The present invention is a device for preparing a non-flammable filler based on sodium or potassium silicate, particularly suitable for filling into paper or building materials, the use of which can be removed deficiencies in the state of the art, in particular in that the device allows, on the basis of microwave energy, to dry with low energy consumption of sodium silicate to such a level that it is no longer soluble in water but carried in the molecule crystalline water that provides quenching function. Such a desiccated silicate is characterized by a considerable brittleness, which is particularly advantageous in its grain processing. Filler prepared with this technique is environmentally friendly and does not change physical and utility paper properties.