Synthesis and Characterization of Calcium Carbonate Nanoparticles via Bacterial Mineralization in Steel Slag Comprising Cementitious Materials

Abstract

Bacteria-induced mineralization is a new technique to produce calcium carbonate in steel slag for the preparation of building materials. Calcium carbonate nanoparticles were precipitated as a result of the enzymatic activity of Bacillus mucilaginous subtilis in steel slag. The crystal structure and morphology of the calcium carbonate precipitate were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), atomic force microscopy (AFM), while thermal properties were studied by thermogravimetric-differential scanning calorimetry (TG-DSC) analysis. The experimental results showed that the microstructure of calcium carbonate precipitate induced by the reproductive enzymes of Bacillus mucilaginous differs from the chemical precipitation in simulated pore solution of steel slag. Powder XRD patterns confirmed the formation of Bacillus mucilaginous subtilis-induced calcium carbonate with an average particle size of 42.1 nm, while the average particle size of the chemically synthesized calcium carbonate was 59.3 nm. Compared with the chemical synthesis, we found that the decomposition temperature of calcite by bacterial precipitation was higher than that for the chemically-precipitated calcite. The compressive strength improved with the amount of bacterial content. Bacterial mineralization could accelerate the rate of carbon sequestration in the mineralization process. The content of calcium carbonate in microbial mineralized steel slag increased obviously. The compressive strength of steel slag mortar with 1.5% bacterial reached up to 51.5 MPa, the compressive strength increased over 50% compared with the carbonized steel slag mortar. The micron-size calcite by bacterial mineralization resulted in a more compact structure. Our study suggests that microbial mineralization technology is a good method to utilize steel slag for building materials.