An extraction sequence in three steps with buffered hydroxylamine hydrochloride, oxalate and dithionite solutions was used for removal of Fe-oxide coatings from standard clay minerals: kaolinite, illite and mixed layer smectite/illite. After each extraction step the cation exchange capacity, specific surface area and the concentrations of Al, Si, Fe, Mg, K and Ca in solution were measured. For all minerals the specific surface area increases after treatment with hydroxylamine hydrochloride and oxalate, but is decreases after treatment with dithionite solution. The cation exchange capacity shows no significant change for smectite/illite, a small decrease for illite and a continuous increase for kaolinite after treatment with the extractants. K, Ca, and Mg are mainly extractable by hydroxylamine hydrochloride. After each extraction step an additional exchange of these cations could be observed by treatment with ammonium acetate.
