Rare earth metal compounds, particularly lanthanum, cerium, and yttrium,
are formed as porous particles and are effective in binding metals, metal
ions, and phosphate. A method of making the particles and a method of
using the particles is disclosed. The particles may be used in the
gastrointestinal tract or the bloodstream to remove phosphate or to treat
hyperphosphatemia in mammals. The particles may also be used to remove
metals from fluids such as water.