以盐湖氯化镁制备高附加值镁铝尖晶石新工艺的基础研究

A large amount of byproduct MgCl2 which were obtained during the process of KCl fertilizer using carnallite as material in Qinghai saltlake district, are not used effectively right now. Producing high value-added product using this kind of material will be an effective method to solve comprehensive utilization of magnesium resource of saltlake. Therefore, a new green technology of Mg-Al spinel production has been put forward in this project as followed: Mg4Al2(OH)14∙3H2O precursor which can be obtained with the reaction of byproduct MgCl2 and AlCl3 through introducing of NH3. Precipitate can be further calcined at lower temperature (500 °C) to produce Mg-Al spinel which is a high value-added magnesium-based product. The obtained NH4Cl-rich solutions provided an opportunity to recover NH4Cl with the aid of the common ion effect by feeding MgCl2-AlCl3. This process realized the objective of water recycling and reduced sewage discharge. Therefore, this is a green new technology. In this project, the specific research contents include: (1) The reactive crystallization kinetics and reactive mechanisms of Mg4Al2(OH)14∙3H2O in the gas-liquid-solid system will be studied. (2) The phase equilibrium data of the complex system NH4-Al-Fe(II)-Mg-Ca-K-Cl-H2O will be measured and the phase behavior will be studied. (3) Based on non-primitive mean spherical approximation (MSA) approach by accounting for electrostatic interaction between ions and hard-sphere perturbation theory by accounting for the dispersion interaction with Cotterman et al.'s equation of state for a Lennard-Jones fluid, a thermodynamic model for the NH4-Al-Fe(II)-Mg-Ca-K-Cl-H2O system will be established. All of these will provide the data and theory foundamentals for the development and industrial scale up of this thchnology.

青海盐湖生产钾肥的过程中，副产大量的水氯镁石没有得到有效利用，以其为原料生产高附加值镁产品是解决盐湖镁资源综合利用的有效途径。本项目提出了以盐湖钾肥副产氯化镁为原料，氨气作为沉淀剂与氯化铝共沉淀得到Mg4Al2(OH)14∙3H2O前驱体，进一步在较低温度下（500 °C）煅烧生产镁铝尖晶石的绿色新工艺。制备前驱体过程中得到的母液则利用原料的共离子效应生产氯化铵产品，从而解决了污水排放的问题。针对这一新工艺，申请人将开展的物理化学基础研究包括：Mg4Al2(OH)14∙3H2O在气-液-固体系的反应结晶机理和结晶动力学的研究；NH4-Al-Fe(II)-Mg-Ca-K-Cl-H2O复杂体系中氯化铵和氯化铝盐析结晶行为的研究；基于积分方程理论和微扰理论建立NH4-Al-Fe(II)-Mg-Ca-K-Cl-H2O体系的热力学模型，为该绿色新工艺的开发和放大提供完善的数据和理论基础。

以盐湖钾肥生产过程中副产的水氯镁石为原料生产高附加值镁产品是解决盐湖镁资源综合利用的有效途径。申请人提出了以盐湖钾肥副产氯化镁为原料，氨气作为沉淀剂与氯化铝共沉淀得到Mg4Al2(OH)14∙3H2O前驱体，进一步在较低温度下煅烧生产镁铝尖晶石产品的绿色新工艺。通过研究Mg4Al2(OH)14∙3H2O在气-液-固体系的反应结晶动力学，确定了制备镁铝尖晶石的最佳工艺参数，得到的产品符合国家标准；基于测定的相平衡数据 (AlCl3-NH4Cl-H2O, AlCl3-MgCl2-H2O, AlCl3-CaCl2-H2O, FeCl2-CaCl2-H2O，AlCl3-CaCl2-FeCl2-H2O)以及从文献上筛选的相平衡数据，建立了NH4-Al-Fe(II)-Mg-Ca-K-Cl-H2O复杂体系的热力学模型；基于建立的热力学模型，通过共离子效应，得到了回收沉淀镁铝尖晶石中间体母液中氯化铵的最佳工艺路线，确保整个工艺过程无废水排放。所有这些为该绿色新工艺的开发和放大提供完善的数据和理论基础。