US EPA

6672332 

Journal Article 

Study on Recovery of Separated Hydrofluoric Acid, Nitric Acid and Acetic Acid Respectively from Mixed Waste Acid Produced during Semiconductor Wafer Process 

Kim, HS; Bae, W; 김주엽 

2009 

18 

4 

62-69 

KJD:ART001372740 

We researched separation of mixed waste acids with HF, CH3COOH, HNO3 that were produced during a semiconductor wafer process to recycle these acids. At first, we manufactured the fluoride compound in form of Na2SiF6 by precipitating HF using NaNO3 and Si powder. The concentration of HF was reduced from the initial concentration of 127 g/L to 0.5 g/L with an HF recovery ratio of 99.5%. After the manufacture of Na2SiF6, the concentration of HNO3 and CH3COOH demonstrated 502 g/L and 117 g/L respectively. Following these findings we added NaOH in this CH3COOH/HNO3 mixed acid in order to obtain pH=4. Next we separated the CH3COOH and recoverd it through the use of vaccum evaporation at -440 ㎜Hg, 95℃. The concentration of the recovered CH3COOH was approximately 15% and the recovery ratio of CH3COOH was over 85%. We precipitated the NaNO3 by cooling the concentrated solution to 20oC with a HNO3 recovery ratio of over 93%. We confirmed that only Na2SiF6 and NaNO3 were manufactured by XRD analysis after drying these precipitants at 90oC. The precipitants demonstrated a purity of approximately 97% and 98% respectively. Therefore, the purity of the precipitants proved to be similar to that of commercial products.