@phdthesis{Gypser2019, author = {Gypser, Stella}, title = {Identification of phosphate adsorption mechanisms on Fe- and Al-hydroxides and the influence of inorganic and organic compounds to reduce long-term phosphorus fixation on mineral surfaces}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:co1-opus4-51311}, school = {BTU Cottbus - Senftenberg}, year = {2019}, abstract = {With regard to the depletion of global phosphorus reserves and with the aim of ensuring sustainable soil fertility on agricultural soils, a fundamental understanding of mechanisms of fixation and mobilization of inorganic phosphorus in soils is required. Amongst others, phosphorus availability is affected by ad- and desorption reactions on pedogenic Fe- and Al-hydroxide surfaces. The characterization of phosphate binding on those contrasting mineral surfaces can help to find solutions for enhancing the mobilization of fertilized but not available soil inorganic phosphate. Fourier-transform infrared spectroscopic experiments were carried out during phosphorus adsorption on crystalline gibbsite, poorly crystalline 2-line-ferrihydrite and amorphous Fe:Al-hydroxide mixtures. Desorption experiments with CaCl₂, CaSO₄, citric acid (C₆H₈O₇), and humic acid (C₉H₉NO₆) were conducted to determine the capacity of phosphate fixation and mobilization in short- and long-term. Additionally, phosphorus release from the Fe- and Ca-phosphates vivianite and hydroxyapatite were analyzed. 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 observed. Fe₂HPO₄ or a Fe₂PO₄ surface complex was deduced for amorphous Fe-hydroxides, an AlH₂PO₄ surface complex was identified for Al-hydroxides. The weakly associated amorphous FeO(OH) molecules enhance the precipitation of FePO₄. With high Al content, a weaker phosphate binding of both inner- and outer-sphere complexes and either no or minor quantities of precipitate were formed. Ferrihydrite showed a more rigid structure and a lower extent of precipitation compared to amorphous Fe-hydroxide. The cumulative phosphorus desorption followed the order CaCl₂ < CaSO₄ < humic acid < citric acid for crystalline and amorphous Fe- and Al-hydroxides as well for vivianite and hydroxyapatite. While inorganic anion exchange took part at easily available binding sites and fast exchangeable phosphorus, organic acids additionally affect the more heavily available binding sites and slow exchangeable phosphorus. For humic acid, the accumulation of metal-organic complexes in the desorption solution was suggested, whereas for citric acid the dissolution of the minerals was maintained. The cumulative release rates of the Flow-Through-Reactor setup were higher compared to batch due to a short residence time and a continuous concentration gradient. This could lead either to an over- or underestimation of the available phosphorus pools and influenced the comparability of both methods.}, subject = {Phosphorus; Adsorption/Desorption kinetics; FT-IR; Hydroxides; FTR; Phosphor; Adsorptions-/Desorptionskinetik; Hydroxide; Adsorptionskinetik; Desorptionskinetik; Hydroxide; Phosphor; Bodenfruchtbarkeit}, language = {en} }