电子垃圾中的钯在超临界流体中的溶出特性研究

This application focuses on the basic theory study on green recovery of noble metals from e-waste, and palladium will be the target element. In the study, organic polymers in the e-waste will be decomposed and palladium will be condensed through supercritical organic reagents disposal based on the theories of supercritical fluids decomposition, extraction and dissolving. The extraction and separation of palladium from the condensed residue will be carried out through two routes: (1) extracting, separating and recovering palladium using supercritical NH3、CO2 accompanied by various carrying and improving agents; (2) separating and recovering palladium in ultra supercritical water, since palladium in e-waste exists as metal particle or alloy and metal element could be dissolved in ultra supercritical water. Various oxidizing agents and electron donors will be introduced into the supercritical system so as to examine the decomposing property and pollution control effect during palladium condensing process. The changing properties of palladium forms and bonds in different supercritical fluids will be analyzed, and the extraction mechanism of palladium will be elucidated. The influences of palladium forms and extraction effect by other metals in the e-waste complicated system will be examined, and interaction mechanisms will be clarified. Moreover, the dissolving property of palladium in ultra supercritical water and the separating out property of palladium after releasing the supercritical condition will be studied, and furthermore, the separation method of palladium from ultra supercritical water will be established, and related mechanisms and routes will be clarified. Finally, a theoretical guidance for green recovery of noble metals from e-waste will be established.

本申请拟开展电子垃圾中贵金属绿色回收方法的基础研究。以贵金属钯为目标元素，利用超临界流体解聚、萃取和熔化理论，通过超临界有机溶剂处理将电子垃圾中的有机高分子聚合物解聚回收单体，同时实现钯的富集。将通过两种方法提取回收富集体中的钯：（1）利用超临界NH3、CO2携带不同夹带剂和改性剂选择性地萃取、分离、回收钯；（2）根据电子垃圾中的钯以单质或合金形式存在的特点，利用超高温高压超临界水熔化单质金属的特性分离回收钯。将通过向超临界体系中导入氧化剂、电子供体探讨钯富集过程中高分子聚合物的解聚特性和污染控制效果，解析钯在不同超临界流体中的形态、价态变化特征，阐明钯的萃取机制，探知电子垃圾复合体系中其它金属对钯形态和萃取效果的影响，阐明交互作用机制；研究超高温高压超临界水中钯的熔化特性和解除超临界条件后的分离析出特征，确立分离回收方法，阐明相关机制与路径，为电子垃圾中贵金属的绿色回收提供理论指导。

项目开展了电子垃圾中钯的回收研究，旨在明晰超临界流体中富集和绿色回收钯的机制。首先利用超临界流体解聚、萃取和熔化理论，通过超临界有机溶剂处理将电子垃圾中的有机高分子聚合物解聚回收单体，同时实现钯的富集。通过向超临界体系中导入氧化剂、电子供体探讨了钯富集过程中高分子聚合物的解聚特性和污染控制效果，解析了钯在不同超临界流体中的形态、价态变化特征，阐明了钯的萃取机制和电子垃圾复合体系中其它金属对钯形态和萃取效果的影响。研究发现NaOH/H2O2修饰后的超临界水氧化系统可将溴化环氧树脂彻底降解为长链烃类 (CnH2n+2)，CO2，H2O和NaBr，反应过程中，H2O2产生的HO•和HO2•引发了中间产物苯酚的氧化开环降解，增强了钯的富集效率。在超临界二氧化碳 (SC-CO2)络合萃取废弃陶瓷电容器中Pd(II)的研究中，阐明了Pd(II)在SC-CO2中与不同类型络合剂(Cyanex272、LIX84I和Cyanex302)的配位机理。研究显示含中心S原子的萃取剂Cyanex302对Pd(II)的萃取效率大大优于中心原子为O的萃取剂Cyanex272和中心原子为N的萃取剂LIX84I。分子杂化轨道理论表明Pd(II)可以与Cyanex302的中心S原子形成π*键，这极大增强了所形成的中性络合物Pd(II)-Cyanex302在SC-CO2中的溶解度和稳定性。研究发现含钯富集体中的Pd(0)先被KI-I2组合利用氧化络合反应转化为碘络阴离子[PdI3]ˉ，随后 [PdI3]ˉ与共溶剂丙酮通过电荷吸引力形成可溶于SC-CO2的含钯中性络合物 [(CH3COCH3)nH][PdI3]。该工艺无需利用酸造液将Pd(0) 转化为Pd(II)，一步即可完成Pd(0)的萃取回收。相比传统贵金属回收工艺，利用SC-CO2作为溶剂回收废弃线路板中的Pd(0)，具有回收步骤简洁、环境负荷小和不产生有机废液的优势。研究成果可以为电子垃圾中贵金属的绿色回收提供理论指导。