The promotion of magnesium ions on aragonite precipitation in MICP process

Abstract

This study examines the magnesium ions effect on carbonate crystal polymorph when Ca(CH3COO)2/urea acts as cementation solution in microbially induced carbonate precipitation (MICP) process. The results of unconfined compressive strength (UCS) indicates that the involvement of Mg ions in Ca(CH3COO)2/urea cementation solution can greatly improve the physical and engineering properties of bio-cemented samples. Compared with the bio-cemented sample without any Mg ions, additional 0.01 M Mg ions in 0.5 M Ca(CH3COO)2/urea solution will contribute to 40% higher UCS, and additional 0.5 M Mg ions in 0.5 M Ca(CH3COO)2/urea solution will make the average UCS twofold higher. While, UCS of the samples treated with MgCl2/urea with poor crystallinity magnesium carbonate is one-tenth of that treated with 0.5 M Ca(CH3COO)2/urea. Furthermore, X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) images show that acicular aragonite and rhombohedral calcite are two main types of calcium carbonate crystal precipitated when Ca(CH3COO)2/urea acts as the cementation solution, and the incorporation of Mg ions modifies the crystal polymorph, promoting more aragonite precipitation but inhibiting calcite growth. The mechanism of magnesium ions effect on crystal polymorph is also summarized in the end. The efficiency of Ca(CH3COO)2/urea with a small amount of Mg ions is particularly noteworthy in MICP process.