The ability of four amorphous Al3+- and Fe3+-doped titanium and zirconium sorbents to separate U(VI) from acidic aqueous solutions (pH(init) = 3, ionic strength 0.1 M established by NaNO3) was investigated using a batch technique and instrumental neutron activation analysis. All investigated sorbents were found to be chemically stable and remove considerable amounts of uranium from acidic aqueous solutions (pH(init) = 3). The scanning electron microscopic and powder-X-ray diffraction examination of the grains of the two investigated titanium phosphates after contacting the uranium solutions revealed the formation of sodium autunite (Na-2(UO2)(2)(PO4)(2)center dot 6-8H(2)O) accompanied, in the case of the Fe3+-doped titanium phosphate, by iron uranyl phosphate hydroxide hydrate (Fe(UO2)(2)(PO4)(2)(OH)center dot 7H(2)O). No crystal formation was observed in the cases of uranium sorbed by zirconium phosphates indicating the different sorption mechanism involved.