Production of new fertilizers by combining distiller's grains waste and wet-process phosphoric acid: Synthesis, characterization, mechanisms and application

Abstract

In China, a large amount of distiller's grains produced by liquor production need to be effectively utilized. Herein, wet-process phosphoric acid was used to treat distiller's grains to achieve the material exchange between them. And water-soluble suspended fertilizer products with sufficient P2O5 (34.57%), N (7.31%), chelated trace elements (4.84%), amino acids (0.42%) and carbohydrates (2.73%) can be prepared by adding 8% EDTA (w: w) in the recovered phosphoric acid. High concentration, high Zeta potential (52.46 mV) and good thixotropy made it resistant to storage and transportation (>30 day). In addition, the residual solid residue capturing sufficient P, Fe, Al and Mg was pyrolyzed into biochar sustained-release phosphate fertilizer. TG-FTIR, in-situ DRAFTS, XRD, Raman, and SEM-EDS demonstrated that polyphosphates and biochar skeleton can be suitably synthesized simultaneously to achieve in situ binding at 400 °C. Long-term observation by ion chromatography showed that polyphosphate could be slowly released from the biochar structure and gradually converted to Ortho-P through hydrolysis reaction. In water, Ortho-P, Fe, Al and Mg can slowly release out from biochar fertilizer within 60 days, whose maximum release rates were 91.72%, 61.5%, 83.5% and 83.6%, respectively. It was confirmed that biochar structure was innovatively combined with polyphosphate to realize the slow-release characteristics and activate impurity ions to become microelement nutrients. This study proposed a clean production strategy to effectively utilize biomass waste residue, improve the utilization rate of phosphorus and impurity ions, and show the potential of carbon sequestration.