Elemental Precipitation and Adsorption through Mixing Experiments of Acid Mine Drainage and Seawater from Chinkuashih, Northern Taiwan

臺灣北部金瓜石酸性礦山排水與海水混合實驗之元素沉澱與吸附作用

陳君榮(Chun-Jung Chen) ； 江威德(Wei-Teh Jiang)

《Collection and Research》 30期 (2017/12) Pp. 1-15

https://doi.org/10.6693/CAR.201712_(30).0001

摘要

A high concentration of yellowish suspended particles in estuarine and inshore waters of Lian-Dong Bay due to contamination by acid mine drainage (AMD) from the Chinkuashih mining area, northern Taiwan triggered our great interest in carrying out mixing experiments to investigate interactions between AMD and seawater. Fresh seawater (pH 8.0) and AMD (pH 2.8) taken from Golden Falls, Chinkuashih were used in the study. Crystallization of nanocrystals of schwertmannite plus minor goethite occurred in mixed solutions of pH ＜ 4.5 and precipitation of non-crystalline nanoparticles of hydrous ferric/aluminum oxide (HFO/HAO) took place at pH ＞ 4.5, as indicated by XRD, TEM, and FTIR analyses. Analyses of mixed solutions with ICP-OES and ICP-MS showed that the non-crystalline HFO/HAO grasped almost all of the Fe, Al, As, Pb, and Cr at solution pHs of 4.5~5.5 and progressively took up significant proportions of Cu, Ni, and Zn at pH ＞ 6.3 and Si at pH ＞ 5 and measurable Mn and Cd at neutral to slightly alkaline pH. In contrast, the schwertmannite-dominated precipitates removed large amounts of only Fe, As, Cr, and Pb from the solutions at pH ＜ 4.5. The mineralogical, microstructural, and chemical variations of the solid precipitates resembled those of suspended particulates in the AMD-contaminated estuarine and inshore waters of Lian-Dong Bay. The results implied that solution pH could have controlled the mineralogical and chemical variations of suspended particulates in the mixing experiments and previous field studies. Precipitation of non-crystalline HFO/HAO is suggested to be kinetically favorable in solution at a critical pH of ＞ 4.5 with supersaturation being rapidly reached, and capable of taking up heavy metals and arsenic as an effective way of natural remediation in estuarine and inshore environments impacted by AMD.

關鍵字

acid mine drainage ； schwertmannite ； HFO ； HAO ； estuarine contamination

並列摘要

臺灣北部金瓜石地區濂洞灣入海口和近岸海水受酸性礦山排水影響，形成高濃度黃色懸浮粒子，此現象引起我們研究酸性礦山排水與海水混合實驗和交互作用之興趣，本研究使用金瓜石黃金瀑布酸性礦山排水（酸鹼值2.8）和鄰近新鮮海水（酸鹼值8.0）為混合實驗材料。固體反應產物之Ｘ光繞射、穿透式電子顯微鏡和紅外光譜分析指出酸鹼值小於4.5和大於4.5之混合溶液，分別結晶四方硫酸纖鐵礦（schwertmannite）＋少量針鐵礦奈米晶體，及沉澱出鐵與鋁氫氧化物（HFO/HAO）之非晶質奈米粒子。混合溶液之感應耦合電漿放射光譜及質譜分析顯示該非晶質HFO/HAO在酸鹼度4.5-5.5，幾乎完全擷取溶液中之鐵、鋁、砷、鉛和鉻；酸鹼度大於5，即開始明顯地從溶液中取去矽，酸鹼度大於6.3，逐漸補捉溶液中顯著比例之銅、鎳和鋅；接近中性和弱鹼性，則開始吸取溶液中相當比例之錳和鎘。另一方面，四方硫酸纖鐵礦則於酸鹼度小於4.5之溶液中，僅移除顯著比例之鐵、砷、鉻和鉛。前述沉澱物之礦物學、微組構和化學變化與濂洞灣入海口和近岸海水懸浮粒子之特徵相似。上述結果暗示溶液酸鹼度為影響混合實驗和濂洞灣懸浮粒子礦物學與化學變化之主要控制因素，遭受酸性礦山排水污染之入海口和近岸環境，可透過在臨界酸鹼度大於4.5及快速達到過飽和，達到動力學上有利於形成非晶質HFO/HAO之條件，其沉澱可移除水中重金屬及砷，獲致有效的天然矯治。

並列關鍵字

酸性礦山排水 ； 四方硫酸纖鐵礦 ； 含水氧化鐵 ； 含水氧化鋁 ； 入海口污染