Radiological and non-radiological leaching assessment of alkali-activated materials containing ground granulated blast furnace slag and phosphogypsum

Abstract

Alkali-activated materials (AAMs) based on ground granulated blast furnace slag (GGBFS) and phosphogypsum (PG) were investigated in order to quantify leaching of naturally occurring radionuclides (NOR) and inorganic non-radiological elements according to an up-flow percolation column test as described in CEN/TS 16637-3. Gamma spectroscopy and neutron activation analysis (NAA) were applied for radiological characterization, inductively coupled plasma optical emission spectrometry (ICP-OES) and ion-chromatography (IC) for chemical characterization. Upon leaching, 238U, 226Ra, 210Pb, and 228Ra were retained very well. Both for 232Th and 40K, a decrease in activity concentration was observed due to leaching and their release was influenced by the use of different alkali activators, which was also the case for the leaching of non-radiological elements. Only a small amount of Al (0.5–0.8%), Ca (0.1–0.2%) and Si (0.1–0.3%) was mobilized, while highest release was observed for K (56–94%), Na (49–88%) and S (71–87%). At first glance, drinking water is not endangered by leaching of NOR following the requirements of the European Drinking Water Directive. From the results for porosity, obtained with mercury intrusion porosimetry (MIP), it was concluded that both the porosity and formation of multiple leachable and non-leachable complexes are determining factors for the release of elements from AAMs.