Sodium hypochlorite

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Sodium hypochlorite (NaOCl) is a white inorganic water soluble salt. Commonly found as bleach in general stores.

In refining it is used mixed with hydrochloric acid for dissolving gold. It isn't as effective as aqua regia but it is a workable substitute for people that have difficult to get nitric acid.

Contents

Dissolving gold

Below pH 4 NaOCl breaks down into water and chlorine gas. Then the chlorine gas with hydrochloric acid dissolves gold. Since the leach isn't as powerful as aqua regia the gold needs to be in fine powder or thin flakes. Precipitated gold powders or gold foils is easily dissolved but massive gold objects isn't suitable to dissolve in HCl-Cl.

  • Cover the gold with hydrochloric acid.
  • Add a dab of bleach (sodium hypochlorite dissolved in water) and watch the reaction.
  • If there is undissolved gold left after a couple of minutes then add a dab more and repeat.

PGM processing

Sodium hypochlorite can be used as an alternative for sodium bromate in bromate hydrolysis.

Leaching ore

Sodium hypochlorite together with hydrochloric acid has been used for gold ore leaching. For example in the iGoli method.

Leaching gold from electronics

I haven't done any research if this is a workable leach of plated objects yet.

Destruction of cyanide

Sodium hypochlorite is used in a step of destroying cyanide.

References

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