反应萃取结晶高效提取浓海水钾资源的基础研究

Potassium is an important element in the growth of crops. About two-thirds of potash fertilizer in Chinese market needs to be imported. The potassium resource in seawater is rich but its separation and purification are difficult. Since the potassium ions can be replaced by ammonium ions to form a stable solid solution of potassium chloride and ammonium chloride in crystallization separation process, the purification of potassium chloride from potassium rich solution becomes difficult. A novel integrated process combining the chemical reaction, extraction and crystallization is proposed for the efficient separation of solid solution. The chemical reaction, organic amine solvent and alcohol diluents will be introduced to the crystallization separation of potassium-rich solution, combined with the more soluble in organic solvent complexes generated by reversible chemical reaction material and solvent hydrophilic property, lead to the phase transition of potassium rich solution. By controlling the solubility in different phases, the potassium chloride will be crystallized. According to the key scientific problems of the reaction extraction crystallization processs，such as the formation mechanism of the micro crystal surface, interface reaction and meso scale structure,and so on. The mechanism of heterogeneous reaction extraction and the coupling molecular transfer and diffusion process in the crystallization process are to be investigated. The effects of crystal seed on the enhancement of ion mobility, the relative basic research of crystallization and mass transfer are studied to further reveal the law of unconventional crystallization and separation control of multiphase reaction extraction crystallization process of potassium chloride, so as to efficiently extract the potassium resource from concentrated seawater.

钾是农作物生长重要元素，但我国钾肥约2/3依赖进口，海水中钾资源丰富但分离难度大。针对富钾液结晶时氯化钾晶体中钾离子可被铵离子取代,形成结构稳定固溶体,从而使富钾液不易提纯氯化钾，氯化铵的问题；该申请提出将化学反应、萃取引入固溶体的结晶分离过程，拟开发一种反应萃取结晶新型分离方法。本研究以海水提钾中易形成氯化钾铵固溶体为研究对象,利用化学反应、有机胺萃取剂与醇类稀释剂来耦合结晶,分离富钾液中氯化钾与氯化铵；通过可逆化学反应使亲水性物质与萃取剂结合,生成更易溶解在有机溶剂中的络合物，促使富钾液产生相变,改变两相中溶解度使氯化钾同时结晶析出；针对反应微元及晶体表界面介尺度结构的形成机理与反应萃取结晶调控关键科学问题,探讨多相反应萃取结晶过程耦合、分子传递与扩散过程的作用机制，通过晶种诱导强化离子迁移、结晶及传质相关基础研究，揭示多相反应萃取结晶过程氯化钾结晶及控制规律，从而高效提取浓海水中钾。

面对贫乏的陆地钾资源和丰富的海洋化学资源，从资源的合理利用与可持续发展的角度出发，海水提钾分离研究的意义重大。针对海水提钾富钾液结晶时氯化钾晶体中钾离子可被铵离子取代,形成结构稳定固溶体,从而使富钾液不易提纯氯化钾，氯化铵的问题；本项目将化学反应、萃取引入固溶体的结晶分离过程，开发了一种反应萃取结晶的新型分离方法。主要开展了以下研究工作：.1.研究氯化钾铵固溶体的物理化学特性，探讨了固溶度和结构及热稳定性，mNH4Cl•KCl和NH4Cl•nKCl固溶体特征,并较深入考察了从富钾液中结晶出氯化钾铵固溶体形成特性及多相界面过程作用机理等；.2.系统考察了各种因素对反应萃取结晶过程中的多元体系相图，探讨了氯化钾、氯化铵在不同溶剂体系中的溶解性能；在液-液-固多相区范围内，考察了不同因素对氯化钾、氯化铵分离的影响；.3.揭示了局部组成溶液性质、表/界面自由能等因素对晶体结构和形貌的影响机制；.4.通过有机胺反应转化萃取，分相、晶种/外场强化等手段诱导过饱和溶液相变成核，干预晶体生长过程，以实现能量传递与物质输运过程的协同强化;.5.构建反应萃取均匀分散多相流体结晶体系，分析微流体界面作用对结晶成核与生长的影响规律，探讨反应萃取结晶相平衡规律, 有机胺盐酸盐在醇与水两相中分配规律及氯化钾、氯化铵在不同相中特性，从而实现对固溶体的高效分离。