Bench-scale Acid Mine Drainage Wetland Test Cells

Constructed wetlands (surface flow and vertical flow) using cattail (Typha latifolia) and two different substrates were operated out over à 3-months period. Continuous flow of AMD was applied to the beds with a flow rate of 1,5ml/min and retention time of 5 days. Heavy metals average concentrations in the influent were of 38.0 mg/L Fe, 2.6 mg/L Mn, 0.4 mg/L Ni and 0.9 mg/L Zn, at pH 4.2.

Vertical subsurface-flow Surface-flow

The following parameters were examined in the laboratory: pH, redox potential (Eh) and sulfate. For the dissolved metals, 10 ml of filtered water samples were preserved using nitric acid and then analyzed (ICP-AES).

Metal (Fe, Mn,Ni, and Zn) fractionation in reactive mixtures using a sequential extraction procedure (SEP)

The SEP (Jong et Parry, 2004) used in the present study is based on the classical method of Tessier et al. (1979) and was applied to determine the partitioning of four heavy metals (Fe, Mn, Ni and Zn) into six operationally defined fractions. These fractions were water soluble, exchangeable, bound to carbonates (acid soluble), bound to Fe-Mn oxides (reducible), bound to organic matter and sulfides (oxidizable), and residual.

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ObjectiveObjectiveThe objective of this study is to design a wetland, which can be used in the polishing step of a multi-units passive system for the treatment of an AMD contaminated by Fe, Mn, Ni, and Zn.

The evaluation of removal mechanisms and of operational speciation of metals in the reactive mixture and the plants of wetlands is also performed.

Inflow InflowOutflow Outflow

IntroductionIntroduction

Use of constructed wetlands for treatment of acid mine drainageKarine Dufresne1,2 Carmen M. Neculita2, Jacques Brisson3, Thomas Genty1

1 Centre technologique des résidus industriels, 2 Institut de Recherche en Mines et en Environnement, Université du Québec en Abitibi-Témiscamingue, 3 Institut de Recherche en Biologie Végétale, Université de Montréal.

ResultsResultsBench-scale Acid Mine Drainage Wetland Test Cells: increase the pH , reduce the concentration of sulfate and remove the dissolved iron and other metals

Sequential extraction procedure (SEP): four metal (Fe, Mn, Ni, and Zn) fractionation in reactive mixtures

Figure 1: Variation of pH and sulfate concentration..

Table 1 : Removal of Fe, Mn, Ni and Zn in AMD by constructed wetlands: values are in percent.

Figure 2: Metal (Fe, Mn, Ni, and Zn) fractionation in wetlands reactive mixtures using a sequential extraction procedure (SEP).

ConclusionConclusion

ReferencesReferences

1. Wetlands increased the pH, but released sulfates in the treated effluent from in the substrate.

2. Passive systems, such as wetlands, are effective to remove dissolved Fe and Zn and the presence of plants seems to enhance the effect, whereas the removal of Mn and Ni was negligible.

AbstractAbstract

Champagne, P., Van Geel, P. et Parker, W. 2005. A bench-scale assessment of a combined passive system to reduce concentrations of metals and sulfate in acid mine drainage, Mine Water Environ, 24: 124.

Marchand, L., Mench, M., Jacob, D.L. et Otte, M.L. 2010. Metal and metalloid removal in constructed wetlands, with emphasis on the importance of plants and standardized measurements: A review. Environ Poll, 158 : 3447.

Neculita, C.M. 2008. Traitement biologique passif du drainage minier acide : sources de carbone, mécanismes d’enlèvement et écotoxicité. Thèse de doctorat, Département CGM, Polytechnique Montréal, QC, Canada, 244 p.

Wetland designRemoval of metals

(%)

Fe Mn Ni Zn

Vertical subsurface-flow

98,6 75,5 88,5 96,7

Vertical subsurface-flow unplanted

92,7 23,1 46,4 95,7

Surface-flow 89,8 -20,3 58,1 96,3

Surface-flow unplanted

86,9 -35,2 -6,0 91,2

Material et methodsMaterial et methods

• Significant increase in the pH at the outlet of the vertical subsurface and surface-flow wetlands;• Reduction of sulfate in time; • The concentration of sulfate is higher than in DMA probably caused by release from material.

• Bench scale experiments, such as constructed wetlands, are effective to treat Fe and Zn in AMD with a percentage removal near of 100%;

• Vertical subsurface-flow wetlands are more effective than surface-flow wetlands to remove contaminants (larger contact surface), as well as planted test cells;

• The removal of Mn and Ni was negligible.

• Fractions that contain most of Fe and Zn in planted and unplanted subsurface wetlands were bound to Fe-Mn oxides (more than 90%) and to the organic matter and sulfides (less than 10%), whereas most of the Mn and Ni was found bound to carbonates;

• In surface-flow wetlands substrate, Fe was concentrated mostly to Fe-Mn oxides and residual fraction, Zn to organic matter and sulfides, Mn was found bound to carbonates and in the residual fraction et Ni was essentially found in the residual fraction.

AcknowledgementsAcknowledgementsThe authors of this work would like to thank the following partners: Centre Jardin Lac Pelletier, Hecla Mining Company, IAmGold Corporation, Mine Canadian Malartic, Technosub, l’OBVT, CRIBIQ et CRSNG, FQRNT.

Pollutant removal from acid mine drainage (AMD) by bench-scale wetland (vertical subsurface and surface flow) using cattail (Typha latifolia) was investigated over a 3-months period. Synthetic AMD was prepared in the laboratory and heavy metals average concentrations in the influent were of 38.0 mg/L Fe, 2.6 mg/L Mn, 0.4 mg/L Ni and 9.0 mg/L Zn, at pH 4.2. After treatment, the average effluent quality was as follows: pH 8.0, for vertical-flow, and 7.6 for surface-flow wetlands. In addition, the removal rates were of 95 and 96% for Fe and Zn, respectively, in vertical-flow cells, and of 87 and 94% for Fe and Zn, respectively, in, surface-flow cells. However, the removal of Mn and Ni, as well as of sulfate was negligible. Then, a sequential extraction procedure (SEP) was performed to determine the partitioning of 4 heavy metals (Fe, Mn, Ni and Zn) in spent substrate collected from wetland test cells. In vertical and subsurface flow wetlands, the fractions that contain most of the Fe are the one bound to Fe-Mn oxides and the residual one, Zn was concentrated mostly in the Fe-Mn oxides fraction and bound to organic matter and sulfides, whereas Mn and Ni were bound to carbonates and found in the residual fraction. The results will help the understanding of the processes governing the treatment and the evaluation of design criteria of a constructed wetland.