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US officials consider robots to prevent mine spills

As reported by the Associated Press, Crumbling mine tunnels awash with polluted waters perforate the Colorado mountains and scientists may one day send robots creeping through the pitch-black passages to study the mysterious currents that sometimes burst to the surface with devastating effects.

One such disaster happened at the inactive Gold King Mine in southwestern Colorado in 2015, when the United States Environmental Protection Agency (U.S. EPA) accidentally triggered the release of 3 million gallons of mustard-colored water laden with arsenic, lead and other toxins. The spill tainted rivers in three states.

a man in a hard hat sprinkling lime (white power) into a pool of muddy water next to a culvert. Here, lime is added to a settling pond to assist in the pH adjustment of the water (Credit: Eric Vance/U.S. EPA)

Now the U.S. EPA is considering using robots and other sophisticated technology to help prevent these types of “blowouts” or clean them up if they happen. But first, the agency has to find out what’s inside the mines, some of which date to Colorado’s gold rush in the 1860s.

Wastewater laden with toxic heavy metals has been spewing from hundreds of inactive mines nationwide for decades, the product of complicated and sometimes poorly understood subterranean flows.

Mining creates tainted water in steps: Blasting out tunnels and processing ore exposes long-buried, sulfur-bearing rocks to oxygen. The sulfur and oxygen mix with natural underground water flows to create sulfuric acid. The acidic water then leaches heavy metals out of the rocks.

To manage and treat the wastewater, the U.S. EPA needs a clear idea of what’s inside the mines, some of which penetrate thousands of feet into the mountains. But many old mines are poorly documented.

Investigating with robots would be cheaper, faster and safer than humans.

“You can send a robot into an area that doesn’t have good air quality. You can send a robot into an area that doesn’t have much space,” said Rebecca Thomas, project manager for the U.S. EPA’s newly created Gold King Superfund site, officially known as the Bonita Peak Mining District.

Instruments on the robots could map the mines and analyze pollutants in the water.

They would look more like golf carts than the personable robots from “Star Wars” movies. Hao Zhang, an assistant professor of computer science at the Colorado School of Mines, envisions a battery-powered robot about 5 feet long with wheels or tracks to get through collapsing, rubble-strewn tunnels.

Zhang and a team of students demonstrated a smaller robot in a mine west of Denver recently. It purred smoothly along flat tunnel floors but toppled over trying to negotiate a cluttered passage.

“The terrain is pretty rough,” Zhang said. “It’s hard for even humans to navigate in that environment.”

A commercial robot modified to explore abandoned mines — including those swamped with acidic wastewater — could cost about $90,000 and take three to four years to develop, Zhang said.

Robot in underground mine (Photo Credit: Tatlana Flower/AP File)

Significant obstacles remain, including finding a way to operate remotely while deep inside a mine, beyond the reach of radio signals. One option is dropping signal-relay devices along the way so the robot stays in touch with operators. Another is designing an autonomous robot that could find its own way.

Researchers are also developing sophisticated computerized maps showing mines in three dimensions. The maps illustrate where the shafts intersect with natural faults and provide clues about how water courses through the mountains.

“It really helps us understand where we have certainty and where we have a lot of uncertainty about what we think is happening in the subsurface,” said Ian Bowen, a U.S. EPA hydrologist. “So it’s a wonderful, wonderful tool.”

The U.S. EPA also plans to drill into mines from the surface and lower instruments into the bore holes, measuring the depth, pressure and direction of underground water currents.

Tracing the currents is a challenge because they flow through multiple mines and surface debris. Many tunnels and faults are connected, so blocking one might send water out another.

“You put your finger in the dike here, where’s the water going to come out?” Thomas said.

Once the U.S. EPA finishes investigating, it will look at technologies for cleansing the wastewater.

Options range from traditional lime neutralization — which causes the heavy metals dissolved in the water to form particles and drop out — to more unusual techniques that involve introducing microbes.

The choice has consequences for taxpayers.  If no company is found financially responsible, the EPA pays the bill for about 10 years and then turns it over to the state.  Colorado currently pays about $1 million a year to operate a treatment plant at one Superfund mine. By 2028, it will pay about $5.7 million annually to operate plants at three mines, not including anything at the Bonita Peak site.

The U.S. EPA views the Colorado project as a chance for the government and entrepreneurs to take risks and try technology that might be useful elsewhere.

But the agency — already dealing with a distrustful public and critical politicians after triggering the Gold King spill — said any technology deployed in Colorado will be tested first and the public will have a chance to comment before decisions are made.

“We’re certainly not going to be in the position of making things worse,” Thomas said. “So when I say we want to take risks, we do, but we want to take calculated, educated risks and not worsen water quality.”

Arsenic found to control uranium contamination

As reported by World Nuclear News, an international team led by the University of Sheffield has discovered that the toxic element arsenic prevents uranium from an abandoned mine in the UK migrating into rivers and groundwater.  The discovery could help in the remediation of former uranium mines and other radioactively contaminated areas around the world, the scientists believe.

The team of scientists – led by the Department of Materials Science and Engineering at the University of Sheffield – studied the uranium and arsenic in the topsoil at the abandoned South Terras uranium mine in Cornwall, England.

The researchers used some of the world’s brightest synchrotron X-ray microscopes – the Swiss Light Source and the USA’s National Synchrotron Light Source – to unearth what is believed to be the first example of arsenic controlling uranium migration in the environment.  These microscopes use intense X-ray beams to focus on a spot just one-millionth of a metre in diameter.

“We use synchrotron X-rays to identify and isolate the microscopic uranium particles within the soils and determine their chemical composition and mineral species,” said co-author of the study, Neil Hyatt.  “It’s like being able to find tiny uranium needles in a soil haystack with a very sensitive metal detector.”

Source: © Claire Corkhill
The abandoned South Terras mine in Cornwall where uranium was mined until 1930

According to the study – published on 14 December in Nature Materials Degradation – ore extraction processes and natural weathering of rock at the South Terras mine has led to the proliferation of other elements during degradation, particularly arsenic and beryllium, which were found in significant concentrations.  The arsenic and uranium were found to have formed the highly insoluble secondary mineral metazeunerite.

“Significantly, our data indicate that metazeunerite and metatorbernite were found to occur in solid solution, which has not been previously observed at other uranium-contaminated sites where uranyl-micas are present,” the study says.

Claire Corkhill, lead author of the study, said: “Locking up the uranium in this mineral structure means that it cannot migrate in the environment.”

The researchers concluded that this process at South Terras – which operated between 1873 and 1930, producing a total of 736 tonnes of uranium – is the result of a set of “rather unique” geological conditions.  “To identify this remediation mechanism at other sites, where arsenic and uranium are key co-contaminants, further detailed mineralogical assessments are required,” they said.  “These should be considered as an essential input to understand the ultimate environmental fate of degraded uranium ore.”

“The study has far-reaching implications, from the remediation of abandoned uranium mines across the world, to the environmental clean-up of nuclear accidents and historic nuclear weapons test sites,” according to the scientists.  “It also shows the importance of local geology on uranium behavior, which can be applied to develop efficient clean-up strategies.”