1. Trace metal mobilization at abandoned mining sites due to redevelopment activities in hyperarid climates
DOUGLAS B. SIMS, PHD and JOHN E. KELLER, PHD
College of Southern Nevada
Department of Physical Sciences
Abstract
Methods (continued)
Results and Discussion (continued)
Results and Discussion (continued)
Reclamation of abandoned mine sites in arid environments has been a focus of development in recent years, in part, due to rising land costs. This study monitored various solutions run through mine sediments for 393 days. Results show that fertilizers can provide favorable conditions for mobility of Pb, Mn, Zn, Al, Ba, Cu and As, though on a limited basis. Data show there is a potential for mobilized trace metals and metalloids to enter the wider environment, including water sources, long after development activities are finished, even in an arid environment such as Southern Nevada.
There are studies that show clay, silts and mineral content matter but, there are studies that indicate nutrients are also a factor that alter trace metal behavior with particles (e.g. Cai et al., 2002; Lombi et al., 2000 ).
Figure 2: Al concentration over 393 days of saturation
Sediments were packed in three sets of polyvinyl chloride (PVC) columns that were 20 cm long x 3.18 cm diameter; packed with 100 grams of tailings and capped with a removable top.
Column 1 was filled with DI water; Column 2 DI water fortified with 1 application of Liquid Turf Builder®: (29% total N, 2% P2O5 and 3% K2O) and Schultz®: (16% total N, 16% P2O5 and 16% K2O); Column 3 was fortified with two applications of the same fertilizer. Samples were drawn at day 1, 30, 60, 90, 273, and 393. All columns were in triplicate with the analytical results averaged to reduce variability within 1 standard deviation.
Figure 1. Three Kids Mine Site, Henderson, Nevada
Figure 6: Pb concentration over 393 days of saturation
Introduction
Trace metals (e.g. Cd, Pb) and metalloids (e.g. As, Se) are known to be a risk to human health and the wider environment (Zaharescu et al. 2009). It is widely acknowledged that the source of trace metals and metalloids in bedrock, specifically volcanic, sulfide and sulfosalt rich bedrock are only viable in under specific environmental conditions (Rose et al. 1979; Pearcy et al. 2001). Mining is a large contributor to the removal, concentration and ultimate redistribution of such trace elements (Langmuir et al. 2006; Sims 2011; Sims et al., 2013).
This study presents a broader overview of the potential effect that fertilizers have on trace metals and metalloids in arid conditions. It is not the impact on today’s environment but rather, the potential for geochemical change over time that can occur long after a site is fully developed.
Figure 3: As concentration over 393 days of saturation
Figure 7: Mn concentration over 393 days of saturation
Results and Discussion
Data show Al, As, and Cu increased at day 30 while Ba maintained at approximately 0.01 mg/L. Between day 30 and 60 Al, As, and Ba decreased followed by an increase at day 90 and again at day 273 (Figs. 2- 5). Data from this study show Pb, Mn, and Zn increased at day 30 and between day 90 and 393 (Figures 6 - 8). Between day 30 and 60, Pb and Zn decreased while Mn stayed constant until day 90.
It is likely that the movement is the result of nutrient (e.g. PO42-) input as described by Winter and Dillon (2005) and others. Haque and Johannesson (2006) also state that groundwater, through such aquifers, searches for equilibrium providing opportunities for trace metals to be mobilized that would normally not be soluble.
Figure 4: Ba concentration over 393 days of saturation
Figure 8: Zn concentration over 393 days of saturation
Conclusion
Data show Pb, Mn, Zn, Al, Ba, Cu and As were mobilized, though on a limited basis. This study illustrates there is a potential for trace metals and metalloids to enter the wider environment, including water sources, long after development finalized, even in an arid environment. Long term monitoring is required.
Figure 5: Cu concentration over 393 days of saturation
Methods
This study evaluated mine sediments collected from Three Kids Mine located in Henderson, Nevada as it is well documented to have high levels of trace elements. Sediment was collected from the largest evaporation pond of Three Kids Mine (Figure 1).
Data shows Pb, Mn, and Zn increased at day 30, between day 90 and 393 Figures 6 - 8). Between day 30 and 60, Pb and Zn decreased while Mn was constant until day 90. Between day 90 and 393 , all three trace metals increased, indicating limited availability.
Sims, Douglas B., The Migration of Arsenic and Lead in Surface Sediments at Three Kids Mine: Henderson, Nevada. Masters Thesis in the Geology Department, UNLV.
Sims DB and A Francis, Anthropogenic Influences on Geogenic Trace Elements and Contamination in Wash Sediments from Historical Mining Activities in the Carnation Wash System, Nelson, Nevada (USA). Int. J of Soil, Sediment and Water, 3(1), art. 2.
Sims, D.B., 2011.  Fate of Contaminants at an Abandoned Mining site in an Arid Environment.  Unpublished dissertation in environmental science. Kingston University, London.
Besser, J. M., S. E. Finger, S. E. Church, Impacts of Historical Mining on Aquatic Ecosystems-An Ecological Risk Assessment. Integrated investigations of Environmental Effects of Historical Ming in the Animas River Watershed, San Juan County, Colorado, 1651,
Chae, Gi-Tak; Seong-Taek Yun, Bernhard Mayer, Byoung-Young Choi, Kyoung-Ho Kim, Jang-Soon Kwon, Soon-Young Yu,, Hydrochemical and stable isotopic assessment of nitrate contamination in an alluvial aquifer underneath a riverside agricultural field. Agricultural Water Man.; 96(12):
Heck, J, United States Congressman, Heck Introduces Three Kids Mine Bill. July 13, 2011
Others available upon request
NWRA, 2014, Las VEgas
Selected References