Strong Immobilization of Phosphate in Wastewater onto the Surface of MgO-Modified Industrial Hemp-Stem-Driven Biochar by Flowerlike Crystallization

Removal of phosphate in wastewater is significant and available to control eutrophication, and adsorption is one of the most promising treatment methods. In this work, MgO-modified industrial hemp-stem-driven biochar was formed by in situ precipitation. Different from the adsorption behavior for phosphate using other adsorbents, the doped MgO nanoparticles onto the holes of biochar have been combined with phosphate to form stable crystal substances, e.g., the flowerlike Mg-x(PO4)(y)center dot zH(2)O. The results showed that, during the phosphate removal process, amorphous, single crystal, and polycrystal compounds were formed by ionic bonding and crystallization effect, which could be good for strong immobilization of the phosphate ions onto the surface of biochar. The characterization adsorbent results further confirmed that the carbonization condition also has an impact on the specific surface area of biochar and crystalline performance of MgO, and it affected the adsorption capacity of phosphate. The maximum adsorption capacity of phosphate was 233 mg/g with the Langmuir isotherm model, and the optimal pH value of adsorption was 9. Adsorption thermodynamics and kinetics results indicated that the adsorption process of phosphate was considered spontaneous, monolayer, and chemical sorption. MgO/biochar was highly selective for phosphate through studying the adsorption effect of other anions on phosphate. This application of low-cost hemp stalk provides a suitable method for disposal and a high-value utilization of corresponding agricultural wastes.