Question about mercury's vapor pressure

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  • #1
fluidistic
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Hi,
I've seen a very very small drop of mercury in a little corner of a laboratory table and it likely dates from a whole year. I've been told that mercury is quite volatile. So I shouldn't have seen this little drop if it really dates from the past year.
Looking into wikipedia, I see that mercury's vapor pressure is 1Pa at about 30°C. Converting this into torr, it gives 7.5006×10−3 torr at 30°C. Looking to this graph : http://en.wikipedia.org/wiki/File:Water_vapor_pressure_graph.jpg, I see that water's vapor pressure is around 50 torr.
So if I'm not wrong, it seems that mercury is much less volatile than water. Meaning that it won't evaporate if I manipulate it and it doesn't seem really a problem for safety when it comes to inhale it. Is this right?
 

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  • #2
Integral
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There was a mercury mine near my hometown, so as a kid mercury was not uncommon. We had a great lot of fun pushing it with our bare fingers around the table top, clumping it, unclumping it, and clumping it up all over again and again and again.

To the best of my knowledge it had no negative effects on myself, my sibling or our friends. I do not recall it evaporating quickly, in fact I do not recall it evaporating at all. It does alloy with things thou, for example, I have found that it melts solder easily.
 
  • #3
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After World War II, several mercury mines between Santa Barbara and Sonoma were shut down and abandoned. I panned about 10 pounds of the stuff from residue near the mines' condensation tubes between 1949 and 1952. I had astrays full of the stuff sitting around my bedroom for several years. It amagamates copper and silver easily, but corrodes aluminum. I think I am still healthy.
 
  • #4
fluidistic
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Thank you both for the replies. I get it clearer now. Ah, and I wish I had play with it as a child!
 
  • #6
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The volatility of mercury and its components is mainly a problem related to industrial combustion. As compared to other substances that could enter in a "furnace", these substances have a very high volatility. Actually, for temperatures above 200°C to 400°C, they are totally volatilized. They are then finally released in the atmosphere and will pollute the whole biosphere. They present a very high danger for health even for low concentrations, as do all heavy metals.

This is the reason why mercury components (like others) must be either totally avoided in a combustion system, or they must be removed from the flue gas.
An obvious removal method is condensation. As temperatures of the flue gas are decreased, the mercury components will condensate, typically on dust or (fly) ashes. If these products are not recycled (totally) in the combustion system, the mercury will then be removed. Some industrial kilns by design recycle all or nearly all dust or ashes. In this case a small amount (bypass) of ashes should be removed any way to avoid build-up and later release of mercury.
The standards on mercury emission will be more and more severe in the future.

A short overview on the Mercury cycle:
http://enhs.umn.edu/current/5103_spring2003/mercury/mercfate.html

Industrial control examples:
http://www.epa.gov/ttn/atw/utility/hgwhitepaperfinal.pdf
http://www.netl.doe.gov/publications/proceedings/98/98ps/ps3b-6.pdf
http://www.gcisolutions.com/gcitn0207.html
... google
 
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