半導體為國內經濟發展之主要產業，所排放的工業廢水造成環境汙染之危害為主要來源之一，其中廢水富含鎵的有價金屬，且國內尚無適當回收純化之技術，若隨意拋棄可能造成環境上的二次污染。因此，就經濟價值及環境影響考量，廢液中鎵金屬回收處理為目前資源再利用之重要課題。
本研究以化學沉澱法處理含鎵和矽之半導體磊晶設備清洗之廢液，探討在不同pH值下，其鎵回收率及矽沉澱率之影響。研究結果顯示廢液在沉鎵步驟中，加酸於pH7左右能使鎵與矽同時完全沉澱，沉澱率可達99.8%以上；酸溶鎵步驟中，加酸於pH2時溶液中鎵回收率可達98.4%，而矽沉澱率91.7%，因此鎵與矽之分離有不錯的成效。接著鹼沉鎵步驟，加10N NaOH至中性溶液(從pH=2調整至pH=7)，使鎵再次沉澱，沉澱率達99.4%以上，且得到產品鎵粉末，經XRD分析主要相為氧化鎵，因此對於鎵市場可提高其價值，另方面也解決了環境上之問題。

The wastewater of semiconductor industry has been one of the main industry of economic development in Taiwan. And the main source of environmental pollution is from industrial wastewater, and including valuable Gallium-rich metal.
There is no proper purification technology yet at Taiwan. If the semiconductor wastewater are dispose directly, the released metals may cause a secondary pollution of the environment. Because the economic worth and environmental impact, it is important topic to resource recycling for the recovery of Gallium.
In this study, we wamt to find out the separation of Gallium and Silicate from the wastewater of LED Epitaxial processing by chemical precipitation, and effect of Gallium recovery and Silicate precipitation at different types of acid and pH.
Some important experimental results were observed in this study, the precipitational process (referred to as process I ) results indicated that add by addition of hydrochloric acid of about pH7 can complete precipitation for Gallium and Silicate (the both Gallium and Silicate precipitation were 99.8%).
The Gallium dissolution process (referred to as process II ) results indicated that added in hydrochloric acid of about pH 7 could result in 98.4% Gallium extraction and 91.7% Silicate precipitation . So, the separation of Gallium and Si was good.
The neutralisation process(referred to as process III), the addition of 10N NaOH from pH2 to pH7 could get precipitation of Gallium again ( 99.4% Gallium precipitation ). Therefore, the product of Gallium were required via centrifugation、filter、drying. The main phase and Secondary phase of products were Ga2O3 and NaCl by XRD analysis. So, there's more values for Gallium metal market, and the environment problem could be solved.

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