Variation in Calcite Dissolution Rates: A Fundamental Problem?

摘要: A comparison of published calcite dissolution rates measured far from equilibrium at a pH ∼ 6 and above shows well over an order magnitude in variation. Recently AFM step velocities extend this range further still. In effort to understand the source variation, provide additional constraint new analytical approach, we have by vertical scanning interferometry. areas cleavage surface dominated etch pits, our rate is 10−10.95 mol/cm2/s (PCO2 10−3.41 atm, 8.82), 5 ∼100 times slower than derived bulk powder experiments, although similar velocities. On surfaces free local pit development, limited slow, “global” (10−11.68 mol/cm2/s). Although these differences confirm importance (defect) distribution as controlling mechanism dissolution, they also suggest that “bulk” observed experiments may derive substantial enhancement grain boundaries having high kink density. We significant inhibition introduction dissolved manganese. At 2.0 μM Mn, diminished 10−12.4 mol/cm2/s, formed rhombic pits characterized pure solution were absent. These results are good agreement with pattern manganese velocities, assuming density on smooth terraces ∼9 μm−1.