含铬废水中锌镍离子对铬铁矿成矿行为及磁学性能影响的机理研究

Chromium-containing industrial wastewater is a kind of highly toxic hazardous waste liquid. The common treatment method is chemical precipitation, but this method produces a large amount of toxic hazardous solid waste, which is also called sludge. In order to eliminate the harmness of wastewater and achieve efficient recovery of the resource, the applicant had developed a innovative technology by reduction with iron-based material, followed by preparing artificial minerals, and magnetic separation, during her doctoral study period. The step-by-step recovery of valuable metals was realized while wastewater was purified. However, it was found that coexisting zinc and nickel ions have an important influence on the ore-forming behavior and magnetic properties of chromite, even the magnetic separation of chromite, during the previous studies. However, the influence law and mechanism have not been studied clearly. Therefore, this project will combine reaction thermodynamics with solution chemistry, crystallography, coordination field theory and density functional theory. In macroscopic, the composition, crystal size, surface morphology and magnetic properties of synthetics by ferrite method will be studied when zinc and nickel ions exist in the solution. It will be revealed that the influence law of zinc and nickel ions on the grain growth and magnetic properties of chromite. And the correlation between the ore-forming behavior and magnetic properties will be illuminated. From the microscopic point of view, the transformation law of the crystal structure and magnetic properties of chromite will be studied when zinc and nickel ions are doped. And the mechanism of the influence of zinc and nickel ions on the magnetic properties of chromite will be interpreted. The purpose of the project is to lay a well theoretical foundation for the industrial application and popularization of the innovative technology.

含铬工业废水是一种剧毒危险废液，采用常用的化学沉淀法处理易产生大量毒性危险固体废物-污泥。为从源头上解决含铬废水的危害及资源化难题，申请者博士期间研发了“高性能铁基材料还原-人造矿物分步合成-磁选分离”新技术，在净化水体的同时实现了有价金属的分步回收。但前期研究发现，共存的锌镍离子会对铬铁矿的成矿行为及磁学性能产生影响，进而影响到铬铁矿的磁选回收，但其影响规律及机理尚不明确。因此，本项目结合反应热力学、溶液化学、结晶学、配位场理论和密度泛函理论，从宏观角度研究锌镍离子存在时，铁氧体法合成产物组分、结晶粒度、表面形貌及磁学性能，揭示锌镍离子对铬铁矿晶粒生长及磁学性能的影响规律，阐明铬铁矿成矿行为与磁学性能间的相关性；从微观角度深入研究锌镍离子掺杂时铬铁矿晶体结构及磁学性能的变化规律，诠释锌镍离子对铬铁矿磁学性能影响的作用机理。本项目的研究旨在为新技术的工业应用及推广提供夯实的理论依据。

铁氧体法处理含铬废水既可以实现废水的净化，也可以实现废水中有价金属的资源化，是一种具有工业应用的潜在技术。锌、镍离子常共存于含铬废水中，当采用铁氧体法处理含铬废水时，锌、镍离子容易进入具有磁性的尖晶石晶体结构，从而影响合成产物铬铁矿的磁选回收指标。因此，为查明锌镍离子对铬铁矿成矿行为和磁学性能的影响机制，项目采用FactSage和HSC Chemistry软件，计算了合成化学反应的吉布斯自由能变，确定了含铬废水、锌铬混合废水、镍铬混合废水中不同尖晶石形成的可能性；绘制了Fe-H2O、Fe-Cr-H2O 、Fe-Zn-H2O、Fe-Ni-H2O的Eh-pH图，查明了不同尖晶石出现的优势区域，确定了溶液中合成铁氧体适宜的电位和pH环境；绘制了Cr-Fe-O、Cr-Zn-O、Cr-Ni-O、Cr-Ni-O、Fe-Zn-O三元系相图，分析了金属离子不同摩尔比对产物组成的影响。采用Visual MINTEQ 软件，绘制了锌、镍和铬离子在不同pH环境下的溶液组分图，确定了三种离子在合成尖晶石过程中的存在状态。分别在单一铬离子体系、锌铬离子共存体系、镍铬离子共存体系以及锌镍铬三元共存体系下，研究了锌离子和镍离子对出水水质、产物稳定性和磁学性能的影响，查明了反应过程中溶液pH、氧化还原电位、溶解氧、金属离子浓度的变化规律，揭示了锌镍离子进入铬铁矿的反应路径。通过XRD和毒性浸出试验，揭示了合成产物的物相演变和金属离子的溶出规律。通过SEM-EDS和穆斯堡尔谱分析确定产物的组成、表面形貌和元素分布，推导了锌、镍离子掺杂时合成尖晶石的分子结构。采用量子化学计算软件对单一铬铁矿和不同程度的锌、镍离子掺杂后的铬铁矿晶体结构、能带性质、电荷分布、分子磁矩、自旋极化态密度进行分析，确定了适宜的取代位置和取代量，查明了锌镍离子对铬铁矿原子间相互作用和电荷分布的影响，从微观角度揭示了锌镍离子对铬铁矿磁学性能影响的机理。项目的研究为铁氧体法在工业废水的净化和资源化奠定了夯实的理论基础，有助于推动该技术的产业化应用。