Study On Preparation Of High Purity Magnesium Oxide And Basic Magnesium Sulfate Cement With Bischofite

Qinghai Salt Lake is rich in bischofite?Magnesium chloride hexahydrate,Mg Cl₂·6H₂O?.Due to the limitation of development cost and production technology bottleneck,a large number of bischofite waste in the salt lake has caused serious environmental problems,so it is called "Salt Lake waste".At present,the comprehensive utilization of bischofite with low cost,high efficiency,diversification and large scale is of great practical significance to solve the environmental problems of Salt Lake and the sustainable development of salt lake industry.In this paper,the active Magnesium Oxide and high purity Magnesium Oxide were prepared by using recrystallization;spray drying;two stage pyrolysis;atmospheric pressure hydration;and high temperature calcination process.Furthermore,the preparation and properties of basic magnesium sulfate cement?BMS cement?doped with metakaolin?MK?were studied.The specific research contents and conclusions are as follows:?1?The active Magnesium Oxide and high purity Magnesium Oxide were prepared from the brucite by recrystallization spray drying,two stage pyrolysis,atmospheric pressure hydration and high temperature calcination.The activity of Mg O was determined by citric acid method and the purity of Mg O was determined by X-ray fluorescence spectrometry?XRF?.The results show that when the mass ratio of the bischofite and deionized water is 3:1,the impurity content of the solution is the smallest;after 2 recrystallization,the removal rate of impurity sodium chloride is 52.5%;when the spray drying temperature is 240?,Mg Cl₂·6H₂O dehydration becomes Mg Cl₂·2H₂O;In the two-stage pyrolysis process,when the temperature of the first stage is 320?,the holding time is 1.5h,the heating rate of the second stage is 15?/min,and the pyrolysis temperature is 500?,the Mg O activity of the product is the highest,and its CAA value is 241 s.In the process of atmospheric pressure hydration and high temperature calcination,when the hydration temperature is 60?,the hydration time is 60 min;the high temperature calcination temperature is 500?,the calcination time is 1.5 h,the purity of Mg O product reaches 99.74%.?2?MK-BMS cement was prepared by using active magnesium oxide?PBM?obtained by brine method as raw material and market MK as mineral admixture.The influence of different content of MK on the early hydration behavior and properties of BMS cement was studied systematically.The influence of different MK content on the early hydration behavior and performance of BMS cement was studied systematically.The results show that the active components Al and Si in MK may take part in hydration reaction to form new gel phase and enhance the compactness of BMS cement,thus making up for the strength loss caused by the decrease of 5·1·7 phase crystal size.When the content of MK increases to 50%,the mechanical properties of MK-BMS cement cured for 28 days can still meet the requirements of P·O52.5R Portland cement.