I'm planning to make my own 100 ml 99.99% gold chloride solution from a 1 gram 9999 gold bar as follows:
Requirements:
- 1 gram collector gold bar with 9999 printed on it (for guaranteed purity)
- Hydrogen peroxide of at least 15% (for cleaning)
- Nitric Acid with highest possible purity and 65% concentration (the exact concentration is not important, as it can be lower)
- Hydrochloric Acid with highest purity and 30% (but not higher)
- Deionized or distilled water
- 250 ml Beaker of borosilicate
- A tall Measure Beaker of borosilicate glass of up to 25 ml or so that shows lines of 1 ml
- Glass rod (for stirring acids)
- A 100 ml glass bottle
- PVC-gloves (for protection)
- Goggles (for protection)
- Extractor hood (as the fumes are very toxic)
1) Start cleaning the glass beaker and glass bottle and capsule, first with hydrogen peroxide, then with still water, and finally with distilled/deionized water.
2) Place the 250 ml borosilicate beaker at a hotplate that is placed under a extractor hood.
3) Place the gold bar at the bottom of the beaker.
4) Make a Aqua Regia solution (1:3) as follows...
4a) Pour 100 ml 30% A) hydrochloric acid into the beaker.
4b) Measure 15 ml B) (for a 1:3 solution) of 65% nitric acid and pour it into into the beaker, and mix the acid solution with the glass rod..
4) Turn on the heatplate so it starts to boil gently and watch the chemical process.
Note: Watch out for the toxic fumes, which consists of nitrosyl chloride (NOCl) and chloride gas (Cl2), plus non-toxic nitric oxide (NO) and/or nitric dioxide (NO2).
5) Once all the gold has turned into liquid gold chloride, let it continue to boil.
6) Next step is to "clean" the solution from acids. Both the acids have a lower boiling temperature than water, and it's especially important to have all the nitric acid removed,
so in order to "clean" the gold chloride solution, first add little hydrochloric acid and let it continue to boil so you don't let it dry completely at once. And when almost all the acidic water has boiled away, add little distilled/deionized water, and continue over an over again a few times, and finally let it boil dry.
Note: It's important that the boiling is done at the highest possible temperature, as low concentrated hydrochloric acid have a boiling temperature that is somewhat higher compared to water.
6) Turn off the heat and add distilled water til there's exactly 100 ml.
7) Pour it over to the 100 ml bottle, and mark it
The result is now 100 ml of a gold chloride solution C) that we sure know contains 1000 mg (1 gram) gold, so 1.0 ml of that solution will contain 1000 / 100 x 1 = 10 mg of gold.
A) The lower the concentration is for hydrochloric acid, the higher is also the boiling temperature. At 34% it has about the same boiling temp. as nitric acid, which we don't want, as nitric acid must be able to vaporize away before the hydrochloric acid. For this reason, the hydrochloric acid should not have a higher concentration than 30%, which equals a boiling temp of 90 C. When we then add distilled water, the boiling temp. will rise, and when the concentration of hydrochloric acid is around 25% it has about the same boiling temp. as water, so if we add water it will simply mean that the water will boil off before the remaining hydrochloric acid
B) Calculation is as follows:
1:3 means 1 part nitric acid (HNO3) and 3 parts hydrochloric acid (HCl) measured in volume.
If we use 100 ml of HCl that has a concentration of 30% then we first calculate how much HNO3 that equals if we want the same volume...
30% / 65% x 100 ml = 46.15 ml. However, we only want 1/3 of that, so 46.15 / 3 = 15.38 rounded to 15 ml HNO3 is needed.
C) Reaction formula:
Au + HNO3 + 4 HCl → HAuCl4 + NO + 2 H2O
