The interaction of electrical charges between the fine clay particles suspended in oilsands tailings and water forces the particles into a uniform and stable structure. The U of A team discovered a way to remove water from the mixture. The discovery is an important step in destabilizing fine clay particles suspended in the tailings. Suncor photo.
Recent estimate of cleaning oilsands tailings over $250 billion
By Richard Cairney
This article was published by the University of Alberta on November 29, 2018.
A team of University of Alberta engineering researchers has devised a new way of treating oilsands tailings—the soupy byproduct of separating bitumen from clay.
Researchers around the world have been stymied in efforts to destabilize fine clay particles suspended in the tailings and some estimates suggest it could take a century for the particles to settle to the bottom of the tailings ponds. Recent estimates peg the cost of cleaning the tailings ponds in northern Alberta at more than $250 billion.
The problem is that an interaction of electrical charges between the particles and the water forces the particles into a uniform and stable structure. This so-called “house of cards” formation prevents the clay from settling.
“The effect of the surface charge on micro-sized clay particles becomes huge—it is stronger than the effect of gravity,” explains Tinu Abraham, a chemical engineering PhD graduate who led the research project during her stint as a post-doctoral fellow.
She and her team found that the stable micro- structure can be collapsed by manipulating the surface charges under a signature electrical frequency and field. This electrokinetic manipulation disrupts the electrical forces that stabilize tailings. This causes the particles to aggregate (or “collapse”) and cause dewatering.
The findings were recently published in the Drying Technology Journal.
Abraham, who was doing post-doctoral work in former Canada Excellence Research Chair emeritus Thomas Thundat’s U of A lab, says the first step was to take a micro-scale look at the clay structural arrangement in tailings.
“I’ve always heard of the term “house of cards,” that these tailings are in the form of a house of cards, and I was curious to see what this structure looks like,” she said.
The team first freeze dried tailings samples to remove the water so they could examine the clay structure left behind.
The early results of the imaging were disappointing. High-powered scanning electron microscopes in the Faculty of Engineering nanoFAB Lab showed a flat, featureless surface rather than the internal structure. The researchers tried chipping the samples but in the process, they were left with damaged samples –not the naturally occurring shape.
Eventually, they took advantage of a “shedding” phenomenon, where surface particles began exfoliating, revealing the inner structure.
The microscope delivered images showing that thin edges of clay particles are attracted to the flat surfaces of other particles—the same kind of imagery as a house of cards—at the micro-scale.
“This was an epiphany for me,” Abraham said. “It’s one thing to hear about this house of cards structure but something else to actually see it.”
The hypothesis of the project was that an AC current could disrupt the electrokinetic forces, causing the structure to take shape. By toppling the particles, the spaces between them would be closed, forcing water out of the mixture.
Abraham says this is one small step in an important, long-term challenge.
“This is not the end—it’s the beginning,” she said. “I have not come to the final goal in mind, which is to see if, in time, we can get an instantaneous collapse and instantaneous dewatering.”