Thank you Noman, please let me know how the non-heating black
sludge turns out, I would give that a try also.
What do you neutralize nitric acid with?
and does that process require heat or can I just let it sit in a
plastic bucket, neutralize it and rinse?
How to Refine Gold by the Acid Method
The two acids which are used in this process are concentrated
hydrochloric and nitric acids. These acids are very corrosive.
However, when combined with metals, the fumes become much more
corrosive. So corrosive, in fact, that they will rust the highest
grades of stainless steel with less than 1 second of exposure. For
this reason, this kind of refining must be done outdoors, away from
anything that may be damaged by exposure to these fumes.
Large Scale Gold Refining by Aqua Regia Acid Method
Having described it’s hazards, it must be pointed out that, like
most industrial processes, refining gold in acid is quite safe when
performed under controlled conditions. In addition, the results of
doing your own refining can be quite sweet. Based upon feedback
we’ve gotten from several hundred shops, we estimate that, when you
refine just 10 ounces of scrap gold yourself, you will save about
To refine gold in acid, you will need the following items:
heavy gage plastic buckets or Visionware pots
wood or plastic stir rod
protective clothing–minimum requirement: goggles and rubber
gloves, rubber apron.
hydrochloric or muriatic acid
nitric acid or nitric acid substitute
baking soda (sodium bicarbonate)
gold detection liquid
selective gold precipitant
tap water and distilled water
Melt your gold and make shot. Small open-up granules are best. If
you are refining filigree or ladies rings, shotting is not necessary.
Pour the shot into one or more Pyrex or plastic containers. For
every ounce of scrap gold you are going to refine you will need a
capacity of 300 milliliter. So, for example, if you are refining 10
ounces, you need a 3,000 milliliter (3 liter or 3 quart) container.
To the container, add 30 milliliter of nitric acid (or 2 tablespoons
subzero, nitric acid substitute) for every ounce of metal in the
container. So, if you have 10 ounces of metal in the container, add
300 ml (milliliter) of nitric acid. Let it sit about 30 minutes or
longer. You may or may not get a strong reaction with brown fumes.
There is no way of predicting the strength or speed of acid reactions
in refining. If using subzero, nitric acid substitute, add the
hydrochloric or muriatic acid without waiting. The subzero will not
have any effect until the hydrochloric or muriatic is added.
To the container, add 120 ml of hydrochloric or muriatic acid for
every ounce of metal in the container. So, if you have 10 ounces of
metal in the container, add 1200 ml of hydrochloric. Again, you may
or may not get a strong reaction. The solution will get hot as the
acid reacts with the metal, dissolving it. If using subzero instead
of nitric, you will probably get no fumes except those of the
hydrochloric or muriatic acid.
Usually, but not always, the acid reacts slowly at first. After some
minutes have passed, however, the acid will become very hot and
brown, very corrosive fume (nitric oxides and other fumes) will be
generated. Wait a minimum of one hour after the fumes have
disappeared before pouring off or filtering the acid. If you can,
wait overnight. This will insure that the acid has had sufficient
time to completely dissolve the gold.
Pour the acid into another, larger container. Do not allow any
particles to be poured off. If you have a filter funnel, preferably
a Buchner filter funnel, use it. If any particles are poured off with
the acid, they will contaminate your gold.
The acid will be an emerald green color and should be clear (not
murky or cloudy). If the acid is murky, it may contain particles and
should be refiltered.
Take one quart of tap water and heat to boiling. Remove from heat
and add one pound of urea to the water. Despite the unpleasant name,
this is just a harmless industrial chemical that has no smell and you
will use to adjust the pH of the acid.
Slowly, add the water/urea to the acid. The acid will foam with the
addition of the water/urea. Do not add the water/urea so quickly
that the acid foams out of its container. When the acid stops
reacting to the addition of water/urea, stop adding the water/urea.
You’ve just raised the pH of the acid from 0.1 To 1.0, killing the
nitric acid but not the hydrochloric.
There are many different selective precipitants that can be used
when refining gold. All will do the job well. However, your local
supply house has one or two that they may favor. At Shor, we prefer
Storm precipitant. When using a selective precipitant, follow the
instructions that accompany the product.
Take a quart of water and heat it to boiling in a Pyrex or
Visionware container. Remove it from the heat and add to the water
one ounce of storm precipitant for every ounce of metal you are
refining. If you are refining many ounces of scrap gold, you may need
to use more than one quart of water. Do not put your face near the
opening of the container. The smell is very strong and pungent.
Add the water/precipitant solution slowly to the acid. Immediately
the acid will change to a muddy brown appearance as brown particles
of gold form in the water. This brown “mud” is, despite its
appearance, pure gold.
Give the precipitant about 30 minutes to do its job. Then test the
acid for the presence of dissolved gold.
Testing is generally done with an aqueous mixture of stannous
chloride, hydrochloric acid and pure tin. Generally it’s more
convenient to buy this premixed rather than concoct it yourself. The
premixed is commercially available as “precious metal detection
liquid”. Precious metal detection liquid will detect the presence of
dissolved gold down to 4 parts of gold per million parts of acid )
detecting the presence of about 1/1000th of 1 gram of dissolved gold.
Testing for the presence of dissolved gold is absolutely necessary to
insure that no dissolved gold is thrown away with the waste acid.
To test, first immerse the end of the stirring rod in the acid.
Remove it and touch that end to a paper towel to make a wet spot.
Put a drop of gold detection liquid on the wet spot on the paper
towel. If any gold is still dissolved in the acid, the wet spot will
turn a purple-black or a purple-brown. If you see this color change
then give the precipitant more time to work and/or add more
The acid should now be a clear amber color with a brown mud at the
bottom. Pour off the acid into another container. If you have a
filter, use it. Do not pour off any of the mud. The mud is pure
When all the acid is poured off, add tap water to the mud. Stir and
let the mud settle. Pour off the water into the container with the
acid. If you have a filter, use it. Do not pour off any particles of
brown. Repeat this rinsing 3-4 times or more.
Rinse once with aqua ammonia. White vapors will appear. The aqua
ammonia cleans impurities from the gold mud while, at the same time,
it neutralizes any acid still clinging to the gold mud.
Give the mud a last rinse, this time with distilled water.
Using distilled water, wash the mud into a small Pyrex beaker
Visionware pot. Give the mud a chance to settle and then pour off
Put the beaker on a hot plate to dry the mud. Do not preheat the hot
plate or thermal shock may cause the beaker to break.
Melt the dried mud (now a powder). If using a torch, first wrap the
powder in tissue paper and then soak that in alcohol. Also, use a
Burno crucible, this will keep your gold from being blown away by
the gas pressure from the torch. The gold will again take on the
appearance of metal. If you’ve followed the instructions carefully
and used filters, the gold will be 999.5 % Pure with virtually no
Platinum- If you had platinum in your gold, it will not dissolve, to
any appreciable degree, in the room temperature aqua regia. It will
be left behind when you pour off the aqua regia, prior to
precipitation. To insure high purity of the platinum, you will need
to re-refine this material. Put this material in a fresh aqua regia
bath. This time, however, heat the acid to simmering. Continue
heating until all the platinum is dissolved (that may take 1-2
hours). When completely dissolved at 1 ounce of ammonium chloride
for every ounce of dissolved platinum. The platinum will precipitate
as a red mud. If you want to leave the iridium in the platinum, then
wait for it to precipitate before recovering the platinum. Iridium
will precipitate as a blue-black mud after the platinum precipitates.
Platinum group metals will also show up on the stannous chloride
test. Platinum turns red, palladium Palladium turns orange and
iridium turn blue-black.