Influence of initial calcium ion concentration on the precipitation and crystal morphology of calcium carbonate induced by bacterial carbonic anhydrase

Abstract

Biogenic precipitation of calcium carbonate (CaCO3) has attracted much attention due to its role in many geological processes, applications of Geological and Civil Engineering as well as environmental treatments. The present paper focused on the biocatalytic precipitation of CaCO3 by the extracellular carbonic anhydrase (CA) extracted and partially purified from the culture of Bacillus cereus. The kinetics of CaCO3 precipitation catalyzed by the bacterial CA at different initial concentrations of Ca2+ (C0(Ca2+)) was investigated through the gaseous diffusion system. The polymorph and morphology of CaCO3 crystals obtained in the precipitation process were also analyzed using XRD, FTIR and FESEM. The results showed that in the process of CaCO3 precipitation catalyzed by bacterial CA, the change in the amount of deposited Ca2+ at different C0(Ca2+) fitted well with the exponential model. Greater fluctuation of pH occurred in the water control group during the rising process of pH, while in the CA group the pH increased more steadily. This may be related to the role of CA in pH regulation. The precipitation rate of CaCO3 increased with the increasing C0(Ca2+), but overhigh C0(Ca2+) of 100mmol/L had a certain negative influence on CaCO3 precipitation catalyzed by bacterial CA. The integrated results of XRD, FTIR and FESEM analysis showed that the C0(Ca2+) had greater effect on the polymorph and morphology of CaCO3 crystals formed in the presence of bacterial CA. The lower C0(Ca2+) favored the formation of vaterite and the higher C0(Ca2+) favored the formation of calcite.