Why was it reported so low in the BFS when tests had already been done. Am I missing something here?

Cominco Engineering Services Ltd. (CESL) is a company that is owned by Teck Resources.
According to what you quoted, the tests that brought these results is a proprietary technology that is not used in the real world yet, except for Vale (so says their website.)

It seems reasonable that even if we didn't run the tests ourselves to prove this technology would work, that Teck might have done so as part of their DD. Maybe this is another reason that Teck would like our project, so that they can showcase their leaching technology.