By Blake Flournoy, updated March 24, 2022
While gold is undeniably valuable, the materials you encounter—whether freshly mined ore or jewelry—are rarely pure. Most commercial gold products are alloys, typically containing silver or other metals. To extract the pure metal, chemists often use a powerful solvent known as aqua regia, a mixture of nitric and hydrochloric acids. The following guide walks you through the process, highlighting essential safety precautions and best practices.
1️⃣ Set up a well‑ventilated work area. Wear safety goggles, nitrile gloves, and a splash apron.
2️⃣ Weigh the gold you wish to refine. For every ounce of gold, you will need a 300 mL beaker.
3️⃣ Add 30 mL of concentrated nitric acid per ounce of gold, followed by 120 mL of concentrated hydrochloric acid per ounce. Gently swirl the mixture. Avoid breathing in the fumes; work in a fume hood if possible.
The aqua regia will turn amber‑brown as it begins to dissolve the gold. The reaction is exothermic and will generate heat—do not stir aggressively. Leave the mixture to sit undisturbed for 12–18 hours, allowing the gold to fully dissolve.
After the gold has dissolved, strain the solution through a Buchner funnel to remove any undissolved solids. Repeat the filtration until the filtrate is a clear, pale green color.
Transfer the clarified solution to a large glass vessel. Prepare a separate solution of 1 lb (453 g) of urea dissolved in 1 quart of boiled water. Add this slowly to the gold solution while stirring; the foaming will subside once the urea has reacted.
Boil another quart of water and add 1 oz (28 g) of a precious‑metal precipitant per ounce of gold initially weighed. Add this to the gold solution; the mixture will darken to brown as the gold complexes with the precipitant.
Let the mixture stand for at least 30 minutes. Test for remaining dissolved gold by dipping a glass rod, then a drop of metal‑detection liquid onto a paper towel. A dark purple result indicates unrecovered gold; if the test fails to turn purple, the gold is fully precipitated.
Repeat the addition of precipitant and testing every 30 minutes until the test no longer turns purple.
When the test fails to turn purple, filter the solution through a Buchner funnel to collect the brown gold particles. Set the filtrate aside for neutralization.
Rinse the collected gold in tap water, then repeat the rinse with distilled water to remove residual acid. Finally, add a small amount of aqueous ammonia to neutralize any remaining acid, filter, and rinse once more with distilled water. The resulting solid is refined gold, ready to be melted and cast.
• All steps should be performed in a fume hood or well‑ventilated area.
• Never pour acid directly into a sink. Instead, neutralize the filtrate with a measured amount of sodium bicarbonate until bubbling ceases, then dispose of the resulting solution according to local hazardous waste regulations.
• When melting the recovered gold, use a crucible rated for high temperatures and a proper safety shield.
By following these steps and observing stringent safety protocols, you can reliably refine gold from alloyed sources and obtain a high‑purity product suitable for investment or jewelry use.
