Reduction of acid generation in mine tailings through the use of moisture-retaining cover layers as oxygen barriers: Reply

1990 ◽  
Vol 27 (3) ◽  
pp. 402-403 ◽  
Author(s):  
Ronald V. Nicholson ◽  
Robert W. Gillham ◽  
John A. Cherry ◽  
Eric J. Reardon
Keyword(s):  
Mine Tailings ◽  
Acid Generation ◽  
Oxygen Barriers

Mobility of Ra-226 and Heavy Metals (U, Th and Pb) From Pyritic Uranium Mine Tailings Under Sub-Aqueous Disposal Conditions

2011 ◽  
Author(s):  
Nand K. Dave´
Keyword(s):  
Heavy Metals ◽  
Surface Water ◽  
Mine Tailings ◽  
Ion Concentration ◽  
Uranium Mine ◽  
Acid Generation ◽  
Shallow Zone ◽  
Acidic Conditions ◽  
Waste Repositories

Laboratory lysimeter studies were undertaken to evaluate the leaching characteristics and mobility of Ra-226 and other heavy metals (U, Th and Pb) from pyritic uranium mine tailings under sub-aqueous disposal conditions for assessing the long-term radiological stability of such waste repositories. The experiments were conducted using three types of un-oxidized tailings: fine, coarse and gypsum depleted mill total tailings. The results showed that Ra-226 was leached from surface of the submerged tailings and released to both surface water and shallow zone pore water during initial low sulphate ion concentration of the surface water cover in all three cases. The release of Ra-226 was further enhanced with the onset of weak acidic conditions in the surface water covers of both coarse and gypsum depleted mill total tailings. With additional acid generation and increasing sulphate and iron concentrations, the dissolved Ra-226 concentrations in the water covers of these tailings gradually decreased back to low levels. Pb was also leached and mobilized with the development of moderate acidic conditions at the surface of the submerged coarse and gypsum deplete tailings. No leaching of U and Th was observed.

Reduction of acid generation in mine tailings through the use of moisture-retaining cover layers as oxygen barriers

1989 ◽  
Vol 26 (1) ◽  
pp. 1-8 ◽  
Author(s):  
Ronald V. Nicholson ◽  
Robert W. Gillham ◽  
John A. Cherry ◽  
Eric J. Reardon
Keyword(s):  
Oxygen Diffusion ◽  
Pyrite Oxidation ◽  
Moisture Retention ◽  
Gaseous Oxygen ◽  
Cover Layer ◽  
Fine Grained ◽  
Acid Generation ◽  
Tailings Remediation ◽  
Diffusion Characteristics ◽  
Oxygen Barriers

Acid production in sulphidic tailings can cause severe degradation of water quality in both subsurface and surface systems. The availability of gaseous oxygen and the rate of diffusion of oxygen through the open pore spaces in the upper zone of the tailings are the critical factors controlling the rate of acid generation. Acid generation can be reduced by applying a fine-grained, nonreactive cover layer to the tailings surface. The key process involves moisture retention by capillary forces so that near-saturated conditions can be maintained even when the cover layer occurs at several metres above the water table. Textured layering of fine over coarse materials improves moisture retention in the fine layer when infiltration exceeds evapotranspiration. The application of such a cover layer can theoretically reduce oxygen diffusion coefficients and rates of acid generation by up to four orders of magnitude. This can represent a substantial difference in the potential treatment costs of tailings seepage. Simplified calculations based on Fick's first law can be applied to preliminary laboratory measurements of diffusion characteristics of potential cover materials to evaluate their effectiveness in decreasing acidification. These concepts and methods provide an initial evaluation before field-scale testing of cover performance. Key words: pyrite oxidation, tailings, remediation, covers, acid generation, oxygen diffusion.

scholarly journals The Potential Role of Halothiobacillus spp. in Sulfur Oxidation and Acid Generation in Circum-Neutral Mine Tailings Reservoirs

2019 ◽  
Vol 10 ◽  
Author(s):  
Kelly Whaley-Martin ◽  
Gerdhard L. Jessen ◽  
Tara Colenbrander Nelson ◽  
Jiro F. Mori ◽  
Simon Apte ◽  
...  
Keyword(s):  
Mine Tailings ◽  
Potential Role ◽  
Sulfur Oxidation ◽  
Acid Generation

Oxidation of flooded mine tailings due to resuspension

1999 ◽  
Vol 36 (5) ◽  
pp. 826-845 ◽  
Author(s):  
Ernest K Yanful ◽  
Ajay Verma
Keyword(s):  
Mine Tailings ◽  
Laboratory Experiments ◽  
Quality Data ◽  
Metal Release ◽  
Water Quality Data ◽  
Acid Generation ◽  
Static Water ◽  
Water Cover ◽  
Cover Up

Laboratory experiments were performed to assess the contribution of resuspension to the oxidation of pyrrhotite mine tailings flooded with a shallow water cover (up to 80 cm). Resuspension was produced by a paddle rotated at prescribed speeds in the water cover. The quality of the water cover was monitored over a 126 day period and the results were compared to the case where the tailings were kept still (no resuspension). The results showed that resuspended tailings oxidized considerably more than tailings at rest. The pH and dissolved oxygen concentration of the stirred water covers were 2.6 and 14 times lower, respectively, than those of the static water covers where there was no resuspension. Sulphate production increased by about 26-64 times, while the release of metals such as zinc, copper, and nickel was 1020, 318, and 138 times greater, respectively. The suspended tailings were finer and had lower pyrrhotite content at the end of the experiments than the tailings at rest and the original tailings. Tailings oxidation and metal release increased with increasing stirrer speed and decreasing depth of water cover. These findings pertain to laboratory conditions and the water-quality data cannot necessarily be extrapolated to the field, except in a general sense. Key words: acid generation, oxygen flux, mass transfer, precipitation, ripples, hydraulic sorting.

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

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.

Numerical simulations to investigate moisture-retention characteristics in the design of oxygen-limiting covers for reactive mine tailings

1991 ◽  
Vol 28 (3) ◽  
pp. 446-451 ◽  
Author(s):  
Festus F. Akindunni ◽  
R. W. Gillham ◽  
R. V. Nicholson
Keyword(s):  
Numerical Simulations ◽  
Mine Tailings ◽  
Atmospheric Oxygen ◽  
Pressure Head ◽  
Moisture Retention ◽  
Residual Saturation ◽  
Acid Generation ◽  
Water Influx ◽  
Protective Cover ◽  
Retention Characteristics

Acid generation in reactive mine tailings is an oxidation process that is dependent on availability of molecular oxygen. As a consequence of the diffusion coefficient of oxygen being several orders of magnitude higher in air than in water, influx of atmospheric oxygen into a material at depth can theoretically be minimized by maintaining a protective cover layer at high moisture content. Such oxygen-limiting covers are generally of finer texture than the material being protected. A numerical model was used to investigate the importance of moisture-retention characteristics in the transient drainage of such two-layer systems. The results show that the effectiveness of a material as a moisture-retaining cover is dependent on the magnitude of its air-entry value. The thickness of the cover maintained at full saturation after prolonged drainage also depends on the pressure head at which the underlying material approaches residual saturation. Key words: geologic covers, tailings, numerical simulations, air-entry value, residual saturation, textural layering.

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