Parametric Study on the Water Content Profiles and Oxidation Rates in Nearly Saturated Tailings Above the Water Table

Abstract

A promising concept, known as the elevated water table, is emerging as a management and possible closure technique to limit AMD production from tailings impoundments. This prevention approach is based on the principle that tailings in the capillary zone can be maintained in a state close to full saturation which minimizes oxygen diffusion and thus limits acid generation. A parametric study was conducted to evaluate the effect of various factors on the water content profiles in reactive tailings. The results presented here show that the position of the water table has a large influence on the water content profiles and on the oxygen flux at the tailings surface. For a water table depth value smaller or equal to the tailings' air entry value ( a ), the degree of saturation S r varies between 90 to 99 % at the tailings surface, covered by a sand protection layer. These high S r values yield effective diffusion coefficient D e comparable to that of O 2 diffusion in water. The study also shows that the efficiency of the elevated water table concept can be negatively affected when the tailings are highly reactive.

Measurement of Oxygen Consumption and Diffusion in Exposed and Covered Reactive Mine Tailings

“…3 and 4 show that the mine tailings studied are fairly reactive. They also emphasise the necessity to keep the materials at a high degree of saturation (an issue that is explicitly addressed elsewhere in this conference by Dagenais et al, 2006 andOuangrawa et al, 2006 The second case studied (Mine B) consists of a base metal mining operation that has been closed for a multitude of years, and whose TSF has been restored with a three layer cover with capillary barrier effects (CCBE): a base layer consisting of 50 cm of sand used as capillary break layer; a moisture-retaining layer made of slightly reactive but non-acid generating tailings material with a thickness of 80 cm; and a 50 cm top layer consisting of sand and gravel to protect the silt layer from evaporation and biointrusion (Aubertin et al, 2000b). Ricard et al (1999) describe the properties of the cover materials in greater detail.…”

Repeatability Evaluation of Instrumented Column Tests in Cover Efficiency Evaluation for the Prevention of Acid Mine Drainage

“…It involves keeping most of the tailings saturated to limit oxygen migration. Details on this technique are available in Ouangrawa et al (2005Ouangrawa et al ( , 2006Ouangrawa et al ( , 2009, Dagenais et al (2006) andSENES (1996). In Demers and collaborators' study, two duplicated un-covered columns were installed and monitored to evaluate the elevation of water table technique on tailings behaviour when submitted to atmospheric conditions.…”

Preventing Acid Mine Drainage with an Elevated Water Table: Long-Term Column Experiments and Parameter Analysis

“…1), Aubertin et al (1999) proposed the use of a sand and gravel layer to protect against evaporation. These types of coarse-grained cover layers act as capillary barriers against upward migration of moisture because of their low water content (and hence low hydraulic conductivity; Dagenais 2005;Dagenais et al 2006).…”

“…To ensure environmental protection, regulations are becoming increasingly demanding, and new environmentally effective and economically viable techniques are being developed to prevent tailings oxidation. In relatively humid climates, two of the more promising alternatives are water covers Adu-Wusu et al 2001;Vigneault et al 2001;Mian and Yanful 2003;Malmström et al 2006) and covers with capillary barrier effects (CCBEs; see Nicholson et al 1989;Collin and Rasmuson 1990;Aubertin et al 1998;Bussière et al 2003;Dagenais et al 2006;Adu-Wusu and Yanful 2006). Oxygen consumption covers made of organic matter have also been proposed (Tassé et al 1996).…”