Preparation Of Magnesia Cement Using Magnesium-rich Byproducts From The Production Of Lithium Carbonate From Salt Lakes

The use of salt lake brine to extract lithium carbonate by-product magnesium slag mainly prepared two kinds of cement which are the most widely used and outstanding in magnesium cementitious materials,namely magnesium oxychloride cement?MOC?and basic magnesium sulfate cement?BMSC?.The MOC is usually a mixture of magnesium oxide and a certain proportion of magnesium chloride solution.The BMSC is prepared by mixing magnesium oxide,a certain proportion of magnesium sulfate solution and an admixture?sodium citrate?.At present,in the market application and academic research fields of MOC and BMSC,magnesium oxide?referred to as light burning powder,LBM?obtained from calcined magnesite is mainly used as a main raw material to form a complete system for preparing MOC and BMSC by LBM.However,according to national policies?restricted mining?and long-term large-scale development of LBM,the LBM deficiency in the western salt lakes is in a state of being in response to the national green environmental protection,resource conservation and development of new energy,and the promotion and application of the MOC and BMSC western salt lake areas.From the perspective of this paper,the preparation of MOC and BMSC was carried out by extracting magnesium carbonate by-product magnesium slag?lithium-magnesium slag?from calcined salt lake brine to obtain magnesia?Li-MgO?as the main raw material.The preliminary framework of the preparation of MOC and BMSC with Li-MgO was established by studying the calcination temperature of lithium magnesium slag and the molar ratio of cement,hydration history,microstructure and admixture of cement raw materials.The further development of BMSC is used as a basic study.The main conclusions are as follows:?1?The difference between Li-MgO and LBM.The difference of composition:Li-MgO is mainly composed of MgO,Mg₃B₂O6and NaCl;LBM is mainly composed of MgO,CaCO₃ and SiO₂.The difference of MgO activity content:Under the same calcination conditions,the MgO activity content of Li-MgO is higher than that of LBM.?2?Advantages and disadvantages of MOC in a system using Li-MgO as a raw material.Advantages:1)MOC has strong adaptability to Li-MgO,calcination temperature is 500-900?,calcination time is 1h,molar ratio a-MgO/MgCl₂ is 5-9,MgCl₂/H₂O=1:13,can be prepared.A strong,early-strong MOC.2)Incorporating mineral admixtures can ensure that the compressive strength is not reduced,and the cost is greatly reduced.3)Alleviate the problem of magnesium damage in the western salt lake area and the recycling of waste.Disadvantages:1)Poor stability,the main hydration phase is easy to decompose.2)The use of mineral admixture and KH₂PO₄admixture can not improve the water resistance of MOC for a long time?effective within 3 days?,which limits its application range.?3?Advantages and disadvantages of BMSC in a system using Li-MgO as a raw material.Advantages:1)Strong comprehensive performance,good water resistance,early strength,high strength and wide application range,and strong self-stability.2)The use of Li-MgO effectively reduces the cost of BMSC,and it is expected to alleviate the situation that high-performance magnesium-based building materials in the western salt lake area are constrained by magnesite resources.Disadvantages:BMSC has poor adaptability to Li-MgO,is easy to crack,and has low compressive strength.It needs to be modified with LBM and 517 seed crystals.?4?In the system using Li-MgO as raw material,the optimum mixture ratio of MOC and BMSC was prepared,and the comprehensive performance was evaluated.1)The optimum mixing ratio of MOC:calcination temperature is 600?,calcination time is 1h,molar ratio is a-MgO/MgCl₂/H₂O=8:1:13;2)optimal mixing ratio of BMSC:calcination temperature is 600?,calcination time is 2h,517 seed dosage is 3%of Li-MgO mass,molar ratio is a-MgO/MgCl₂/H₂O=6:1:20;3)although the compressive strength of MOC is much higher BMSC,but the comprehensive performance of BMSC is good,the stability of hydration products is high,and the water resistance is much higher than MOC.It is more suitable for real life and has a wide range of applications.