Hydrothermal synthesis of hydroxyapatite and pollucite from calcium phosphate

Conference · Sun Dec 31 04:00:00 EST 1995

OSTI ID:382853

Kaneko, Masaaki; Shoji, Yuichi; Matsuura, Hiroyuki ^[1]; Yamasaki, Nakamichi ^[2]

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1. Toshiba Corp., Kawasaki (Japan)
2. Kochi Univ. (Japan)

One of the methods of recovering uranium and plutonium in reprocessing plants is solvent extraction. Usually, TBP (tributyl phosphate: 2(C{sub 4}H{sub 9}O){sub 3}PO)/n-dodecane mixture has been used in such a solvent extraction process. Spent solvent premixed with calcium hydroxide (Ca(OH){sub 2}) is supplied to the pyrolysis reactor, where the TBP thermally decomposes and reacts with Ca(OH){sub 2} to form a powder of calcium phosphate. This powder consists of calcium pyrophosphate (Ca{sub 2}P{sub 2}O{sub 7}) and calcium metaphosphate (Ca(PO{sub 3}){sub 2}). It is desirable that these phosphates should be converted into the stable structure of hydroxyapatite and the radioactive materials should be immobilized into a stable compound which is highly durable, in order to maintain long-term radioactive waste stability. Hydroxyapatite (HAP:Ca{sub 10}(PO{sub 4}){sub 6}(OH){sub 2}) and aluminosilicate were easily synthesized using a hydrothermal process with mixing ratios of Ca/P = 1.67 (Ca(PO{sub 3}){sub 2} and Ca(OH){sub 2}) and Si/Al = 4 (SiO{sub 2} and Al(OH){sub 3}). The temperature was kept constant at 573 K for 60 minutes. Cesium (Cs) and Cerium (Ce) contained in Ca(PO{sub 3}){sub 2}, were found to take on a stable form in the pollucite (CsAlSi{sub 2}O{sub 6}) structure and the monazite (CePO{sub 4}) structure.

• OSTI ID: 382853
• Report Number(s): CONF-941075--; ISBN 1-55899-253-7
• Country of Publication: United States
• Language: English

Related Subjects

05 NUCLEAR FUELS
36 MATERIALS SCIENCE
ALPHA-BEARING WASTES
AMERICIUM
APATITES
CERIUM
CESIUM
CRYSTAL STRUCTURE
HYDROTHERMAL SYNTHESIS
LEACHING
NEPTUNIUM
PLUTONIUM
POLLUCITE
RADIOACTIVE WASTE PROCESSING
SIMULATION
WASTE FORMS
X-RAY DIFFRACTION