Hydrogel-Assisted Enzyme-Induced Carbonate Mineral Precipitation

Benchtop experiments demonstrate the promise of hydrogel-assisted enzyme-induced carbonate precipitation (EICP) as a means of enhancing EICP for soil stabilization. Enzyme-induced carbonate precipitation uses hydrolysis of urea (ureolysis) catalyzed by the urease enzyme to precipitate ${\mathrm{CaCO}}_3$ in the presence of urea and calcium in a water-based solution. Xanthan and guar gum biopolymers and an inert polyol-cellulose hydrogel were used to assess the ability of a hydrogel to enhance EICP by retaining reaction product around the soil particles. The experiments were conducted in sand-filled paper cups and soilless glass beakers at 1.66 and 0.33 M of initial calcium chloride (${\mathrm{CaCl}}_2$) concentrations using high-activity and low-activity plant urease. Ureolysis and ${\mathrm{CaCO}}_3$ precipitation occurred in all hydrogel-assisted EICP tests, suggesting that the hydrogels used in this study do not interfere with EICP. Furthermore, hydrogel-assisted EICP appeared to retain moisture for extended periods of time and reduce penetration of the EICP solution into the soil, extending reaction time, increasing precipitation efficiency, and enhancing the formation of a crust. Gas bubble formation in the hydrogel solutions suggests that ammonia (${\mathrm{NH}}_3$) and/or carbon dioxide (${\mathrm{CO}}_2$) off-gassing may be reduced, which may also increase precipitation efficiency. Guar and xanthan gums were found to have the greatest water retention ability and to significantly reduce water evaporation.