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

We researched separation of mixed waste acids with HF, $CH_3COOH$, $HNO_3$ that were produced during a semiconductor wafer process to recycle these acids. At first, we manufactured the fluoride compound in form of $Na_2SiF_6$ by precipitating HF using $NaNO_3$ 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 $Na_2SiF_6$, the concentration of $HNO_3$ and $CH_3COOH$ demonstrated 502 g/L and 117 g/L respectively. Following these findings we added NaOH in this $CH_3COOH/HNO_3$ mixed acid in order to obtain pH=4. Next we separated the $CH_3COOH$ and recoverd it through the use of vaccum evaporation at -440 mmHg, $95^{\circ}C$. The concentration of the recovered $CH_3COOH$ was approximately 15% and the recovery ratio of $CH_3COOH$ was over 85%. We precipitated the $NaNO_3$ by cooling the concentrated solution to $20^{\circ}C$ with a $HNO_3$ recovery ratio of over 93%. We confirmed that only $Na_2SiF_6$ and $NaNO_3$ were manufactured by XRD analysis after drying these precipitants at $90^{\circ}C$. 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.

반도체 웨이퍼 제조공정(製造工程) 중 발생혼합폐산(發生混合廢酸)으로부터 불산, 질산 및 초산의 각 산 회수(回收)에 관한 연구(硏究)

반도체 웨이퍼 제조 공정 중 발생하는 질산, 불산, 초산으로 구성된 혼합폐산을 재활용하기 위한 연구를 수행하였다. 초기에 $NaNO_3$와 Si powder를 사용하여 불산을 $Na_2SiF_6$로 침전시켜 불소화합물을 제조하였고, 이 때 혼산 중 불산의 농도는 초기 127g/L에서 0.5g/L로 낮아져 불산 회수율은 99.5%였다. $Na_2SiF_6$ 제조 후 남은 혼산의 질산과 초산의 농도는 각각 502g/L, 117g/L였고, 이 혼산에 NaOH를 투입하여 pH=4로 맞춘 후 -440 mmHg, $95^{\circ}C에서 증발농축을 하여 초산 분리 회수하였다. 회수된 초산의 농도는 약 15%였고, 회수율은 85.3% 이상이었다. 또한, 농축여액을 $20^{\circ}C$까지 냉각하여 $NaNO_3$ 결정을 석출시킴으로 질산나트륨을 제조하였고, 그 회수율은 약 93%이상이었다. 제조된 $Na_2SiF_6$와 $NaNO_3$를 $90^{\circ}C$에서 건조시킨 후, XRD 분석한 결과, 순수 $Na_2SiF_6$와 $NaNO_3$만 합성된 것을 확인하였고, 그 순도는 각각 약 97%, 98%로 시판용과 유사하였다.