『Abstract
The dissolution rate of apatite was determined in batch reactors
in organic acid solutions and in microbial cultures. Inoculum
for the cultures was from biotite plus apatite crystals from a
granite weathering profile in South Eastern Australia. In both
the biotic and the abiotic experiments, etching of the apatite
surface leads to the formation of elongated spires parallel to
the c axis. Apatite dissolution rates in the inorganic,
acetate, and oxalate solutions increase as pH decreases from approximately
10-11 mol/m-2・s-1 at initial
pH 5.5 to 10-7 mol/m-2・s-1 at
initial pH 2. Under mildly acidic to near neutral pH conditions,
both oxalate and acetate increased apatite dissolution by up to
an order of magnitude compared to the inorganic conditions. Acetate
catalyzed the reaction by forming complexes with Ca, either in
solution or at the mineral surfaces. Oxalate forms complexes with
Ca as well, and can also affect reaction rates and stoichiometry
by forming Ca^oxalate precipitates, thus affecting solution saturation
states. In all abiotic experiments, net phosphate release to solution
approaches zero even when solutions are apparently undersaturated
by several orders of magnitude with respect to the solubility
of an ideal fluoroapatite mineral. In the microbial experiments,
two enrichment cultures increased both apatite and biotite dissolution
by producing organic acids, primarily pyruvate, fermentation products,
and oxalate, and by lowering bulk solution pH to between 3 and
5. However, the microorganisms were also able to increase phosphate
release from apatite (by two orders of magnitude) without lowering
bulk solution pH by producing pyruvate and other compounds.
Keywords: apatite; bacteria; mineral weathering; organic acids;
phosphate』
(Introduction)
Methods
Mineral
Microbiology
Solutions
Experimental
Results
Solution chemistry - Abiotic experiments
Rates
Chemical affinity
Stoichiometry
Solution chemistry - Biological experiments
Scanning electron microscopy
Discussion
Rates
Effect of organic ligands
Organisms
Morphology
Conclusions
References