{"title":"Precipitation of NH4UO2PO4·3H2O—Solubility and Structural Comparison with Alkali Uranyl(2 +) Phosphates","authors":"M. Marković, N. Pavković, N. Pavković","doi":"10.6028/jres.093.148","DOIUrl":null,"url":null,"abstract":"Precipitates formed in the system UO2(NO3)2-NH4OH-H3PO4-H2O, aged for 30 days at 298 K, were studied. The precipitates were characterized by chemical and thermogravimetric analyses, x-ray powder diffraction, infrared spectroscopy, polarized light microscopy, and by their fluorescent properties. The precipitation boundary was established tindallometrically and microscopically. On the basis of these measurements, the stability conditions, structural parameters, and solubility of the tetragonal polymorph of NH4[UO2PO4]·3H2O were determined. This compound shows a close structural relationship with H3O[UO2PO4]·3H2O (space group P4/ncc) and alkali uranyl(2+)phosphates polyhydrates M[UO2PO4]·nH2O (n =4 for M=Li; n =3 for M=Na, K, Rb and n =2.5 for M=Cs). The unit-cell dimensions determined for NH4UO2PO4·3H2O are: a=b=7.02 Å, c=18.08 Å (P4/ncc). The thermodynamic solubility product constant, Ks=a(NH4+)×a(UO22+)×a(PO43−), for NH4UO2PO4·3H2O was determined: log Ks= −26.50±0.09. The Ks values of M[UO2PO4]·n H2O (at ionic strength, I=0.23 mol dm−3) calculated from previously published experimental data by using correct stability constants of uranyl(2+)phosphate complexes are: log Ks=−22.61±0.08 for M=Na; log Ks= −23.92±0.12 for M=K; log Ks= −24.13±0.19 for M=Rb; log Ks= −23.80±0.20 for M=Cs; and log Ks= −24.74±0.10 for M=NH4,showing that NH4UO2PO4·3H2O is less soluble than corresponding alkali uranyl(2+)phosphates.","PeriodicalId":17082,"journal":{"name":"Journal of research of the National Bureau of Standards","volume":"93 1","pages":"557 - 563"},"PeriodicalIF":0.0000,"publicationDate":"1988-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"16","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of research of the National Bureau of Standards","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.6028/jres.093.148","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 16
Abstract
Precipitates formed in the system UO2(NO3)2-NH4OH-H3PO4-H2O, aged for 30 days at 298 K, were studied. The precipitates were characterized by chemical and thermogravimetric analyses, x-ray powder diffraction, infrared spectroscopy, polarized light microscopy, and by their fluorescent properties. The precipitation boundary was established tindallometrically and microscopically. On the basis of these measurements, the stability conditions, structural parameters, and solubility of the tetragonal polymorph of NH4[UO2PO4]·3H2O were determined. This compound shows a close structural relationship with H3O[UO2PO4]·3H2O (space group P4/ncc) and alkali uranyl(2+)phosphates polyhydrates M[UO2PO4]·nH2O (n =4 for M=Li; n =3 for M=Na, K, Rb and n =2.5 for M=Cs). The unit-cell dimensions determined for NH4UO2PO4·3H2O are: a=b=7.02 Å, c=18.08 Å (P4/ncc). The thermodynamic solubility product constant, Ks=a(NH4+)×a(UO22+)×a(PO43−), for NH4UO2PO4·3H2O was determined: log Ks= −26.50±0.09. The Ks values of M[UO2PO4]·n H2O (at ionic strength, I=0.23 mol dm−3) calculated from previously published experimental data by using correct stability constants of uranyl(2+)phosphate complexes are: log Ks=−22.61±0.08 for M=Na; log Ks= −23.92±0.12 for M=K; log Ks= −24.13±0.19 for M=Rb; log Ks= −23.80±0.20 for M=Cs; and log Ks= −24.74±0.10 for M=NH4,showing that NH4UO2PO4·3H2O is less soluble than corresponding alkali uranyl(2+)phosphates.