Shrinking the Tailings Pond 

Canadian Natural Resources Limited (Canadian Natural) is commercializing promising new ways to manage the tailings pond at its Horizon Oil Sands facility, 70 kilometres north of Fort McMurray. The company is improving the tailings settling rate by adding carbon dioxide (CO₂) to the tailings, and will apply new technologies that will create trafficable tailings and accelerate the reclamation process.

Horizon includes a surface mine and bitumen extraction plant with on-site upgrading and associated infrastructure to produce synthetic crude oil. This process results in solid and liquid wastes called tailings which are stored in a pond. Mature Fine Tailings (MFT), a component of tailings, is the middle layer of the pond where fine clay particles remain suspended in water.

Even a small addition of CO₂ significantly improves
settling of tailings after only 10 days. Beakers
on the right and left are noticeably clearer than
the original tailings sample in the middle.

Canadian Natural has been adding waste CO₂ into the tailings before it enters the pond, creating a reaction that allows the solids – fines clays, silts and sand – to settle more quickly. This process increases the clarity of the tailings water which can then be recycled and re-used in the extraction process.

As part of the company’s tailings management plan, other pilot technologies are being run and will be implemented during the next phase of Horizon development in 2015. A MFT dewatering technology produces dry, solid, trafficable tailings by treating the MFT with a reagent. Any water released from the dried MFT is returned to the tailings pond for recycling to further reduce fresh water use. Also, Canadian Natural will employ cyclones and thickeners to recover and recycle hot water, removing dewatered coarse sand and clay fines. The dewatered streams will then be combined with CO₂ captured from the Horizon hydrogen plant. The resultant tailings will be deposited in the disposal area, where even more water will be released and reused.

These new processes will help reduce the footprint of the tailings pond and decrease the amount of fresh water needed to process bitumen by increasing the amount of reusable water available. This process of sequestering CO₂ into tailings will also reduce GHG emissions by capturing CO₂ from the upgrader in the next phase of Horizon development.

Progressive reclamation of the tailings pond (bringing the area back to its natural state) takes place throughout the life of the mine, which is approximately 40 years.