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Ascorbic acid isn't very selective when it comes to what it precipitate from solution. It can quantitatively precipitate gold, palladium, silver and copper from solutions, both chloride and nitrate solutions. At least when the solution is boiled.
Some properties :
- The precipitate is a lot finer than several other methods gives.
- The selectivity is low, if the liquid contains palladium, silver or copper some of it will be reduced to metal too. Especially if the solution is close to boiling.
- By cooling a gold chloride solution the co-precipitation of other metals is kept to a minimum.
- Does not emit any noxious gases as sulfur dioxide.
- Does not create any false positives when testing with stannous chloride.
- It will precipitate silver from a silver nitrate solution as a fine powder.
- It will precipitate palladium from a palladium nitrate solution.
There are several places where ascorbic acid can be bought. For example via ebay or amazon.
- US4078918 : Method for precious metal recovery.
- GRF : Experience of using ascorbic acid by Jon.
- GRF : Using ascorbic acid to precipitate palladium.
- GRF : Discussion about ascorbic acid and selectivity.
- GRF : Silver recovery with ascorbic acid.
- GRF : Formula for reducing gold with ascorbic acid.
- GRF : Ascorbic acid in the making of Adam's catalyst.
- Elsevier : The kinetics of redox reaction of gold(III) chloride complex ions with l-ascorbic acid (https://doi.org/10.1016/j.ica.2012.10.031)
- Wikipedia : Vitamin C.