Effect of pyrolysis temperature on phosphate adsorption characteristics and mechanisms of crawfish char.

The purpose of this study was to investigate the characteristics of crawfish char (CFC) derived at different pyrolysis temperature and to evaluate its adsorption characteristics on phosphate. Phosphate adsorption by CFC occurred rapidly at the beginning of the reaction, and the time to reach equilibrium was dependent on the pyrolysis temperature. Maximum adsorption capacities of phosphate by CFC at different pyrolysis temperatures were high in order of CFC800 (70.9 mg/g) > CFC600 (56.8 mg/g) > CFC400 (47.2 mg/g) ≫ CFC200 (9.5 mg/g) ≈ uncharred crawfish feedstock (CF) (7.1 mg/g). Spectroscopic analyses using SEM-EDS and FTIR showed that the phosphate present in the CFC itself was associated with carbon, while the phosphate adsorbed on the CFC was closely related to calcium. The adsorption of phosphate by CFC is dominantly affected by pH. Phosphate adsorption of CFC600 primarily occurred at acid and neutral pH which is related to dissolved calcium from surface and phosphate hydrolysis product (H2PO4-), while phosphate adsorption of CFC800 mainly took place at alkaline pH, with precipitation mechanism between PO43- and calcium dissolved from free CaO and Ca(OH)2. Overall, CFC derived at pyrolysis temperatures above 400 °C is effective for waste reduction and phosphate treatment in wastewater.