Hazardous ions uptake behavior of thermally activated steel-making slag

This study concerns the utilization of waste steel-making slag, a by-product that contains mainly CaO, Fe ₂O ₃ and SiO ₂. The as-received slag was ground and thermally activated by temperature treatment from 110 to 1000°C 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 Ni ²⁺, PO ₄ ^3- and NH ₄ ⁺ by the samples was investigated from solutions with initial concentrations of 10 mmol/l. The sample calcined at 800°C showed the highest Ni ²⁺ uptake (4.85 mmol/g) whereas the highest simultaneous uptake of PO ₄ ^3- (2.75 mmol/g) and NH ₄ ⁺ (0.25 mmol/g) was achieved by calcining the material at 700°C. The principal mechanism of Ni ²⁺ uptake is thought to involve replacement of Ca ²⁺ by Ni ²⁺. The mechanism of PO ₄ ^3- uptake is mainly by formation of calcium phosphate while that of NH ₄ ⁺ involves sorption by the porous silica surface of the samples.