A sorbent for sorbing radioactive ions is described. The sorbent comprises a porous crystalline powder of a metal oxide or mixed metal oxide. A process for making the sorbent comprises the steps of reacting a metal halide or a mixture of metal halides and an alcohol to form a gel; heating the gel to form a particulate material; exposing the particulate material to an oxidant to form a powder; and heating the powder to a temperature sufficient to at least partially melt or sinter particles of the powder so as to form the sorbent.