Purifying Mercury





The following question appeared in the sci.chem.electrochem newsgroup. 

> I need to separate mercury from mercury oxide and then get
> rid of some contamination of Zn (Zn amalgam probably) present
> in the mercury. Is there any relatively simple and most important
> safe procedure to do that?

The procedure we used was to place mercury in an "oxifier" and suck air through it for a week or so. The oxifier  (available then from Bethlehem Apparatus) was a thick glass cylinder containing some rotating disks with many large holes in them. As the disks spun, the mercury was 'chopped up' to maximize the contact with air. It ran continuously for a week or more. The mercury was then allowed to settle in a separatory funnel (to allow the oxides to float to the top) and then transferred to a thick-walled, glass suction flask. 300-500 ml of  ~1M HClO4 careful !  ) was added and air was bubbled  through it for several days or more. The bubbling tube (a sintered-glass gas dispersion frit) was immersed in the Hg to help stir it and to insure good contact between the air and the mercury. 

The mercury was then washed with distilled water and dried with filter paper. Finally, it was 'pinholed' twice through filter paper. To do this, place a piece of filter paper in a filter funnel (does anyone remember how to fold filter paper anymore?) and put a pinhole at the tip.  Slowly fill the funnel with mercury until small droplets of mercury come through the pinhole. The filter paper will catch the smaller particles of HgO and other oxides and finish drying the mercury.  The filter funnel can be kept filled by using a separatory funnel adjusted to drip mercury into the filter funnel at the correct rate.

See 'Polarographic Techniques, 2nd ed'  .by Louis Meites, J Wiley & Sons, NY, (1965) p 82. It may be available used through amazon.com. It may also be available through Powells.com.

Alternatively, recycle mercury by sending it to Bethlehem Apparatus. This is a preferred method if the mercury is contaminated with gold, silver, palladium, platinum, or other noble metal. They will exchange it for triple-distilled mercury for a reasonable cost. Contact them first. Used mercury is generally shipped in a 76 lb iron 'flagon.'

Bethlehem Apparatus Co., Inc.
890 Front Street
Hellertown PA 18055

Tel: 610 838-7034
Fax: 610 838-6333
Contact: Bruce Lawrence

Warning!Mercury is heavy! Thick plastic beakers and flasks are preferred to glass ones for temporary storage and handling: They are much less prone to having the bottom fall out due to the weight of the mercury!

Warning!Mercury is Toxic. We have all heard of mercury contamination in fish, and the toxicity of organo-mercury compounds (e.g., methyl mercury) but mercury vapor is not healthy either. Sore gums (early warning sign) and mental disorders and tremors are symptoms of mercury poisoning. The Mad Hatter in "Alice in Wonderland" is an example of a sloppy hatter who used mercury to 'silver' metal pieces on hat bands. The vapor pressure of mercury is high enough (check the CRC Handbook!) that air, in equilibrium with metallic mercury, has an mercury content that is above the allowed occupational limit in the US. Never heat mercury! Always use mercury in a well ventilated room, and always place a plastic or stainless steel tray under your work or storage areas to catch any spills. Keep the tray clean! Clean up any spill immediately. Mercury is also absorbed through the skin. Minimize contact.

Mercury can be safely used if these simple precautions are taken. Please be careful. 

Most of the information on mercury toxicity and mercury poisoning came from: 

"Safety and Health Practices for Working with Metallic Mercury", Woodhall Stopford, M.D., Bethlehem Apparatus, Inc., Hellertown, PA (1985).


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