廢冷陰極管汞回收處理效率之研究

Recovery and Treatment of Mercury for Waste Cold Cathode Fluorescent Lamp

吳彥儒(Yen-ju Wu)

指導教授 ： 李俊福

國立中央大學/工學院/環境工程研究所碩士在職專班/碩士(2008年)

摘要

冷陰極燈管（Cold Cathode Fluorescent Lamp,CCFL）為TFT-LCD(Thin-Film Transistor Liquid-Crystal Display) 面板主流背光模組光源之關鍵性零組件，而每支冷陰極燈管中之含汞量約為3mg。目前國內生產之冷陰極燈管已佔全球26.5%之市場，據Display Search研究統計指出目前冷陰極燈管產量約達2,100百萬支，由此可見，國內每年高科技產業廢棄之冷陰極燈管含汞量相當可觀，而廢棄後之汞在環境中很可能隨生物作用而轉變其型態或濃縮，或經由化學、光化學等反應，形成毒性更強之烷基汞(Alkyl mercury)，進而造成急性或慢性的毒害。
過去相關研究結果指出，處理業者藉由瑞典MRT(Mercury Recovery Technology)汞回收處理技術進行處理目前產業所使用之曝光燈管、UV燈及日光燈管等高汞燈管後，其汞回收處效率皆可達99.99％，唯廢冷陰極燈管之汞回收處理效率僅約81.24％。相關研究結果亦顯示廢冷陰極燈管之純螢光粉於高溫管狀脫附爐熱加熱至200℃後僅剩少量殘餘之汞，與實廠之汞釋出溫度大不相同。
本研究以實廠之瑞典MRT汞回收處理設備，進行冷陰極燈管熱脫附處理之實驗，並設定系統之加熱溫度、加熱時間、冷凝溫度及真空抽吸壓力等控制條件，以探討各操作條件對汞回收效率之影響，尋求設備之最佳操作條件。實驗結果顯示加熱溫度於400℃時，平均處理效率為75.44％，已可回收大部份之汞。熱脫附溫度另一高峰期為500~700℃，因此推論冷陰極管中之氧與汞原子交互作用形成氧化汞，提升汞之熱脫附溫度。經調整各操作條件結果顯示加熱溫度850℃、冷凝溫度-6℃、加熱時間12小時、抽吸壓力15mbar為MRT之最佳操作條件，其汞回收處理效率可達99.53％。本研究另將5種廠牌之冷陰極管含汞螢光粉分別以實廠MRT設備及操作條件進行實廠熱脫附處理，實驗結果顯示其與混樣處理效率差異不大，平均處理效率約為80.58％。
冷陰極管中之電極經SEM(Scanning Electron Microscope)及EDS( Energy Dispersive Spectrometer)照射後發現其電極表面於點燈後有明顯變化，並於點燈後電極表面汞原子重量百分比約為10.53％，因此推論冷陰極管點燈時電極於高溫10000 K激發電子狀態下，使得電極表面NI與Hg產生NI-Hg合金，於前處理設備分選效果不佳情況下，提升蒸餾系統中汞熱脫附所需溫度。因此推論若將冷陰極管中之電極有效分離，僅處理冷陰極燈管之純螢光粉，應可大幅增加汞回收處理效率。

關鍵字

熱脫附 ； 汞 ； 冷陰極燈管

並列摘要

Cold cathode fluorescent lamp (CCFL) is a primary component of thin-film transistor liquid-crystal display (TFT-LCD) that is major back light module for faceplate. Each CCFL contains about 3.0mg mercury. The market share of CCFL produced in Taiwan has reached to 26.5%. According to statistics for the display search, the numbers of CCFL products are 21 millions. The result could result in a great number of waste mercury. The wasted mercury in environment possibly is converted to other type via microbes or concentrated. Alkyl mercury, high toxic chemical, is formed via chemical or photochemistry reaction to lead to acute or chronic response.
Mercury recovery technology (MRT) from Sweden was frequently used for the waste mercury treatment. The targets treated using the technology are high mercury content lamps include exposure lamp, UV lamp and fluorescent lamp. Recovery of mercury for the lamps exceeds 99.99%. However, recovery and treatment for CCFL only reach to 81.24%, which is relatively lower among these lamps. A number of investigators presented the desorption of pure fluorescent powder obtained from waste CCFL could use a tube furnace under 200oC to generate low residual mercury. The above operation temperature is different from temperature of mercury release in the realistic plant.
In this study, mercury recovery equipment in the realistic plant was applied to run the experiment of mercury desorption from the CCFL. The controlled parameters include heating temperature, heating time, condense temperature and vacuum pressure to investigate the dominant factors on the mercury recovery. Moreover, the best operation parameters can be obtained in this study. The result indicated average treatment rate was 75.44% under 400oC. This approach could recover largely mercury. Another high desorption efficiency was found in temperature of 500~700oC that similar to boiling point of mercury oxide. The result is thought to oxygen reacts with mercury in the CCFL to form mercury oxide. This lead to a higher temperature for the mercury desorption. By examining the different operation parameters, it can be found that the heating temperature of 850 oC, the condense temperature of -6oC, the heating time of 12hours, the vacuum pressure of 15mbar are selected as the most appropriate operation parameters. The rate of recovery and treatment for mercury reached to 99.53% under the above conditions. In addition, fluorescent powder containing mercury for five types of CCFL was treated using realistic plant equipment under the appropriate operation condition to run the experiment of the mercury desorption. The result indicates the efficiency of recovery and treatment about 80.58% for alone and composite sample is similar.
The surface of CCFL is examined via scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). A significant change can be found in the surface of the electrode after the CCLF was lighted. In the time, the weight percent of mercury on the surface of electrode is about 10.53%. It can be concluded that the surface of electrode for CCFL in lighting under 1000 K would excite the electron to result in that Ni alloyed with Hg on the surface. If efficiency for the screen of pretreatment is low, the approach can increase temperature of the mercury desorption in a distillation system. Thus, it was assumed that the efficiency will increase significantly, if targets that was the fluorescent powder separated from CCFL were treated.

並列關鍵字

Thermal Desorption ； Mercury ； Cold Cathode Fluorescent Lamp

參考文獻

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