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.

Relationships between oxygen diffusion characteristics of polycrystalline and single crystal 2MgO · TiO2

1977 ◽  
Vol 50 (3) ◽  
pp. 459-462 ◽  
Author(s):  
S. Shirasaki ◽  
I. Shindo ◽  
H. Haneda ◽  
M. Ogawa ◽  
K. Manabe
Keyword(s):  
Single Crystal ◽  
Oxygen Diffusion ◽  
Diffusion Characteristics

Oxygen Diffusion Characteristics of Gas Diffusion Layers With Moisture

2008 ◽  
Author(s):  
Daigo Iwasaki ◽  
Yoshio Utaka ◽  
Yutaka Tasaki ◽  
Shixue Wang
Keyword(s):  
Porous Media ◽  
Liquid Water ◽  
Oxygen Diffusion ◽  
Gas Diffusion ◽  
Vacuum Impregnation ◽  
Impregnation Method ◽  
Moist Air ◽  
Oxygen Diffusivity ◽  
Diffusion Characteristics ◽  
Experimental Apparatus

The mass transfer characteristics of the gas diffusion layer (GDL) in a polymer electrolyte fuel cell (PEFC) are closely related to the performance. In this study, the oxygen diffusivity of paper and cloth type porous media, which are generally used as GDLs, were measured with respect to liquid water content, using experimental apparatus consisting of an oxygen sensor based on a galvanic battery. Paper type porous media, both non treated and hydrophilic treated, and the cloth type porous media with non treated surface were used as GDL specimens. The porosity of both specimens was almost the same, but the representative pore diameter of the cloth type GDL was approximately three times larger than that of paper type GDL. Two methods were utilized to impregnate liquid water into the porous GDL media to realize different water distributions in the specimens at the initial state; vacuum impregnation and moist air condensation impregnation. The oxygen diffusivities of the specimens were measured to clarify the influence of the two impregnation methods on the oxygen diffusion characteristics. Moreover, the relation between the measurement of oxygen diffusivity and the visualization of the liquid water distribution by using Neutron Radiography [Tasaki et al. (2007)] was investigated for the paper and cloth type GDLs. The oxygen diffusivity in the paper type porous media decreased precipitously with increasing water saturation by the vacuum impregnation method, whereas the diffusivity decrease was relatively small when impregnated by the moist air condensation method. For the cloth type porous media with weaving threads, oxygen diffusion characteristics were independent of the water impregnation method. Thus, the porous medium’s microstructure plays an important role in determining diffusion characteristics, especially in the presence of liquid water.

G133 Oxygen Diffusion Characteristics of Gas Diffusion Layer with Moisture

2007 ◽  
Vol 2007 (0) ◽  
pp. 239-240 ◽  
Author(s):  
Yutaka TASAKI ◽  
Shixue WANG ◽  
Yasushi ICHIKAWA ◽  
Denis. Kramer ◽  
Pierre. Boillat ◽  
...  
Keyword(s):  
Diffusion Layer ◽  
Oxygen Diffusion ◽  
Gas Diffusion Layer ◽  
Gas Diffusion ◽  
Diffusion Characteristics

E144 Oxygen Diffusion Characteristics for Wet Gas Diffusion Layer

2006 ◽  
Vol 2006 (0) ◽  
pp. 177-178
Author(s):  
Shixue WANG ◽  
Yoshio UTAKA ◽  
Yutaka TASAKI ◽  
Masanori MOCHIMARU
Keyword(s):  
Diffusion Layer ◽  
Oxygen Diffusion ◽  
Gas Diffusion Layer ◽  
Gas Diffusion ◽  
Wet Gas ◽  
Diffusion Characteristics

First Principles Suggestions of Targeted Diffusion Experiments on SiO2

2005 ◽  
Vol 237-240 ◽  
pp. 127-132 ◽  
Author(s):  
Guido Roma ◽  
Yves Limoge
Keyword(s):  
Hydrostatic Pressure ◽  
Oxygen Partial Pressure ◽  
Point Defects ◽  
First Principles ◽  
Oxygen Diffusion ◽  
First Principles Calculations ◽  
Bulk Silicon ◽  
Equilibrium Conditions ◽  
Gaseous Oxygen ◽  
Silicon Diffusion

In this paper we propose a couple of experimental lines in order to probe specific features of oxygen and silicon diffusion in -quartz and SiO2 in general. We start from the results of atomistic first principles calculations and from their predictions concerning point defects formation free enthalpies; we suggest that measurements with variable oxygen partial pressure could confirm that, in well defined regimes, oxygen diffusion is controlled by doubly negative oxygen interstitials. Along similar lines, for silicon diffusion, one should check the real equilibrium conditions of samples, with gaseous oxygen or bulk silicon, or closed conditions. We discuss our predictions for silicon diffusion, that could clarify some discrepancies between experimental results. Another possible probe would be to perform measurements under hydrostatic pressure, in order to measure the formation volume of the migrating species and to compare it to the theoretical values.

Thermal Expansion, Oxygen Non-Stoichiometry and Diffusion Mobility in some Ferrites-Nickelites

2013 ◽  
Vol 200 ◽  
pp. 86-92 ◽  
Author(s):  
Vladimir Vashook ◽  
Jean Rebello ◽  
J.Y. Chen ◽  
Leonid Vasylechko ◽  
Dmytro Trots ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Electrical Conductivity ◽  
Thermal Expansion ◽  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Oxygen Diffusion ◽  
Oxygen Exchange ◽  
Diffusion Mobility ◽  
Diffusion Characteristics ◽  
And Diffusion

Crystal structure,thermal expansion, oxygen non-stoichiometry, electrical conductivity and diffusion characteristics of two analogous LaFe0.7Ni0.3O3‑d and PrFe0.7Ni0.3O3‑d compositions were investigated depending on temperature (201000 °C) and oxygen partial pressure (0.6–21000 Pa). The found oxygen diffusion and oxygen exchange coefficients for the both compositions at similar conditions are near to each other and varied in the range of 110‑7110‑5 cm2s‑1 and 510‑6110‑4 cms‑1, respectively.

scholarly journals Control of Acid Generation from Pyrite Oxidation in a Highly Reactive Natural Waste: A Laboratory Case Study

Minerals ◽  
2017 ◽  
Vol 7 (6) ◽  
pp. 89 ◽  
Author(s):  
Yan Zhou ◽  
Michael D. Short ◽  
Jun Li ◽  
Russell C. Schumann ◽  
Roger St. C. Smart ◽  
...  
Keyword(s):  
Pyrite Oxidation ◽  
Acid Generation
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