Advice on cleaning large amounts of rusty sidewalk

I’ve treated many patios and driveways with rust staining. My next project is to treat these sidewalks in a condo complex with heavy rust staining from the sprinklers.

Any advice to sped things along?

Also, for rust this heavy, I would assume I would apply three light coats of oxalic acid and let it sit for five minutes and then spray it off. I suspect it will take several treatments using this process, correct?
or would I just lightly spray 5-7 coats and rinse once?


F9 BARC process.