UA SRC Director Raina Maier Presents at Arizona Science Lecture Series

April 7, 2022

 

University of Arizona Superfund Research Center (UA SRC) Director Raina Maier presented “Mining in a Greener Future” at the Arizona Science Lecture Series, titled “Minerals,” on April 7, 2022. The public lecture discussed sustainable mining practices and the future of mining to an audience of community members in Tucson, Arizona, and viewers online via a live stream.

The lecture presented two examples of mining in a greener future: phytostabilization for reclamation of mining sites and aqueous mining as an alternative to hardrock mining.

Reclamation of mining sites

Starting with an overview of metals and hardrock mining, a method to obtain metals, Dr. Maier discussed the large environmental footprint of mining, especially mine tailings, or mine waste, which makes up one of the largest waste streams in the world. Taking the audience through some of the most impactful environmental consequences of mining, Dr. Maier discussed acid mine drainage and the Gold King Mine Spill, deforestation, and mining accidents causing pollution and even human deaths. These devastating effects of mining have led to action toward cleaner and greener mining.

Reclamation of mining sites, Dr. Maier’s first example of greener mining, can prevent dangerous exposure of mine tailings to surrounding communities. One method, cap-and-plant, has been used to cover mine tailings with protective layers between the tailings and the top soil and plants. Dr. Maier and the UA SRC have been researching another method for reclamation, though, that doesn’t require protective layers and added top soil – which could be up to 1,000 acres to cover a mine site – but instead uses phytostabilization.

Phytostabilization uses an amendment added to the mine tailings to encourage plant growth in the mixture of soil. This method would offer a greener solution, where if there were to be erosion of the tailings, the environmental impacts would be less severe than erosion from the cap-and-plant method.

Dr. Maier discussed the UA SRC field study at the Iron King Mine Superfund site in Dewey-Humboldt, Arizona, from 2010 to 2017, where researchers mixed dairy manure compost into the mine tailings and grew native plants in the resulting soil. With different amounts of the compost amendment added to the tailings, the researchers were able to achieve plant growth on the test sites.

However, acidophilic organisms – organisms that grow best in acidic environments, like mine tailings – appeared in higher numbers as more time went by, warring with the plant growth promoting microbes, which appeared in fewer and fewer numbers in the soil by the end of the study. This study at the Iron King Mine site offered insight into reclamation of mining sites: “We have an opportunity to predict when we need to go back and perhaps re-amend with compost so that the site can maintain its plants and integrity,” Dr. Maier said.

While researching at the Iron King Mine site, the UA SRC also measured whether the vegetation planted reduced dust emissions of the mine tailings. The researchers found that plants at the sites actually removed dust from the air versus the control plot with no plants and the plot that was irrigated (watered), both of which showed local dust transport of the mine tailings. This removal of dust by the plants showed the importance of reclaiming the mine sites to lower negative environmental impacts.

To translate these research findings into practice in mining, the UA SRC and the Lowell Institute for Mineral Resources developed what would become the Center for Environmentally Sustainable Mining (CESM) as a research translation tool for transfer of research results to active mining operations.

Aqueous mining and new technologies

Dr. Maier also presented on aqueous mining – mining in a water system – as an alternative to hardrock mining, the second example of a greener future for mining. While aqueous mining wouldn’t offer a solution to satisfying global supply needs for base metals, this alternative could recover rare earth elements, which are considered critical because of potential supply chain issues.

Looking to a collaborative study of the Berkley Pit, a closed copper mine in Butte, Montana, filled with acid mine drainage, Dr. Maier showed that in that one site anywhere from 17 to 41 percent of global demand for five rare earth elements – holmium, terbium, ytterbium, scandium, and lutetium – could be satisfied. This study shows that with appropriate technologies to capture and remove metals, global demand for some rare earth metals could be met with aqueous mining.

In Dr. Maier’s lab, researchers have been studying a possible approach to aqueous mining technology to capture rare earth metals using surfactants, or soaps. The surfactants have “water-hating” tail group in their molecular structure and a “water-loving” head group.

Rhamnolipid, a complex surfactant that Dr. Maier has studied for 30 years, binds metals by folding its head group into a binding pocket, like a claw, and wraps around a metal. This surfactant is impressive because rhamnolipids are much better at complexing with rare earth elements than common soil and water elements, meaning that when rhamnolipid is added to solutions, it will selectively pick out the rare earth elements.

To implement this approach to capturing rare earth elements with rhamnolipid, Dr. Maier’s lab studied recovery of uranium from a site in Monument Valley using ion flotation. One of the outcomes of this research was a new collaboration with chemists that created synthetic rhamnolipids using green chemistry, allowing more precision and lower cost for the surfactants.

“[Rhamnolipids] are just one example of a new technology that are being developed all over the country, all over the world, to make metal mining more sustainable,” Dr. Maier said.

Ending the lecture with optimism, Dr. Maier said, “There are so many ways, if we put our minds to it, if we use human ingenuity, that we can solve the problems that our world is facing. We need to support science. We need to support science education. We need to support research. Human ingenuity will overcome all of the problems that have been caused by human ingenuity.”

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