Gold Refining with Borax

According to the GEUS, the Geological Survey Office of Denmark and Greenland, it is possible to concentrate and isolate gold from the ore using borax and charcoal. This method has the immediate benefit of making mercury “redundant” in gold isolation.

Extraction of gold by amalgamation with mercury is a simple means of producing metallic gold in the field.  After contact with gold enriched ore, mercury is evaporated into the air by direct application of a torch flame to the puddle of metal leaving purified gold metal.

It is thought that there are millions of miners who scratch out a subsistance living working a small patch of ground for gold. It’s called small scale mining. In the course of this activity, environmental contamination can accrue to the immediate area as well as the watershed at large. Sadly, the toxicological insult to the miners from exposure to mercury vapor can be severe.

This method is an inexpensive and simple alternative to the mercury process. Perhaps the chemistry community has something to contribute by way of education or improved methods of extraction.

8/25/10  Update.  I have revisited this post and am compelled to comment further.  While I am unable to offer a good chemical explanation for the effect of borax on gold ore, I can say that the use of borax as a flux  for smelting goes back to the 19th century during the American gold rush period.  The process described in the link appears to be a smelting process for enriched ore containing elemental gold, as opposed to sulfide, or sulphuretted ore. The function of a flux is to modify the flow and phase separation properties of host rock so as to partition away from the gold phase or layer.  In other words, a flux modifieds the slag to help the gold to separate cleanly from the rock.

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About gaussling

Gaussling is a senior scientist in the chemical business. He occasionally breaks glassware and has been known to generate new forms of hazmats. Gaussling also digs aerospace, geology, and community theatre. View all posts by gaussling

15 responses to “Gold Refining with Borax

  • borgs

    Nice info! i hope many will read this especially those who are planning a small scale gold mining.. with the current global financial crisis and skyrocketing price of gold, people turned into gold prospecting.
    I think they should do some research first before anything else…

  • Mercury Mining « Lamentations on Chemistry

    [...] viable possibilities. Beyond macroscopic placer gold there is amalgamation with mercury, borax, cyanidation with NaCN, and chlorination with Cl2 or [...]

  • Andy Liepa

    It may be that this only works in the presence of certain “black sands”. For example, cassiterite (SnO2) might be reduced (by charcoal) to metallic tin under these conditions. Tin alloys with gold can have a considerably lowered melting point e.g. with about 20% tin the melting point of the alloy is only 270 deg C !. The function of the borax would be to provide a liquid medium to facilitate interaction between the tin oxide and charcoal and then subsequent liquid tin microdroplets and gold particles etc. I expect that this procedure might not apply to some other “black sands” such as titanium compounds (too hard to reduce easily with charcoal under these conditions) or iron compounds (magnetite for example) since, apparently, it is difficult to alloy iron with gold.

    • gaussling

      Hi Andy,

      Thanks for the informed input. I appreciate it. In my part time studies in this area I have not encountered a good explanation of exactly what it is that the borax does chemically. Borates have been used in slag modification. Boron can provide tri- and tetravalent crosslinking in inorganic networks, modifying melting points and viscosity. That is basically what it does in pyrex glass. Boron is also very oxophilic, so perhaps that drives its utility here.

  • paul austero

    can you send me instructions for refining gold with borax. i found stones while gardening, it look like there are gold contents on these stones it has a greenish and golden color, and way too heavier than a regular stone/rock of its size.
    …i really enjoyed reading evrythin on this page. thanks!

    • gaussling

      Hi Paul,

      All I have here is the link to the primary source. I have not personally used borax for purposes other than fluxing. I’m sorry I do not have a procedure for you. Have you looked at the stones under magnification? You can try showing the stones to a geologist at the local university for a better understanding of them. Maybe even a rockshop, though you should be cautious.

  • prospectorjack

    Good post This is something I have been thinking of using to refine gold from magnetite. I understand that a 50/50 mixture of borax and pot ash works well as a flux when refining gold, what whould be your thoughts on this as chemist?

    • gaussling

      Hi,
      The world “flux” in extractive metllurgy is used in several ways. Sometimes a fluxing agent is used just to form a lighter insoluble liquid layer (think oil and water) which protects the molten metal from air oxidation. Bronze casting comes to mind where glass and borax is added to the melt to slow down oxidation. Sometimes a flux layer serves as a liquid phase for contaminants to migrate to. In other contexts a fluxing agent participates in some chemistry. Borax is a cross-linking species that can form …-O-B-O-Si-O-… network linkages that may serve to sequester oxophilic metals like iron, calcium, magnesium, aluminum, etc. While silicate can do this by itself, the addition of a flux like borate may also lower the melting point of the slag so as to keep it fluid and pourable. Fluorspar has been used as a flux as well. I recall that is also lowers the mp of the slag. My guess is that it does this by donating fluoride to silicon or other acceptors and thus providing a chain or three dimensional network terminating effect. If the silicate network has chain terminators in it, it causes the silicate to have a lower melting point. This is the difference between regular glass and quartz. Soda ash and/or lime is added to interrupt network formation and thus the glass meltes at a lower temperature. I think the 50/50 mixture you mention works for the same reason. It lowers the mp of the slag and makes it a better extractant for the things you want to remove from the gold.

  • Pure

    Can anyone help me,i have a problem i have bin Refining gold from gold pins using Nitric Acid and distilled water,the gold has turned in to dust but mixed with what looks like silver is there a way to make the gold cluster or a good way to separate gold/silver ?

  • mearg

    i have not comment but I haven’t more information in this method so if you can please feed me some documents in borax method

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  • Timothy Bopp

    what is the impact of using Borax pentahydrate vs Sodium Tetraborate as a flux in gold smelting?

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