The structure evolution of kaolinite flocs during their formation in aqueous medium was studied under a scanning electron microscope by hypercritical drying with liquid CO2, as a function of Fe electrolyte content. Without any Fe electrolyte, a sediment with uniform porosity formed by accumulation of particles under gravity. Fresh Fe electrolytes made it possible to aggregate the kaolinite particles to flocs with an architecture consistent with diffusion limited aggregation (DLA). With 0.67 mM Fe, a single shrinking DLA flocs layer formed. With 3.33 mM Fe, extensive face to face aggregation of the clay particles occurred and a sediment with preferred horizontal orientation accumulated. With 0.17 mM Fe a shrinking DLA flee layer and a uniformly porous accumulated sediment formed concurrently, while with 1.67 mM Fe a shrinking DLA flocs layer and an accumulated sediment with preferred orientation formed concurrently.