Metallic technetium sequestration in nickel core/shell microstructure during Fe(OH)₂ transformation with Ni doping

Area of Science:

• Environmental Science
• Materials Science
• Radiochemistry

Background:

• Technetium-99 (Tc) poses a significant environmental challenge due to its long half-life and mobility.
• Effective sequestration methods are crucial for managing radioactive waste containing Tc.
• Iron-based materials offer potential for radionuclide remediation.

Purpose of the Study:

• To investigate the effect of nickel (Ni) doping on Tc sequestration.
• To understand the mineralogical and chemical transformations during Fe(OH)2(s) to iron spinel conversion.
• To characterize Tc and Ni speciation and distribution within the solid phases.

Main Methods:

• Synthesis of Ni-doped Fe(OH)2(s) and transformation to iron spinel under alkaline conditions.
• Solid characterization using X-ray diffraction (XRD).
• High-resolution microscopy (STEM-EDS, EELS) and focused ion beam (FIB) preparation for detailed phase analysis.
• Mass balance analysis for Tc removal efficiency.

Main Results:

• Iron spinel was the dominant mineral product; Ni did not incorporate into the spinel structure.
• Ni precipitated as Fe/Ni oxide/hydroxide particles, including metallic Ni phases.
• Tc was found in nanocrystals and a Tc-rich metallic phase, often encapsulated in Ni-rich nanoparticles with a core/shell structure.
• Nearly 100% Tc removal was achieved from 4.8 × 10⁻⁴ M Tc solutions.

Conclusions:

• Ni doping facilitates Tc sequestration through the transformation of Fe(OH)2(s) to iron spinel.
• Metallic Tc encapsulation within Ni-rich phases is a key mechanism for Tc removal.
• This process offers a promising alternative treatment pathway for technetium waste management.