Thank you for that question.
It is an interesting term, and as somebody coming new to the forest sector, I had to ask the same question.
Black liquor is a residue produced by the kraft pulping process. There's a chemical kraft pulping process that creates the pulp, and there's kind of a nasty stew that comes out at the end called black liquor. A large proportion of that is lignin, which is kind of the other part of...trees are made of cellulose and lignin, so it's lignin, and then depending on the chemicals that are used, there might be some other things, like sulphur. It's a residue which historically has been burned as fuel back into the boilers. That's how it was used, but we now know we can get much higher value out of that, for instance, by extracting the lignin.
What happened in the United States was they had a biofuel-type subsidy. What folks were doing, as I understood it, was basically mixing this stuff with diesel fuel and getting a subsidy. It was a complete misuse of the tax system, but it worked, and it was worth about $25 billion to the American industry.