Co-Mixing: Simple Technology Tackles Tailings
Jul 18, 2016
Syncrude has a suite of options to deal with fluid fine tailings – the layer of water, clay and fine solids that results from the bitumen extraction process. Composite tailings (dewatering), centrifuge and water capping are methods used to draw out the solids and free up water for evaporation or to recycle for extraction.
A new innovation that mixes the fluid fine tails (FFT) with unusable overburden could soon be added to the list. FFT and Overburden Co-mixing is a simple process that can have a huge impact on tailings management and land reclamation.
When mining begins the layers of earth above the oil sands deposit are stripped away and used to reclaim mined out sites. The Clearwater Formation is a layer directly above the oil sand that is rich in clay. Often referred to as Kc, this material has limited use because it is hard to work with.
Co-mixing takes two unwanted materials – FFT and Kc – and combines them to make a useful construction material.
Originally developed by researchers Ted Lord and Wayne Mimura at Syncrude’s R&D department, co-mixing technology has evolved over many years. Jim Lorentz and his R&D Tailings Technology Team have taken the torch and implemented a series of successful co-mixing pilot programs in 2014 and 2015.
The success is credited to the mixing ratios. “It’s like cookie dough,” said Nan Wang, Research Associate. “It’s a mix of wet and dry. If you have too much liquid, you add more flour.”
And that’s basically what the team has done. Kc material is placed on a conveyor where it is sprayed with FFT. The mixture is then deposited in a mined out pit where it hardens.
Depending on its end use the product can be mixed in different ways with varied results. It can be used to build roads, berms, or as a base for reclamation soils. Make a road with it and light equipment can drive on it within a month of the material being placed. Build a formation and a month later you can reclaim it.
“The best part is that we didn’t have to create anything new to make this happen,” said Nan. “We used off the shelf technology – equipment we already had and put it to use.” In fact, in the first field tests the team used a cement mixer to combine the materials.
Test cells that were filled with co-mixed materials last fall will be tested after the spring thaw to examine the strength of the material and to see if water has penetrated. Smaller scale tests have shown that once the material has hardened its strength is maintained.
In 2016 the co-mixed material will be tested for use in site reclamation.
Thanks to co-mixing technology, two previously unusable materials have become a cost-effective way to create a solid landscape in a short period of time to accelerate reclamation activity, and provide Syncrude with another option to manage its fluid fine tailings.