The specific surface, or specific surface area, is the total surface area of all particles of crushed material, usually dispersed or porous, divided by the mass or volume of the material. The boundary ranges of the specific surface of iron ore concentrate for pelletizing are 1600-2100cm2/gram, at which the cohesive forces of the particles provide optimal strength properties of green and roasted pellets (diagram). At specific surface values less than 1600cm2/gram, the strength properties of the pellets decrease due to a decrease in the contact area of the particles. With an increase in the specific surface above 2100cm2/gram, due to an increase in the contact area of the particles and the formation of a denser structure of green pellets, the processes of moisture removal and oxidative firing slowdown, which leads either to a decrease in the strength characteristics of the pellets or to a decrease in the productivity of the firing machine in order to maintain their quality.

     With an increase in the specific surface area of the charge particles by every 80-100 cm2/gram, the optimum moisture content of the charge increases by 0.1%. An increase in the moisture content of the charge leads to an increase in the porosity of the dry pellets and a decrease in the productivity of the firing machine due to an increase in the drying time of the raw pellets. Usually, the optimum moisture content of concentrates and charges is determined experimentally by the yield of suitable raw pellets, their shape and indicators of compressive and crushing strength.