5. Gold powder cleanup.
The washing process is probably the most important one as it will remove the majority of contaminates that ha been dragged out of solution along side the gold.
Metal contaminates such as Copper, Nickel, Platinum, Palladium and Silver (Chloride).
Cover the gold powder with tap water, swirl it around gently, let it settle and decant to the filter. Repeat this wash two more times.
Hydrochloric Acid (HCl) washes:
Cover the powder with HCl (CP 32%) and place the beaker on heating element of your choice, make sure you cover the beaker with a watch glass or other sort of condensation device.
Slowly ramp up the heat until a gentle boil has reached. Let it boil for 5-10 minutes. Remove from heat and allow to cool back.
At this point, change the receiving flask (from under the filter) and decant the bulk of the liquid. The HCl boil has the potential to dissolve traces of gold along side the other base metals. These washes are to be kept separately and will be sent later to the Stockpot.
Repeat this wash + boil until no more color (greenish yellow) is gained to the wash solution, usually 3-5 times, depending on how dirty the gold drop was.
Tip: Once boiled the gold powder agglomerate and adhere tightly to form chunks that do not easily break apart and settle immediately. Makes decanting easy and fast.
After you decant the acid for the last time, wash one more time with tap water to remove the majority of the remaining acid and decant. No need for a boil this time.
Ammonia (NH4OH) wash:
Now cover the powder with dilute Ammonia solution and again bring to a boil.
Keep boiling for 20 minutes at least and remove from heat.
Once cooled, filter this wash solution to a new receiving flask and discard.
This wash will dissolve all traces of Silver Chloride in the gold powder.
Distilled Water Wash:
Again, wash the powder 3 more times with distilled water, where the last wash is boiled.
At this point, your gold is pretty pure and is anywhere from 99.75-99.95%.
You can now choose if you want to melt it, or process it again to ensure 99.95 (and even above that) purity.
6. Re-refining (optional – recommended).
Repeat steps 2-5 (to the letter).
When done washing with distilled water, pour off the bulk of the water to the filter.
Place the beaker with the powder on heating element set on low and let the water slowly evaporate to dryness.
Place the powder in a new clean crucible, or one that had been used only for melting pure gold.
If you torch melt, make sure the tip of the torch is squeaky clean.