印刷電路板產業化學鎳廢液回收鎳金屬之研究

Abstract

印刷電路板(Printed circuit board 或Printed wiring board；簡稱 PCB 或PWB)乃是提供電子零組件安裝與插接時主要的支撐體，在全球主要PC board生產區域中，日本、美國、大陸(及香港)、台灣、德國為前五大PCB生產地。隨著電子產品日新月異的進步，對於表面處理技術之要求也就越來越高，因此開發出化鎳金製程，但因廢液中含有高COD 及高鎳離子，造成後續廢水處理系統處理不易。目前化學鎳廢液之處理多以委外處理及化學沉澱法為主，但是因為其處理過後會產生大量的污泥，並且無法直接得到鎳金屬，因此利用化學沉澱法的操作成本相當高。如何有效的利用電解方式回收廢液中之鎳金屬並且減低廢水處理系統之負荷，將是本研究之主要方向。 本研究主要是利用電解回收法回收印刷電路板(PCB)產業所產生的化學鎳廢液之鎳金屬，藉由改變不同的參數來探討最佳的回收條件，包含改變pH值、陰極材質、電流密度以及電解時間。實驗結果顯示其電解回收效率，會因調整pH值以及電流密度而有所改變。然而，由分別使用銅片與不□鋼作為陰極材質的研究中發現，陰極材質對電解效率的影響有限，本實驗因銅片較易取得且較經濟(廠內報廢銅片)，在後續實驗中，將全數使用銅片作為電解之陰極材質。 在不同pH的實驗中，可發現pH 在2~5時其鎳離子幾乎無法利用電解方式進行回收。但是當pH 逐漸提高其回收率亦跟著提高，當pH 9時其回收率已達99%。另外，回收率隨著電流密度升高而提高。在電流密度為15.3 mA/cm2時，其回收率已達96.95%，當電流密度再提高至23 mA/cm2回收率甚至可達99%。綜合上述實驗結果，以最佳化的實驗條件組合來評估其經濟效益，依實驗結果得知，小型批次實驗在電解時間4 hr可獲得最佳的鎳回收獲益。但是在實廠大型電解設備上，因為電解效率較差，所以最佳電解時間經過計算以10 hr最符合實廠回收之經濟效益。若以每天化學鎳廢液之電解處理量為1000 L來設計，預估電解設備購置後其回收年限為0.67個月。 化學鎳廢液經過電解處理後將以定量方式添加至實廠之廢水處理流程中。為避免其影響原有之放流水水質，以模擬比例添加至處理系統方式進行實驗，藉此了解化學鎳廢液添加後之COD與銅離子變化趨勢。經實驗結果得知，添加量在400 ppm內其COD與銅離子皆符合放流水排放標準，表示經過電解處理後的化學鎳廢液添加至實廠之廢水處理流程，仍可符合法規標準。

A printed circuit board (PCB), or a printed wiring board (PWB), is used to mechanically support and electrically connect electronic components. Japan, United States of America, Mainland China (and Hong Kong), Taiwan, and Germany are top five among the major PCB manufacturing nations in the world. To develop new electronic products in this highly growth industry, the requirement of surface treatment technology (including anti-oxidized treatment, circuit protection, and conductivity enhancement) on PCB is higher and higher. The ENIG (Electroless Nickel and Immersion Gold) process, which is commonly used in PCB industry, is one of the best solutions to do surface treatment. However, the manufacturing cost of ENIG is very expensive, and the further wastewater treatment is very difficult due to high concentration of COD and Ni ions in the wastewater. The chemical precipitation method is the most popular one used in the treatment of Ni wastewater. However, large amount of sludge is generated after the treatment and Ni can not be recovered directly. The major objective of this research is to investigate how to efficiently recover Ni from Ni wastewater using electrolysis process and reduce the loading from the wastewater treatment system. This thesis focuses on the feasibility study of using electrolysis process to recovery Ni from Ni waste liquor in PCB industry. The conditions of electrolysis recovery are optimized by modifying several parameters including pH, the cathode material, current density and electrolysis time. Experimental results show that the recovery efficiency is different by changing the pH and the current density in electrolysis process. However, the electrolysis efficiency is limited for the cathode material, which can be demonstrated from the investigation of copper and stainless steel. The selection of cathode material is based on the convenience in obtaining the material and the cost of the material. Thus, cooper is selected based on easier to obtain as the cathode material in all following experiments. From the experimental results of pH effect, Ni almost cannot be recovered via the electrolysis process when the pH is at 2~5. However, the recovery efficiency is better in higher pH, and the recovery efficiency attains 99% at pH 9. In the experiments about current density effect, it can be seen that the higher current density, the better recovery efficiency. The 96.95% of recycling efficiency can be obtained when the current density attains 15.3 mA/cm2. Furthermore, the recovery efficiency even can be improved to 99% while the current density is 23 mA/cm2. According to the above experimental results, the optimal conditions are combined to evaluate the economic effectiveness. It can be seen from the results of bench-scale reactor, the highest Ni recovery benefit can be obtained after 4 hours of electrolysis. However, in full-scale electrolysis facility, the cost efficient timing for the recycling efficiency is 10 hours. Therefore, for a daily recovery capacity of 1000 L waste liquor, the estimated payback time is 0.67 month. After the electrolysis treatment, the Ni waste liquor will be added to the on-site wastewater treatment plant. To evaluate the effect on effluent quality, some jar tests were conducted by simulating the adding ratio to understand the change of COD and Cu after the addition. Based on the experimental results, the effluent COD and Cu can meet the effluent stand when the Ni waste liquor dosage is below 400 mg/L. It indicates that the Ni waste liquor after electrolysis can be added to on-site wastewater treatment plant.