河川水中氟離子對於底泥重金屬溶出的影響

Abstract

在半導體及光電業的製程中需要大量的氫氟酸作為蝕刻的溶液，因此會產生大量的含氟廢水，而在一般典型的半導體製造廠中其廢水中的氟離子濃度為 1,000-3,500 mg/L，因此在半導體的廢水處理中，又特稱為氟系廢水，雖然經過廢水的處理使其濃度降至放流水標準 15 mg/L 以下，但氟離子進入河川之後的宿命是如何，是否對環境有潛在的危害，目前這方面的研究並不多。 氟離子本身對人類來說並沒有太大的危害，故排放至河川中並不會引起太大的注意，但是氟離子對於河川中底泥的影響卻是很少人注意，河川底泥扮演著重金屬的儲存和排放角色，重金屬以游離態進入河川水，並藉著物理沈降、化學錯合、生物濃縮等作用吸附於砂石上，而後沈積於河川底部，這些重金屬短時間也許不會釋放至水體中，一旦河川的物化性質有改變，如翻動、pH值變動等等這些重金屬會再度進入水體中，造成危害。 而氟離子進入水中因為與底泥接觸，會造成底泥重金屬的鍵結形態改變，而底泥中重金屬再釋出的機率就和其鍵結形態有關，其鍵結形態可分為可交換態、碳酸鹽結合態、鐵錳氧化態、有機結合態、殘存態等，所以本研究探的目的在於討氟離子進入河川後對底泥中的重金屬鍵結形態的影響，並進一步評估底泥重金屬的危害潛勢。 由研究結果顯示，氟離子會使得底泥中重金屬的鍵結形態改變，造成其移動至可交換態及碳酸鹽結合態，尤其是對鉻的影響最大，而在銅的鍵結則是移動至碳酸鹽結合態及有機態為主，鋅的鍵結則以碳酸鹽結合態為主，鎳和鉛的鍵結形態則是沒有顯著的影響，而底泥中最易受到環境因為改變而釋出的鍵結形態依序為可交換態及碳酸鹽結合態，因此氟離子對於底泥中的鉻、銅、鋅有使其再釋出的危害潛勢。

The semiconductor industry in Taiwan was the 4th of the world. It was also the most important industry which leaded the Taiwan to High-technology production. The hydrofluoric acid (HF) is a chemical which used to wafer etching and quartz cleaning in semiconductor industry. Fluoride concentration is 1,000-3,500 mg/L found in typical wastewater of local semiconductor industry. In Taiwan the discharge standard of fluoride is 15 mg/L. When the fluoride discharge into the river how the fate it would be and if it would have the potential to damage the environment. The subject above is the aim of our research. The river sediment was a storage which accepted the pollution form various source. The heavy metal was the most important pollutant in river sediment. The heavy metal deposits in the river bottom sediment have a potential to leaching to the aquatic environment again. The releasing probability depends on the binding phases of the heavy metal. The binding phases of heavy metal have five classifications, such as Exchange, Carbonate, Fe/Mn Oxides, Organic and Residaual. The Exchange and Carbonate phases are the most easily releasing again bindings. When the environmental factor changes the metal storages in the two phases will leaching to the aquatic environment. The results of our study find the quantity of Chromium binds to the Exchange and Carbonate phase increase. The Copper shifts to the Carbonate and Organic phase. The Zinc moves to the Carbonate phase. The fluoride does not affect the Nickel and Lead binding phases significantly. On the results of our study deduced that the fluoride would influence the Cr, Cu, Zn to move to the binding phases which have the potential to leach again.