Cold sintering of ammonium phosphomolybdate ((NH₄)₃PMo₁₂O₄₀·xH₂O) as soild-state matrices for cesium immobilization

Ammonium phosphomolybdate (APM) is often used for the adsorption of Cs⁺. However, the decomposition temperature of cesium-containing ammonium phosphomolybdate waste is low and difficult to dispose of. This study introduces the first use of cold sintering to solidify ammonium phosphomolybdate monomers at low temperatures. The maximum adsorption capacity of the synthesized ammonium phosphomolybdate was 112.58 mg/g. Cold sintering results indicate that the HNO₃ was more effective than other acidic or salt solutions for densifying ammonium phosphomolybdate. The optimal conditions for cold sintering were 200 °C, 500 MPa, 10 wt% HNO₃, and 10 min. The cold-sintered Cs-ammonium phosphomolybdate ceramic exhibited impressive compressive strength (624.7 MPa), Vickers microhardness (165.2 HV) and relative density of (97.61 %). The Cs leaching rate of Cs-ammonium phosphomolybdate ceramics was as low as 7.38 × 10^-5 g m^-2·d^-1 after measured at 90 °C for 7 days.