ALUMINUM-BEARING GOETHITE IN VENEZUELAN LATERITES

The presence of Al-bearing goethites has been unequivocally established in Venezuelan laterite sediments by means of infrared spectroscopy (IR), chemical dissolution, and X-ray powder diffraction (XRD) methods. The composition of these samples ranges from left bracket Fe//0//. //8//9Al//0//. //1//1 right bracket O(OH) to left bracket Fe//0//. //7//6Al//0//. //2//4 right bracket O(OH). The data of dissolution experiments using amodified dithionite (CDB) treatment suggest a parallel behavior between Fe and Al; the gradual dissolution of Al is associated with the destruction of the Al-containing goethite. The interpretation of the CDB dissolution results for SiO//2Fe//2O//3 is different; silica was only slightly extracted from phases other than goethite. Substitution of Fe**3** plus by Al**3** plus in these goethites was represented on the XRD patterns by a lowering of the (110) and (111) reflections corresponding to a reduction in size of the unit cell of goethite. IR spectroscopy showed the formation of such solid solutions. Refs.