Calcium carbonate (CaCO₃) is a mineral with several polymorphs, of which calcite is the most stable under ambient conditions. It is the cementing phase produced by Microbially Induced Calcite Precipitation (MICP) and the reason that bio-cementation works.
Relevance to bio-mediated mineralization
In MICP, calcium carbonate is not supplied as a solid. It is formed in situ from dissolved calcium and dissolved inorganic carbon:
- Calcium is supplied in the feed solution, typically as calcium chloride or calcium lactate.
- Carbonate is generated by microbial metabolism — most commonly by Ureolysis-Driven Carbonate Precipitation, which raises pH and dissolved inorganic carbon simultaneously.
When the pore solution becomes supersaturated with respect to CaCO₃, calcite nucleates on grain surfaces and bacterial cell surfaces and grows outward, bridging adjacent particles. The amount and distribution of precipitated calcite determine the mechanical outcome: calcite concentrated at grain contacts increases strength, while calcite coating grain surfaces reduces permeability.
Other polymorphs
Calcite is the form usually targeted in engineering applications because it is the thermodynamically stable polymorph at ambient temperature and pressure. Other polymorphs — aragonite and vaterite — can form depending on solution chemistry and the presence of organic additives, and vaterite in particular is metastable and may transform to calcite over time.
A 2020 test-tube study of three Sporosarcina strains under identical treatment reported calcite from one, a calcite–vaterite mix from another and mostly amorphous calcium carbonate from the third, and argued that non-calcite phases are more common in microbial precipitation than usually assumed; see Not Always Calcite: How Three Sporosarcina Strains Produced Different Calcium Carbonate Phases (Clarà Saracho et al., 2020).
Evidence status in this wiki
This page describes calcium carbonate as it is generally understood in mineralogy and materials chemistry. The source dossier that prompted it — Microbially Induced Calcite Precipitation: The source archive Materials Dossier (Provisional Record) — could not be read in full at the time of writing, and no specific measurements, polymorph analyses or product claims from that dossier are reproduced here.
Related
- Microbially Induced Calcite Precipitation (MICP) — the process that forms it.
- Ureolysis-Driven Carbonate Precipitation — the biochemical route.
- Bio-Cementation — the engineering application.
- chemistry — topic guide.
Source notes & attribution
- https://rexresearch.com/MicrobeInducedCalcitePptn/MICPrecipitation.html