Properties of regenerated MgO–CaO refractory bricks: Impurity of silicon dioxide

Regenerated MgO-CaO refractory brick samples with 0, 1.5, 3.0 wt-% SiO2 addition were prepared by using spent MgO-CaO bricks and fused magnesia as raw materials. Their phases, microstructures and flexural strength at room and 1573 K were investigated, respectively, and the maximum content of SiO2 impurity in regenerated samples had been subsequently achieved. The results showed that main phases of regenerated samples were all MgO, free CaO (f-CaO), Ca3SiO5 (C3S) and Ca2FeAlO5. Because some Al3+, Fe3+ had dissolved in the crystal lattice of C3S, it resulted in the decreasing of content of f-CaO and low melting point phase of C(4)AF along with the increasing of SiO2 addition, moreover, the flexural strength of regenerated samples at room temperature reduced while flexural strength at 1573 K enhanced. The maximum content of SiO2 impurity was about 4 u 11 wt-% in regenerated samples considering their properties for cement kiln.