Chemical characteristics and acid drainage assessment of mine tailings from Akara Gold mine in Thailand |
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| Authors: | Chulalak Changul Chakkaphan Sutthirat G Padmanahban Chantra Tongcumpou |
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| Institution: | (1) International Postgraduate Programs in Environmental Management (Hazardous Waste Management), National Center of Excellence for Environmental and Hazardous Waste Management (NCE-EHWM), Chulalongkorn University, Bangkok, 10330, Thailand;(2) Department of Geology, Faculty of Science, Chulalongkorn University, Bangkok, 10330, Thailand;(3) Environmental Research Institute, Chulalongkorn University, Institute Building 2, Bangkok, 10330, Thailand;(4) Department of Civil Engineering, North Dakota State University, Fargo, ND, USA; |
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| Abstract: | Acid Mine Drainage (AMD) is a great concern in many abandoned mines because of its adverse effect on the environment. In mining
processes, many kinds of wastes are produced. These wastes may become eventually sources of environmental degradation. The
focus of this study is the geochemical characterization of the end-processed tailings generated by Akara Gold Mine, the biggest
gold mine in Thailand. Tailing samples were systematically collected for analyses of chemical and mineralogical compositions.
As a result, their quantitative chemical analyses are slightly different from place to place, but mineral components cannot
be clearly differentiated. For instance, it may be assumed that the end-processed tailings, which were a mixture between high
and low grade concentrates, would have similar mineral components. However, the little variation of chemical composition may
be caused by the ore refining processes that are somehow varied in proportion to chemical additives, alkali cyanide and quick
lime in particular. In addition, clay composition in ore-bearing layers may also influence alumina content of tailings, accordingly.
Distribution of the tailings is not related to depth and distance of the tailing storage pond because the disposal has sped
them over the pond during operation. Total heavy metals of the tailing samples were analyzed on the basis of the EPA 3052
method. Consequently, the most toxic elements (e.g., Co, Cu, Cd, Cr, Pb, Ni and Zn) were found falling within the standard
of Thailand Soil Quality Standards for Habitat and Agriculture. Only Mn appears to have higher content than the standard.
In addition, leaching tests proved that these tailings contain low metal concentrations. As a result, at pH 2, Mn can leach
out exceeding the Thailand Surface Water Quality Standard for Agricultural (Mn <1 ppm) and the Thailand Industrial Effluent
Standard (<5 ppm). Although leachate at pH 4 and neutral conditions contains lower Mn than the Industrial Effluent Standard
it still exceeds the surface water quality standard. Interestingly, Pb can be leached out exceeding both standards (0.2 ppm
for the industrial effluent standard and 0.05 ppm for the surface water quality standard). For Ni leaching, its concentration
is lower than the Industrial Effluent Standard at all pH conditions but still exceeds the Surface Water Standard at pH 2 and
4. This information should be taken into consideration for further environmental monitoring. Acid generating potential of
the tailings was estimated using acid–base accounting (ABA) and net acid generation (NAG) tests. The results of ABA and NAG
tests show that the tailing samples contain a high amount of sulfur. However, they also contain high acid neutralization capacity.
Consequently, these tailings may not have potential to generate acid drainage; in the other words, they can be classified
as a non-acid forming (NAF) material. However, since these tailings contain some heavy metals (e.g., Ni, Mn and Pb) that are
observed in leachates exceeding the standards at low pH, the AMD conditions may lead to heavy metal release. Therefore, prevention
of oxidizing process and dissolution should be considered with great care. In addition, Mn and Pb can also be leached at neutral
conditions. Barrier of air and water, clay layer for example, should be placed over the tailings pound before covering by
topsoil for re-vegetation. Growing native grass is recommended for stabilization of the surface and reducing erosion rate.
Monitoring of water quality should also be carried out annually. |
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