以廢鑄鐵還原電鍍廢液中高濃度六價鉻之研究

Using Scrap Iron for the Reduction of High-Concentration Cr(VI) from Electroplating Wastewater

洪儷瑋(Li-Wei Hung)

指導教授 ： 陳孝行

國立臺北科技大學/工程學院/環境規劃與管理研究所/碩士(2006年)

https://doi.org/10.6841/NTUT.2006.00134

摘要

近年已有使用零價鐵處理電鍍廢水之研究，然由於零價鐵成本並不低廉，故近年來低成本的重金屬吸附物質也逐漸被研究開發來取代高成本的方法，本研究即以工廠之廢棄鐵屑進行相關研究，期望除可達到良好的六價鉻去除效果，並與使用零價鐵後一般，產生大量的鐵離子，省去後段混凝處理程序所需之加藥。
以管柱式程序處理含高濃度六價鉻之電鍍廢水，控制進流pH值為1.3、1.5、1.7和2.0。當溶液pH值上升，六價鉻被還原速率會隨之遞減，pH值是造成反應速率不同的主要影響因子。當進流水pH值≦1.5，其對六價鉻的最佳去除率都可以到達或是相當接近100%的去除效果。在低pH情況下，氧化還原電位下降，廢鐵與六價鉻反應後會形成亞鐵離子，所以當氧化還原電位逐漸上升時，表示亞鐵離子的含量正逐漸減少，此時六價鉻濃度開始逐漸上升。停留時間越短，對六價鉻的去除率越低，反應操作時效也隨之降低。對於六價鉻有最佳的去除效果時，pH1.3下僅需20分鐘即可達到100%去除效果，於pH1.5時則需約40分鐘的停留時間。
反應初期pH值可達pH3~pH4，水樣有渾濁情形發生，此時由於出流水pH值上升，通過廢鐵之溶液中，形成的三價鐵與三價鉻便會開始混凝反應，進而沉澱，於是當進流pH值越低，OH-產量也越多，同時廢鐵與六價鉻反應之後產生的大量亞鐵離子，有利於能迅速得到混凝的效果，於實場操作上原本是兩個處理單元－還原與混凝，可合併於同一處理單元，減少設備與處理所需花費。

關鍵字

廢鐵 ； 電鍍廢水 ； 六價鉻 ； 三價鐵 ； pH值

並列摘要

There have been studies of electroplating-wastewater treatments with zero valent iron (ZVI) in recent years. Due to the expensive cost of ZVI, scrap iron, a low-cost adsorbent, were used to treat chromate from electroplating wastewater in column reactors. High Cr(VI) removal is expected to achieve and coagulant cost is expected to reduce due to the generation of ferric ion.
The influent pH values were controlled at 1.3, 1.5, 1.7 and 2.0. Cr(VI) reduction was reduced as pH increased. When pH≦1.5, the Cr(VI) removal achieved 100%. When Cr(VI) removal was increased, ferrous ion was produced and oxidation-reduction potential (ORP) was getting lower. As the retention time decreased, Cr(VI) removal were less and the operation time increased. For 20 minutes of detention time at pH1.3 or 40 minutes of detention time at pH1.5, 100% Cr(VI) removal were achieved.
Effluent pH was 3-4 for the initial stage with high turbidity due to the occurrence of iron coagulation. Hence reduction and coagulation were able to achieved for adding just one chemical (scrap iron) and the cost for the scrap/Cr(VI) was lower than ZVI/Cr(VI) process due to the generation of ferric ion to save extra ferric ion needed.

並列關鍵字

scrap iron ； electroplating wastewater ； Cr(VI) ； Fe(III) ； pH value

參考文獻

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