This study concerns the utilization of waste steel-making slag, a by-product that contains mainly CaO, Fe2O3 and SiO2. The as-received slag was ground and thermally activated by temperature treatment from 110 to 1000degreesC for 24 h. Although the as-received slag was amorphous, it became partially crystallized during grinding. These crystalline phases were larnite and iron oxide but other crystalline phases also appeared in addition to larnite after calcination. The uptake of Ni2+, PO4 (3-) and NH+4 by the samples was investigated from solutions with initial concentrations of 10 mmol/l. The sample calcined at 800degreesC showed the highest Ni2+ uptake (4.85 mmol/g) whereas the highest simultaneous uptake Of PO4 (3-) (2.75 mmol/g) and NH4+ (0.25 mmol/g) was achieved by calcining the material at 700degreesC. The principal mechanism of Ni2+ uptake is thought to involve replacement of Ca2+ by Ni2+. The mechanism Of PO43- uptake is mainly by formation of calcium phosphate while that of NH4+ involves sorption by the porous silica surface of the samples. (C) 2004 Elsevier B.V. All rights reserved.