A device for dedusting loose materials in which there is provided an inclined covered trough along which the loose material travesl downwards. The trough bottom has an opening with a slot type grate through which from a bottom inlet, a flow of compressed air is delivered to pass through the bed of material and be extracted together with dust particles of the material through an inlet in the top portion of the trough. The slotted grate is composed of separate and parallel strips positioned in a step-like fashion perpendicular to the longitudinal axis of the trough. These strips are installed for possible turning in relation to their longitudinal axes to adjust the width of the slots therebetween.