Duckworth & Martin(2004)による〔『Dissolution rates and pit morphologies of rhombohedral carbonate minerals』(554p)から〕

『菱面体晶系炭酸塩鉱物の溶解速度とピット形態』


Abstract
 The dissolution and precipitation rates of rhombohedral carbonate minerals, such as CaCO3, ZnCO3, MnCO3, FeCO3, and MgCO3, affect the alkalinity and redox state of natural waters. In the current study, the rates and mechanisms of carbonate dissolution are investigated utilizing an atomic force microscope/flow-through reactor. Based on time series changes of the microtopography, we classify the studied minerals as type I (Ca, Mn), type II (Fe, Mg), or type III (Zn) carbonates. Type I carbonates develop shallow rhombohedral pits, and the step-retreat velocities are pH-dependent for pH<4. Type II carbonates form deep rhombohedral pits at circumneutral to alkaline pH. The rhombohedral shape alters for pH<4, and the step retreat velocities are weakly pH-dependent. Type III carbonates develop shallow distorted puts at circumneutral to alkaline pH and triangular pits at acidic pH. Groups of point defects vs. line dislocations apparently give rise to type I vs. type II behavior, whereas the unique tetrahedral surface coordination of adsorbed Zn2+ may explain type III behavior. For type I at all pH values and type II carbonates for pH<4, geometric models employing the microscopic step retreat velocities are accurate predictors of the absolute rates of macroscopic dissolution. Macroscopic circumneutral dissolution rates, which trend with both water exchange rates and lattice formation energies, vary from 10-5.5 to 10-9.1 mol/m2・s at circumneutral pH and 25℃.』

Introduction
Experimental methodology
 Experimental preparation
 Simultaneous AFM/flow-through reactor experiments
Results and discussion
 Pit shape and distribution
  Type I carbonates
  Type II carbonates
  Type III carbonates
  Pit morphology, defects, and chemical composition
 Microscopic dissolution rates
  Calculation of microscopic dissolution rates
  Calculation of step retreat velocities
 Macroscopic dissolution rates
 Comparing macroscopic and microscopic rates
  Type I carbonates
  Type II carbonates
 Correlation of dissolution rate with other properties
Concluding remarks
Acknowledgments
References cited



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