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Investigating reaction mechanisms of the solubilization of P from runoff sediments using low molecular weight organic acids
Ensuring that there continues to be a supply of phosphorus (P) is critical for continued food security into the later decades of the twenty-first century. P, which is currently a mined and nonrenewable resource, is used in agriculture to boost crop yields. The recovery of P from agricultural runoff sediment is currently seen as a potential new source of P for reuse in agriculture. Therefore, we propose the development of a phosphate solubilizing fungi (PSF)-mediated bioextraction process to recover P from agricultural runoff sediments. Aiding the development of the proposed process, this study determined the solubilization kinetics and speciation dynamics of the solubilization of P from runoff sediments using low molecular weight organic acids (LMWOAs) generated by PSF. The LMWOAs systems used in this study were 60 mM citric acid and a 60 mM mixture of oxalic acid and citric acid in a 2:1 molar ratio. Sediment from Woods Lake in Kalamazoo, Michigan was chosen due to the lake’s known eutrophic qualities. Kinetic and dynamic properties of the solubilization process was measured at five time points using previously determined optimal extraction process conditions. Solubilization kinetics and speciation dynamic results were used to gain a better understanding of system mechanisms. It was found that the citric acid reagent and the acid mixture reagent were able to solubilize P from sediment comparably. However, the mechanism of P solubilization was different between the two systems. The results imply that citric acid solubilized P through ligand-induced dissolution mechanism in both systems and oxalic acid solubilized P primarily through ligand exchange desorption mechanisms. In the future, the findings of this study will aid in the development of the proposed (PSF)-mediated bioextraction process by allowing the development of system models and process simulations.