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Calcite interaction with acidic sulphate solutions; a vertical scanning interferometry and energy-dispersive XRF study

Radostina Atanassova, Jordi Cama, Josep M. Soler, Francesco G. Offeddu, Ignasi Queralt and Ignasi Casanova
Calcite interaction with acidic sulphate solutions; a vertical scanning interferometry and energy-dispersive XRF study
European Journal of Mineralogy (September 2013) 25 (3): 331-351

Abstract

Calcite dissolution on (1014) cleavage surface was investigated by means of ex situ vertical scanning interferometry (VSI) measurements using flow-through and batch experiments at ambient pCO (sub 2) , pH 1-7 and room temperature in metal (Fe(II), Zn, Cu and Cd) and metal-free chloride solutions, and metal sulphate and metal-free sulphate solutions, undersaturated with respect to calcite and undersaturated or in equilibrium with respect to gypsum. Based on the VSI measurements, surface retreat was quantified at different pH and Delta G (sub r) < -8.1 kcal mol (super -1) , yielding intrinsic dissolution rate constants of calcite. These rates were used to derive an empirical rate law that takes into account the pH effect on calcite dissolution at room temperature and far from equilibrium with respect to calcite and is expressed as Rate (sub calcaite) (mol.cm (super -2) .8 (super -1) =3.3+ or -1.8X10 (super -6) .(a (sub H+) ) (super 0.94+0.08) +k (sub 2) where a (sub H+) is the proton activity and k (sub 2) equals 2.5 + or - 0.8 X 10 (super -11) mol cm (super -2) s (super -1) . The rhombic etch pit morphology changes at very low pH (pH < 3) due to the catalytic effect of pH on calcite dissolution, yielding rounded pseudo-rhombic etch pits. The presence of Fe(II), Cu, Zn and Cd inhibits calcite dissolution at pH 3, in contrast to the presence of sulphate, which does not affect calcite dissolution. The presence of Zn affected the etch pit morphology, yielding triangular etch pits. Under gypsum saturation conditions, gypsum (or other metal-bearing sulphate phases) precipitated on calcite as calcite dissolved, yielding a decrease in dissolution rate with time due to loss of calcite reactivity. Based on energy-dispersive X-ray fluorescence (EDXRF) measurements the precipitation rates of Zn (sub 4) SO (sub 4) (OH) (sub 6) . 5H (sub 2) O and Cu (sub 4) SO (sub 4) (OH) (sub 6) . 2H (sub 2) O were calculated to be between 1 X 10 (super -7) and 6 X 10 (super -7) mol m (super -2) s (super -1) .


ISSN: 0935-1221
EISSN: 1617-4011
Serial Title: European Journal of Mineralogy
Serial Volume: 25
Serial Issue: 3
Title: Calcite interaction with acidic sulphate solutions; a vertical scanning interferometry and energy-dispersive XRF study
Affiliation: Bulgarian Academy of Sciences, Geological Institute, Sofia, Bulgaria
Pages: 331-351
Published: 201309
Text Language: English
Publisher: Schweizerbart'sche Verlagsbuchhandlung (Naegele u. Obermiller), Stuttgart, Germany
References: 72
Accession Number: 2013-083987
Categories: General geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables
Secondary Affiliation: Institute of Environmental Assessment and Water Research, ESP, SpainInstitute of Earth Sciences "Jaume Almera", ESP, SpainUniversitat Politecnica de Catalunya, ESP, Spain
Country of Publication: Germany
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Schweizerbart'sche Verlagsbuchhandlung. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201349
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