Effect of Mica and Hematite (001) Surfaces on the Precipitation of Calcite

Huifang Xu,H Teng,Mo Zhou,Yihang Fang

doi:10.3390/min8010017

Huifang Xu, H Teng + Show 2 more

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https://doi.org/10.3390/min8010017

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Abstract

The substrate effect of mica and hematite on the nucleation and crystallization of calcite was investigated using scanning electron microscope (SEM), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD) methods. On mica, we found, in the absence of Mg2+, the substrates’ (001) surfaces with hexagonal and pseudo-hexagonal two-dimensional (2-D) structure can affect the orientation of calcite nucleation with calcite (001) ~// mica (001) and calcite (010) ~// mica (010) to be the major interfacial relationship. On hematite, we did not observe frequent twinning relationship between adjacent calcite gains, but often saw preferentially nucleation of calcite at surface steps on hematite substrate. We suggest that calcite crystals initially nucleate from the Ca2+ layers adsorbed on the surfaces. The pseudo-hexagonal symmetry on mica (001) surface also leads to the observed calcite (001) twinning. A second and less common orientation between calcite {104} and mica (001) was detected but could be due to local structure damage of the mica surface. Results in the presence of Mg2+ show that the substrate surfaces can weaken Mg toxicity to calcite nucleation and lead to a higher level of Mg incorporation into calcite lattice.

Highlights

The most recent (2013) Intergovernmental Panel on Climate Change (IPCC) report cogently concluded that increased anthropogenic greenhouse gas emissions (CO2 being the leading component) are the extremely likely cause for the observed warming since 1950s when atmospheric pCO2 increased from ~300 ppm [1] to today’s level around 390 ppm [2,3], resulting in globe-wide changes, such as diminishing of polar ice and sea level rise [4]
Based on cross-section (Figure 2c) and high-angle tilted scanning electron microscope (SEM) images (Figure 2a), we found the interface between epitaxial calcite and biotite substrate appears to be triangular and has a comparatively large area
Our results indicate that substrate effect may alleviate the Mg inhibition on calcite crystallization as (1) calcite did not cease to precipitate until the ratio of Mg/Ca reached above 5; and (2) the Mg incorporation in calcite was higher than the reported values for Mg-bearing calcite grown in systems without substrates

Summary

Introduction

The most recent (2013) Intergovernmental Panel on Climate Change (IPCC) report cogently concluded that increased anthropogenic greenhouse gas emissions (CO2 being the leading component) are the extremely likely cause for the observed warming since 1950s when atmospheric pCO2 increased from ~300 ppm [1] to today’s level around 390 ppm [2,3], resulting in globe-wide changes, such as diminishing of polar ice and sea level rise [4]. Given the unlikely occurrence for alternative energy to replace fossil fuels in the immediate future, this conclusion reinforces the consensus that a carbon sequestration strategy needs to be implemented to curtail future CO2 rise. Geological sequestration, among all other possible choices, stand out to be the most widely advocated. By forming carbonate minerals, this approach contains CO2 in environmentally benign and stable forms for a geologically significant time-frame [5,6,7]. While there is a plethora of literature work concerning carbonates crystallization on carbonate seeds or on structured organic surfaces [8,9,10,11,12,13], only a few studies have dealt with the effect of non-carbonate minerals on carbonate nucleation and crystallization [14,15]

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