Pellets were produced from carefully sized iron ore and silica sand fractions, under controlled moisture conditions, using a sealed balling drum. The strength of these pellets was measured as a function of moisture content and particle size. The results showed that the strength of the pellets could be adequately described by a model which equates the strength of the pellets with the negative pressure developed within the porous mass, provided that the particle size distribution was narrow and the mean particle size relatively large._x000D_
However this model failed to account for the observed strengths of pellets produced from systems containing even small quantities of ultrafine particles ( < 5 Itm) and could offer no explanation for the existence of dry strength in such systems. This phenomenon has been semi-quantitatively interpreted in terms of I Van der Waal's forces.