Particulate foams are of great interest in mineral processing, water treatment, and soil remediation. One of the first conditions allowing the capture of a particle by an air bubble is surface hydrophobicity. An alkylammonium bromide surfactant (TTAB) was used to perform in situ hydrophobication of negatively charged illite clay particles. This treatment causes the neutralization of clay surface charge and the irreversible aggregation of particles. At a fixed amount of TTAB in solution, foams generated from illite clay suspensions present a better foaming ability and stability than bare TTAB solutions. The relative quantity of TTAB necessary to reach the "ideal foaming ability" corresponding to the capture of all injected gas by the foam decreased when clay concentration increased. Capture and collision probability increase may explain this phenomenon. Moreover, selectivity for the smallest clay particle size fraction (3 mu m) in foams was observed and is correlated with foam height and drainage time.