Synthesis and Analysis of Hydroxyapatite as a slow-release, phosphorus-based fertilizer

• Lauren Sorrentino, Plant Science, University of Delaware

• Deb Jaisi, Plant and Soil Science, University of Delaware

Sorrentino, et. al

Synthesis and Analysis of Hydroxyapatite as a phosphorus based slow-release fertilizer 

Acknowledgements: Pavlo Ivanchenko and Deb Jaisi

Traditional fertilizers can boost phosphorus concentration in soil and increase crop yield, however, they have been proven to cause eutrophication and runoff. Eutrophication and runoff cause degraded water quality and imbalanced ecosystems. Previous studies have shown that hydroxyapatite can be used as a slow-release P-based fertilizer effectively decreasing eutrophication and runoff, however, requiring the enhancement of the dissolution. In this work, we aimed to increase hydroxyapatite dissolution rate by altering the synthesis’s pH (a set of materials was prepared at pH 10, 9, and 8). The prepared samples were analyzed with powder X-ray diffraction to ensure they exhibited HA crystal structure.  The dissolution rate of the hydroxyapatite samples was measured using a custom-made flow-through macro-dialysis cell. Acetic and Citrate buffers (pH 4.8, 0.01 M) were used and repeated twice per sample. buffer solution was filtrated through the material in a custom-made flow-through macro-dialysis cell at a pressure of 50 psi. The collected eluate was dripped into a series of vials at equal volume points (i.e. 80 microliters per vial).  pH probing of the collected eluates witnessed a consistent dissolution procedure. Thermogravimetric analysis was used to determine the amount of citrates and acetates present (as detected by FTIR spectroscopy)  in each residual solid sample post-dissolution. Comparing dissolution with acetate buffer and citrate buffer, the efficiency of citrate buffer to remove phosphates is much higher in all cases. In reality, citrate buffer would be much more beneficial for plants than acetate buffer   Overall, our experiment showed that there is potential for the use of hydroxyapatite in slow-release P fertilizer.