Dissolution kinetics and mechanisms at dolomite-water interfaces: effects of electrolyte specific ionic strength.
Elucidating dissolution kinetics and mechanisms at carbonate mineral-water interfaces is essential to many environmental and geochemical processes, including geologic CO(2) sequestration in deep aquifers. In the present work, effects of background electrolytes on dolomite (CaMg(CO(3))(2)) reactivity were investigated by measuring step dissolution rates using in situ hydrothermal atomic force microscopy (HAFM) at 90 °C. Cleaved surfaces of dolomite were exposed to sodium chloride and tetramethylammonium chloride (TMACl) aqueous solutions with ionic strengths (I) ranging from 0 to 0.77 m at pH 4 and pH 9. HAFM results demonstrated that dolomite step retreat rates increased with increasing solution ionic strength and decreasing pH. Comparison of [481] and [441] steps revealed that the anisotropy of [481] and [441] step speeds became significant as solution ionic strength increased, with NaCl exerting more pronounced effects than TMACl for the same I. To interpret the different trends observed for NaCl and TMACl, a dissolution mechanism involving orientation-dependent ion adsorption and consequent edge free energy changes is proposed.
Department of Chemistry, Wright State University, 3640 Colonel Glenn Highway, Dayton, Ohio 45435, United States.
Man
M
Xu
Katie
K
Sullivan
Garrett
G
Vanness
Kevin G
KG
Knauss
Steven R
SR
Higgins
D002119:Calcium Carbonate / Q000737:chemistry*; D057965:Carbon Sequestration; D007700:Kinetics; D008274:Magnesium / Q000737:chemistry*; D018625:Microscopy, Atomic Force; D009994:Osmolar Concentration; D000644:Quaternary Ammonium Compounds / Q000737:chemistry; D012965:Sodium Chloride / Q000737:chemistry; D012995:Solubility; D014867:Water / Q000737:chemistry
D000644:Quaternary Ammonium Compounds; D014867:Water; D012965:Sodium Chloride; D002119:Calcium Carbonate; C027917:tetramethylammonium; D008274:Magnesium; C028042:calcium magnesium carbonate