不同實際鉻蝕刻廢液中Ce(IV)電再生之研究

Electrochemical regeneration of Ce(IV) in different real spent Cr-etching solutions

蔡仁瑋(Ren-Wei Tsai)

指導教授 ： 黃國林

國立屏東科技大學/工學院/環境工程與科學系所/碩士(2015年)

https://doi.org/10.6346/NPUST.2015.00223

摘要

台灣是全球薄膜電晶體液晶顯示器(TFT-LCD)主要供應國之一。然而，TFT-LCD產業會產生大量屬於有害廢棄物之鉻蝕刻廢液，若能將其再生及利用，可減少污染物之排放與回收有價資源。因此，本研究探討實際鉻蝕刻廢液(硝酸介質)中Ce(IV)之電再生，測試不同參數：電極(BDD、PbO2和Pt)，電流(1.5、1.0和0.5 A/cm2)，溫度(10 ℃、25 ℃和40 ℃)，離子交換膜(NEOSEPTA CMX，AMX，Nafion-324，Nafion-424，Nafion-212和Nafion-117)，電極面積(1 cm2，2 cm2和4 cm2)，陰極(鈦電極和不鏽鋼)，離子交換樹脂(OH型和Cl型)、實際鉻蝕刻廢液(A廠、B廠、C廠及D廠)及反應器(單槽和雙槽)對Ce(IV)電再生之影響。
實驗結果顯示，在BDD和Pt電極上Ce(III)/Ce(IV)之電化學反應特性皆為準可逆(quasi-reversible)。在A廠實際鉻蝕刻廢液中，以循環伏安法(CV)掃描所得片狀Pt和BDD電極Ce(III)之擴散係數分別為4.37×10-6 cm2/s及3.91×10-6 cm2/s。在不同實際鉻蝕刻廢液中，片狀BDD電極CV掃描所得Ce(III)之擴散係數，以C廠鉻蝕刻廢液者最高(4.67×10-5 cm2/s)；而旋轉圓盤Pt電極線性伏安掃描(LSV)所得平均Ce(III)之擴散係數，以D廠者最大(7.66×10-6~9.42×10-6 cm2/s)。在Ce(IV)電再生反應中，增加電流密度、陽極工作面積或溫度可提高Ce(IV)的產率。BDD及Pt電極Ce(IV)電再生之活化能分別為6.25 kJ/mol及10.81 kJ/mol。使用BDD陽極及不鏽鋼陰極之組合，可得到較佳之Ce(IV)產率及電流效率。使用Nafion-424較其他分隔膜可得到較佳的Ce(IV)產率及電流效率。在測試的實際鉻蝕刻廢液中，以B廠者可得到較高的Ce(IV)濃度(0.79 M)。使用雙槽電再生Ce(IV)之效果比單槽為佳。獲得的參數有助於設計實際鉻蝕刻廢液Ce(IV)電再生之雙槽反應器。

關鍵字

薄膜電晶體液晶顯示器(TFT-LCD) ； 實際鉻蝕刻廢液 ； 擴散係數 ； 電再生 ； Ce(IV)產率 ； 電流效率 ； BDD電極 ； Pt電極

並列摘要

Taiwan is one of the main suppliers of thin film transistor liquid crystal displays (TFT-LCDs) in the world. However, the TFT-LCD industry may generate a considerable amount of hazardous spent Cr-etching solutions. If the spent Cr-etching solutions are regenerated and reused, the discharge of pollutants can be reduced and valuable resources may be recovered. Accordingly, in this study we explored the electro-regeneration of Ce(IV) in real spent Cr-etching solutions (nitric acid matrix) from TFT-LCD manufacturing under different operating parameters: electrode (BDD, PbO2, and Pt), current (1.5, 1.0, and 0.5 A/cm2), temperature (10, 25, and 40 oC), separator (Neosepta CMX and AMX; Nafion-324, -424, -212, and -117), electrode area (1, 2, and 4 cm2), cathode (titanium and stainless steel), anion-exchange resin (OH and Cl types), real spent Cr-etching solution (A, B, C and D factory), and reactor (divided and undivided).
Experimental results show that the electrochemical characteristics of Ce(III)/Ce(IV) redox reaction on BDD and Pt electrodes were quasi-reversible in cyclic voltametric (CV) analysis. In real spent Cr-etching solution A, the Ce(III) diffusion coefficient obtained from CV for the planar Pt and BDD electrodes were 4.37×10-6 and 3.91×10-6 cm2/s, respectively. Among the tested real spent Cr-etching solutions, solution C exhibited the highest Ce(III) diffusion coefficient (4.67x10-5 cm2/s) for the planar BDD in CV analysis, whereas solution B had the highest Ce(III) diffusion coefficient (7.66×10-6~9.42×10-6 cm2/s) on a Pt rotating disc electrode in linear scan voltametric (LSV) scan. For the electro-regeneration of Ce(IV) in different real spent Cr-etching solutions, the increase of current density, anode area, or temperature increased Ce(IV) yield. The activation energy Ce(IV) electro-regeneration on BDD and Pt were 6.25 and 10.81 kJ/mol, respectively. The use of BDD anode/stainless steel cathode, in comparison tothe other electrode combinations achieved greater Ce(IV) yield and efficiency. The Nafion-424 was superior to the other tested separators for the Ce(IV) regeneration process. Of all the tested real spent Cr-etching solutions, solution B showed the highest Ce(IV) concentration (0.79 M). The divided cell was better than the undivided one for the electro-regeneration of Ce(IV). The obtained parameters are useful to design divided batch reactors for the Ce(IV) electro-regeneration in real spent Cr-etching solutions.

並列關鍵字

Thin film transistor liquid crystal display (TFT-LCD) ； Real spent TFT-LCD Cr-etching solution ； Diffusion coefficient ； Electrochemical regeneration ； Ce(IV) yield ； Current efficiency ； BDD electrode ； Pt electrode

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