That looks more like rust, is that a rsg at the top of the wall? As long as you get all the loose crap off you should be ok to stick a few coats on top without any problems, if you spend weeks wire brushing the crap out of the brickwork you will just damage the bricks. You might want to google 'wirebrush brick' before you go any further it is pretty much universally condemned. Just using a hard yard broom and then a soft floor broom then a good hoovering should get rid most of the crap use a scraper to get rid anything flaking off. Anything that doesn't shift after that is probably going to rip chunks of the brick surface off if you try to remove it so just let it be. If you have any mould/fungal growth give the place a good nuking and then stick an antifungal undercoat on.

Might also want to get the dehumidifier in and give the beam a bit of tlc, steel is much better at holding up your house than rust.