REACTIONS OF IRON HYDROUS OXIDE WITH WYOMING BENTONITE

Abstract

Iron hydrous oxides were precipitated in Wyoming bentonite suspensions. With these preparations, close agreement was obtained between experimental corrected lime-potential and base saturation values and the titration curve calculated for the Wyoming bentonite-Fe hydrous oxide system, if (a) the exchangeable cations were extracted with NaNO3, (b) titration was used to determine the sum of trivalent ions extracted and (c) Fe and Al were considered to be equivalent exchangeable cations. The sum of cations extracted with NaNO3, therefore, was used as a measure of the effective cation exchange capacity (CEC) of the clay preparations containing excess iron oxides.The effective CEC's were low after short reaction intervals, but increased rapidly with time and were approaching the original CEC of the clay. The extent to which the CEC may have been reduced initially could not be determined because charged polynuclear hydroxy Fe complexes were present on the exchange complex. The fact that these complexes disappeared by 2 weeks and that the CEC values were approaching the original value clearly show that the Fe hydrous oxide clay complexes were not stable. Because of this and the low pH values at which the complexes were formed, the existence of Fe hydrous oxide-clay complexes in most natural soils was considered unlikely.