Toward Sustainable Radioactive Waste Management: Geopolymerization of Sewage Sludge Ash as a Viable Solution

This study examines
the geopolymerization potential of sewage sludge
ash (SSA) for immobilizing radioactive waste through a series of experimental
phases. The initial phase of the study involved processing sewage
sludge from three different treatment plants, followed by calcination
and subsequent characterization. The initial synthesis of geopolymers
was conducted using 100% SSA, followed by compressive strength testing.
In the second phase, a full factorial design was employed to optimize
a metakaolin-based geopolymer formulation, with adjustments made to
five variables: metakaolin (MK), activating solution (AS), sand, water,
and lime. The optimal conditions were identified as 120 g MK, 125
g AS, 360 g sand, 55 g water, and 14.5 g lime. Under these conditions,
the compressive strength increased from 15.0 ± 1.0 to 21.3 ±
0.6 MPa when the specimens were cured at 60 °C for 6 h. The optimized
formulation was then augmented with SSA, and its characteristics were
examined through a series of analytical techniques, including ICP–OES,
XRF, XRD, SEM, and EDS. In the third phase of the study, immobilization
of simulated radioactive activated carbon and ion-exchange resin wastes
contaminated with 137Cs within the geopolymer matrix was
investigated. Leaching and compressive strength tests were conducted
to evaluate the performance of the material, and the results indicated
that the release rates of 137Cs were between 2.55 ×
10–5 and 3.23 × 10–5 cm d–1. These findings suggest that SSA-derived geopolymers
can effectively immobilize radioactive waste, offering a sustainable
alternative to traditional Portland cement.