Temperature effect on the strength and Cs-137 leaching behaviour of cemented radioactive electric arc furnace dust

Electric arc furnace dust (EAFD) contaminated with Cs-137 was solidified using ordinary Portland cement (OPC) to investigate the effects of EAFD content and temperature on mechanical strength and leaching behaviour. EAFD-OPC waste form specimens containing 0 – 40 wt% EAFD were prepared at a fixed water-to-binder ratio of 0.40 and cured for 28 days. Leaching tests were conducted according to ANSI/ANS-16.1-2003 at 5, 25, and 60 °C. All specimens satisfied the minimum compressive strength requirement, although strength decreased with increasing EAFD content. Strength variations under leaching and temperature effects were attributed to the combined influence of leachable component release, temperature-accelerated hydration, and ZnO-induced hydration retardation. The release of Cs-137 increased with both higher EAFD contents and elevated temperatures, with leachability index values ranging from 5.9 ± 0.4 to 7.0 ± 0.1. Multiple-process modelling indicated that Cs-137 leaching occurred mainly through loosely bound Cs-137 release and surface wash-off, with minor diffusion. The Arrhenius plots indicated that the dominant leaching behaviour remained broadly consistent with temperature, while activation energies decreased from 22.27 to 8.65 kJ/mol as EAFD content increased, confirming a predominantly surface-controlled process. These findings support the optimization of cementitious matrices for the safe immobilization of EAFD.