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Analysis of ion exchange phenomena occurring in silicate glasses immersed in a molten salt bath
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A. Mamo, T.G. Heeb, and K.S. Knaebel, Ohio State University, Columbus, OH, U.S.A.: Equilibrium and Diffusion Rate Effects of Univalent and Divalent Ions in a Bifunctional Resin Many applications of bifunctional resins involve multiple salts comprised of univalent and divalent species. Previous work has been devoted almost exclusively to single salts, usually sodium chloride. The present work describes the effects of differing affinities of NaCI, Na2SO 4 and CaSO4 in Amberlite XD-5. Equilibrium studies conducted with the individual salts and with these salts have identified the extent of affinity differences at 25 and 95°C. The equilibrium isotherms are represented by an additive combination of the Langmuir form with the linear form. The slopes of the linear component were positive, zero, and negative for the various species. This dependence is apparently due to the effect of ionic strength on the ultimate capacity and relative affinity. Rate studies conducted with individual salts have yielded effective diffusivities and pore fluid diffusivities, for temperatures between 25 and 35°C. The effective diffusivities of the species are described by Fick's law for specific linearized portions of the respective isotherms. The measured pore fluid diffusivities are about one quarter of the values in bulk solution.
G. Battaglin, M. Berti, G. Della Mea, P. Mazzoldi, and M. Guglielmi, Unita GNSM-CNR, Padova, Italy: Analysis of Ion Exchange Phenomena Occurring in Silicate Glasses Immersed in a Molten Salt Bath When a glass is immersed in a molten salt bath, ions move in and out of the glass via an ion exchange mechanism occurring at the glass/salt interface. If the exchange is carried out at a temperature well below the glass transition, the network of the glass cannot adjust to the different sizes of the exchanging ions and the result is the appearance of stresses. If the salt bath ions are larger than the host in the glass, a compression layer is formed at the surface of the glass, highly increasing its technological strength. In the present work we investigated the N a + ~ K ÷ and L i + ~ K ÷ exchange processes in silicate glasses with per cent molar composition: 80.7 SiO2, 4.2 AI203, 15.1 NazO, and 67.9 SiO2, 9.2 A1203, 22.9 Li20, respectively, immersed in a molten KNO 3 bath at the temperature of 380°C. Exchange times varied between 15 s and 8 h. Samples were analysed with a non-destructive nuclear technique: the Rutherford backscattering of 1.8 MeV 4He + ions. Such a technique allows the determination of the depth concentration profiles of the detected elements with a depth resolution lower than 30 nm. Results of the two exchanges differ markedly. From our own, as well as from literature results it appears that if the ratio of the ionic radius of the cation of the salt to the ionic radius of the mobile cation of the host matrix is lower than about 1.5, an error function-like diffusion profile is observed, but when such a ratio is higher than about 1.5, the formation of a plateau in the diffusion profile is detected. Finally we also observed that the surface K concentrations after very long exchange times are lower than the initial concentrations of Na or Li ions in the untreated glasses.
L. Liberti, G. Boari, N. Limoni, G. Longobardi, and R. Passino, Istituto di Ricerca Sulle Acque, Bari, Italy: The R I M - N U T Process for Removal and Recovery of N - P Fertilizer From Sewage: Start-Up of Bari's Plant The R I M - N U T process, aimed primarily at preventing eutrophication phenomena associated with excessive concentration of N and P derivatives in conventionally treated biological effluents, employs the natural zeolite clinoptilolite and a strong-base macroporous resin to remove selectively both species from effluents. From resin regeneration, performed with a 0.6 M neutral NaC1 solution, a fractional precipitation procedure permits quantitative recovery of ammonium and phosphate ions as a slow-release, premium quality fertilizer (MgNH4PO4) from the eluates, which can then be recycled for further regeneration. After successful evaluation of the process in a fully automatic laboratory plant, which treated the secondary effluent from the town of Bisceglie, with full recycle of eluates, the characteristics and initial operation results of a 250 m3/day demonstration plant, whose construction in Bari's Sanitary Station was terminated in April 1982, are presented.
A. Mamo, T.G. Heeb, and K.S. Knaebel, Ohio State University, Columbus, OH, U.S.A.: Equilibrium and Diffusion Rate Effects of Univalent and Divalent Ions in a Bifunctional Resin Many applications of bifunctional resins involve multiple salts comprised of univalent and divalent species. Previous work has been devoted almost exclusively to single salts, usually sodium chloride. The present work describes the effects of differing affinities of NaCI, Na2SO 4 and CaSO4 in Amberlite XD-5. Equilibrium studies conducted with the individual salts and with these salts have identified the extent of affinity differences at 25 and 95°C. The equilibrium isotherms are represented by an additive combination of the Langmuir form with the linear form. The slopes of the linear component were positive, zero, and negative for the various species. This dependence is apparently due to the effect of ionic strength on the ultimate capacity and relative affinity. Rate studies conducted with individual salts have yielded effective diffusivities and pore fluid diffusivities, for temperatures between 25 and 35°C. The effective diffusivities of the species are described by Fick's law for specific linearized portions of the respective isotherms. The measured pore fluid diffusivities are about one quarter of the values in bulk solution.
G. Battaglin, M. Berti, G. Della Mea, P. Mazzoldi, and M. Guglielmi, Unita GNSM-CNR, Padova, Italy: Analysis of Ion Exchange Phenomena Occurring in Silicate Glasses Immersed in a Molten Salt Bath When a glass is immersed in a molten salt bath, ions move in and out of the glass via an ion exchange mechanism occurring at the glass/salt interface. If the exchange is carried out at a temperature well below the glass transition, the network of the glass cannot adjust to the different sizes of the exchanging ions and the result is the appearance of stresses. If the salt bath ions are larger than the host in the glass, a compression layer is formed at the surface of the glass, highly increasing its technological strength. In the present work we investigated the N a + ~ K ÷ and L i + ~ K ÷ exchange processes in silicate glasses with per cent molar composition: 80.7 SiO2, 4.2 AI203, 15.1 NazO, and 67.9 SiO2, 9.2 A1203, 22.9 Li20, respectively, immersed in a molten KNO 3 bath at the temperature of 380°C. Exchange times varied between 15 s and 8 h. Samples were analysed with a non-destructive nuclear technique: the Rutherford backscattering of 1.8 MeV 4He + ions. Such a technique allows the determination of the depth concentration profiles of the detected elements with a depth resolution lower than 30 nm. Results of the two exchanges differ markedly. From our own, as well as from literature results it appears that if the ratio of the ionic radius of the cation of the salt to the ionic radius of the mobile cation of the host matrix is lower than about 1.5, an error function-like diffusion profile is observed, but when such a ratio is higher than about 1.5, the formation of a plateau in the diffusion profile is detected. Finally we also observed that the surface K concentrations after very long exchange times are lower than the initial concentrations of Na or Li ions in the untreated glasses.
L. Liberti, G. Boari, N. Limoni, G. Longobardi, and R. Passino, Istituto di Ricerca Sulle Acque, Bari, Italy: The R I M - N U T Process for Removal and Recovery of N - P Fertilizer From Sewage: Start-Up of Bari's Plant The R I M - N U T process, aimed primarily at preventing eutrophication phenomena associated with excessive concentration of N and P derivatives in conventionally treated biological effluents, employs the natural zeolite clinoptilolite and a strong-base macroporous resin to remove selectively both species from effluents. From resin regeneration, performed with a 0.6 M neutral NaC1 solution, a fractional precipitation procedure permits quantitative recovery of ammonium and phosphate ions as a slow-release, premium quality fertilizer (MgNH4PO4) from the eluates, which can then be recycled for further regeneration. After successful evaluation of the process in a fully automatic laboratory plant, which treated the secondary effluent from the town of Bisceglie, with full recycle of eluates, the characteristics and initial operation results of a 250 m3/day demonstration plant, whose construction in Bari's Sanitary Station was terminated in April 1982, are presented.