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Mine Water and the Environment

, Volume 34, Issue 4, pp 430–441 | Cite as

Passive Treatment of Neutral Mine Drainage at a Metal Mine in New Zealand Using an Oxidizing System and Slag Leaching Bed

  • Dave TrummEmail author
  • James Pope
Technical Article

Abstract

Rehabilitation at a metal mine in New Zealand is complete with the exception of a 22 L/s discharge pumped from underground. The discharge has a pH of ≈6, alkalinity of ≈150 mg/L, dissolved oxygen (DO) <1 mg/L, elevated Fe and Mn, as well as elevated concentrations of Zn and As. Planning passive treatment was difficult because historical total Fe ranged from 20 to 200 mg/L, and Mn (11–22 mg/L) is soluble in the circumneutral pH range, due to conditions in the workings. Speciation analysis and modelling of the mine drainage chemistry indicated four factors were important for passive treatment design: (1) dissolved Fe is ≈20 mg/L and all is dissolved Fe(II); (2) Fe(II) concentration is stable because it is limited by saturation with respect to siderite (FeCO3); (3) the remaining Fe is colloidal Fe(OH)3 with a variable concentration; and (4) Mn is limited by saturation with respect to rhodochrosite (MnCO3). Equilibrium of Fe and Mn with minerals means that dissolved concentrations have an upper limit and are relatively stable, allowing an optimized treatment system. A pilot-scale passive treatment system was installed that included an oxygenation cascade of drops through V-notch weirs, settling ponds, and a slag leaching bed. Oxidation of Fe(II) to Fe(III) was followed by precipitation and settling of Fe(OH)3. Bicarbonate alkalinity in the mine drainage prevented acidification, and release of dissolved CO2 caused the pH to increase slightly. Manganese was removed by precipitation (of carbonates, oxides or oxy-hydroxides) in the slag leaching bed at elevated pH and high DO. Zinc and As were removed by adsorption onto Fe(OH)3. The oxygenation system removed 82–96 % of the Fe and 10 % of the Mn. The slag leaching bed removed 99 % of the remaining Mn.

Keywords

Ferrous Fe oxidation Mn Fe hydroxide V-notch weir Passive treatment Slag leaching bed 

Passive Behandlung von neutralem Grubenwasser eines Erzbergwerks in Neuseeland unter Verwendung eines Oxidationssystems und eines Schlackebetts

Zusammenfassung

Die Renaturierung eines Erzbergwerkes in Neuseeland ist bis auf die Behandlung des abzupumpenden Grubenwassers (22 L/s) abgeschlossen. Das Grubenwasser hat einen pH-Wert von ≈6, eine Alkalinität von ≈150 mg/L CaCO3, gelösten Sauerstoff < 1 mg/L, hohe Konzentrationen an Fe und Mn sowie erhöhte Konzentrationen an Zn und As. Die Planung der passiven Behandlung war schwierig. Historische Messergebnisse für die Fe-Konzentration reichten von 20 bis zu 200 mg/L und Mn (11–20 mg/L) ist bei neutralem pH und den Bedingungen in den ehemaligen Bergwerksstollen und –schächten löslich. Die Analyse der chemischen Speziation der Metalle und die Modellierung des Chemismus des Grubenwassers ergaben vier Faktoren, die für die Gestaltung der passiven Grubenwasserbehandlung entscheidend waren: (1) der Anteil an gelöstem Fe beträgt ≈20 mg/L und ist vollständig Fe(II); (2) die Fe(II)-Konzentration ist stabil, da sie durch die Sättigung von Siderit (FeCO3) begrenzt ist; (3) weiteres Fe ist kolloidales Fe(OH)3 in variablen Konzentrationen; und (4) die Mn-Konzentrationen sind durch die Sättigung von Rhodochrosit (MnCO3) begrenzt. Die Gleichgewichte von Fe und Mn mit Mineralen bedeuten, dass die Konzentrationen von gelöstem Fe und Mn begrenzt sind und relativ stabil. Das erlaubt ein optimiertes Behandlungssystem. Eine Pilotanlage der passiven Behandlung wurde errichtet, die eine Oxidationskaskade aus V-förmig eingekerbten Rinnen, Absetzbecken und ein Schlackebett umfasst. Nach der Oxidation von Fe(II) zu Fe(III) erfolgte die Fällung und Sedimentation von Fe(OH)3. Die Alkalinität des Grubenwassers, bedingt durch Hydrogenkarbonat, verhinderte eine Versauerung. Die Abgabe von CO2 bewirkte eine leichte Anhebung des pH-Wertes. Mn wurde durch Fällung als Karbonat, Oxid oder Oxi-Hydroxid im Schlackebett bei erhöhtem pH-Wert und hoher Sauerstoffkonzentration zurückgehalten, Zn und As durch Adsorption an Fe(OH)3. Das Oxidationssystem bewirkte eine Rückhaltung von 82–96 % Fe und 10 % Mn. Das Schlackebett hielt 99 % des verbleibenden Mn zurück.

Tratamiento pasivo de drenaje neutro de mina en la mina metalífera en Nueva Zelanda usando un sistema oxidante y de lecho fijo de escoria

Resumen

La rehabilitación de una mina metalífera en Nueva Zelanda ha sido completa con la excepción de una descarga de 22 L/s bombeada desde la zona subterránea. La descarga tiene un pH de ≈6, alcalinidad de ≈150 mg/L, oxígeno disuelto (DO) < 1 mg/L, exceso de Fe y Mn, y elevadas concentraciones de Zn y As. La decisión sobre el tratamiento pasivo fue dificultosa porque las concentraciones de Fe total (históricamente se mantuvieron entre 20 y 200 mg/L) y de Mn (entre 11 y 22 mg/L) son solubles en el rango de pH cercano a la neutralidad. El análisis de especiación y el modelado de la química del drenaje de mina indicaron cuatro factores para el diseño del tratamiento pasivo: (1) Fe disuelto es ≈20 mg/L y existe como Fe(II); (2) la concentración de Fe(II) es estable porque está limitado por la saturación de siderita (FeCO3); (3) el Fe remanente es Fe(OH)3 coloidal con una concentración variable; y (4) Mn está limitado por la saturación de rodocrosita (MnCO3). Los equilibrios de Fe y Mn con los minerales implican un límite superior para las concentraciones que son relativamente estables, permitiendo un sistema optimizado de tratamiento. Se instaló un sistema de tratamiento pasivo a escala piloto que incluyó una cascada de oxigenación por gotas a través de vertederos en forma de V, estanques de sedimentación y un lecho fijo con escoria. La oxidación de Fe(II) a Fe(III) fue seguida por precipitación y sedimentación de Fe(OH)3. La alcalinidad del bicarbonato en el drenaje de mina previno la acidificación y la liberación de CO2 disuelto causó que el pH se incremente ligeramente. Mn fue removido por precipitación (de carbonatos, óxidos o oxohidróxidos) en el lecho fijo con escoria a pH elevado y alta DO. Zn y As fueron removidos por adsorción sobre Fe(OH)3. El sistema de oxigenación removió entre 82 y 96 % del Fe y 10 % del Mn. La lixiviación de escoria removió 99 % del Mn remanente.

金属矿(新西兰)中性矿山废排水的曝气及渣浸床被动处理

摘要

除了从地下抽排的22 L/s的矿山废水外,某金属矿(新西兰)的采后治理已经完成。该金属矿山废水pH ≈6,碱度 ≈150 mg/L,溶解氧(DO) < 1 mg/L,含过量Fe、Mn,Zn、As浓度增高。受采场条件影响,矿山废水呈近中性,Fe(浓度20 mg/L ~ 200 mg/L)、Mn(浓度11 mg/L ~ 22 mg/L)多可溶态,给被动处理带来困难。矿山废水化学形态分析及水化学模拟结果表明,废水被动处理主要受4个因素影响:(1)溶解性Fe浓度为20 mg/L且均为Fe(II);(2)受菱铁矿(FeCO3)饱和度控制,Fe(II)浓度较稳定;(3)其余Fe为浓度不稳定的胶体态Fe(OH)3;(4)Mn浓度受菱锰矿(MnCO3)饱和度控制。Fe、Mn浓度因矿物溶解平衡存在稳定上限,为废水被动处理系统优化提供了条件。小规模的被动处理系统包括V型堰跌水曝气池、沉淀池和渣浸床。Fe(II) 被氧化为 Fe(III)后生成 Fe(OH)3沉淀。矿山废水中重碳酸盐碱度阻碍了废水进一步酸化,并释放出可溶CO2,pH值略增大。锰在渣浸床pH值升高和溶解氧(DO)增多的条件下生成碳酸盐、氧化物及氧氢氧化物沉淀。锌和砷被Fe(OH)3吸附。曝气系统的铁、锰去除率分别为82 % ~ 96 %和10 %。渣浸床的余锰去除率为99 %。

Notes

Acknowledgments

We acknowledge the mining company that funded the construction and operation of the treatment system, and allowed the results to be published. Detailed analysis, write up, and publication of this data was financed by the Ministry for Business, Innovation and Employment.

Supplementary material

10230_2015_355_MOESM1_ESM.pdf (13 kb)
Supplemental Figure l Fe Eh–pH diagram for speciation of Fe in mine pool water based on pH and ORP measurements (n = 124) (PDF 13 kb)
10230_2015_355_MOESM2_ESM.pdf (13 kb)
Supplemental Fig. 2 Mn Eh–pH diagram for speciation of Mn in mine pool water based on pH and ORP measurements (n = 124) (PDF 12 kb)

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Copyright information

© Springer-Verlag Berlin Heidelberg 2015

Authors and Affiliations

  1. 1.CRL Energy LimitedChristchurchNew Zealand

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