Foam in grinding and role of ground mineral in its stability

Surfactants are usually used as grinding aids. However, surfactant foaming during the grinding process is rarely mentioned in the literature with no clarification of its effect on the grinding process. In this paper, the generation of foam during the grinding of talc and quartz, as two different minerals in their hardness and hydrophobicity, was observed in the presence of sodium dodecyl sulfonate (SDS). The effect of generated foam on the fineness of ground product under different grinding conditions such as solids%, grinding time, and pulp pH was investigated. The results indicated that the foam was formed during the grinding of both minerals. The foam volume depends not only on the presence of surfactant but also on the characteristics of the mineral along with grinding conditions. The foam was intense and more stable particularly at pH 10 and high solid content (i.e., 60% solids) in the case of talc due to its fineness and hydrophobicity that result in bubbles stabilization. Remarkably, there is no foam at acidic pH due to the high ionic strength that leads to bubble instability. Most importantly, the presence of surfactant foams improves the size reduction process by providing more dispersion of particles, as one of the grinding aid mechanisms, due to particle-particle and particle-SDS repulsive electrostatic forces.