SMART DOG MININGTM
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Back to the Future in plant Construction
Rust and corrosion can eat the heart out of a
mineral processing plant, especially with a tight or nearly closed
water circuit. A coal preparation plant I worked at many, many years
ago had closed it’s water circuit. After a few years we started
noticing significant corrosion on the beams near the jigs. After
first suspecting a coating failure on the paint, further study
indicated it was from the plant process water. Closing the water
circuit had lead to a drastic buildup of chlorides, which was eating
the metal.
The buildup of chemicals and salts can be extremely destructive,
requiring a lot of care and maintenance. Now switch to a plant
processing salt bitterns (such as a lithium operation), and the
action can get to the point that it seems to be melting in front of
you. Why, well because salt water and metal just do not mix. Salt
water causes metal to corrode.
Salt Water and Metal
The combination of moisture, oxygen and salt, especially chlorides,
is more damaging to metal than just rust. This combination corrodes,
or eats away at, the metal, weakening it and causing it to fall
apart. Salt water corrodes metal five times faster than fresh water
does and the salty, humid air in a brine plant can cause metal to
corrode 10 times faster than air with a normal amount of humidity
would. Bacteria in ocean water also consumes iron and what is
excreted turns to rust.
Corrosion comes in basicly two forms: Electrochemical and anerobic
One form of corrosion that occurs when metal and salt water get
together is called electrochemical corrosion. Metal ions dissolve in
water and salt water conducts electricity and contains ions, which
attract ions from other compounds. During electrochemical corrosion,
electrons from other compounds are attracted to the metallic ions.
Salt water attacks the metal and corrosion occurs.
Anaerobic corrosion is the second type of corrosion that occurs when
metal is exposed to salt water for an extended period of time.
Deposits that contain sulfates surround the metal as it sits in salt
water. Hydrogen sulfide is produced which corrodes metals. At the
same time, bacteria grows in the salt water which used hydrogen to
corrode the metal as well. Between the ions, sulfates and bacteria,
metal is attacked from all angles when it is in salt water.
There are many options to help prevent this, from sacrificial
anodes, to galvanic protection systems, to special alloys, and
special coatings. All designed to limit or inhibit this corrosion.
And all work to some degree, but do drive up the capital and
operating costs.
In mineral processing this is not a new problem. Years ago, when
steel metallurgy was young, it was common to build leach tanks of
wood, due to this problem. In fact whole plants were built of wood,
mostly due to the cost and availability of wood versus steel.
Perhaps, in some cases it might be time to rethink this concept,
especially in high corrosion operations.
Wood for the future!
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40+ years’ experience in the mining industry with strong mineral
processing experience in precious metals, copper, industrial
minerals, coal, and phosphate
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Operational experience in precious metals, coal, and phosphate plus
in petrochemicals.
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Extensive experience performing studies and determining feasibility
in the US and international (United States, Canada, Mexico, Ecuador,
Columbia, Venezuela, Chile, China, India, Indonesia, and Greece).
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E-mail:
info@smartdogmining.com
