Sodium metabisulfite is commonly used to precipitate dissolved gold out of aqua regia and gold chloride solutions. When it is dissolved into water, sulfur dioxide gas is created which is excellent at precipitating gold from the solution. Sodium metabisulfite is a popular choice in this process because it is more selective in precipitating gold by itself. Use about 1-1/2 tablespoons of sodium metabisulfite (SMB) for every ounce of dissolved scrap metal in solution. Good ventilation is critical as adding SMB to aqua regia produces corrosive vapors.
In the process of gold extraction from e-waste, Sodium Metabisulfite is commonly used after neutralizing the nitric acid in aqua regia solutions with Urea.
Wine (and beer) makers use Sodium Metabisulfite to inhibit the growth of wild yeast and bacteria in the wine. It also works well as a sanitizer for wine making equipment.
Dosage:
- Wild Yeast: One quarter teaspoon per five gallons of must.
- Sanitation: Two ounces to one gallon of water.
CAUTION. When mixed with water or a strong acid solution, sodium metabisulfite releases sulphur dioxide (SO2), a pungent, rotten eggs smelling gas that can also cause breathing difficulties in some people.