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Cross-Layer Leaching of Coal Fly Ash and Mine Tailings to Control Acid Generation from Mine Wastes

Der Einfluss unterschiedlicher Einbauweisen von Flugasche auf die Säurebildung in Bergbauabfällen

Lixiviación cruzada de cenizas de carbón y relaves de minas para controlar la generación de ácido a partir de desechos de minas



Coal fly ash can be used in in various configurations (e.g. as cap, bottom liner, or blending) at a mine site, but comparative studies investigating their capacity to control acid mine drainage are limited. Batch and column leaching experiments were conducted to investigate the effects of fly ash-mine tailings mix ratios and system configurations on leachate chemistry. Acidic mine tailings (pH 2.72) were obtained from waste piles at a former gold and pyrite mine. Mixing the fly ash with the tailings in a 1:1 (w/w) ratio decreased Zn, Ni, Fe, Mn, Pb, and Cu leaching by 90 ± 6%, increased the pH from extremely acidic (2.9) to alkaline (8.0), and decreased electrical conductivity from 4 to 2.5 mS cm−1 due to solute precipitation. Using the fly ash as a ‘chemical liner’ beneath the tailings, applying the fly ash as both a cap and bottom liner, or blending the fly ash with tailings produced significantly less acidity, salinity, and metal leaching than using the fly ash as a cap. The capacity of fly ash to control acid generation is attributed to its acid neutralizing capacity and high pH (11.1).


Kohle-Flugasche kann auf verschiedene Weise, z. B. als Oberflächen- und/oder Basislage bzw. in verschiedenen Mischungsverhältnissen an Bergbaustandorten verwendet werden. Studien, welche den Einfluss der Einbauarten auf die Bildung saurer Grubenabwässern untersuchen, sind jedoch selten. Um die Auswirkungen unterschiedlicher Flugasche-Bergbauabfall-Gemische und Einbauarten auf die Laugungschemie zu untersuchen, werden Batch- und Säulenexperimente durchgeführt. Die untersuchten sauren Bergbauabfälle (pH-Wert 2.72) stammen aus Abraumhalden einer ehemaligen Gold- und Pyritmine. Ein Mischungsverhältnis von Flugasche mit Bergbaurückständen von 1:1 (Gew./Gew.) verringert die Zn-, Ni-, Fe-, Mn-, Pb- und Cu-Auswaschung um 90 ± 6%. Gleichzeitig wird der pH-Wert von extrem sauer (2.9) auf alkalisch (8.0) erhöht und die elektrische Leitfähigkeit von 4 auf 2,5 mS/cm, aufgrund der Ausfällung gelöster Stoffe, verringert. Der lagenweise Einbau von Flugasche („chemical liner“) unterhalb der Rückstände, das gleichzeitige Einbringen von Flugasche als Oberflächen- und Basislage oder die Mischung von Flugasche mit Bergbaurückständen führt zu einer wesentlich geringeren Säurebildung sowie geringeren Salz- und Metallauswaschungen als eine singuläre Verwendung der Flugasche als Oberflächenlage. Die Fähigkeit von Flugasche, die Säurebildung zu kontrollieren bzw. zu beeinflussen, wird auf ihre Säureneutralisationskapazität und ihren hohen pH-Wert (11.1) zurückgeführt.


Las cenizas de carbón se pueden usar en varias configuraciones (por ejemplo, como cobertura, barrera inferior o mezcla) en un sitio de la mina aunque los estudios comparativos que investigan su capacidad para controlar el drenaje ácido de la mina son limitados. Se llevaron a cabo experimentos de lixiviación en lotes y columnas para investigar los efectos de las proporciones de mezcla de relaves de las cenizas de las cenizas volantes y las configuraciones del sistema en la química de los lixiviados. Los relaves de las minas ácidas (pH: 2,72) se obtuvieron de pilas de desechos en una antigua mina de oro y pirita. La mezcla de las cenizas volantes con los relaves en una proporción 1:1 (p/p) disminuyó la lixiviación de Zn, Ni, Fe, Mn, Pb y Cu en un 90 ± 6%, incrementó el pH de extremadamente ácido (2,9) a alcalino (8,0) y una conductividad eléctrica reducida de 4 a 2,5 mS/cm debido a la precipitación de solutos. Usando la ceniza volante como una “barrera química” debajo de los relaves, aplicando la ceniza tanto como cobertura como barrera inferior o mezclando las cenizas con los relaves produce significativamente menos acidez, salinidad y lixiviación metálica que el uso de la ceniza como cobertura exclusivamente. La capacidad de las cenizas para controlar la generación de ácido se atribuye a su capacidad neutralizadora de ácidos y su alto pH (11,1).


粉煤灰在采场有多种用途(例如,做盖层、底衬或混合物),但有关粉煤灰控制酸性废水产出能力的比较研究并不多。通过批次和柱淋滤试验,研究了粉煤灰与尾矿混合比及其淋滤液的化学特性。酸性尾矿(pH: 2.72)取自从前金矿和黄铁矿的矸石堆。粉煤灰与尾矿按1:1(w/w)混合,它们可以减小90 ± 6%的锌、镍、铁、锰、铅和铜滤出,将pH从酸性2.9到碱性8.0,使电导率因沉淀反应而从4 降到 2.5 mS/cm。相对于粉煤灰作尾矿盖层,粉煤灰在尾矿底作 “化学衬垫”、粉煤灰同时铺设于尾矿盖层和底衬、粉煤灰与尾矿混合的方式都可以大幅降低尾矿酸性、盐度和金属滤出。粉煤灰控制产酸的能力源于它酸中和能力和较高的pH值。

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We are grateful to the technical staff from the Department of Soil Science and Agricultural Engineering for laboratory support. We also thank the three anonymous reviewers and the editor whose comments greatly improved the quality and presentation of the manuscript. This research was solely funded by the authors and received no additional external funding.

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Correspondence to Willis Gwenzi.

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Mungazi, A.A., Gwenzi, W. Cross-Layer Leaching of Coal Fly Ash and Mine Tailings to Control Acid Generation from Mine Wastes. Mine Water Environ 38, 602–616 (2019).

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  • Acid-neutralizing capacity
  • Breakthrough curves
  • Cumulative leaching
  • Electrical conductivity
  • Metals