Microbial Carbonation of Monocalcium Silicate

Area of Science:

• Biotechnology
• Materials Science
• Environmental Science

Background:

• Microbially induced calcium carbonate precipitation (MICP) offers a sustainable alternative to conventional concrete production.
• Existing MICP methods often rely on highly soluble calcium sources, limiting scalability.
• This research investigates MICP using a solid-state calcium source, monocalcium silicate.

Purpose of the Study:

• To investigate the microbial physiology, chemical thermodynamics, and kinetics of MICP using monocalcium silicate.
• To identify parameters critical for scaling up MICP for high-density cement and concrete production.
• To assess the impact of organic acids on calcium solubility and carbonation extent.

Main Methods:

• Utilized Sporosarcina pasteurii (S. pasteurii) for ureolysis to supply CO2 for carbonation.
• Performed chemical kinetic modeling to identify rate-limiting steps.
• Investigated microbial urease activity under various conditions (pH, temperature, CaCl2 concentration).
• Analyzed the effect of organic acid addition on calcium solubility and carbonation.

Main Results:

• Monocalcium silicate dissolution is the rate-limiting step, but organic acids significantly enhance calcium solubility.
• Extensive carbonation was achieved, reaching up to 37 mol %.
• Sporosarcina pasteurii demonstrated urease activity up to pH 11 and 70 °C, producing calcite.
• Cell-free extracts also produced calcite, though with varying physical properties at extreme pH.

Conclusions:

• Optimizing calcium solubility through organic acid addition is crucial for efficient MICP.
• Sporosarcina pasteurii exhibits robust urease activity suitable for industrial applications.
• The study provides critical parameters for scaling up microbial carbonation for sustainable cement and concrete.