【作者】 李陇岗；

【导师】 钟辉； 杨建元；

【作者基本信息】 成都理工大学 ， 应用化学， 2005， 硕士

【摘要】 我国青海省拥有极为丰富的盐湖水氯镁石资源,但长期以来并没有得到很好的利用,水氯镁石一般作为钾肥生产中的废弃物排放,造成了严重的资源浪费和环境污染,因此,盐湖镁资源的综合利用成为刻不容缓的任务。而镁系产品中因高纯镁砂具有高附加值、市场需求大等优点成为各国镁资源利用的研究热点,本研究以青海察尔汗盐湖水氯镁石为原料,开展了以氨法为基础的高纯镁砂制备工艺研究,解决了其难合成、难高纯化的关键技术问题,成功地合成出了MgO>99.5%,表观密度为3.55g/cm³的高纯镁砂产品,形成了较为经济、合理的工艺路线,为该地区钾肥生产中镁的综合利用问题提供了一条新的技术方法和工艺。 传统的氨沉淀法制Mg（OH）₂侧重于氨体系中Mg²⁺浓度和加料时间对Mg（OH）₂过滤性能影响的研究,未注意到Mg（OH）₂晶体形成和生长环境对其过滤性能的重要影响,因而得到的产物Mg（OH）₂过滤性能低,滤饼含水率高达30～40%,难以达到高纯Mg（OH）₂的技术指标。本研究针对这一技术难题,认为Mg（OH）₂沉淀反应体系提供的晶体生长环境对Mg（OH）₂晶体的形成和生长、Mg（OH）₂沉淀的过滤性能有重大影响。本课题研究出一种反向加料和料浆部分回返的新工艺,利用晶种和缓冲体系的双重效应,制备出结晶形态的高纯度Mg（OH）₂沉淀,过滤性好,滤饼含水率仅为10～15%,为高纯镁砂的制备提供了性能优良的前驱体。 前人认为Mg（OH）₂热分解动力学机理属单一的成核控制机理。本研究通过对Mg（OH）₂热分解动力学的深入研究,发现Mg（OH）₂的热分解是一较为复杂的过程,其热分解机理可分为两个阶段:低温段（280～397.8℃）热分解机理为成核控制机理,A3模型;高温段（T>397.8℃）为扩散控制机理,G-B模型。较为合理地解释了Mg（OH）₂热分解反应后期热分解速率变慢的现象。本研究对计算Mg（OH）₂热分解动力学参数Freeman_Carroll法进行了改进,解决了Freeman-Carroll法求算动力学参数不准确的问题,计算更为简单、快捷、精确,对于一般的固体热分解反应具有普遍的意义,采用改进后的方法计算Mg（OH）₂热分解活化能E为122kJ/mol,反应级数n为0.68。 本研究根据Mg（OH）₂热分解机理研究结果,结合实验研究确定了最佳的高温煅烧及烧结工艺条件,认为轻烧氧化镁的物化性质对其烧结显微结构有较大影响,低温煅烧Mg（OH）₂将提高MgO活性,增大烧结推动力,有利于MgO烧结的进行,高温烧结过程中,1600～1700℃是MgO发生烧结致密化的主要阶段,在1700℃后烧结进入后期,致密化缓慢,实验结果表明烧结温度为1700℃,烧结5小时获得的高纯镁砂ρ_app为3.55g/cm³,粒度均一,显微结构较好。更多还原

【Abstract】 There are extremely abundant of bischofite resources existing in Qinghai salt lakes of our country, but for a long time they did not get enough use. Because of the technological problems to be resolved, they are discharged as a waste in the production of potassium fertilizer, resulting in a huge waste of resources and brought serious environment pollution. The exploitation of them becomes urgent mission.For a solution to these problems, extensive studies on preparation of high purity magnesia have been carried out in the paper. We selected bischofite in ChaErHan as raw material and placed emphasis on the studies of the preparation process based on ammonia method, some key problems were resolved which would greatly lower the production cost. The MgO content reaches 99.5%, and apparent density reaches 3.55g/cm³ using the new production process flow. A new preparation method of high purity magnesia has been successfully developed which will greatly alleviates the environment pollution and will turns the waste into a valuable product if being industrialized.Traditional ammonia method has many problems in filtration of Mg（OH）₂ soliquoid and its purity, for a long time they were not well resolved. Generally the water percentage of Mg（OH）₂ precursor reaches 30-40% and its quality is inferior than high grade Mg（OH）₂ quality standard. Different from the traditional ammonia method, we think that the generation and the growth environment of Mg（OH）₂ crystal in depositing reaction system show great effects on filtration of Mg（OH）₂ deposit. The paper brought forward a new process using the recombination effect of the buffer system and the crystal particle action, which evidently improved the filtration of Mg（OH）₂ soliquoid. The Mg（OH）₂ product in the new ammonia method has properties superior than that of the traditional one: lower water content （<15%） and higher purity.Intensified studies were carried out on thermo-decomposition kinetic mechanism of Mg（OH）₂, we think that the thermo-decomposition of Mg（OH）₂ is a complex process and the whole decomposition process cannot be represented by only one mechanism function. The process can be divided into two parts and two mechanism functions can represent it, the dividing temperature is 397℃. The nucleation mechanism can represent kinetic control type before this temperature, and kinetic model is A3, while after this temperature the kinetic control type is diffusion control, the kinetic model is the famous Ginstling-Broustein model（D4）. We also improved Freeman-Carroll method, a method used to calculate the solid state thermo-decomposition kinetic parameters which usually has problems in accuracy. We resolved the problems by improving the differential equation of conversion degree α . The activation energy ’E’ is 122kJ/mol, the value of reaction order ’n’ is 0.68 by the improved method.更多还原