『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