晶圓廠含氟廢水加藥模式之探討

Abstract

半導體廠需使用大量氫氟酸來清洗晶圓，而除了氫氟酸外也常常混有磷酸或硫酸等混酸在其中；含氟廢水之處理主要添加氯化鈣形成氟化鈣的沈澱，但是當含氟廢水含有磷酸、硫酸皆有可能與氫氟酸競爭鈣鹽，為了達到放流標準常常需要添加非常過量的氯化鈣並會產生大量的污泥。 本實驗主要是探討磷酸與硫酸與氫氟酸競爭鈣鹽的影響，在實驗中發現氯化鈣的加藥量為2倍的理論加藥量便可達到放流標準，過多的加藥量對氟離子之去除已無經濟效益；而pH大於5時，皆可達到放流標準，但是在高pH值下會產生大量的磷酸鈣污泥，所以最佳操作條件為Ca/F=1 及 pH 5，在這操作條件下除了可以達到放流水標準，也使污泥產生量最少。

A great deal of hydrofluoric acid is used to clean wafers in semiconductor factories. Besides hydrofluoric acid, semiconductor wastewater also contains other mixed acids, such as phosphoric acid or sulfuric acid. The treatment of wastewater and fluoride mostly by adding calcium chloride produce settable solid of calcium fluoride. However, phosphoric acid or sulfuric acid in wastewater might compete with hydrofluoric acid for calcium. In order to comply with the limits of effluent, the one dosing of calcium chloride is usually applied, and therefore, generating huge amount of sludge. The aim of this stubby is to investigate the competition among phosphoric acid, sulfuric acid and hydrofluoric acid for calcium salt. The result shows adding double theoretical dose of calcium chloride can reduce the concentrations of fluoride in wastewater to comply with the effluent limit. For removal of Fluorine ion, adding more than twice dose of chloride calcium will not increase the economic benefit. To fit the standard of effluent, the pH value should be greater than 5. However, High pH value will cause much mud of calcium phosphate. Rate of Ca to F at pH 5 is recommended an optimal condition for operation. At this condition, the quick of treaded effluent could comply with the effluent limits with the least product in of sludge.