The addition of gypsum, or calcium sulphate, has been quite well known for a long time. What's been more transformative is the techniques the companies have developed to mix it. They take the tailings, mix in gypsum and sand, and then they can put that mixture back into the mine. Basically, they can empty the sludge from the tailings pond and put it back into the mine.
The difficulty in this whole process is that once you add gypsum, the resulting water is awful for recycling into the plant to recover the bitumen. In the past, companies picked their water composition to get the most oil possible out of the oil sands. The downside was that it created the worst possible tailings problem. If you treat the water to get the best possible tailings behaviour, you get the worst possible bitumen recovery when you recycle that water. That's the challenge they're trying to juggle right now.
To me, this provides an opportunity to come up with new approaches. If you can change the water chemistry between the tailings pond and the plant, you may be able to get the bitumen and get rid of the tailings problem at the same time. That's one of the potential paths forward, using water. The other path forward is to use technologies that don't use water at all—you don't remove water from the Athabasca River and you don't create wet tailings in the first place. There's certainly a lot of merit in those approaches.