Goethite dispersed corn straw-derived biochar for phosphate recovery from synthetic urine and its potential as a slow-release fertilizer

In this study, goethiete (alpha-FeOOH) -biochar (BC) composites were successfully developed from a coprecipitation reaction under alkaline conditions (pH = 11.93) and used as the adsorbent for phosphate recovery from urine. The morphology and crystallinity of alpha-FeOOH-BC composites were characterized by scanning electron microscopy and X-ray diffraction. alpha-FeOOH loaded BC was found to be amorphous. This may be caused by the Si residue in BC. The Elovich model and the Langmuir model fit better to the kinetic and isotherm results of alpha-FeOOH-600BC, respectively, indicating that phosphate adsorption is mainly a chemisorption and monolayer adsorption process. The alpha-FeOOH-600BC with amorphous structure showed higher adsorption capacity than crystalline alpha-FeOOH, and the maximum phosphate sorption capacity reached 57.39 mg g(-1). Additionally, the extractable phosphate of this material was approximately 967.5 mg P.kg(-1) suggesting the alpha-FeOOH-600BC after adsorption could be a promising alternative as a slow-phosphate-release fertilizer. Fourier-transform infrared and X-ray induced photoelectron spectroscopy results showed that the active sites of the adsorption of phosphate were the Fe-OH bonds that formed inner-sphere complexes (Fe-O-P). (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

In this study, goethite-biochar composites were developed and used for phosphate recovery from urine. The amorphous structure of the composites showed higher adsorption capacity compared to crystalline goethite, making it a promising alternative for slow-phosphate-release fertilizers. The active sites for phosphate adsorption were identified as the Fe-OH bonds forming inner-sphere complexes.