Inline Dewatering of Oil Sands Tailings

Lead Proponent: InLine Dewatering Limited
Location: Edmonton, Alberta
ecoEII Contribution: $ 759,000
Project Total:  $ 2,014,000

Project Background:

Mining and mineral processing activities such as bitumen production from oil sands create waste by-products.  These include waste rocks and tailings (a combination of water and fine-grained rock or low-grade ore particles).  The tailings streams are typically discharged into constructed impoundments, also known as tailings ponds. During its disposal, coarse fraction of the tailings typically settles out near the discharge point while the fines, which will become mature fine tailings (MFT), remain in suspension. Under the current tailings management schemes in oil sands industry, MFT are still being accumulated within surface impoundments. Due to the extremely slow consolidation and settlement of MFT, the containment of the tailings poses significant long-term challenges and liability for the oil sands industry.  The regulators and industry are therefore shifting from wet tailings storage and aiming towards a dry landscape disposal, thus reducing the use of tailings ponds and enhancing land reclamation.  Recognizing the need to develop technologies that dewater tailings efficiently and effectively, Inline Dewatering Ltd. conceived and proposed the project “Dewatering of Oil Sands Tailings” for ecoEII funding.  The project was awarded $759K to establish the technical feasibility of using the Inline Dewatering Process to dewater tailings to a predetermined density before discharged.

Results:

The Inline Dewatering Process uses the concept of cross flow filtration (CFF) whereby a slurry of tailings, flowing through a special pipe, is dewatered.  Filtrate (primarily water) is released through the pipe wall while most of the mineral solids are retained.  Some of the solids are deposited along the inside wall of the pipe, forming a filter cake.  The filter cake remains porous with significant ability to allow fluid to pass through it, as it is continuously eroded by the slurry that flows through and imparts shear on its surface.  New filter cake is deposited as the old filter cake is eroded.

A dewatering CFF test system was designed and fabricated at Inline Dewatering’s laboratory in Sherwood Park, Alberta.  The test system incorporated a pipe flow loop, pumps and control valves.  Various parametric experiments and studies were conducted.  It was determined that the dewatering rate was controlled by several key factors.  First, the characteristics of the dewatering pipe.  Various types of dewatering pipes with different diameters, lengths, and porosity were evaluated, and their dewatering capabilities under varied pumping conditions were assessed.  It was concluded that a perforated stainless steel pipe performed best with up to three times the dewatering rate compared to the other pipes. Further testing focused on the performance of the perforated pipe with different tailings.  The perforated pipe was able to dewater all tailings with particle size and fines content typical of gold tailings to high fines content oil sands tailings, which have a large variation in the median size (50 to 155 mm) and fines content (<44mm) of between 10% and 41%.  However, it was noted that recirculation of oil sands tailings through the test loop resulted in lower dewatering rates.  The tailings became progressively more viscous due to continuous shearing.  It is therefore recommended that a dewatering system for oil sands tailings should be operated using a once-through-flow to optimize the dewatering rate.

Second, the dewatering rate is also strongly influenced by the hydraulics of the pumping system used to transport the slurry through the dewatering pipeline.  For example, formation of a filter cake on the inside wall of the dewatering pipe requires an appropriate pressure differential between the inside and outside of the pipe.  The rate that the filtrate passes through the cake is controlled by the pressure differential (i.e. water is forced through the filter cake) in the dewatering pipe, as well as the velocity of the slurry travelling through the pipe.  Test results show that the filter cake can be formed quickly, provided that the appropriate pressure differential is applied, and that the filter cake can release filtrate consistently below 0.5% solids content.  Furthermore, it was discovered although the slurry side of the filter cake is actively eroded and renewed, the cake itself does not slide along the pipe wall surface.  This finding confirms that the cake protects and reduces wear on the inside wall, and coincidently reduces the need for costly pipe replacement.

Benefits to Canada:

Reducing the environmental impacts of oil sands extraction by addressing the challenges associated with volume of tailings ponds through successful deployment of dewatering technology will advance Canada’s oil sands industry.

Next Steps:

An Inline Dewatering demonstration plant will have to be constructed in order to establish field dewatering rates and determine if the total oil sands tailings stream can be dewatered while returning heated water to the extraction circuit.