Lanthanum orthophosphate with the monazite structure was proposed on examinations as a suitable matrix for immobilization of future americium-containing liquid wastes, which could be formed in conversion of metallic plutonium into oxide at PA “Mayak.”

Specimens of monazite non-active ceramics were fabricated from LaPO4 powders obtained using a thin-film evaporator by either hot-pressing or cold-pressing and sintering at 900–1300 °C. According to electron microprobe analysis (EMPA), scanning electron microscopy (SEM), and X-ray diffraction (XRD), which were used for characterization of produced samples, all specimens did not contain any phase other than the monoclinic monazite phase. Ceramics having the specific activity of Am-241 2.13×107 Bq/g were prepared by only cold-pressing with subsequent sintering at 1300°C during 1 hour. The normalized leach rates of lanthanum and americium in distilled water at 90°C were less than 1.2×10−4 and 2.3 10−4 g/m2×day, respectively.

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