Optimization of Mineralization Curing System for Efficient and Safe Utilization of Steel Slag Wastes

Abstract

The crystal structure and morphology of the mineralization products were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and the thermal properties were studied by thermogravimetric-differential scanning calorimetry (DSC) analysis. The changes of microorganism quantity and enzyme activity in pore solution with time were measured. The experimental results show that microorganism quantity and enzyme activity in pore solution reach the maximum at 50–60 h, mineralization curing begins at this time, the strength of microbial mineralized steel slag reaches the maximum. This study provides a good selection basis for selecting the optimum mineralization system for the production of microbial mineralized steel slag products. Bacterial mineralization can accelerate the rate of carbon sequestration in the mineralization process. The compressive strength of steel slag with 1.5% bacterial can reach up to 55.6 MPa. The microstructure and thermal properties of calcium carbonate precipitate induced by the enzymes of bacillus subtilis differs from the chemical precipitation in pore solution of steel slag. Through the analysis of the mineralized products of steel slag, the reaction rate of free calcium oxide and free magnesium oxide in steel slag after the addition of microorganisms is significantly increased, which improves the stability of steel slag as cementitious material. Meanwhile, the production of calcium carbonate, the main mineralized product, is significantly increased.

Keywords

steel slag / microorganism / bio-mineralization / enzyme activity / curing system