A possible solution would be applying Prosoco, Inc.'s Enviro Klean registered Safety Klean per the manufacturer's recommendations.
This product is an alternative to acidic compounds for cleaning brick surfaces.
Note: Do not use acid to clean bricks. It will remove the outside layer and expose the more porous interior, which will allow the bricks to absorb more moisture and hasten cracking during freeze/thaw cycles.
Hope this helps.