According to Los Alamos' Tom Robison, a co-investigator on the project, there are thousands of abandoned mine sites in the United States alone. "Some of these abandoned mines, like the Berkeley Pit in Butte, Montana, pose hazards to local aquifers due to acid mine drainage," said Robison. "To address this problem, we developed a technology to remove toxic metal contaminants such as lead from acid mine drainage and, in the process, recover the economically valuable metals, like silver, copper and zinc. Typically these metals are lost in conventional remediation processes."
Known as Polymer Filtration, the patented Los Alamos technology couples unique water-soluble polymers with a process known as ultrafiltration. Scientists use a homogeneous polymer solution that binds with metal ions in the wastewater. After the polymer binds to the metal ions, the polymer-metal combination is filtered and concentrated using ultrafiltration. At process end, clean water is discharged and the metals are recovered for disposal or refining when the pH of the polymer solution is changed and the metal ions come unbound.
Since the polymers are recycled back into the polymer filtration system, there is no secondary waste or sludge stream - unlike that produced by hydroxide precipitation wastewater treatments. Perhaps most importantly, instead of working with individual batches the technology is designed to be an in-line treatment so it can rapidly and continuously process mine wastewater. Polymer filtration operates at low pressure and low temperature. It is more efficient than conventional ion-exchange resin processes.
In tests conducted on water samples taken from the Berkeley Pit, as part of a proof-of-principle experiment, the polymer filtration process began working immediately after researchers added a dilute solution of basic polymer to the samples. The addition of the polymer decreased acidity in the water causing the precipitation of nearly all the iron and aluminum in the samples. The samples were then treated with another polymer and ultrafiltered. Tests of this treated Berkeley Pit water showed below detectable limits for copper, aluminum and iron, less than 10 parts per billion of zinc and less than 3 ppb of nickel, chromium, lead and cadmium all far below current EPA discharge limits.
The polymer filtration technology is based on Laboratory-Directed Research and Development funded work conducted at Los Alamos in this area since 1992. Prior successes included actinide removal from aqueous streams and electroplating process waste minimization. The technology, as it was adapted for the electroplating industry, received R&D Magazine's R&D 100 Award in 1995.
To facilitate the continued diffusion and advancement of the polymer filtration technology Los Alamos has created a user facility in the Separation Science & Technology Technical Deployment Center and is actively seeking interested industrial mining partners to establish the technology.
An EPA Superfund site, the Berkeley Pit is an abandoned open-pit copper mine near Butte, Montana, containing more than 20 billion gallons of tainted water.
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