摘要
含铵(NH_(4)^(+))蒙脱石不仅存在于陆地土壤中,还广泛存在于蚀变洋壳、远洋和陆源沉积物中,是N的主要载体矿物,对地表N向地球深部的传输路径和效率具有重要影响。本文利用微区和粉晶X射线衍射(XRD)、漫反射傅里叶红外光谱(DRIFT)和元素分析等表征技术,研究了不同温度(25~700℃)和压力(常压和2.5 GPa)条件下含铵蒙脱石的物相及结构演化,以及N的赋存状态和N含量的变化特征。结果表明,在常压条件下,温度上升会导致蒙脱石层间距从1.20 nm(25℃)逐渐减小至0.96 nm(700℃)。同时,蒙脱石Al_(2)–OH(914 cm^(−1))和AlMg–OH(844 cm^(−1))振动峰强度在升温过程中逐渐减弱,表明蒙脱石结构羟基逐渐脱失;在500℃时,蒙脱石结构羟基完全脱失,并导致层间完全坍塌。在高压(2.5 GPa)条件下,温度上升会造成蒙脱石层间距从1.20 nm(25℃)逐渐减小至1.02 nm(700℃),但蒙脱石结构羟基在700℃时依然存在。在此过程中,蒙脱石膨胀性逐渐降低,表明蒙脱石逐渐向伊利石转变。在常压加热条件下,随着温度升高,含铵蒙脱石N含量从初始的1.52%减少到0.10%;而在高压条件下,温度升高对含铵蒙脱石的N含量影响极小,保持在约1.26%。这两者的差异可能与产物层间域结构的变化有关,即常压下温度升高会导致蒙脱石层间域逐渐坍塌,NH_(4)^(+)失去赋存空间,分解逃逸;而高压下温度升高并不破坏蒙脱石层间域,而是逐渐转变为伊利石,从而为NH_(4)^(+)提供储存空间。因此,高压条件下蒙脱石的层间域对NH_(4)^(+)具有高温保护效应,表明黏土矿物可将N元素向地球更深部输送。该发现为揭示地表N向地球深部运移机制提供了新思路。
Ammonium-bearing montmorillonite is not only found in terrestrial soils but also widely found in altered oceanic crust,pelagic and terrigenous sediments.It is the main nitrogen-hosting mineral and has an important influence on the transport path and efficiency of surface nitrogen to the deep earth.In this study,micro-and powder X-ray diffraction(XRD),diffuse reflectance Fourier transform infrared spectroscopy(DRIFT),and elemental analysis were used to investigate the mineral phase and structure evolution of ammonium-bearing montmorillonite,as well as the consequent variations in the occurrence state and nitrogen content under different temperatures(25–700℃)and pressures(atmospheric pressure and 2.5 GPa).The results show that the spacing between themontmorillonite layers gradually decreases from 1.20 nm(25℃)to 0.96 nm(700℃)under atmospheric pressure conditions.At the same time,the vibration intensities of Al_(2)-OH(914 cm^(−1))and AlMg-OH(844 cm^(−1))of montmorillonite gradually decreased during the heating process,indicating that the hydroxyl of the montmorillonite structure was gradually lost.At 500℃,the hydroxyl of the montmorillonite structure is completely lost,resulting in complete interlayer collapse.Under high pressure(2.5 GPa),the temperature increase causes the basal distance of montmorillonite to gradually decrease from 1.20(25℃)to 1.02 nm(700℃),however,thehydroxyl of montmorillonite structure still exists at 700℃.During this process,the expansion of montmorillonite gradually decreased,indicating that montmorillonite gradually transitioned to illite.Al is dissolved from the octahedral sheet of montmorillonite during phase transformation.A part of the dissolved Al replaced Si in the tetrahedral sheet of montmorillonite via isomorphous substitution,leading to the dissolution of Si and crystallization of quartz,and transformation of montmorillonite to illite.This procedure also increases the proportion of Mg in the octahedral sheet,forming a trioctahedral structure.Another part of the A
作者
曾庆进
陶奇
吉世超
谭伟
何宏平
ZENG Qingjin;TAO Qi;JI Shichao;TAN Wei;HE Hongping(CAS Key Laboratory of Mineralogy and Metallogeny/Guangdong Provincial Key Laboratory of Mineral Physics and Materials,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,Guangdong,China;CAS Center for Excellence in Deep Earth Science,Guangzhou 510640,Guangdong,China;University of Chinese Academy of Sciences,Beijing 100049,China)
出处
《地球化学》
CAS
CSCD
北大核心
2024年第1期132-141,共10页
Geochimica
基金
国家自然科学基金项目(41921003)资助。
关键词
含铵蒙脱石
伊利石
层间域
N循环
ammonium-bearing montmorillonite
illite
interlayer space
nitrogen cycling
