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MINING
AND TECHNOLOGY
THE
SOUND
OF SILENCE
BY
HAROLD
HOUGH
Explosives
have been a big part of mining since that first unknown miner figured out that
gunpowder could break rock faster and cheaper than hammers or fires. Since then,
the industry hasn’t looked back.
But, another technology is actually harking back to a time before
explosives, when miners would light bonfires in mining tunnels that would heat
the rock and make it crack.
This technology is called Soundless Chemical Demolition Agents. Although
they are more popular overseas and in the construction demolition business, they
are gaining adherents in quarrying and in some mines.
The
problem with traditional explosives is the shock wave, which can send rock
flying or cause unwanted damage. There are also the additional costs of
training, safety, transportation, licensing, permits, and security.
Soundless Chemical Demolition Agents (SCDA) are proving to be an
alternative to some mining and quarrying problems. SCDA are chemical compounds
that expand when mixed with water. The expansion creates pressures great enough
to actually break the strongest rock (18,000 pounds per square inch). A miner
drills a pattern of holes much like they would do for traditional explosives.
Then, they mix the chemicals with water and pour it into the holes. Depending on
the compound, the expansion process takes from 15 minutes to 24 hours. The
result is broken rock without the hazards of explosives.
The
makeup of the compound depends on the manufacturer and how it is intended to be
used. Some of the major components are calcium oxide, silicon, and aluminum. As
it hydrates, it creates heat and begins to crystallize. The process of
crystallization causes the mixture to expand, which creates the pressure that
cracks the rock. The advantages are clear. There is no explosion, so there is no
need to clear the area of workers. Since there is no fire or shock wave, the
chances of secondary damage are lessened considerably. In the case of quarries
that mine rock slabs like granite or marble, this method also means the rock is
free of fire marks or small fractures.
The
biggest downside is cost. Currently, high explosives are more cost effective in
many applications. And, since the mixture is sensitive to water, ground water
can change the expansion of the mixture. However, there are mining applications
where these chemicals are being used effectively.
One application is mining gemstones or the gold/quartz matrix that is
used in jewelry. Since explosives can damage gemstones, digging by hand is often
the only method for recovering them without damage. SCDA, however, can break the
rock without damaging any of the valuable material.
Smaller independent miners who find the cost of using explosives for
small applications too expensive are also using SCDA. Michael Martinez of Archer
tells of a small Alaskan gold miner who ran across a large boulder the size of a
car that he had to move to get to the placer gold underneath it. The area was
too remote to use heavy equipment and using traditional explosives would be a
regulatory hassle. Archer, who produces Dexpan, provided the miner with a blast
pattern that would break up the rock into manageable pieces for a reasonable
cost.
SCDA
are ideal for quarrying operations that produce slabs of marble, granite,
limestone, or onyx. The right pattern of drill holes and SCDA can produce near
perfect slabs of rock with no blast marks or waste.
Even large mines are looking at these agents for use in addition to
traditional explosives. They offer a safe method of breaking rock or coal in
situations where shock waves might be dangerous. They also can be used in mines
where the presence of methane would make traditional explosives unsafe. As a
result, some mines like Sufco, the largest coal mine in Utah, are buying and
using SCDA, even as they continue to use other methods for mining.
Although SCDA will not make conventional explosives obsolete anytime in
the near future, they are proving to be an alternative in situations where a big
bang isn’t warranted. It’s definitely a technology that more mines will be
hearing about in the future.
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