Environmental Studies

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    The Tulsequah Chief Mine, previously owned by Redfern Resources Ltd., is a proposed mine in Northern British Columbia.

     Over a 3 year period, MEA provided Redfern with assistance in designing, building, operating, monitoring, maintaining, and preparing reports to regulators regarding a passive mine water treatment system located 400 m underground.   Microbial Technologies provided the biological aspects of the process development while MEA determined the scale up factors required.  Klohn Crippen Berger provided geotechnical and hydrological design support.  Construction of the system was performed by Ampex Mining.


The system consisted of several different treatment stages:

  1. BulletA mechanical NaOH feed system, powered through a small microhydro turbine fed by a flowing drillhole, raised the pH just enough to cause the ferric iron to precipitate.  A gravity mixing zone was followed by a settling area to remove most of the precipitates. 

 

Environmental Studies

  1. BulletThis then overflowed into a series of gravity draining limestone cells that were kept anoxic by bacteria fed with a battery operated mechanical drip system dosing a glycol solution.  These cells were very effective at removing copper and aluminum by raising the pH to around pH 6. 

  2. BulletAfter the limestone cells, the underflow was fed to a Sulphate Reducing Bacteria (SRB) bioreactor which was designed to remove Zn from solution. 

  3. BulletThe system was designed to operate for 3-6 months between each servicing (replenishing the NaOH, glycol and batteries).  Additional maintenance requirements included removing residual iron precipitates from the surface of the limestone cells because the low head available to drive water through the system limited the amount of filter cake that could be tolerated.


Unique features incorporated into the design included: 

  1. BulletAll flows, including reagent dosing, were by gravity with no pumping required;

  2. BulletAccumulating iron precipitates were removed without requiring heavy equipment;

  3. BulletTreatment rates could be controlled and adjusted;

  4. BulletNo sunlight was available to provide energy for the biological aspects of the system.