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Groundwater Remediation Technologies
Groundwater contamination is one of the most concerning issues from uranium mining activities. Radionuclides cannot be destroyed or degraded, unlike some organic contaminants (and similar to metals). Besides, sites, where radionuclides may be found, are mainly radioactive and mixed waste disposal areas, and therefore many other contaminants may also be present in groundwater.
Historically, mine sites have been a significant source of contamination to the environment, particularly in sites where the mining activity has ceased without an existing closure plan or a rehabilitation project. Such practices are no longer acceptable. Upon closure, decommissioning and environmental remediation of the site must take place, and in most cases, long-term monitoring to ensure the long-time stability of the site. Closure and decommissioning plans are mandatory at the initial design stage of the project.
Uranium mining can impact groundwater in several ways, mainly from the exploration, mining, processing, and waste management phases of the project. The contamination can occur from the ground surface (by infiltration of contaminated surface water, waste piles, tailings facilities, airborne particles, etc.), from above the water table (leaks in pipelines, leachates, etc.), or from below the water table (drainage wells, groundwater withdrawal, etc.) . When considering impacts associated with uranium in water, it is essential to note that the risk of chemical toxicity can be much more significant than the radiological risk for a given uranium concentration.
Different in-situ and ex-situ remediation options exist for contaminated groundwater: containment of the contaminants to prevent migration (e.g., using geotechnical measures), removal of the contamination source (e.g., by excavation and subsequent soil washing), groundwater treatment at the point of use, removal of the groundwater for treatment and replacement, or remediation of the groundwater in situ (e.g., the in-situ transformation of the contaminants to reduce their mobility and the toxicity). Many of these options are put in operation through the pump-and-treat systems, in situ permeable treatment wall system, monitored natural attenuation, enhanced attenuation technologies, and biological processes.
All these mechanisms have their advantages and limitations. Moreover, they are contaminant specific and strongly dependent on the subsurface environmental conditions of the site, which may constrain the entire remediation of the site or the application of some technologies which may be too costly to implement on a large scale or inadequate to address the magnitude and combinations of contamination problems. Besides, multiple technologies may be involved simultaneously at a particular site and change over time. Therefore, it is recognized that there is no single technology or a single combination of technologies that would apply to all contaminants under all subsurface environmental conditions.
On the other hand, sites, where radionuclides may be found, are mainly radioactive and mixed waste disposal areas, and therefore many other contaminants may also be present in groundwater. In all situations, designing and implementing effective prevention measures to avoid contamination are preferred over-relying on groundwater remediation after contamination has occurred. The groundwater clean-up systems which are widely used are expensive and need to be applied in practice for a long time, although, in recent years, remediation research has been focused on the development of new clean-up systems and improvement of the efficiency of the existing ones.
Remediation of groundwater impacted with dissolved metals, metalloids, and radionuclides is perhaps one of the biggest challenges for in situ environmental remediation today. Remedial strategies for the treatment of metals in groundwater generally involve direct precipitation or sorption/coprecipitation, with the goal of permanently sequestering and immobilizing the metals in the aquifer soil matrix. The success of this process is dependent upon many factors, such as the kinetics of the reaction, the equilibrium solubility (the solubility of the precipitated solid phases as they form), and durability/permanence (long-term stability of the precipitated solids) . The result is a reduction in the groundwater radionuclide and metals concentrations, but these remain in situ.
2. Remediation Technologies
2.1. Chemical Separation
2.2. Physical Separation
2.3. Biological Treatment
2.4. Natural Attenuation
Monitored Natural Attenuation
The entry is from 10.3390/geosciences11060250
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