Refrigeration – Ground Freezing / Shaft Sinking
Giant Mine, NWT
From 1948 to 2004 Giant Mine, located near Yellowknife NWT, produced about 7.6 million oz. of gold. The mining company went bankrupt and left behind 237,000 tonnes of toxic arsenic trioxide dust, stored in 13 underground chambers, and a very large environmental problem for the federal government. After years of study on how to safely remove the environmental hazard, it was concluded that the safest way to handle the potential deadly and dangerous effects of the arsenic dust was to freeze it in place — forever.
The freeze is being performed using a Frozen Block Method.Step 1
- Drill holes in the rock and chambers.
- Install pipes into the wells.
- Connect the pipes to a freeze plant on the surface.
- Circulate a super-cooled liquid through the pipes, which freezes the rock and any nearby water under the chambers.
- Drill vertical holes alongside the chambers, and insert pipes into the holes.
- Circulate super-cooled liquid from the freezing plant through the pipes to freeze walls around and chambers.
- Steps 1 and 2 form a secure cup-like shape of frozen rock around the arsenic chambers, which prevents water circulation. Install thermosyphons to aid in the freezing process and maintain the frozen area.
- Water is added to slowly fill the cup-like shape.
- The freeze plant continues to operate until the entire contents of the "cup" are frozen, including the arsenic chambers.
- This prevents any water from entering or exiting the chambers.
Startec designed and manufactured a portable 120 TR Ammonia Refrigeration and Refrigeration pumping system that will be used to super cool and circulate Dynalene through the ground freeze piping system. Once the block is frozen, the unit will be moved to one of the other 13 chambers.