Utilizing bovine carbonic anhydrase II for enzyme-induced carbonate precipitation (EICP) in recycled concrete aggregate.

This study presents a novel approach to enzyme-induced precipitation of calcium carbonate (CaCO3) using bovine carbonic anhydrase II (bCAII) purified from bovine erythrocytes, focusing on the effective use of a purified enzymatic system to facilitate controlled biomineralization. The enzyme was successfully purified with a recovery of 18% and a 516-fold purification, as confirmed by Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis (SDS-PAGE) analysis. The effects of various parameters, including pH, temperature, and CaCl2 concentration, on bCAII-induced CaCO3 precipitation were examined. The results revealed that pH 8.0 was optimal for CaCO3 formation, and the highest precipitation occurred at a temperature of 22 °C. The crystalline phases of the precipitated CaCO3 were identified using X-ray diffraction (XRD) analysis. The results confirmed the presence of calcite, vaterite, and minor amounts of aragonite in the precipitate, with calcite being the dominant phase. Thermogravimetric (TG) analysis and Fourier-transform infrared spectroscopy (FTIR) further confirmed the presence of calcite and its stability in the bCAII-mediated precipitate. Furthermore, recycled concrete aggregate (RCA), both untreated and treated with bCAII, was exposed to carbonation in a CO2 chamber. The results showed a significantly higher formation of CaCO3 on the surface of the bCAII-treated RCA compared to the untreated RCA. This enhancement suggests that bCAII can effectively promote the carbonation process in RCA, potentially improving its performance and making it more suitable for reuse in concrete production. Overall, the study introduces an environmentally friendly and efficient biocatalytic method for mineralization, with promising implications for carbon sequestration and circular construction technologies.