Recovering phosphorus from aqueous solutions using water hyacinth (Eichhornia crassipes) toward sustainability through its transformation to apatite

Abstract This work provides circular leveraging strategies for using water hyacinth (Eichhornia crassipes) (WH) in the removal and recovery of phosphorus (P) from aqueous solutions. This study also assesses the transformation of the adsorbed phosphorus into a high value-added product (apatite) and its potential as a soil amendment. The materials evaluated were recovered from WH calcination at temperatures ranging between 350 °C and 700 °C, which evidenced great amounts of Ca(OH)2, MgO, Al2O3, and Ca5(PO4)3OH. The material that evidenced highest P removal capabilities was CWH-650, which was produced from calcination at 650 °C; hence, it was used during the P adsorption process. The results showed that chemisorption is the limiting step in the adsorption process, with a maximum adsorption capacity determined by its adaptation to the Langmuir model at 21.21 mg P/g. Likewise, the study determined that the exchange of ligands followed by precipitation in the apatite formation process were the dominant mechanisms during the adsorption process. An additional calcination step conducted on the CWH-650 adsorbent previously used in the removal of P denoted an increase in the amount of apatite (up to 41.0%), as demonstrated through Fourier-transform infrared spectroscopy and X-ray diffraction analysis. Subsequently, this study concluded that the Ca- and P-enriched phases exhibited a higher solubility of P in 2% formic acid than in deionized water, which fostered the release of up to 60 mg P/g, indicating its potential use as a phosphate fertilizer and an acid-soil amendment.