The broadcast salt spreader works exactly like a generic or seed and fertiliser broadcast spreader. The salt is placed in a hopper, which will be made of a corrosion proof material like polyurethane or stainless steel.
As you push or tow, gravity drops the material through an aperture onto a spinning broadcast plate, situated between the wheels
The wheels of the salt/grit spreader control the spinning broadcast (distribution) plate,* which then distributes the material in a wide, even pattern.
*On some large commercial /industrial spreaders this is done by an electric motor