Mercury again,

I just tried to drain mercury from a compressor gas scrubber (IP pressure, about 800 psi operating pressure).  This vessel had been out of service for about a week, depressurised, but not drained.

The vessel has a liquid outlet from the side, and a drain line at the bottom.  My idea was to drain off any mercury, and the repeat the exercise after the unit has been in operation for a while (about a month) to get a feeling for the quantity of mercury dropping out at this stage of the process.

The vessel has been in operation for about 4 years, and as far as anyone knows, has never been drained.  The drain line consists of a 2" ball valve, and a blind blange.

I removed the flange, and carefully opened the ball valve (using full protection gear, etc).  A couple of droplets of mercury came out, but it turned out the entire line was blocked by a silvery material, which had small droplets of mercury in it..  Consistency somewhas similar to wet sand, although not really grainy.  Anyway, I scooped out about 2-3 spoonfuls of the stuff, and closed the valve/flange.

The sample was left with the chemist, but after about an hour in the lab (ambient temp) and with no additives, it gradually turned into pure liquid mercury, leaving a small amount of brownish residue behind.

Has anyone seen this happening before?  I presume there has been some kind of reaction with oxygen, and will send the residue for analysis, but would like to hear if anyone has similar stories.

Of course, this complicates my plan to measure the mercury dropout rate - open to suggestions, comments, etc

Cheers,

Trond