混合电镀污泥资源化过程中铬优先深度分离及高值利用技术基础

The recovery of the valuables of Cu, Ni and Zn is mostly concerned in the resourcization of electroplating sludge, while Cr has not been effectively utilized yet. The metal of Cr accouts for 65% of the total values of the metals in electroplating sludge. The high-valence Cr does present a serious threat to enviroment and human health. The deep separation of Cr/Fe in acidic leaching solutions of electroplating sludge is the key technical problem unresolved. Thus, the mixed electroplating sludge with huge production in China is selected as the research subject and the fundamental research on the deep separation as well as the high-value utilization of Cr is further proposed on the basis of a new selective phosphate precipitation method. The research includes: ①the deep reduction equilibrium of Fe2+/Cr3+ in acidic solutions; ②the selective deep-separation mechanism and the control of phosphate precipitation of Cr; ③the preparation of high-purity Cr(OH)3 through the unconventional hydrolysis of CrPO4 and the crystal control of Cr(OH)3. The complete reduction of Fe under the lowest consumption of reductant prior to the phosphate precipitation as well as the crystal control of Cr compounds, such as the intermediate of CrPO4 and the ultimate of Cr(OH)3 are focused. This research is essential to the system integration of techniques of harmless disposal and high-value utilization of Cr in mixed electroplating sludge.

目前电镀污泥资源化多着眼于铜、镍、锌等有价金属，而约占电镀污泥中金属价值65％的铬未能有效综合利用。高价铬等重金属对环境及人体健康都构成严重威胁。就电镀污泥中铬资源化而言，其常规酸浸溶液中铬铁深度分离是关键技术难点。鉴于此，本课题以我国大量的混合电镀污泥为研究对象，基于选择性磷酸沉铬分离新方法，研究铬优先深度分离及高值利用过程中的共性及关键科学问题：①酸性溶液体系铬、铁深度还原平衡机制；②选择性磷酸沉淀优先深度分离铬的机理及调控机制；③磷酸铬非常规转型及高纯氢氧化铬晶形调控机制。其中，重点解决选择性磷酸沉淀前如何控制还原剂最低反应量条件下铁全还原及铬资源化过程中各种铬化合物（如中间产物磷酸铬、最终产物氢氧化铬）晶形控制的问题，为混合电镀污泥中铬无害化及高值利用技术集成奠定理论基础。

鉴于目前国内外在电镀污泥全组分资源化利用方面支撑产业化的关键技术尚未突破，本项目以混合电镀污泥中铬铁分离问题为研究对象，开展多金属低能耗低成本选择性提取分离与组分协同资源化利用关键技术耦合研究。.（1）提出“优先络合-水解沉淀”分离Cr/Fe新方法。用紫外分光光度法、质谱法对甲酸钠与Fe/Cr配位机理进行研究。结果表明，在相同条件下Fe3+优先于Cr3+与甲酸钠形成配合物，过程为吸热反应；基于条件实验结果，最终使Fe沉淀率达93.65%，而Cr沉淀率低至13.37%，Cr/Fe分离效果良好；.（2）提出选择性磷酸沉淀方法分离Cr/Fe新方法。基于热力学分析和正交实验方法，分析了选择性沉Cr影响因素；进一步借助工艺矿物学手段对沉淀产物进行分析。在电镀污泥浸出液经萃取提铜和活性炭吸附脱油等工序处理后，经选择性磷酸沉淀方法处理，溶液中Cr浓度可降至0.04 g/L左右，沉Cr反应迅速，工艺运行稳定。沉Cr渣经稀酸洗涤，Ni、Zn、Fe含量可分别降至～0.4%、～0.1%和～0.2%，实现有价金属的深度分离和高效回收。.（3）实现磷酸铬渣中P/Cr有效分离并转型制取高品质Cr(OH)3产品。基于正交实验，分析了磷酸铬渣转型过程的影响因素主次顺序，经工艺条件实验，使P浸出率高达97%，达到了有效分离P/Cr的目的；碱浸液在补充适量碱的情况下，历经十次循环，仍能使P浸出率保持在90%以上。由于碱浸液循环，所以不存在Cr溶解损失问题，Cr收率得以保证。.相关研究成果为电镀污泥有价金属回收（特别是Cr的无害化和资源化）开辟了一条可行、经济的新途径。