菱镁矿差异化煅烧及氢氧化镁可控水合制备机理研究

The method for the synthesis of magnesium hydroxide by hydration of magnesium oxide, which generated by calcination of the raw material magnesite, has advantages of simple technology and low cost, however, the morphology and purity of magnesium hydroxide synthesized by this method can hardly meet the requirements of flame retardant agent. This project aims to establish a thermodynamics model for the calcination of magnesite by researching the influence law of magnesite calcination process to the activity of the products, thereafter complete active differential calcination of each component, finally, it will realize activity control and acid dissolution decontaminate of light burning magnesia powder; besides, this work also aims to establish a hydration kinetics model for magnesium oxide through researching the essential rule of hydration recrystallization for magnesium oxide, and then control the nucleation speed by reducing the nucleation energy of inhomogeneous nucleation, meanwhile, reduce the the influence of inhomogeneous nucleation in the process of magnesium oxide hydration and improve the hydration rate of magnesium oxide; furthermore, this study will reveal the hydration synthesis mechanism of magnesium hydroxide by the hydration of magnesium oxide through researching the development process of magnesium hydroxide magnesium hydroxide, in addition, it will realize the preparation of magnesium hydroxide which the particle size and morphology is controllable under room temperature water bath (lower than 100 ℃), moreover, it will complete surface modification during the process of hydration synthesis, in the end, monodisperse modified nanometer magnesium hydroxide will be generated. The research results of this project will provide theoretical foundation for the magnesite utilization of high value-added for our country.

以菱镁矿为原料，煅烧生成的氧化镁水化法制备氢氧化镁，虽工艺简单成本低廉，但制备的氢氧化镁形貌和纯度都很难满足阻燃剂的要求。本项目拟通过研究菱镁矿煅烧过程对产品活性的影响规律，建立菱镁矿煅烧的热动力学模型，完成各组分的活性差异化煅烧，实现轻烧氧化镁粉的活性控制和酸溶除杂；通过研究氧化镁水化再结晶的本质规律，建立氧化镁的水化动力学模型，通过降低非均匀成核的成核功，控制成核速度，降低氧化镁水化过程中非均匀成核的影响，提高氧化镁的水化率；通过研究氢氧化镁晶体的生长历程，揭示氧化镁水合法制备氢氧化镁的水化合成机理，在常压水浴（低于100℃）条件下，实现氢氧化镁粒度、相貌的可控制备，并在水化合成过程中完成表面改性，制备出单分散改性纳米氢氧化镁。本项目的研究成果将为我国菱镁矿的高附加值利用奠定理论基础。

氢氧化镁因其无毒、无味、热稳定性好而成为一种非常具前景的阻燃剂，尽管我国镁资源也极其丰富，但纳米氢氧化镁（简写MH）因形貌难以控制、团聚严重、生产流程复杂、成本高而限制了其在阻燃剂方面的推广和应用。为了将我国菱镁矿的资源优势转化成产品优势，本项目以菱镁矿为原料，通过其热分解特性和煅烧产品中各成分的物性差异，研究煅烧产物酸化除杂的提取方法，制备水合试验的氧化镁前驱物；通过研究水化环境对氧化镁水化率和MH形貌的影响规律，探索水合法制备MH的生长机理。结果表明，菱镁矿的热分解属于典型的相边界反应，控制其煅烧温度和时间可实现氧化镁的可控制备，通过差异化煅烧，轻烧镁粉可在除杂中提质，制备出超纯高活性氧化镁；在水合法制备MH的过程中，镁离子的扩散是影响氧化镁水化率和负离子八面体生长基元成核与长大的关键，其中生长基元在MgO表面的非均匀成核会阻碍氧化镁水化，且成核速度太快，生长基元来不及生长，MH晶体团聚严重。可见，控制镁离子释放速度、阻止非均匀成核是制备均一单分散纳米MH的关键。因此，通过添加有机添加剂和超声空化作用在常压条件下水浴2h便可制备出单一六方片状纳米MH。.本项目根据我国菱镁矿的资源现状，利用矿石中矿物的个性差异和最终MH的合成特点，除杂过程中盐酸重复利用，所以整个工艺简单且无污染。通过控制镁离子的释放速度，打破了以往纳米MH阻燃剂的三步法制备工艺，简化了MH的制备工艺、缩短了制备时间，且水合制备方法环境友好，晶体生长可控。此研究成果和思路不仅为我国菱镁矿资源的高附加值利用提供理论和技术支持，也为我国非金属矿的高附加值利用和纳米材料的合成提供一个新思路。