Calcium silicate solid-state matrices from boric acid production waste for ⁶⁰Co removal and immobilization by spark plasma sintering

A mesoporous adsorbent based on calcium silicate CaSiO3 for the removal and immobilization of cobalt Co-60 radionuclides in durable ceramic CaCoSi2O6 matrices was synthesized by hydrothermal conversion of boric acid production waste. The obtained material had a high Co2+ ions adsorption capacity of 220.8 mg/g. Cobalt adsorption was carried out mainly by ion exchange, which led to the formation of CaCoSi2O6 precursor ceramic matrices. The use of spark plasma sintering (SPS) technology at an optimal temperature of 1000 degrees C allowed the safe immobilization of Co2+ ions in CaCoSi2O6 ceramic matrices characterized by density (3.33 g/cm(3)), compressive strength (481 MPa) and microhardness (similar to 9.81 GPa). Sintered CaCoSi2O6 ceramic samples were characterized by high hydrolytic stability (cobalt leaching rate R-Co similar to 10(-7) g/(cm(2) x day)) and complied with the requirements for cured highly active waste GOST R 50926 96/ANSI/ANS 16.1.