Biochar-supported natural zeolite composite for recovery and reuse of aqueous phosphate and humate: Batch sorption–desorption and bioassay investigations

Abstract The incomplete inert nature of engineered biochar and the low desorbability/recyclability of its disposals are still questionable. Herein, water hyacinth biochar-supported natural zeolite (ZB) was compared with the original biochar (OB) on the recovery and reuse of aqueous phosphate and humate under batch sorption–desorption experiments. In addition, the potential reuse of the exhausted biochar on ameliorating nutrient supply potentials of sandy soil was investigated using a bioassay on early-growth seedlings. Physicochemical analysis revealed the successful functionalization of ZB and improving its thermal stability. Physisorption and chemisorption forces participated mutually in sorption process. In this regard, precipitation mechanism showed a high contribution for chemisorption of phosphate into brushite and hydroxylapatite minerals. The calculated q m a x values of Langmuir model showed the lower affinity of ZB to phosphate and humate compared to OB due to lowering/vanishing of amine functional groups and the dramatic reduction in specific surface area through cover/clog of micro-and meso-pores by zeolite fine particles. However, phosphate desorbability from ZB was significantly higher than OB suggesting its higher renewability potentials. The exhausted biochar additives (particularly ZB-loaded phosphate and humate) stimulated plant biomass yield, photosynthetic pigments and nutrients uptake by arugula seedlings. Furthermore, the residual effect of these additives on stimulating the aforementioned parameters of the successive maize seedlings confirmed the higher phytoavailability and usability of ZB-loaded additives. The high thermal stability and desorbability of natural zeolite, therefore, support its potentiality to improve stability and recyclability of engineered biochar.