【作者】 赵鑫；

【导师】 方莉；

【作者基本信息】 山西大学 ， 化学工程， 2019， 硕士

【摘要】 水氯镁石是盐湖中钾盐提取之后剩余的镁盐,也是卤水固化后的主要存在形式,其产量是钾盐产量的8~12倍。由于技术工艺和经济条件的双重限制,水氯镁石尚未得到合理的利用,导致其大量堆积,危害生态环境,同时也加剧了钾盐的生产难度。此外,碱式硫酸镁水泥是通过在硫氧镁水泥中添加合适的外加剂得到的高强度水泥,具有轻质早强、耐酸碱腐蚀性强,同时还具有良好的耐高温和护筋性能。本文是以盐湖水氯镁石为主要原料,开展了活性氧化镁和碱式硫酸镁水泥的制备研究。首先采用了重结晶-喷雾干燥-低温热解相结合方法制备活性氧化镁,研究了重结晶次数、喷雾干燥温度、低温热解时间和温度等因素对活性氧化镁性能的影响;然后,以超细粉煤灰为矿物掺合料,制备了高性能碱式硫酸镁水泥,研究了煤粉炉粉煤灰(PCFA)和流化床粉煤灰(CFBFA)超细粉对碱式硫酸镁水泥力学性能、水化产物、耐水性以及微观形貌的影响。采用XRD、SEM-EDS、激光粒度分析仪、TG-DTG、FT-IR等手段对产物进行了表征和分析。主要研究结论如下:(1)通过重结晶工艺对水氯镁石进行精制除杂,发现,当重结晶3次之后,水氯镁石中的主要杂质NaCl由原来的0.19%减低到0.006%,去除率达到96.84%;同时结合喷雾干燥和分散剂来降低热解前氯化镁的粒径。结果表明,当喷雾干燥温度为240℃时得到的氯化镁粉末粒径较小(15.4μm),并且分布均匀;低温热解在600℃下热解2 h得到的活性氧化镁粒径较小(4.99μm),比表面积大(2693m~2/kg),结晶度低,活性高,其CAA值为7.62 min,活性氧化镁含量为95.43%。(2)以PCFA和CFBFA超细粉作为矿物掺合料制备碱式硫酸镁水泥,探讨了粒径与掺量对碱式硫酸镁水泥力学性能、水化产物、耐水性以及微观形貌的影响。结果发现,PCFA掺量为20%时碱式硫酸镁水泥力学性能最好,其抗压强度为63.92MPa,抗折强度为11.65 MPa;CFBFA掺量同样在20%时力学性能最好,抗压强度为61.02 MPa,抗折强度为11.40 MPa,稍低于PCFA制备的碱式硫酸镁水泥的强度;掺加PCFA和CFBFA两种超细粉均能显著提高碱式硫酸镁水泥的耐水性能,其中PCFA掺量为30%时,软化系数达到最大,为0.98;CFBFA掺量为20%和30%时,其软化系数持平,为0.95,与未掺UFA的碱式硫酸镁水泥的软化系数(0.90)相比分别提高了8.89%和5.56%,这是由于适量粉煤灰可以起到微集料的作用,填充原有试块中的孔隙,使得试块更加密实,耐水性提高;而超细粉煤灰掺量越多,对水泥试块力学性能越不利,这是由于超细粉煤灰会使517相晶型变差,结晶度降低,因此本实验条件下超细粉煤灰的最佳掺量为20~30%。更多还原

【Abstract】 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 μm)and the distribution was uniform.Active magnesium oxide obtained by pyrolysis at 600 degrees cesius for 2 hours smaller particle size(4.99 μm),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%.更多还原