Abstract:

Carbonic anhydrase (CA) is a ubiquitous enzyme present in nearly all living organisms except fungi. It is non-toxic, environmentally benign, cost-effective, and already produced at industrial scale, with widespread applications in the food and beverage industries. CA dramatically accelerates the hydration of CO₂ to generate carbonate ions (CO₃²⁻), enhancing the reaction rate by approximately 10⁸-fold. In this study, CA is employed to improve the biocarbonation process of reactive magnesia cement (RMC) for sustainable soil stabilization. By catalyzing the carbonation reactions of RMC, CA promotes greater CO₂ sequestration, increases the degree of carbonation, and facilitates the formation of hydrated magnesium carbonates (HMCs)—specifically hydromagnesite and nesquehonite—which act as cementing agents between soil particles, thereby achieving green, low-cost, and highly efficient strength enhancement. The key findings are as follows: (1) CA effectively promotes the carbonation of Mg(OH)₂ (formed from RMC hydration), significantly increasing the precipitation of hydromagnesite and nesquehonite, leading to a strength improvement of up to 74.6%. (2) The beneficial effects of CA on both strength development and carbonation degree intensify with prolonged curing time, with enhancement rates reaching 42.6% in strength and 153.7% in carbonation degree over the testing period. (3) Microstructural analyses reveal that the CA-catalyzed formation of HMCs modifies the soil pore structure by transforming larger intra-aggregate macropores into finer interparticle pores, resulting in a denser and more compact soil matrix. (4) A notable synergistic mineralization effect exists between urease and CA during RMC carbonation, where CA incorporation enhances biomineralization kinetics and biological mineral transport processes, substantially accelerating the overall bio-carbonation reaction rate and increasing carbonate precipitation. The CA-enhanced RMC bio-carbonation technology proposed in this study demonstrates strong potential and favorable conditions for practical field applications.

Key words: reactive magnesia cement (RMC), carbonic anhydrase (CA), urease, hydrated magnesia carbonates (HMCs), hydration reaction