Investigation of the Use of Low Sulphide Coal Tailings in Covers with Capillary Barrier Effects to Prevent Acid Mine Drainage

Lime treatment of acid mine drainage (AMD) generates sludge that is commonly stored in ponds for dewatering. The use of soil-aged sludge-based mixtures for mine site rehabilitation can allow the emptying of existing basins, thus extending their storage capacity, reducing the volume of the borrow soil pit required for mine site rehabilitation, and consequently reducing the mine footprint. The authors investigated the geotechnical properties of silty soil–sludge mixtures (SSMs) as possible components of covers with capillary barrier effects (CCBEs) to prevent AMD generation from mine waste. SSMs with β values of 10%, 15%, 20%, and 25% sludge (β = wet sludge mass / wet soil mass) were studied. Two water contents were considered for each of the mixture components: 175% and 200% for the sludge and 7.5% and 12.5% for the soil. Results indicate that saturated hydraulic conductivity (ksat) values were in the range of 10−5 cm/s for the soil and SSMs at void ratios ranging from 0.28 to 0.53, with values decreasing slightly when β was increased from 0% to 25%. The air-entry value (AEV) increased from 20 kPa for the soil alone to 35 kPa for the SSM with β = 25%. These values of ksat and AEV are comparable to those of materials used in the moisture retention layers of existing efficient CCBEs. However, the volumetric shrinkage increased from about 2% for the soil alone to values ranging between 24% and 32% for the SSM with β = 25%, depending on the initial water contents of the components. Tools are provided to estimate to which extent the use of sludge in SSMs can reduce the volume of borrow natural soil required for a moisture retention layer of a CCBE.

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Field experimental cells to evaluate the hydrogeological behaviour of oxygen barriers made of silty materials

Canadian Geotechnical Journal ◽

10.1139/t06-120 ◽

2007 ◽

Vol 44 (3) ◽

pp. 245-265 ◽

Cited By ~ 37

Author(s):

Bruno Bussière ◽

Michel Aubertin ◽

Mamert Mbonimpa ◽

John W Molson ◽

Robert P Chapuis

Keyword(s):

Acid Mine Drainage ◽

Unsaturated Flow ◽

Mine Drainage ◽

In Situ Monitoring ◽

Oxygen Flux ◽

Capillary Barrier ◽

Barrier Effects ◽

Acid Mine ◽

Hydrogeological Behaviour

An in situ study was initiated to evaluate the efficiency of silts as moisture-retaining material in covers with capillary barrier effects (CCBEs) that aim at controlling the production of acid mine drainage (AMD). This investigation included the construction of four experimental cells covered by different layered cover configurations. Each CCBE was instrumented to monitor its hydrogeological behaviour. The degree of saturation (Sr) in the moisture-retaining (silty) materials was usually maintained above 85%, while Sr in the two sand layers placed above and below the silts was generally lower than 30%–50% (typical hydrogeological behaviour of efficient CCBEs). Suction measurements in the different layers of the four CCBEs were consistent with the observed Sr measurements during the four years of monitoring. The suctions measured in the moisture-retaining materials were lower than their respective air-entry values (AEV), while suctions largely exceeded the AEV of the sand in the capillary break layers. The oxygen flux calculations confirm that in each of the four CCBEs the flux through the CCBEs remained low for the entire duration of the experiment, hence limiting the generation of AMD. This study also confirmed the ability of silty materials to act as moisture retaining in a CCBE. Key words: cover with capillary barrier effects, acid mine drainage, experimental cells, in situ monitoring, unsaturated flow, diffusion, oxygen flux.

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Implication of biofilms in the sustainability of acid mine drainage and metal dispersion near coal tailings

The Science of The Total Environment ◽

10.1016/j.scitotenv.2021.147851 ◽

2021 ◽

pp. 147851

Author(s):

Sadanand Pandey ◽

Elvis Fosso-Kankeu ◽

Johannes Redelinghuys ◽

Joonwoo Kim ◽

Misook Kang

Keyword(s):

Acid Mine Drainage ◽

Mine Drainage ◽

Metal Dispersion ◽

Acid Mine ◽

Coal Tailings

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Natural oxidation of coal tailings from Middelburg area (South Africa), and impact on acid-generation potential

Journal of the Southern African Institute of Mining and Metallurgy ◽

10.17159/2411-9717/1205/2020 ◽

2020 ◽

Vol 120 (11) ◽

Author(s):

N. van Wyk ◽

E. Fosso-Kankeu ◽

D. Moyakhe ◽

F.B. Waanders ◽

M. Le Roux ◽

...

Keyword(s):

South Africa ◽

Acid Mine Drainage ◽

Coal Mine ◽

Mine Tailings ◽

Mine Drainage ◽

Acid Base ◽

Acid Base Accounting ◽

Acid Mine ◽

Acid Generation ◽

Coal Tailings

SYNOPSIS The aim of this study was to determine the acid-generating potential of coal mine tailings located in the Middelburg area, South Africa, using conventional assessment techniques. Four coal-tailing samples were collected from different layers of a coal-tailing pile. The acid-base accounting (ABA), acid-buffering characteristic curve (ABCC), and net acid generation (NAG) methods were used in conjunction with a mineralogical investigation to assess the potential of acid mine drainage (AMD) formation from the tailings. The results showed that the top layer of the pile, which was exposed to the atmosphere, was most likely to form AMD, exhibiting the lowest paste pH (2.5) and ABA of zero kg H2SO4 per ton. The ABA results were compared to ABCC results and mineralogical calculations to confirm the findings. The results from the ABCC test and calculations based on mineralogy indicated that the ABA method overestimates the effective or readily available acid neutralization capacity (ANC) and the true MPA of each sample; only three of the four samples could therefore be classified as acid-forming, but with low acid-generating capacity. Although the findings show that the top layer of the coal tailings in the Middelburg area is most likely to form AMD, it is important for future studies to further investigate the kinetics of acid formation. Keywords: acid mine drainage, acid-base accounting, mineralogy, net acid generation, coal mine tailings.

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