Basics

Also known as coal combustion by(-)products or coal combustion residuals / waste
Essentially all the lefttover material once Coal is burned
This also often includes the Fly Ash , and sometimes material from Flue Gas Desulferization
Can be Greenwashed as benefits of coal, and they can be good products HOWEVER the many forms of Pollution , they, and their role in the process as a whole make that arguement invalid (See The Myth of "Clean Coal" )
The main aspect relevant to OSE is how will Biomass Combustion Products compare to these
- It seems that the issue of heavy metals and lead is (for the most part; trace elements and all that) out of the question, so that alone is a major improvement

Internal Links

Coal Tar / Creosote (Usually more intentional, and requiring a special reactor design, but could be "recovered waste" in some cases)
Clinkers
Fly Ash
Slag
Gypsum / Gypsum Board (seems it is only Drywall for now? Need to check in on this)