Preparation Of Active Magnesium Oxide And Basic Magnesium Sulfate Cement

Brucite is the residual magnesium salt after potassium salt extraction in salt lakes,and is also the main existing form after brine solidification.Its output is 8~12 times that of potassium salt.Due to the double restrictions of technological process and economic conditions,brucite has not been rationally utilized,resulting in a large number of accumulation,harming the ecological environment,but also exacerbating the difficulty of potassium production.In addition,basic magnesium sulfate cement is a high strength cement obtained by adding appropriate additives in magnesium sulfate cement.It has light weight,early strength,strong acid-alkali corrosion resistance,and good high temperature resistance and reinforcement protection performance.In this paper,the preparation of active magnesium oxide and basic magnesium sulfate cement was studied,Using salt lake brucite as the main raw material.Firstly,the active magnesium oxide was prepared by recrystallization spray drying and low temperature pyrolysis.The effects of recrystallization times,spray drying temperature,low temperature pyrolysis time and temperature on the properties of activated magnesium oxide were studied.Then,high performance basic magnesium sulfate cement was prepared with ultrafine fly ash as mineral admixture,and the pulverized coal ash(PCFA)and fluidized bed were studied.The effect of fly ash(CFBFA)superfine powder on mechanical properties,hydration products,water resistance and micro-morphology of basic magnesium sulfate cement.The products were characterized and analyzed by XRD,SEM-EDS,laser particle size analyzer,TG-DTG and FT-IR.The main conclusions are as follows:(1)Through the recrystallization process,the chlorite is refined and impurity removed.It is found that after the recrystallization 3 times,the main impurity Na Cl in the brucite decreases from 0.19% to 0.006%,and the removal rate reaches 96.84%.Meanwhile,spray drying and dispersant are used to reduce the particle size of magnesium chloride before pyrolysis.The results showed that when the spray drying temperature was 240 degrees celsius,the particle size of magnesium chloride powder was smaller(15.4 ?m)and the distribution was uniform.Active magnesium oxide obtained by pyrolysis at 600 degrees cesius for 2 hours smaller particle size(4.99 ?m),larger specific surface area(2693 m2/kg),lower crystallinity and higher activity.Its CAA value is 7.62 minutes,and the content of active magnesium oxide is 95.43%.(2)The basic magnesium sulfate cement was prepared by using PCFA and CFBFA ultrafine powder as mineral admixtures.The effects of particle size and dosage on the mechanical properties,hydration products,water resistance and micro-morphology of basic magnesium sulfate cement were investigated.The results showed that the basic magnesium sulfate cement had the best mechanical properties when the content of PCFA was 20%.,the compressive strength is 63.92 MPa and the flexural strength is 11.65 MPa;the mechanical properties of CFBFA are the best when the content of PCFA is 20%,the compressive strength is 61.02 MPa and the flexural strength is 11.40 MPa,which is slightly lower than that of basic magnesium sulfate cement prepared by PCFA;the addition of PCFA and CFBFA can significantly improve the basic sulfur.The water resistance of magnesium sulfate cement is the highest when the content of PCFA is 30%,the softening coefficient is 0.98;when the content of CFBFA is 20% and 30%,the softening coefficient is equal to 0.95.Compared with the basic magnesium sulfate cement without UFA,the softening coefficient is increased by 8.89% and 5.56%,respectively.This is because the proper amount of fly ash can play the role of micro-aggregate and fill the pore in the original test block.The more superfine fly ash is added,the more unfavorable the mechanical properties of cement blocks are.This is because superfine fly ash will make 517 phase crystalline form worse and crystallinity lower.Therefore,the optimum content of superfine fly ash under the experimental conditions is 20~30%.