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Phosphorus release from vivianite and hydroxyapatite by organic and inorganic compounds

Pedosphere 2020年第2期30卷 190-200页

作者： stella gypser Dirk FREESE Brandenburg University of Technology Cottbus-Senftenberg Faculty of EnvironmentProcess EngineeringBiotechnology and ChemistryDepartment of Soil Protection and RecultivationKonrad-Wachsmann-Allee 6Cottbus 03046Germany

Based on recent mining rates and the exhaustion of global phosphorus(P)reserves,there is a need to mobilize P already stored in soils,and its recovery from secondary resources such as Ca-and Fe-phosphates is *** Ca-phosphate hydroxyapatite forms a good fertilizer source,while vivianite is formed in waterlogged soils and *** sludge treatment,the formation of vivianite has been identified,being mainly ***-term P release from both hydroxyapatite and vivianite was studied using different inorganic(CaCl2 and CaSO4)and organic(citric and humic acid)reagents during batch *** CaCl2 and CaSO4 represent the soil solution,while citric and humic acids as organic constituents affect P availability in the rhizosphere and during the process of ***,the flow-through reactor(FTR)technique with an infinite sink was used to study the long-term P release *** cumulative P release was higher by organic acids than by inorganic *** cumulative P release rates were higher in the FTR with CaCl2 as compared to the batch *** infinite sink application caused a continuously high concentration gradient between the solid and liquid phases,leading to higher desorption rates as compared to the batch *** predominant amount of the total P released over time was available for a short *** inorganic anion exchange occurred at easily available binding sites,organic acids affected the more heavily available binding sites,which could be embedded within the mineral *** results showed that organic compounds,especially citric acid,play a superior role as compared to the inorganic constituents of the soil solution during the recovery of already stored P from the tertiary phosphates vivianite and hydroxyapatite.

关键词： anion exchange batch technique citric acid flow-through reactor humic acid ligand exchange phosphate phosphorus recovery

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Impact of crystalline and amorphous iron-and aluminum hydroxides on mechanisms of phosphate adsorption and desorption

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Journal of Environmental Sciences 2018年第8期30卷 175-189页

作者： stella gypser Florian Hirsch Anja M.Schleicher Dirk Freese Brandenburg University of Technology Cottbus-Senftenberg Faculty of Environment Process Engineering Biotechnology and Chemistry Department of Soil Protection and Recultivation Brandenburg University of Technology Cottbus-Senftenberg Faculty of Environment Process Engineering Biotechnology and Chemistry Department of Geopedology and Landscape Development German Research Centre for Geosciences Section 3.1 Inorganic and Isotope Geochchemistry

Fourier-transform infrared（FT-IR） spectroscopic experiments were carried out during phosphate adsorption on highly crystalline gibbsite, poorly crystalline 2-line-ferrihydrite and amorphous iron–aluminum–hydroxide mixtures in the molar ratio 1：0, 10：1, 5：1, 1：1, 1：5, 1：10 and 0：1. The OH stretching vibrational bands were utilized to analyze changes in structural and surface OH groups during adsorption, because the position of characteristic P／O vibrational bands can shift depending on reaction conditions, pH or adsorbed phosphate *** and desorption kinetics were studied at pH6 and different initial phosphate concentrations to achieve varying phosphate coverage on the mineral surfaces. For gibbsite the formation of AlHPO4 and Al2HPO4 can be assumed, while for ferrihydrite, a FeHPO4 or Fe2PO4 complex and the precipitation of FePO4 with longer equilibration time were ***2HPO4 or a Fe2PO4 surface complex was deduced for Fe-hydroxides, an AlH2PO4 surface complex was identified for Al-hydroxide, and both displayed either hydrogen bonds to neighboring hydroxyl groups or hydrogen bonds to outer-sphere complexes. Fe：Al-hydroxide mixtures with high Al ratios showed a low phosphate desorption rate, while ferrihydrite and the Fe：Al-hydroxide mixtures with high Fe ratios had almost negligible desorption rates. It was concluded that within the weakly associated amorphous FeO（OH） materials, FePO4 precipitated, which was bound by outer-sphere hydrogen bonds. With high Al ratios, desorption increased, which indicated weaker phosphate binding of both inner-sphere and outer-sphere complexes and hence, either no or minor quantities of precipitate. Ferrihydrite showed a more rigid structure and a lower extent of precipitation compared to amorphous Fe-hydroxide.

关键词： Phosphate Adsorption Desorption Surface complexation Precipitation FT-IR

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