Utilization of (Ca, Mg)-Zr phosphates adsorbents saturated by Cs⁺, Sr²⁺, Co²⁺ ions in NZP ceramic matrices

A novel approach to the utilization of (Ca, Mg)-Zr phosphate adsorbents saturated by Cs⁺, Sr²⁺, Co²⁺ ions was developed. The main stages include: (i) Cs⁺, Sr²⁺, Co²⁺ ions adsorption, (ii) the drying and shaping by cold pressing, (iii) the sintering. Metal ions leaching from the powder of the spent adsorbent were 0.2–26.5 % in distillation water (рН 4.0–10.0) and tap water, and increased to 6.4–68.2 % in seawater. Calcination of spent adsorbents at 1000 °C led to a decrease in Cs⁺, Sr²⁺, Co²⁺ ions leaching to less than 1.0 % in tap and seawater. The ceramic matrices with a Cs⁺, Sr²⁺, Co²⁺ content of 8.0–30.2 wt %, mechanical compressive strength of 2.9–260.9 MPa, leaching rate of 1.0×10⁻⁴ - 4.3×10⁻⁷ g/(cm²×day), density of 1.4–3.4 g/cm³ were obtained by cold pressing with subsequent sintering. The samples obtained at molar ratios Zr/(Ca+Mg) of 0.35 and 0.21 were characterized by the highest compressive strength and Cs⁺ and Sr²⁺, Co²⁺ leaching resistance, respectively. The obtained ceramic matrices fitted to the requirements of GOST R 50926–96 and NRC 1991 for solid high-level waste forms.