Further studies of the hydration of MgO-hydromagnesite blends

The hydration of magnesium oxide in the presence of hydromagnesite (Mg5(CO3)4(OH)2·4H2O) was investigated. The hydration products are a poorly-crystalline form of brucite (Mg(OH)2) and an unknown amorphous or poorly crystalline hydrate, which was evidenced by X-ray diffraction analyses and Raman spectroscopy. By thermogravimetry it was found that in the presence of hydromagnesite more water is bound in hydrate phases than can be explained by the formation of brucite only. The unknown hydrate is hypothesized to lead to cohesive binding in MgO-hydromagnesite blends. Due to thermodynamic predictions artinite (Mg2(CO3)(OH)2·3H2O) should be the stable hydrate in this system. The addition of artinite crystal seeds, however, had no significant effect on hydration kinetics or nature of the reaction products. The hypothesis that the addition of sodium bicarbonate (NaHCO3) could modify or accelerate the hydration reactions due to its high solubility and the supply of additional HCO3− ions was also not supported by the experiments.