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The mercury is contaminated with iron. Is there any way to remove iron from mercury?

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    $\begingroup$ Does the question "is mercury magnetic?" strike you? $\endgroup$ – Nilay Ghosh May 15 at 16:47
  • $\begingroup$ What physical form does the iron have? Fine powder, shavings, small lumps, an entire I-beam, ...? And does it matter to you whether the iron retains that form after the iron and the mercury have been separated? $\endgroup$ – zwol May 15 at 19:40
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As iron is one of few metals not forming amalgams,

Almost all metals can form amalgams with mercury, the notable exceptions being iron, platinum, tungsten, and tantalum.

..it should preferably contaminate the mercury surface.

I would try, perhaps repeated, dropping mercury, e.g via punched filtration paper to sulphuric acid bath.

It can be combined with agitating mercury - acid phase border.

Important can be the origin of impurity and the intended purpose of purified mercury. There is possible the only reasonable way would be distillation, mentioned in the other answer, respecting the warning.

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    $\begingroup$ I say this might work, but what has this got to do with the fact that iron does not form an amalgam? $\endgroup$ – Karl May 15 at 19:31
  • $\begingroup$ Cleaning mercury surface should be easier than extracting iron from the whole mercury volume. $\endgroup$ – Poutnik May 16 at 2:49
  • $\begingroup$ @karl It is relevant that iron doesn't form an amalgam as, if it did, there would be a homogeneous solution and the iron would be hard to separate without something like distillation. Because iron doesn't dissolve in mercury, physical separation is likely to work. $\endgroup$ – matt_black May 16 at 13:38
  • $\begingroup$ @matt_black it could be combination of physical and chemical separation. $\endgroup$ – Poutnik May 16 at 13:41
  • $\begingroup$ Well, for physical separation, you can just put a bit of soap water on your mecury and bubble air through it. For chemical separation, mixing with acid and subsequent phase separation might work. The latter however would also work if the metal (say, zinc instead of iron) was dissolvend. $\endgroup$ – Karl May 16 at 19:38
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Non-amalgamation of mercury with iron means that the iron is not dissolved, and therefore floats on the surface as a dross. However, non-amalgamation does not mean total insolubility. If a few ppm of iron needs to be removed, washing with a dilute solution of HNO3 might be best, with much agitation.

There will be some dissolution of mercury to Hg++. That's just a loss due to purification, and can be minimized. Hg++ ion in solution will be reduced by Fe metal in the mercury liquid until there is no more iron in the mercury and there is some slight excess of Hg++ ion in solution. This approach will also remove other contaminants. You will be able to see a bright mercury surface when it is purified.

Other methods have relied on agitation (oxidation) in air and removal of dross, and might suffice, but is probably not as complete as washing with nitric acid.

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  • $\begingroup$ Interesting! I had not anticipated the redox reaction. $\endgroup$ – Eashaan Godbole May 16 at 16:25
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Several decades ago I used a lot of mercury (in polarography with a dropping mercury electrode) and purified it by distillation in a still looking something like this https://www.researchgate.net/figure/Distillation-apparatus-for-mercury-cells-a-and-design-b-del-Campo-et-al-2008_fig1_325075540

However, mercury is toxic, especially in vapour, I strongly recommend against doing this unless you really know what you're doing.

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