In
the late 1800s, the copper mining industry in Butte and Anaconda, Mont., left
large piles of waste riddled with arsenic, lead and other heavy metals. Now
the largest Superfund site in the United States, with more than 300 square miles
of contaminated soil and water, Anaconda may also hold what could be a promising
solution for cleaning up similar areas: a newly discovered mineral that soaks
up the harmful pollutants.
A University of Montana graduate student stands above Silver Bow Creek, Mont.
The highly acidic banks consist of 2-meter-thick tailing deposits — waste
from the mining industry — that contain high concentrations of metals and
arsenic. Courtesy of John Moore.
At the meeting of the Geological Society of America in Denver, Colo., in November,
Virginia Tech professor Michael Hochella described a new mineral found in Anaconda
— manganese oxide hydrate — that absorbs heavy metals, including zinc,
copper and lead, in a fast reaction. Sending a sample of polluted groundwater
through a sediment sample containing the new mineral, Hochella says, results
in clean water. Toxic metals "ignore" everything but iron and manganese
oxides, and the contaminant finds a spot within the mineral structure of the
manganese oxide. "It's like pulling iron filings out of a pile with a magnet,"
Hochella says.
Compared to other chemical compounds that react with heavy metals, manganese
oxides "are much more reactive because they have internal sites that can
take up heavy metals," Hochella says. The compound's chemical structure
is similar to clay minerals' sheet-like structure, he says.
Injecting an area such as Anaconda with the manganese oxide compound could create
a reactive barrier to prevent the spreading of the contamination. "The
reaction is very rapid — on the order of minutes," Hochella says.
Hochella and his colleagues discovered the mineral in samples taken from the
Anaconda Superfund site, using transmission electron microscope (TEM) imaging.
This differs from scanning electron microscopes in that the electron beam, which
is of much higher energy in TEM, passes directly through the sample. "TEM
allows chemistry to be done on much smaller particles," Hochella says.
Although researchers have yet to field-test the application of the new cleanup
method, John Moore of the University of Montana says that understanding how
manganese oxide hydrate reacts with heavy metals is a step in the right direction
for cleaning contaminated mine sites. "The point is, we have to make sure
what we're doing is really going to work," Moore says, noting that the
method has promise. "It took over 100 years to create this site. You can't
just dig it up and take it somewhere; you have to manage a site in situ."
Laura Stafford
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One of the routine parts of the mining process involves a geologist going belowground
to assess rock walls where rich veins of minerals may occur. As any underground
activity is inherently dangerous, some researchers are working on technologies
to automate the mapping process — already successfully testing a new remote
sensing and infrared technology.
Working with mining companies and using thermal infrared reflectance spectroscopy,
researcher Benoit Rivard of the University of Alberta in Edmonton and colleagues
tested 37 samples of 10 different rock types — some containing mineable
amounts of sulfides (the minerals being mined in the area) and some containing
nominal amounts of sulfide — from eight different mines in the Sudbury
Basin in Ontario. The researchers found that overall, they were able to correctly
classify the rock type and mineral load nearly 80 percent of the time, as reported
in the November GSA Bulletin.
The long-term goal, Rivard says, is to put instruments in mines to log the rock
types and identify rich mineral seams to help guide the mining process. Right
now, he says, mining companies frequently employ one geologist to log cores
from multiple mines. "If we can establish an automated approach using instruments
that systematically obtain objective results," Rivard says, it can improve
efficiency, save money, remove humans from a risky underground environment and
remove some of the subjectivity that comes with human analysis of a rock core.
The approximately 80-percent accuracy rate that the researchers obtained for
their rock-type classification "is a very good figure," says Alvaro
Crósta, a geologist with the University of Campinas in Brazil. Their
approach represents a novel use of the technology and should offer a "major
advantage for operational applications in an underground mining environment,"
he says.
The biggest advantage the thermal infrared reflectance spectroscopy offers over
other visible infrared spectroscopy, Crósta says, is that the presence
of water on the rocks — frequently found in underground environments —
does not interfere with the rock-type analysis.
The researchers have not, however, been able to work around the presence of
dust or drilling lubricant yet, Rivard says. "But we're working on the
technology and instrument development, and we will get there in the next few
years," he says. So far, the researchers have focused on hard-rock mines
such as those in Sudbury, but they have recently begun working with some companies
mining tar sands to see how the technology might apply there.
John F. Papp, the U.S. Geological Survey chromium commodity specialist, has compiled the following information on chromium, an important metal essential to health and property.
Chromium is one of the most indispensable industrial metals and it plays an
essential but hidden role in daily life. Chromium is used in many consumer and
building products, and it contributes to a clean, efficient and healthy environment.
As a trace mineral, chromium is also vital for good health. Insufficient amounts
result in glucose intolerance. Organ meats, mushrooms, wheat germ and broccoli
are all good dietary sources of chromium.
Chromium is also critical in the manufacturing of stainless steel. Chromium
makes stainless steel "stainless" by providing a protective coating,
which prevents rust and is easily sterilized. It is popular in kitchen fixtures
such as countertops and sinks, and also in flatware, cooking ware and utensils.
In factories, food-processing equipment parts that come in contact with food
are composed of stainless steel. And because of its hygienic properties, medical
and dental tools and equipment are also made of stainless steel.
Another one of chromium's critical uses is in transportation. In automobiles,
outside of chrome decorations such as ornaments, trim and hubcaps, a more important
use of chromium is in the engineering alloys, which are useful in applications
where temperatures are high. Exhaust pipes are commonly made of stainless steel,
and the catalytic converter, used in most parts of the world to reduce exhaust
emissions, is housed in stainless steel. Buses and passenger trains also use
stainless steel to reduce vehicle weight and maintenance costs. Chromium in
superalloys permits jet engines to operate in a high-temperature, high-stress,
chemically oxidizing environment.
On U.S. roadways, chromium pigments are used to make the yellow lines indicating
traffic lanes. Chromium-containing pigments also find their way into beauty
products.
Fortunately, chromium is in abundant supply, produced from the mineral and ore
chromite. In nature, the deposits are of two major geologic types: stratiform
and pod-shaped (podiform).
Stratiform deposits occur in South Africa and India, with one of the largest
found in the Bushveld Complex of South Africa, a layered intrusion containing
more than 11 billion metric tons of chromite resources. One layer alone, informally
named the Steelport Seam, contains 1.5 billion metric tons of chromite resources.
Podiform deposits are found in Kazakhstan where parts of the ocean floor were
pushed over continental rocks by tectonic forces. Together, South Africa, Kazakhstan
and India (in order, by tonnage produced) accounted for 79 percent of global
production of chromite in 2003.
Since 1965, there has not been chromite ore production in the United States.
Small, marginally economic resources are available and could be exploited in
the event of a national emergency. U.S. import dependence is only about 75 percent
because substantial amounts of chromium are recycled as part of the incorporation
of stainless steel scrap in the stainless steel production process, reducing
energy consumption and conserving natural resources. The United States produces
about 2 million metric tons of stainless steel per year that contains, on average,
about 17 percent chromium.
For more information about chromium, visit minerals.usgs.gov/minerals.
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