Preparing old Concrete floor for tiling (ed.)

Hello
We removed old vinyl tiles from our bathroom floor and scraped it as much as we could. It's still left the old adhesive in some patches. It's quite thin though. Is it ok to tile over using porcelain tiles or do we need to prep it further?

 

That's ok for going over with the tiles.

 

Cool thank you! I'm just wondering if I should prime the floor before tiling as the black stuff may be bitumen? Is that right? Sorry total novice here!

 

Yes prime it first then tile.