Title: Hydrothermal atomic force microscopy observations of barite step growth rates as a function of the aqueous barium-to-sulfate ratio

Abstract

The rate of growth of ionic minerals from solutions with varying aqueous cation:anion ratios may result in significant errors in mineralization rates predicted by commonly-used affinity-based rate equations. To assess the potential influence of solute stoichiometry on barite growth, step velocities on the barite (001) surface have been measured at 108 °C using hydrothermal atomic force microscopy (HAFM) at moderate supersaturation and as a function of the aqueous barium:sulfate ratio (r). Barite growth hillocks at r ~ 1 were bounded by $$\langle$$120$$\rangle$$ steps, however at r < 1, kink site densities increased, steps followed a direction vicinal to $$\langle$$120$$\rangle$$, and the [010] steps developed. At r > 1, steps roughened and rounded as the kink site density increased. Step velocities peaked at r = 1 and decreased roughly symmetrically as a function of r, indicating the attachment rates of barium and sulfate ions are similar under these conditions. We hypothesize that the differences in our observations at high and low r arise from differences in the attachment rate constants for the obtuse and acute $$\langle$$120$$\rangle$$ steps. Based on results at low r, the data suggests the attachment rate constant for barium ions is similar for obtuse and acute steps. Based on results at high r, the data suggests the attachment rate constant for sulfate is greater for obtuse steps than acute steps. In conclusion, utilizing a step growth model developed by Stack and Grantham (2010) the experimental step velocities as a function of r were readily fit while attempts to fit the data using a model developed by Zhang and Nancollas (1998) were less successful.

Authors:

Bracco, Jacquelyn N. ^[1]; Gooijer, Yiscka ^[2]; Higgins, Steven R. ^[1]

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+ Show Author Affiliations

1. Wright State Univ., Dayton, OH (United States). Dept. of Chemistry
2. Wright State Univ., Dayton, OH (United States). Dept. of Chemistry; Hogeschool Utrecht, Utrecht (The Netherlands). Inst. for Life Sciences and Chemistry

Publication Date:

Sat Mar 19 00:00:00 EDT 2016

Research Org.:

Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1376308

Alternate Identifier(s):

OSTI ID: 1359156

Grant/Contract Number:  

AC05-00OR22725

Resource Type:

Accepted Manuscript

Journal Name:

Geochimica et Cosmochimica Acta

Additional Journal Information:

Journal Volume: 183; Journal Issue: C; Journal ID: ISSN 0016-7037

Publisher:

The Geochemical Society; The Meteoritical Society

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY