What is fixamol?

Can fixamol be used on grass burns after sport?

As a qualified sports first aider I would say no. You should wash it first, then apply some betadine or similar then leave it open to dry out and maybe apply an antiseptic cream nightly. If you want to cover it - I would use a non-adherent dressing. You can buy dressings that 'breathe' and are specifically for burns. Bear in mind, however, that this is just my opinion and I am not a medical professional.