溶氧、pH值、鹽度及天然有機物對於底泥硫化金屬氧化溶解動力學之影響

Abstract

硫化金屬在厭氧底泥中能夠穩定具有生物毒性之溶解態重金屬，然而，暴雨發生或是河口潮汐作用可能使底泥懸浮並暴露於好氧狀態，硫化金屬可能因此發生氧化溶解反應而提高重金屬之生物有效性並傷害生態系，本研究之目的係探討水中溶氧、pH值、鹽度及天然有機物對於三種硫化金屬: 硫化銅、硫化鉛及硫化鋅氧化溶解動力學之影響。 本研究利用可控制水中溶氧(0 mg/L, 5 mg/L 和 8.4 mg/L)之連續曝氣裝置執行三天之批次實驗，結果顯示硫化銅、硫化鉛及硫化鋅於溶氧存在之環境下確實會發生氧化溶解，反應速率之序列為:硫化鉛>硫化銅>硫化鋅，且此序列在以個別之比表面積正規化前後並無改變；低pH值及高鹽度一般而言會造成更多及更快之金屬釋出；腐植酸可以抑制硫化銅及硫化鉛之金屬釋出但會促進硫化鋅的金屬釋出；FE-SEM分析發現在10 mg/L 腐植酸反應前後，硫化金屬之外型變得更為圓滑且蓄聚情形更為明顯，而在半鹹水反應前後，除了硫化銅之外並沒有明顯變化。

Metal sulfides can stabilize toxic soluble heavy metals in anaerobic sediments. However, sediments may suspend and expose to aerobic conditions during storm events or in the estuary with tidal effects. This may cause oxidative dissolution of metal sulfides and increase metal bioavailability that can harm the ecosystem. The objective of this research is to investigate the effects of dissolved oxygen (DO), pH, natural organic matter (NOM) and salinity on the kinetics of oxidative dissolution of copper sulfide (CuS), lead sulfide (PbS) and zinc sulfide (ZnS). Batch experiments were conducted using a continuous aeration setup that can control the dissolve oxygen concentrations (0 mg/L, 5mg/L and 8.4 mg/L) for a period of 3 d. Results demonstrated that oxidative dissolution of CuS, PbS and ZnS truly occur in the presence of DO and the rate showed the following sequence: PbS >CuS>ZnS. Low pH and high salinity generally cause more and faster metal release. Humic acid can inhibit the metal release of CuS and PbS but promote the metal release of ZnS. FE-SEM analysis showed that the morphology of three metal sulfides became rounded and aggregated in the 10mg/L HA reaction, morphology change of CuS also found in brackish water reaction but PbS and ZnS had no changed.