Effects of calcium impurities on properties of magnesium oxychloride cement

Abstract

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