Effects of calcium impurities on the properties of magnesium oxychloride cement

Abstract

China's salt lakes contain an abundance of magnesium resources as high-magnesium brine, a by-product of potash fertiliser production is often discharged into salt lakes, causing environmental damage. Magnesium oxide from salt-lake brine can be used to produce magnesium oxychloride cement (MOC), but the calcium impurities present in salt lakes affect the properties of MOC. To investigate the effects of these impurities, magnesium oxide was produced by calcining a magnesium hydroxide precursor. By adding calcium hydroxide or calcium chloride, the incorporated calcium impurities were 0, 5 and 10% by mass of magnesium oxide. The compressive strength, heat of hydration, composition of the hydration product phases and the pore structure development of MOC samples were evaluated. It was found that Ca2+ ions increased the early strength and the rates of setting and hardening of the MOC. However, the presence of calcium impurities did not change the hydration phase composition. This is primarily because the Ca2+ ions promoted the participation of magnesium oxide in the hydration reaction and enhanced the early strength of the MOC. The findings of this study demonstrate the technical feasibility of utilising magnesium resources from salt lakes to prepare magnesium oxide and apply it in the production of MOC.