Function and effect of borax on magnesium phosphate cement prepared by magnesium slag after salt lake lithium extraction

Abstract

Magnesium phosphate cement (MPC) is a chemically bonded ceramic with early strength and fast hardness. It is formed through the interaction of phosphate salts and magnesia (MgO). Using salt lake lithium extraction magnesium slag (MS) as the MgO raw material to prepare MPC may be an effective way to lessen the manufacturing cost of MPC. In this study, salt lake magnesium phosphate cement (SLMPC) was prepared using the MS, with salt lake lithium extraction as the raw material, which was calcined and then reacted with KH2PO4. After adding an appropriate amount of borax, the effects of the borax content on the water–cement ratio, setting time, compressive strength, and strength retention of the SLMPC were investigated. Meanwhile, the phase, thermal stability, and microstructure of the SLMPC were characterized by XRD, TG-DSC, and SEM. The results showed that the incorporation of borax could effectively reduce the water–cement ratio, delay the setting time, and reduce the 7-day compressive strength of SLMPC. However, it improved the water resistance of the SLMPC significantly, and when the borax content was 8 %, the setting time was extended to 18 min, and the compressive strength retention rate in the 28-day water reached 117.46 %. Phase quantitative analysis showed that the Mg3B2O6 impurity in MS did not participate in the hydration process.