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.

Evaluation of the saturated–unsaturated groundwater conditions of a thickened tailings deposit

1993 ◽  
Vol 30 (6) ◽  
pp. 935-946 ◽  
Author(s):  
S. Lee Barbour ◽  
G. Ward Wilson ◽  
L.C. St-Arnaud
Keyword(s):  
Atmospheric Oxygen ◽  
Shallow Groundwater ◽  
Groundwater Levels ◽  
Acid Generation ◽  
Zinc Mine ◽  
Retention Characteristics ◽  
Copper Zinc ◽  
Rate Of Evaporation ◽  
Thickened Tailings

The method of thickened tailings disposal has been in use at an active copper–zinc mine near Timmins, Ontario, for approximately 25 years. The thickened tailings deposit that has been formed was investigated. Field and laboratory tests were conducted to determine particle-size distribution at various horizontal locations, in situ values of hydraulic conductivity, moisture-retention characteristics, groundwater levels, and in situ water contents. The results of the investigation show that the thickened tailings deposit is relatively homogeneous. Shallow groundwater levels were also observed to follow the gently sloping topography of the tailings surface. Upward-seepage analyses were conducted for various steady-state evaporative fluxes. The analyses showed the tailings tend to maintain saturated conditions for the highest potential rate of evaporation observed. The ability of the tailings to maintain saturation is attributed to the shallow groundwater levels and the high air-entry value of the tailings. The tendency to saturated conditions at the tailings surface is a positive result. Saturated conditions in the tailings minimize the diffusion of atmospheric oxygen into the tailings. This aids in the prevention of acid generation in these tailings, which have the potential to oxidize and produce acid drainage. Key words : tailings, saturation, evaporation, acid generation.

Evaluation of Municipal Sludge Drying and Dewatering with Respect to Sludge Volume Reduction

1990 ◽  
Vol 22 (12) ◽  
pp. 153-161 ◽  
Author(s):  
Maryla Smollen
Keyword(s):  
Moisture Content ◽  
Treatment Strategies ◽  
Vacuum Drying ◽  
Municipal Sludge ◽  
Moisture Retention ◽  
Sludge Dewatering ◽  
Sludge Treatment ◽  
Energy Inputs ◽  
Retention Characteristics ◽  
Sludge Drying

A number of parameters that influence sludge dewatering behaviour have been identified, but there is a lack of consensus which of these are of the greatest concern in sludge treatment strategies. Moisture retention characteristics were obtained from vacuum drying of centrifuged sludge samples to subdivide moisture into immobilised, physically and chemically bound fractions. Physically bound moisture is responsible for unsatisfactory dewatering by centrifugation. Polyelectrolyte releases some of the immobilised water, but simultaneously increases the physically bound moisture content which gives rise to large energy inputs during mechanical dewatering. Commonly used dewaterability measurements do not appear to be linked to moisture retention characteristics.

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.

Pedotransfer functions for the estimation of moisture retention characteristics of Ferralsols and related soils

Geoderma ◽  
1997 ◽  
Vol 78 (3-4) ◽  
pp. 161-180 ◽  
Author(s):  
M. van den Berg ◽  
E. Klamt ◽  
L.P. van Reeuwijk ◽  
W.G. Sombroek
Keyword(s):  
Pedotransfer Functions ◽  
Moisture Retention ◽  
Retention Characteristics

scholarly journals Laboratory Experiments of Drainage, Imbibition and Infiltration under Artificial Rainfall Characterized by Image Analysis Method and Numerical Simulations

Water ◽  
2019 ◽  
Vol 11 (11) ◽  
pp. 2232 ◽  
Author(s):  
Belfort ◽  
Weill ◽  
Fahs ◽  
Lehmann
Keyword(s):  
Image Analysis ◽  
Numerical Simulations ◽  
Water Content ◽  
Laboratory Experiments ◽  
Pressure Head ◽  
Richards Equation ◽  
Analysis Method ◽  
Image Analysis Method ◽  
Artificial Rainfall ◽  
Classical Image

Two laboratory experiments consisting of drainage/imbibition and rainfall were carried out to study flow in variably saturated porous media and to test the ability of a new measurement method. 2D maps of water content are obtained through a non-invasive image analysis method based on photographs. This method requires classical image analysis steps, i.e., normalization, filtering, background subtraction, scaling and calibration. The procedure was applied and validated for a large experimental tank of internal dimensions 180 cm long, 120 cm wide and 4 cm deep that had been homogenously packed with monodisperse quartz sand. The calibration curve relating water content and reflected light intensities was established during the main monitoring phase of each experiment, making this procedure very advantageous. Direct measurements carried out during the water flow experiments correspond to water content, pressure head, temperature, and cumulative outflow. Additionally, a great advantage of the proposed method is that it does not require any tracer or dye to be injected into the flow tank. The accuracy and other benefits of our approach were also assessed using numerical simulations with state-of-the-art computational code that solves Richards’ equation.

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