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| Instructions for Large Scale Gold Refining By the Aqua Regia Acid Method* |
| Updated 9/9/09 |
These are probably very similar to the units used by many large professional refiners. These have their own set of disadvantages
and are not as suitable for the small lots and needs of individual jewelry manufacturers. The amounts which have been refined
range from small lots of about 45 g (1½ oz Troy) of fine gold recovered from about l00 g (3 on Troy) of scrap, to more than 3 Kg
(100 oz Troy) from about 6 Kg (200 on Troy) of scrap. The latter is about the maximum that is reasonably handled in the equipment
herein described.
The usual refining lot in practice is 300-1000 g (10 to 30 oz Troy) of fine gold recovered from 600-3000 g (20 to 100 oz Troy) of
scrap. A knowledge of chemistry is not required to do this work.
OUTLINE OF THE PROCESS
The gold refining technique described here is the rather ancient wet chemical method whereby the gold-bearing scrap is dissolved
in aqua-regia. m is gold solution is then filtered and the jewelers bench dirt, sandpaper grit, grinding wheel grains and similar
material remains on the filter as a solid sludge, together with any silver present which will be in the form of silver chloride.
The filter and sludge are washed with repeated small amounts of water to wash all gold chloride solution down through the filter.
Other metals that were in the alloy or in the scrap (nickel, zinc, copper, iron, etc.) are also in this solution which is usually green in
color. However, if no nickel or copper is present it will most likely be the characteristic yellow of gold chloride. The nitric acid from
the excess of aqua-regia used in the digestion is removed either by boiling or chemical reaction.
To recover the gold as metal a reducing chemical is added to selectively change the gold chloride into solid gold particles and leave
the other metal chlorides unchanged and in solution. When tests show this to be complete the solution is filtered and the gold in the
filter thoroughly washed. The clean gold is then melted and poured into molds or made into shot.
The acids used in the process are very corrosive and highly toxic fumes are produced. Safety precautions in the operation of the
process and should be carefully studied before any part of this work is undertaken. CONTINUED>>>
and are not as suitable for the small lots and needs of individual jewelry manufacturers. The amounts which have been refined
range from small lots of about 45 g (1½ oz Troy) of fine gold recovered from about l00 g (3 on Troy) of scrap, to more than 3 Kg
(100 oz Troy) from about 6 Kg (200 on Troy) of scrap. The latter is about the maximum that is reasonably handled in the equipment
herein described.
The usual refining lot in practice is 300-1000 g (10 to 30 oz Troy) of fine gold recovered from 600-3000 g (20 to 100 oz Troy) of
scrap. A knowledge of chemistry is not required to do this work.
OUTLINE OF THE PROCESS
The gold refining technique described here is the rather ancient wet chemical method whereby the gold-bearing scrap is dissolved
in aqua-regia. m is gold solution is then filtered and the jewelers bench dirt, sandpaper grit, grinding wheel grains and similar
material remains on the filter as a solid sludge, together with any silver present which will be in the form of silver chloride.
The filter and sludge are washed with repeated small amounts of water to wash all gold chloride solution down through the filter.
Other metals that were in the alloy or in the scrap (nickel, zinc, copper, iron, etc.) are also in this solution which is usually green in
color. However, if no nickel or copper is present it will most likely be the characteristic yellow of gold chloride. The nitric acid from
the excess of aqua-regia used in the digestion is removed either by boiling or chemical reaction.
To recover the gold as metal a reducing chemical is added to selectively change the gold chloride into solid gold particles and leave
the other metal chlorides unchanged and in solution. When tests show this to be complete the solution is filtered and the gold in the
filter thoroughly washed. The clean gold is then melted and poured into molds or made into shot.
The acids used in the process are very corrosive and highly toxic fumes are produced. Safety precautions in the operation of the
process and should be carefully studied before any part of this work is undertaken. CONTINUED>>>
It is known that the aqua-regia technique herein described is not the only method. It may not be the best, and for the sake of
experience electrolytic cells for refining precious metals have been examined
experience electrolytic cells for refining precious metals have been examined
* Posted with Permission from Shor International
| Introduction |
| Aqua Regia Information: |
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