建構同步催化破壞Co(II)-EDTA螯合物並回收有價金屬鈷資源之先進電化學方法

Abstract

近年來，隨著高科技半導體產業的蓬勃發展，為了延續莫爾定律，晶片製程中對於重金屬鈷的使用日益增加，導致每年含鈷廢水的產生及污染。這些廢水中的鈷通常與螯合劑(例如乙二胺四乙酸(Ethylenediaminetetraacetic acid, EDTA)、檸檬酸(Citric acid, CA)等)以重金屬螯合物(Heavy metal complexes, HMCs)的形式穩定存在，導致傳統分離技術難以將其去除。最近研究表明螯合物的降解往往是去除重金屬的先決條件。近年的研究趨勢，以電化學驅動的先進氧化處理技術(Electrochemical advanced oxidation processes, EAOPs)能夠透過陽極的電催化生成大量活性氧物質(Reactive oxygen species, ROS)，有效破壞重金屬螯合物中的強配位鍵結，將有機污染物轉化為CO2、H2O等小分子，並同時電沉積有價金屬於陰極回收，作為一種具發展潛力的可行技術。因此本篇研究中，採用以具備良好電催化效率的鉑(Platinum, Pt)作為陽極，並結合廢水中常見的電解質Na2SO4建立一套EAOP系統對於含有Co(II)-EDTA螯合物的模擬廢水進行降解性能測試。根據本研究結果顯示，在施加5 V的電壓下，超過99.8%的Co(II)-EDTA在三小時內被成功解螯合，甚至同時達到71.5%的TOC去除並於陰極表面回收97%有價金屬鈷資源。此外本研究還透過一系列分析方法的建立，探討Co(II)-EDTA降解的機制與途徑。在添加苯酚作為自由基(·OH與SO4·-)清除劑後發現，溶液中釋放之游離鈷離子與電沉積於陰極之鈷物種濃度顯著下降，因此推測透過自由基(·OH與SO4·-)的間接氧化途徑為降解Co(II)-EDTA的主導反應機制。此外無機氮的高效轉化率(96%)也輔助說明了EDTA含氮官能基的斷鍵與礦化。最後透過SEM與XPS分析，推測回收鈷資源以金屬鈷(Co0)、氫氧化鈷(Co(OH)2)、氧化鈷(CoO)的化學形態存在，可進一步用於合金、染料、鋰電池等材料的製備。 綜上所述，透過Pt介導的EAOP系統能夠有效於Na2SO4中電催化生成大量活性氧自由基，以同時達到Co(II)-EDTA的解螯合與有價金屬鈷資源的回收，展現出其作為含Co(II)-EDTA廢水的有效處理技術，有助於實現永續發展目標。

In recent years, with the flourishing development of the high-tech industry, the utilization of the cobalt in manufacturing processes has grown significantly, leading to the generation and contamination of wastewater containing cobalt. Typically, cobalt in these wastewaters exists in the form of heavy metal complexes (HMCs) stabilized by chelating agents such as ethylenediaminetetraacetic acid (EDTA) and citric acid (CA), making it challenging to remove using traditional separation techniques. Thus, this study establishes an electrochemical advanced oxidation process (EAOP) aimed at evaluating the in-situ electrogeneration of reactive oxygen species and decomplexation performance for synthetic wastewater containing Co(II)-EDTA complexes utilized platinum (Pt) as the anode, in combination with the common electrolyte Na2SO4. The results indicate that over 99.8% of Co(II)-EDTA was successfully decomplexed within 3 hours under voltage of 5 V. Furthermore, it achieved a simultaneous 71.5% removal of TOC and 97% of the valuable cobalt resources was recovered at the cathode surface. We also employed a series of analytical methods to explore the mechanisms and pathways of Co(II)-EDTA decomplexation. Upon the addition of phenol as a scavenger for radicals (·OH and SO4·-), a notable decrease in the concentration of released free cobalt ions in the solution and cobalt species deposited at the cathode was observed. This suggests that the primary decomplexation of Co(II)-EDTA occurs through indirect oxidation by radicals (·OH and SO4·-). Additionally, the high conversion efficiency (96%) of inorganic nitrogen supported the mineralization of the nitrogen-containing functional groups in EDTA. Finally, SEM and XPS analysis suggested that the recovered cobalt resources exist in chemical forms such as metal cobalt (Co0), cobalt hydroxide (Co(OH)2), and cobalt oxide (CoO), which can be further reused in the production of alloys, dyes, lithium batteries, and other applications. In summary, the Pt-mediated EAOP can effectively electrocatalyze the generation of abundant ROS in Na2SO4, and it has proven effective for the simultaneous processes of Co(II)-EDTA decomplexation and the recovery of valuable cobalt resources. This highlights its potential as an efficient technology for treating wastewater containing Co(II)-EDTA, contributing to the pursuit of sustainable development goals.