Welch et al.(1999)による〔『Microbial extracellular polysaccharides and plagioclase dissolution』(1405p)から〕

『微生物細胞外多糖類と斜長石溶解』


Abstract
 Bytownite feldspar was dissolved in batch reactors in solutions of starch (glucose polymer), gum xanthan (glucose, mannose, glucuronic acid), pectin (poly-galacturonic acid), and four alginates (mannuronic and guluronic acid) with a range of molecular weights (low, medium, high and uncharacterized) to evaluate the effect of extracellular microbial polymers on mineral dissolution rates. Solutions were analyzed for dissolved Si and Al as an indicator of feldspar dissolution.
 At neutral pH, feldspar dissolution was inhibited by five of the acid polysaccharides, gum zanthan, pectin, alginate low, alginate medium, alginate high, compared to an organic-free control. An uncharacterized alginate substantially enhanced both Si and Al release from the feldspar. Starch, a neutral polysaccharide, had no apparent effect. Under mildly acidic conditions, initial pH≒4, all of the polymers enhanced feldspar dissolution compared to the inorganic controls. Si release from feldspar in starch solution exceeded the control by a factor of three. Pectin and gum xanthan increased feldspar dissolution by a factor of 10, and the alginates enhanced feldspar dissolution by a factor of 50 to 100. Si and Al concentrations increased with time, even though solutions were supersaturated with respect to several possible secondary phases. Under acidic conditions, initial pH≒3, below the pKa of the carboxylic acid groups, dissolution rates increased, but the relative increase due to the polysaccharides is lower, approximately a factor of two to ten.
 Microbial extracellular polymers play a complex role in mineral weathering. Polymers appear to inhibit dissolution under some conditions, possibly by irreversibly binding to the mineral surfaces. The extracellular polysaccharides can also enhance dissolution by providing protons and complexing with ions in solution.』

1. Introduction
2. Methods
 2.1. Mineral preparation
 2.2. Solutions
 2.3. Dissolution experiments
 2.4. NMR
 2.5. TEM
3. Results
 3.1. Evolution of solution composition
 3.2. pH 6 experiments
 3.3. pH 4 experiments
 3.4. pH 3 experiments
 3.5. NMR results
 3.6. TEM results
4. Discussion
 4.1. pH dependence of the effect of organics on dissolution
 4.2. The role of polymer-surface interactions
 4.3. Differences among polysaccharides
 4.4. Formation of secondary phases
5. Conclusions and implications for natural weathering reactions
Acknowledgments
References



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