重金属氨络合废水鸟粪石强化结晶沉淀及调控机制

The water environment of China faces the combined pollution from heavy metals, ammonia and other pollutants. Heavy metals and ammonia could easily form chelated ions that are stable and difficult to be decomposed, which makes the complex wastewater being one of the most refractory wastewaters in the field. Especially, there is still no effective treatment method for the high-strength heavy metal ammonia chelated wastewater. Our previous studies revealed that the struvite crystallization could effectively decompose the heavy metal ammonia chelated ions and realized simultaneous removal of heavy metal and ammonia from the high-strength chelated wastewater. In the present study, based on the key scientific issues concerning in the struvite crystallization and precipitation process, the formation of struvite-heavy metal hydroxide precipitates will be investigated to illustrate the mechanism of simultaneous removal of heavy metal and ammonia. Secondly, the interface interaction between struvite and metal hydroxide will be studied to illuminate the high-rate precipitation and separation mechanism from solution. Subsequently, the regulation principle and control strategies for struvite and metal hydroxide precipitation will be investigated to optimize the co-crystallization-precipitation processes. Finally, the separation mechanism of heavy metal from the struvite precipitate and the recycling technologies will be set up to realize the sustainability of the struvite crystallization method. The major objectives of the present proposal are to clarify the mechanisms of enhanced treatment of heavy metal ammonia chelated wastewater and the related simultaneous removal of heavy metal and ammonia pollutants, which would expand the theoretical basis for enhanced treatment of heavy metal ammonia complex wastewater and would be useful for the application of the enhanced struvite crystallization technology in heavy metal ammonia chelated wastewater treatment.

我国水生态环境面临重金属、氨氮等污染物的复合污染。重金属与氨在废水中易形成稳定且难降解的重金属氨络合离子，一直是废水处理领域的难题。尤其是对于高浓度的重金属氨络合废水，目前尚无有效的处理方法。前期研究发现，鸟粪石结晶沉淀法可促进重金属氨络合离子的解离，实现高浓度重金属氨络合废水中重金属与氨氮的同步净化。本项目拟通过研究鸟粪石-重金属氢氧化物沉淀的形成机制，解析重金属与氨氮同步净化机理；通过研究鸟粪石与重金属氢氧化物的界面作用，探明沉淀物高效沉降及固液分离机理；通过研究鸟粪石-重金属氢氧化物沉淀的调控原理，建立工艺过程强化及调控方法；通过研究鸟粪石-重金属氢氧化物沉淀的回收机制，形成有价金属开路回收及沉淀产物循环沉氨技术原型。本项目旨在弄清鸟粪石结晶沉淀强化处理重金属氨络合废水的过程机理，揭示重金属、氨氮同步高效净化机制，为重金属氨络合废水的高效强化处理及推广应用提供科学依据。

稀土、锂电池生产等有色行业产生的重金属氨络合废水具有浓度高、毒性强等特点，生物脱氮工艺难以应对。因此，重金属氨络合废水的处理需要朝着高效化学沉淀的方向拓展。本项目基于鸟粪石结晶共沉淀协同去除氨氮重金属的新发现，系统研究了络合废水鸟粪石结晶破络-共沉淀机制、界面作用力以及沉淀产物的回收机制等关键科学问题，取得如下成果：.1）提出了鸟粪石结晶沉淀法强化处理重金属氨氮复合废水新思路，揭示了鸟粪石结晶破络-共沉淀的形成机制。热力学平衡分析及优势区域模拟发现，络合体系中加入Mg和P元素使Cu从络合态向Cu(OH)2转变，有利于铜氨络合物解离。条件试验结果表明，鸟粪石法处理铜氨络合废水在pH=9.0，反应30min下，Mg与P添加量为n(Mg):n(P):n(N)=1.2:1.4:1时效果最佳，氨氮和重金属协同去除率分别达到98.9%和99.95%。.2）阐明了鸟粪石结晶共沉淀法处理重金属氨络合废水的界面作用力。试验发现，针对不同浓度范围的铜氨络合废水, 氨氮和铜离子去除率均在99%以上。进一步研究发现，鸟粪石表面的羟基、氨根基团等与氢氧化铜羟基间可形成氢键，对氢氧化铜具有较强吸附作用；同时观察到鸟粪石与氢氧化铜胶体颗粒间存在静电引力和铜离子进入鸟粪石晶体的掺杂行为。这些作用共同促进重金属与氨氮的高效去除。.3）发现了重金属氢氧化物在鸟粪石晶体表面的异相成核机制。建立了重金属氢氧化物在鸟粪石晶体表面异相成核的热力学模型，拟合系数达到95%。模拟计算结果表明，鸟粪石晶体共存下，重金属氢氧化物沉淀的成核能垒大幅度降低98%，仅0.156 KJ/mol，其异相成核极易发生，是实现氨氮与重金属共沉淀去除的重要原因。.4）优化了鸟粪石结晶生长过程工艺参数，建立了鸟粪石纯化和氨氮资源回收方法。构建了两种气升循环式鸟粪石强化结晶流化床反应器，对反应器内部工况模拟计算发现，文丘里管和气升循环作用大幅提升了传质效率；壁面剪切速率和流体剪切速率差是鸟粪石生长快、粒径大的关键原因。.5）建立了重金属氨氮废水鸟粪石法沉淀产物“热解脱氨-水解-电沉积回收重金属-磷、镁源循环利用”的工艺流程，实现了重金属开路回收及磷镁循环利用。热解脱氨最优条件为热解温度130-140℃、热解时间3h，脱氨率99%，电沉积回收重金属过程最优条件为电流密度200A/m2、电解液浓度200g/L、pH值2.0，铜镍回收率95%