Process-oriented study of Fe–Si–Ca–Zn precipitation in borated alkaline solutions relevant to nuclear recirculation systems
Year: 2026
Type: article
Abstract: Chemical effects of iron, silicon, calcium and zinc on precipitation and fouling in borated alkaline waters representative of post-LOCA containment sumps were investigated to better understand clogging risks in safety-related recirculation systems. Lab-scale batch reactors (1 L, 40–100 °C, pH ≈ 8, H₃BO₃/NaOH/borax) were operated for 24 h with Fe(II)/Fe(III), Si, Ca and Zn at concentrations relevant for PWR environments. Precipitation kinetics were monitored by ICP-AES, and the solids were characterized by XRD, SEM-EDX, FTIR, XPS and UV-Vis DRS. Thermodynamic calculations were performed with PHREEQC (Thermoddem database) to support process interpretation and extrapolation. In iron-only tests, partial precipitation of amorphous ferric hydroxides/oxides was observed. Addition of dissolved silicate induced a fast, coupled removal of Fe and Si, consistent with the formation of Fe–Si amorphous silicates that strongly control aqueous speciation. Ca and Zn had limited impact on overall kinetics, but significantly modified solid yield, composition and morphology, leading to more fragmented, porous precipitates. A strong temperature dependence was evidenced: lower temperatures increased the total mass of solids, in line with the temperature dependence of amorphous silica solubility. PHREEQC simulations reproduced the main trends in phase assemblages and the decrease in precipitated mass with temperature, but systematically overpredicted solid amounts because equilibrium was not reached and some metastable phases were missing from the database. The combined experimental–modelling approach provides quantitative insight into multi-component precipitation phenomena relevant for designing, operating and mitigating fouling in safety-related filtration and recirculation units in nuclear systems, enhancing that the possibility of chemical effect should be considered in safety assessment.
Language: English
Subfield: Aerospace Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,050
OpenAlex ID: W7147375980