Abstract
We report here on structure-related aggregation effects of short-range ordered aluminosilicates (SROAS) that have to be considered in the development of synthesis protocols and may be relevant for the properties of SROAS in the environment. We synthesized SROAS of variable composition by neutralizing aqueous aluminium chloride with sodium orthosilicate at ambient temperature and pressure. We determined elemental composition, visualized morphology by microscopic techniques, and resolved mineral structure by solid-state 29Si and 27Al nuclear magnetic resonance and Fourier-transform infrared spectroscopy. Nitrogen sorption revealed substantial surface loss of Al-rich SROAS that resembled proto-imogolite formed in soils and sediments due to aggregation upon freezing. The effect was less pronounced in Si-rich SROAS, indicating a structure-dependent effect on spatial arrangement of mass at the submicron scale. Cryomilling efficiently fractured aggregates but did not change the magnitude of specific surface area. Since accessibility of surface functional groups is a prerequisite for sequestration of substances, elucidating physical and chemical processes of aggregation as a function of composition and crystallinity may improve our understanding of the reactivity of SROAS in the environment.
Highlights
We report here on structure-related aggregation effects of short-range ordered aluminosilicates (SROAS) that have to be considered in the development of synthesis protocols and may be relevant for the properties of SROAS in the environment
We report here on the structure of synthesized SROAS, studied by X-ray diffractometry (XRD), Fourier-transform infrared (FTIR) and solid-state 27Al and 29Si nuclear magnetic resonance (NMR) spectroscopy, and its consequences on specific surface area (SSA) of dry solids because we consider them relevant for future syntheses and possibly the behaviour of similar minerals in soils and sediments
Our results demonstrate that nanoscale compaction of synthetic SROAS cannot be reversed by cryomilling as it does not change the magnitude of SSA, limiting the feasibility of a top-down approach to mineral synthesis
Summary
We report here on structure-related aggregation effects of short-range ordered aluminosilicates (SROAS) that have to be considered in the development of synthesis protocols and may be relevant for the properties of SROAS in the environment. Sufficient release of aluminium (Al) and silicon (Si) by weathering of siliceous parent material facilitates precipitation of hydrous, short-range ordered aluminosilicates (SROAS) Accumulation of these phases results in coatings and alteromorphs in volcanic r ocks[1,2], clay-sized particles in andic s oils[3,4,5] or stream deposits from waters passing through extrusive rocks[6,7]. We report here on the structure of synthesized SROAS, studied by X-ray diffractometry (XRD), Fourier-transform infrared (FTIR) and solid-state 27Al and 29Si NMR spectroscopy, and its consequences on specific surface area (SSA) of dry solids because we consider them relevant for future syntheses and possibly the behaviour of similar minerals in soils and sediments. We describe the effects of cryomilling on the physical and structural properties of SROAS
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