Magnesium inhibition of calcite dissolution kinetics

Journal Article · Wed Feb 01 00:00:00 EST 2006 · Geochimica et Cosmochimica Acta

DOI:https://doi.org/10.1016/j.gca.2005.10.005· OSTI ID:878670

Arvidson, Rolf S; Collier, Martin; Davis, Kevin J; Vinson, Michael D; Amonette, James E; Luttge, Andreas

We present evidence of inhibition of calcite dissolution by dissolved magnesium through direct observations of the (104) surface using atomic force microscopy (AFM) and vertical scanning interferometry (VSI). Far from equilibrium, the pattern of magnesium inhibition is dependent on solution composition and specific to surface step geometry. In CO2-free solutions (pH 8.8), dissolved magnesium brings about little inhibition even at concentrations of 0.8 x 10-3 molal. At the same pH, magnesium concentrations of less than 0.05 x 10-3 molal in carbonate-buffered solutions generate significant inhibition, although no changes in surface and etch pit morphology are observed. As concentrations exceed magnesite saturation, the dissolution rate shows little additional decrease; however, selective pinning of step edges results in unique etch-pit profiles, seen in both AFM and VSI datasets. Despite the decreases in step velocity, magnesium addition in carbonated solutions also appears to activate the surface by increasing the nucleation rate of new defects. These relationships suggest that the modest depression of the bulk rate measured by VSI reflects a balance between competing reaction mechanisms that simultaneously depress the rate through selective inhibition of step movement, but also enhance reactivity on terraces by lowering the energy barrier to new etch-pit formation.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 878670
• Report Number(s): PNNL-SA-49046; GCACAK; 4391; KC0303020; TRN: US200611%%429
• Journal Information: Geochimica et Cosmochimica Acta, Vol. 70, Issue 3; ISSN 0016-7037
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ATOMIC FORCE MICROSCOPY
CALCITE
DEFECTS
DISSOLUTION
GEOMETRY
INTERFEROMETRY
KINETICS
MAGNESIUM
MAGNESIUM ADDITIONS
MORPHOLOGY
NUCLEATION
REACTION KINETICS
SATURATION
VELOCITY
calcite
dissolution
magnesium
atomic force microscopy
AFM
vertical scanning interferometry
VSI
kinetics
carbonate
CO2
etch pit
surface chemistry
Environmental Molecular Sciences Laboratory