Sodium metabisulfite (also known as sodium bisulfite) is an affordable and effective selective precipitant for gold. This chemical can recover up to 99.95% of pure gold when the precipitated gold is thoroughly rinsed. It works well even at room temperature. This product has a chemical grade purity of 99.98%.
Proper ventilation is required. This precipitant has a very strong, pungent, acid odor and is corrosive.
Precipitated gold particles vary in size, but tend to be small and float easily in the rinse water. For this reason, special care must be taken to avoid accidentally pouring off gold with the rinse water.