察温度、pH、有机质类型及浓度、黄铁矿中掺杂元素类型及含量、黄铁矿表面物理化学结构等对纳米金在黄铁矿及掺杂黄铁矿表面吸附的影响，阐明微观吸附机制并建立能解释宏观吸附规律的吸附模型。相关结果有助于从纳米及分子尺度理解地球环境中纳米金的迁移归趋及矿床中纳米金的成因及富集机制，同时为环境保护及能源与矿产资源勘探开发提供科学依据。

纳米金等纳米颗粒在地球系统中广泛存在并已被大量发现，其与硫化物矿物（特别是黄铁矿和含砷黄铁矿）的吸附作用等表界面反应过程被认为是控制纳米金在热液流体中迁移沉积以及在地表环境中迁移归趋的关键机制。本项目以实验合成黄铁矿和含砷黄铁矿为研究对象，系统地研究了纳米金在黄铁矿及含砷黄铁矿表面的吸附规律及机制，获得了一系列创新性结果，主要包括：.通过水热法合成了纯黄铁矿及含砷黄铁矿。发现了由于较高静电斥力的存在，纯黄铁矿不吸附纳米金；然而，即使含砷黄铁矿与纳米金之间有静电斥力，但含砷黄铁矿仍能吸附纳米金，表明砷的掺杂有利于纳米金的吸附富集。这主要归因于低表面电荷密度的含砷黄铁矿表面能与纳米金表面的配体间形成静电辅助氢键。溶液pH对纳米金的吸附过程具有决定性影响，由于静电斥力的显著增加，吸附速率随pH的升高而降低。当有机配体浓度从1 mM 增加到 7.5 mM，纳米金吸附速率先下降后升高，这主要受静电斥力、竞争表面吸附位点、pH缓冲作用以及离子强度改变等机制共同制约。增加离子强度导致纳米金与含砷黄铁矿间的静电斥力下降，进而促进了吸附。总体而言，范德华力、静电辅助氢键、静电斥力等作用力共同影响了纳米金在含砷黄铁矿表面的吸附。此外，我们还发现正电的铁/铝氧（氢氧）化物矿物（包括赤铁矿、针铁矿、磁铁矿、水铁矿、勃姆石、三水铝石）能快速吸附纳米塑料颗粒，而粘土矿物（包括蒙脱石、高岭石、伊利石等）不能吸附纳米塑料颗粒。在腐殖酸存在条件下，由于静电斥力、空间位阻以及竞争吸附效应的增加，所有矿物均不能吸附纳米塑料颗粒。以上研究结果为理解金属纳米颗粒以及塑料纳米颗粒在热液流体以及地表环境中的迁移、归趋等地球化学行为提供了新的视角和科学依据。

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