How to Recover Scrap Gold From Circuit Boards
There is as much as 1 oz. of gold in every ton of scrap circuit boards from older computers and electronics that have been discarded. Obtaining this gold is a matter of separating the gold bearing material from the plastic and other metals and then chemically recovering the gold and refining it to a reasonable purity level. Gold recovery and refining on a small scale can be performed in the back yard with some specialized equipment and some widely available chemicals.
Things You'll Need
- Circuit board scrap
- Glass Pyrex containers
- Nitric acid
- Hydrochloric acid
- Coffee filter
- Baking soda
- Gold detection liquid
- Small plastic tubing
- Distilled water
- Gold refining kiln
- Mold for gold
Remove the gold bearing connections and edges from scrap circuit boards using pliers and a strong back and forth motion to break the gold "fingers" from the edge of circuit boards. Be careful not to scrape the gold off the connectors in the process.
Place the gold connectors into a glass Pyrex container.
Mix nitric acid and hydrochloric acid together slowly, in a 1:3 ratio, in a separate glass Pyrex container in a ratio that makes the desired proportion of "aqua regia." The ratio will vary significantly according to the concentration of each acid used.
Pour the acid mixture over the gold connectors so that they are completely submerged in the acid, and allow the mixture to stand for one hour.
Pour the acid off into another glass Pyrex container, using a coffee filter to trap any contaminants or undissolved particles.
Introduce a precipitant such as zinc into the mixture slowly, watching as the material gets dissolved in the acid until it is no longer absorbed and then test the acid for gold using the gold detection liquid and following the instructions that are included with the liquid. Add more precipitant if necessary until no gold is detected in the mixture.
Add approximately a teaspoon of baking soda for every cup of acid being used to neutralize the remaining acid. Allow the mixture to settle for an hour.
Decant the acid from the top slowly without disturbing the precipitant (brown mud) on the bottom of the container using a small plastic tubing as a syphon. Add some distilled water and stir into the brown mud. Allow this to settle for an hour and decant the water into the same container as the discarded acid.
Place the mud into the kiln and bring the temperature up to approximately 2,200 degrees Fahrenheit and allow the gold to melt. Power off the kiln and pour the molten gold into a mold.
Tips & Warnings
- Perform gold recovery operations outside and away from any populated areas or buildings. Use a small amount of scrap to learn the procedures and have another person standing by at a distance in case of any problems requiring emergency help.
- Fumes from the recovery process are highly toxic. Acid is dangerous and can cause burns to the skin, eyes and internal organs. Mixing acids is highly dangerous and adding water to an acid can cause explosive reactions. Acid and fumes from it can cause serious corrosion problems for any equipment or metal hardware in the vicinity. These techniques may be regulated by local, state or federal law in some areas. Always use proper safety equipment including gloves, coveralls, boot protectors, and most importantly eye protection and self-contained breathing apparatus or a breathing filter designed for use with strong acids. Dispose of used acid properly and never pour it into a household drain or storm drain.
References & Resources
- Chemistry Comes Alive: Aqua Regia
- US Geological Survey: Obsolete Computers: "Gold Mine" or High-Tech Trash?
- Chemistry Comes Alive: Aqua Regia Demonstration Notes, Warnings, Safety Information
- US Geological Survey: Recycled Cell Phones -- A Treasure Trove of Valuable Metals
- Shor International: Refining Gold from Circuit Boards & Electronic Scrap