Sodium Metabisulfite aka MBS is used for pH control in froth flotation to control Pyrite depression. Below is a graph showing pH VS pyrite recovery at various collector addition rates. It is also used to prevent flotation of sphalerite by copper activation in the presence of Tennantite/Covellite in the ore.
For pyrite flotation, you see maximum iron/pyrite depression using Sodium Metabisulfite/MBS takes effect at around pH 6.
MBS will depress metals/minerals in the order as dosage increases:
- Fe/Iron (Pyrite)
- Zn/Zinc (Sphalerite)
- Pb/Lead (Galena)
- Cu/Copper (Chalcopyrite)