Research On Preparation Of High Purity Magnesia With Mgcl₂·6H₂O

High purity magnesia is a kind of raw material, which is used to make refractory material with high melting point (>2800℃), strong ability to resist alkaline slag and iron slag erosion and high rul starting temperature.The impurities of high purity magnesia are CaO、SiO2、Fe2O3. At present, high purity magnesias are obtained mainly by calcining magnesite, however,this process induces large energy consumption, high cost, serious environmental pollution, and not getting high purity magnesia. In the developed countries, high purity magnesias are mainly from the sea and salt lake brine.China is rich in salt lake resources. Salt lakes have main distribution area of qing hai, xin jiang, Tibet and Inner Mongolia and other inland provinces. The number of salt lake whose area is more than one square kilometers is731.Salt lake in xin jiang lop nur is the largest brine containing potassium magnesium sulfate subtype deposit so far. It is one of the largest dry salt lake in the world.Mg2+in the salt lake brine is form of bischofite (MgCl2·6H2O). Recent years, the potash project makes a large number of brine emissions, resulting in large amount of "magnesium pollution" and a great waste of resources.This paper, We focus on a technology for preparing a precursor, which uses bischofite (MgCl2·6H2O) as raw materials, Na2CO3as precipitant, then active MgO obtained by calcining precursor is sintered by high temperature under vacuum condition to gain magnesia.As a consequence, salt lake brine resource is effectively utilized in this way, with less environmental pollution. The technology makes a contribution to produce magnesia for greatly reducing the production cost.The following conclusions are mainly listed:(1)Bischofite (MgCl2·6H2O) as raw materials and Na2CO3as precipitant are droping into the reactor at the same time. The cocurrent flow feeding way maximize the utilization rate of raw materials. The main composition of the precursor is MgCO3·2H2O by XRD result.(2)The appropriate light burning condition is:1073k,2h, in order to get high purity MgO of uniform particle size distribution.(3)In the process of sample preparation, a small amounts of nanometer MgO are added into, which can improve the bulk density of sintered magnesia and lower porosity in the process of sintering.(4) In order to gain high density of sintered magnesia in vacuum sintering process, activated carbon is chosen as the second phase particle additives with three different types. Coconut shell activated carbon is an optimal choice by contrast experiment to improve the densification rate of sintering process, reduce the activation energy and the porosity at the same time, of which content is0.03%～0.05%has the best result.(5) The volume shrinkage rate is faster when temperature is below1473k under the vacuum degree of1.33～10-1pa, in contrast,the volume shrinkage rate is lower when continuing to heat up. Eventually, high quality magnesia is obtained at1873K for5h.