Interaction of manganese(II) with the surface of calcite in dilute solutions and seawater
The interaction of Mn/sup 2 +/ with the surface of calcite in aqueous solutions is complex. In dilute solutions the Mn/sup 2 +/ is rapidly adsorbed, MnCO/sub 3/ nucleates on the calcite surface and then grows by a first order reaction with respect to the initial Mn/sup 2 +/ concentration. At higher ionic strengths, in NaCl solutions, the rate of these processes is slower, but the same general pattern persists. In solutions containing Mg/sup 2 +/, at the concentration of seawater and in seawater, the nucleation phase of the uptake process does not appear to occur. The long term uptake rate of Mn/sup 2 +/ on the surface of calcite in seawater is first order with respect to the disolved Mn/sup 2 +/ concentration. The rate constant is over 3 orders of magnitude smaller than that found in dilute Mg/sup 2 +/-free solutions. A probable explanation for the slower growith rate in seawater is that MnCO/sub 3/ is not nucleated on the calcite surface due to the presence of high Mg/sup 2 +/ concentrations. These, through site competition, prevent enough Mn/sup 2 +/ from being adsorbed to reach a critical concentration for MnCO/sub 3/ nucleation. This behavior is similar to that found for orthophosphate with calcite surfaces in dilute solutions and seawater. Measurements of the solubility of rhodochrosite in seawater gave results from an undersaturation approach to equilibrium in excellent agreement with those found in previous studies in dilute solutions. When equilibrium was approached from supersaturation, approximately 50 times more calcium was precipitated than Mn/sup 2 +/. The measured solubility was over twice that determined from undersaturation. It is possible that a Mn-calcite containing 25 to 30 mole percent MnCO/sub 3/ formed on the rhodochrosite from the supersaturated solutions. Consequently, it is doubtful that rhodochrosite controls the concentration of Mn/sup 2 +/ in calcium carbonate rich marine environments.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Miami Univ., FL (USA). Rosenstiel School of Marine and Atmospheric Sciences
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 5530808
- Report Number(s):
- LBL-13707; ON: DE82011104
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
54 ENVIRONMENTAL SCIENCES
14 SOLAR ENERGY
CALCITE
CHEMICAL REACTION KINETICS
MANGANESE COMPOUNDS
ADSORPTION
AQUEOUS SOLUTIONS
CATIONS
EXPERIMENTAL DATA
MAGNESIUM COMPOUNDS
MANGANESE CARBONATES
SEAWATER
SODIUM CHLORIDES
SURFACES
ALKALI METAL COMPOUNDS
ALKALINE EARTH METAL COMPOUNDS
CALCIUM CARBONATES
CALCIUM COMPOUNDS
CARBON COMPOUNDS
CARBONATE MINERALS
CARBONATES
CHARGED PARTICLES
CHLORIDES
CHLORINE COMPOUNDS
DATA
DISPERSIONS
HALIDES
HALOGEN COMPOUNDS
HYDROGEN COMPOUNDS
INFORMATION
IONS
KINETICS
MINERALS
MIXTURES
NUMERICAL DATA
OXYGEN COMPOUNDS
REACTION KINETICS
SODIUM COMPOUNDS
SOLUTIONS
SORPTION
TRANSITION ELEMENT COMPOUNDS
WATER
400201* - Chemical & Physicochemical Properties
520301 - Environment
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140400 - Solar Energy- Environmental Aspects