The continuous improvement of tailings management is an integral component of successful oil sands mining operations. Reducing the size and need for tailings ponds, and increasing the speed with which they can be reclaimed are ongoing challenges being addressed by the industry.
Canadian Natural has invested more than $1.6 billion in tailings management research and technologies to date. Our investments in tailings management technologies demonstrate our approach to research and development and how we take technologies from pilot project to commercialization. Canadian Natural is using and also researching new processes to reduce the footprint of the Horizon tailings pond and the amount of fresh water required for bitumen processing. These innovative methods will accelerate the process of reclamation, increase water recycling and reduce carbon dioxide (CO2) emissions.
Tailings are the sand, silt, clay and water found naturally in oil sands that remain following the mining and bitumen extraction process. Tailings are transported by pipeline and deposited in ponds where the majority of the solids – mostly sand – settle to the bottom. The remaining fluid – mostly clay, silt and water – flow to the middle of the pond. This mixture is called Fluid Fine Tailings (FFT). As the solids in the FFT begin to settle it becomes thicker, turning into a mixture called Mature Fine Tailings (MFT). MFT remain in tailings ponds while the solids continue to settle and the water evaporates.
Advancing tailings management technologies
The processing of bitumen extracted from mining requires the operation of tailings facilities to manage the water used in processing. In 2015, we commenced production of non-segregating tailings (NST) at Horizon. NST are tailings that have been significantly treated (dewatered) to form a homogeneous, semi-cohesive mass when deposited. The treatment process includes cyclones, to separate the coarse sand, and thickeners, to capture and remove water from the fines in the tailings streams prior to being sent to the tailings pond. The warm water that is removed and recovered is then re-used in the bitumen recovery process. The coarse sand and thickener underflow are then mixed and further combined with CO2 to produce NST. The addition of CO2 to NST has been proven to accelerate the settling of the clay fines in the tailings stream.
The NST process and our ongoing pilots to reduce MFT are enhancing the production of dry, solid tailings to ultimately reduce our environmental footprint and accelerate land reclamation. Using NST also allows warm process water to be recycled before it cools; reducing the amount of energy and greenhouse gases required to reheat the water for use in our bitumen extraction process. We are also decreasing the amount of fines going to the tailings pond by using smaller equipment and a selective mining process.
For more information on our tailings management technologies, read our 2015 Stewardship Report to Stakeholders.
Addition of CO2 into tailings
Horizon has been adding CO2 to tailings since 2009 to enhance solids settling rates, keeping the pond at roughly half the size it would have been without that process. The CO2 is added into the tailings stream before it enters the pond, where it creates a chemical reaction that changes the tailings water pH to the same as river water, allowing the solids to settle more quickly. This accelerated settling enables the quick release of clear and warm process water for recycling.