Ann: AGM Presentation, page-20

https://www.saltworkconsultants.com/quaternary-potash.html

The article above describes what Compass does.
I think the steps are:
1. Anionic flotation of halide
2. Kainite to schoenite conversion
3. Schoenite to SOP (hot water & addition of MOP)

The APC DFS suggests the following:
1. Kainite to schoenite conversion
2. Flotation of schoenite (to remove halite)
3. Schoenite to SOP (hot water & addition of MOP)

KLL DFS:
1. Kainite to schoenite conversion
2. Direct flotation of schoenite
3. Schoenite to SOP (hot water, no MOP)

SO4 DFS
1. Reverse flotation of kainite salts to remove halite
2. Kainite to schoenite conversion
3. Schoenite to SOP (hot water & addition of MOP)

You can check out the details yourself. Without doubt there is much more to it than the 3 main steps but the main point is flotation has proven to be troublesome in two of the WA projects. What does APC know that the others don't? As for German engineering, they do have previous potash processing experience.