Influence of initial pH on the precipitation and crystal morphology of calcium carbonate induced by microbial carbonic anhydrase

The dynamics of calcium carbonate (CaCO3) precipitation induced by microbial intracellular or extracellular carbonic anhydrase (CA) at initial pH 6.0, 6.5, 7.0 and 8.0 were investigated through the gaseous diffusion method. The results indicated that both the intracellular and extracellular CA could promote CaCO3 precipitation. The Ca2+ ions in the enzymatic systems at initial pH 8.0 were completely deposited at 48 h, which were respectively 21 h, 15 h and 14 h earlier compared with that at initial pH 6.0, pH 6.5 and pH 7.0, indicating that higher pH favored CaCO3 precipitation in the experimental pH range, and was beneficial to the catalytic action of microbial CA on CaCO3 precipitation. In addition, XRD analysis indicated that the CaCO3 precipitates were mainly calcite crystals in the presence of microbial CA. With increasing deposition time, the crystals gradually changed from prism shape to pyramid-like or irregular polyhedral shape based on FESEM analysis.