The invention relates to a process for preparing a modified mineral product to be used in the treatment of contaminated fluids. According o the invention, the process consists in pretreating a silicate/alumino-silicate material with 0.1...5% sodium-ion donor solutions for 4...48 h, at a temperature of 20...30°C, the solid material being dried until a humidity of 1...5% is reached, after which it is subjected to ion exchange with 0.1...10% salt solutions of alkali or alkali-earth metal cations, at a temperature of 20...30°C, for 3...15 min, to result in a modified product having a humidity of 3...10% and a grain size of 20...100 &mum.
