Oxygen depletion of static air by backfill material at the Thompson mine

Abstract

The depletion of oxygen from airways in contact with backfill material containing pyrrhotite can create a dangerous environment in underground operations using cut and fill mining methods. Oxygen is removed from the air via two major mass transfer processes; transfer from the air to oxygen-depleted water and transfer from the water to the solid surfaces. Both of these mechanisms are highly influenced by diffusion through the liquid phase. Transfer from liquid to solid is directly related to the pyrrhotite content of the fill material for pyrrhotite contents greater than 7% and inversely to the solution volume. The oxygen content of the water affects the rate of transfer according to a half-order reaction rate equation. Removal of pyrrhotite using sizing, magnetic or flotation techniques is not likely to be a practical solution to this problem since the rate coefficient is independent of pyrrhotite content below 7%. The effects of this problem can be minimized through the use of good ditching practice for water flow control and by mimimizing the height of fill poured in one lift. All employees working in fill areas should be made aware of this problem and the importance of water flow control to minimize the risk.