The formation of aluminosilicate scales in the High Level Waste Evaporators at the Savannah River Site led to curtailed operation and an expensive cleaning evolution due in part to the presence of enriched uranium in the scale. Therefore, the sorption behavior of uranium species and sodium aluminosilicate (NAS) solid phases in nitrate/nitrite-rich sodium aluminosilicate solutions were studied under well-defined conditions at 22degreesC and agitation rate of 400 rpm. The NAS solids comprised four well-characterized phases of amorphous, zeolite A, sodalite, and cancrinite. Pure, synthetic sodium diuranate (Na2U2O7) crystals were precipitated and used as the base/reference U-containing compound. The studies of the sorption behavior of U-containing species on NAS solid phases were conducted under conditions where no detectable dissolution, precipitation, or crystallographic phase transformation of the NAS adsorbent phases were observed over a 6 h test period. The uranium sorption capacities were reached typically within 3 h. The uranium capacities were measured 6.36 to 9.3 mg U kg(-1) NAS solid for the Zeolite A and cancrinite phase. The amorphous and sodalite phase had higher uranium loading that measured between 19 and 58 mg U kg(-1) NAS solid.