醇析强化铝酸钾溶液种分过程研究

The seeded precipitation of potassium aluminate solution is a key technology to promote the new method for the comprehensive utilization of valuable resources from alunite tailings. The low precipitation ratio and the uncontrolled particle size have been technical difficulties in the seeded precipitation process. A method of enhancing seeded precipitation by alcohol solventing-out crystallization is employed, which focuses on the coordinate adjustment mechanism of solution structure and particles behavior. The phase equilibrium data of the quaternary and alcohol system are measured, and the solubility calculation models for the complicated system are developed on the basis of density functional theory. According to the measured thermodynamic data, thermodynamic characteristics of precipitation process with alcohol solventing-out agent are revealed, and thus the suitable solventing-out agent will be selected. Based on the quantum chemistry theory, it is planned to explore the transformation procedure and mechanism of ion species. The adjustment method of solution ionic forms will be optimized. Meanwhile, in order to describe the rule of dissolution and crystallization process of aluminum hydroxide particles quantitatively, the multi-parameter coupled population balance equations are developed. Consequently, the particle size of particles could be adjusted simultaneously by using a dynamic optimization method. The mechanisms for micro-environment of alcohol to affect crystal faces of aluminum hydroxide crystal are illustrated on the scale of molecules, which will be used to predict and control the crystal morphology in the precipitation process. This project is expected to realize the efficient separation of potassium and aluminate resources from the leaching system of alunite tailings and to provide the theoretical basis for the resource development and industrial application of alunite tailings.

铝酸钾溶液晶种分解是明矾石尾矿有价资源综合利用新途径的关键技术。本项目针对铝酸钾溶液种分过程中分解率低、氢氧化铝产品粒度难以调控等难点，采用醇析法强化种分过程，研究醇解过程中溶液结构与粒子行为的协同调控机制。测定含有低元醇的四元体系相平衡基础数据，基于密度泛函理论建立多组分溶解度计算模型，明晰醇解过程中铝酸钾溶解平衡的热力学特征，获取理想的醇析剂；基于量子化学理论，揭示醇解过程中离子形态的转变历程及转化机理，优化溶液离子形态的调控手段，同时采用多参数耦合粒数衡算模型，定量描述氢氧化铝固体颗粒的溶解-结晶过程规律，采用动态优化法实现固体颗粒的粒度调控；从分子尺度揭示低元醇微观环境对氢氧化铝不同晶面的作用机理，实现醇解过程中氢氧化铝晶体形貌的预测与调控。本项目有望实现明矾石尾矿溶出体系中钾铝有价组分的高效分离，为明矾石尾矿资源开发与工程应用奠定理论基础。

明矾石尾矿矿中含有丰富的钾明矾等矿物，是潜在的二次矿物资源。针对明矾石尾矿资源，开发了KOH亚熔盐低温常压条件下梯级溶出明矾石尾矿有价资源的新工艺，过程能耗低，实现近零排放，绿色无污染。但针对亚熔盐溶出复杂体系，铝酸钾溶液传统的晶种分解过程存在分解率低、分解时间长、氢氧化铝产品粒度难以调控的难题。因此，铝酸钾溶液种分过程强化成为明矾石尾矿资源化利用的关键环节。.本项目系统研究了含有低元醇多元体系的热力学平衡，完善了323.15-353.15 K范围内K2O-Al2O3-H2O三元强碱体系相图，构建了Al(OH)3溶解度理论计算模型，准确预测了Al(OH)3在该三元体系中的溶解度。研究发现添加不同体积的甲醇均可与铝酸钾溶液形成均相溶液，氧化铝平衡溶解度大幅降低，从热力学角度甲醇筛选为合适的醇析剂。通过在线拉曼光谱及红外光谱研究，揭示了铝酸钾溶液分解机理，低碳醇与水形成氢键夺取了铝酸根离子的水化层中的水分子，促进了铝酸根离子聚合形成结晶单元。以甲醇作为醇析剂，通过构建醇解过程固体颗粒的多参数耦合粒数衡算模型，计算得到氢氧化铝生长速率与过饱和度呈平方关系，氢氧化铝生长和二次成核的活化能分别为55和80 kJ·mol-1，表明醇解过程中氢氧化铝的生长和二次成核均为表面累积控制。采用分子动力学模拟方法，从分子尺度揭示了甲醇分子与氢氧化铝晶体表面官能团之间的作用机理，甲醇分子会优先附着在氢氧化铝(002)面，阻碍结晶基本单元在(002)面的生长，导致(002)面保持较慢的生长速度而最终保留下来成为主要晶面，从而使氢氧化铝晶体形貌由六棱柱状附聚物变为了薄片状附聚物。通过本项目研究，可大幅提高铝酸钾溶液分解率至91%，同时显著改善氢氧化铝固体粒度，实现了明矾石尾矿溶出体系中钾铝组分的高效分离，为明矾石尾矿资源开发与工程应用奠定理论基础。