Calcium-borosilicate glass-ceramics wasteforms to immobilize rare-earth oxide wastes from pyro-processing

Glass-ceramics containing calcium neodymium(cerium) oxide silicate [Ca₂Nd_8-xCe_x(SiO₄)₆O₂] crystals were fabricated for the immobilization of radioactive wastes that contain large portions of rare-earth ions. Controlled crystallization of alkali borosilicate glasses by heating at T ≥ 750 °C for 3 h formed hexagonal Ca–silicate crystals. Maximum lanthanide oxide waste loading was >26.8 wt.%. Ce and Nd ions were highly partitioned inside Ca–silicate crystals compared to the glass matrix; the rare-earth wastes are efficiently immobilized inside the crystalline phases. The concentrations of Ce and Nd ions released in a material characterization center-type 1 test were below the detection limit (0.1 ppb) of inductively coupled plasma mass spectroscopy. Normalized release values performed by a product consistency test were 2.64·10⁻⁶ g m⁻² for Ce ion and 2.19·10⁻⁶ g m⁻² for Nd ion. Results suggest that glass-ceramics containing calcium neodymium(cerium) silicate crystals are good candidate wasteforms for immobilization of lanthanide wastes generated by pyro-processing. - Highlights: • Glass-ceramic wasteforms containing Ca₂Nd_8-xCe_x(SiO₄)₆O₂ crystals were synthesized to immobilize lanthanide wastes. • Maximum lanthanide oxide waste loading was >26.8 wt.%. • Ce and Nd ions were highly partitioned inside Ca–Nd–silicate crystals compared to glass matrix. • Amounts of Ce and Nd ions released in the material characterization center-type 1 were below the detection limit (0.1 ppb). • Normalized release values performed by a PCT were 2.64• 10⁻⁶ g m⁻² for Ce ions and 2.19• 10⁻⁶ g m⁻² for Nd ions.