磷酸分解磷矿过程配位化学耦合温度场对磷酸稀土沉淀-溶解平衡影响

Phosphorite, with small amount of associated rare earth, is abundant around the world. The phosphorite has important value for comprehensive utilization. Conventional processes are hard to comprehensively utilize the associated rare earth and the phosphogypsum because of the dispersive distribution of rare earth, disposal of large amount of low-quality phosphogypsum, and difficulty in recovery of rare earth with low concentraton from the leach solution, resulting in serious resource and environmental issues. In this project, enhanced digestion based on coordination chemistry and phase reconstruction based on selective precipitation are proposed to solve the above problems. Thermodynamic calculation and experiments are used to select suitable coordination systems, which can coordinate with RE3+ at room temperature to form a coordination complex, which is unstable under high temperatures. These coordination systems will help to enhance the rare earth leaching at room temperature, but induce the precipitation of RE3+ by PO43- at high temperatures using the temperature effect of REPO4. The influence of coordination chemistry and temperature field during the digestion of phosphorite by phosphoric acid on the precipitaiton-dissolution equilibrium of REPO4 is studied to make the equilibrium controlled, thus enhance and regulate the migration of rare earth and phosphorus, realizing the phase reconstruction and efficient separation. The aim of the project is to solve the two key scientific issues, viz. efficient digestion of phosphorite by phosphoric acid and efficient extraction of rare earth from acidic leach solution under mild conditions, and form a new technique for the efficient separation of phosphorus from rare earth using coordination leaching and selective precipitation. This new technique will not only improve the theoretical system of wet-process phosphoric acid process , but also lay the theoretical foundation for the large-scale application of efficient extraction of associated rare earth in the phosphorite.

世界磷矿资源极其丰富，通常伴生有微量稀土，综合利用价值高。现有工艺存在稀土分散分布、大量低品质磷石膏堆弃、以及浸液中低浓度稀土回收困难等问题，难以实现伴生稀土及磷石膏高效综合利用，资源环境问题突出。本课题拟通过配位化学强化分解和基于选择性析出的物相重构，利用热力学计算与试验相结合，筛选合适配位体系，常温下与RE3+具有较强的配位能力，强化RE浸出；高温下配合物不稳定，释放出RE3+，利用磷酸稀土的温度效应使其与PO43-结合析出；揭示磷酸分解磷矿过程配位化学耦合温度场对磷酸稀土沉淀-溶解平衡影响规律，实现该体系REPO4沉淀-溶解平衡可控，从而强化和调控稀土和磷等有价组元的迁移，实现物相重构及高效分离，突破磷酸高效分解磷矿及磷酸分解液中稀土温和高效提取两大关键问题，建立磷酸配位浸取-选择性析出分离磷和稀土的新方法，进一步完善湿法磷酸工业理论体系，为磷矿中伴生稀土资源高效提取奠定理论基础。

世界磷矿总储量超过3000亿吨，稀土平均含量约为0.5‰，其伴生的稀土资源总量将超过1亿吨，甚至超过目前已探明稀土资源总储量。2019年世界磷矿产量2.4亿吨，伴生稀土约为10万吨，相当于全球稀土年产量。我国滇、黔、川、湘等地磷矿资源相对丰富，作为一种潜在的稀土资源，如何实现磷矿中微量稀土的低成本高效提取是该领域研究面临的难点问题。由于磷石膏高的杂质含量和含水率，制约了其综合利用（利用率<10%）。目前，全球磷石膏堆存量高达50亿吨，且每年仍以1~2亿吨的速度增长，如何实现磷石膏综合利用已成为制约磷化工产业发展的瓶颈。. 本项目系统研究了磷酸体系/磷酸二氢钙-磷酸体系中稀土的沉淀-溶解行为，建立了磷酸溶液中稀土溶解度（[RE3+]）与总磷浓度（[P]）之间的数学模型，推导并建立了稀土溶解度与氢离子浓度（[H+]）之间的线性关系、磷酸二氢钙浓度（[Ca2+]）和氢离子浓度之间的数学模型，揭示磷酸分解磷矿过程配位化学耦合温度场对磷酸稀土沉淀-溶解平衡影响规律，实现该体系REPO4 沉淀-溶解平衡可控，从而强化稀土和磷等有价组元的迁移；提出了磷酸配位浸取-选择性析出技术分离磷和稀土的新方法，实现REPO4物相重构及稀土、磷和钙高效分离与综合利用，为磷矿中伴生稀土资源提取的应用提供理论依据和技术支持。项目具有良好的环保、经济和社会效益，应用前景十分广阔。推广应用后，将进一步提高战略性稀土资源的开发利用水平，巩固我国稀土产业的国际领先地位，并促进湿法磷酸行业的健康可持续发展。