Sorption, kinetics and thermodynamics of phosphate sorption onto soybean stover derived biochar

Phosphorus (P) is one of the main sources of eutrophication of water bodies creating ecological problems. Biochar prepared from agricultural waste materials can be used as a potential adsorbent for removing P from waste streams. In the present investigation biochar produced from soybean stover pyrolysed at 700 °C was tested for aqueous P removal in a batch type reactor at different temperatures and solution pHs. The sorption process was evaluated through various isotherms, kinetics models and thermodynamic parameters. It was observed that with an equilibrium time of 24 h, up to 95% of P was removed from water at a temperature of 40 °C at pH 5.5. The sorption experimental data were studied through both Langmuir and Freundlich models and the Langmuir adsorption maximum (Q_m) values were 90.90 and 75.75 mg/g at pH 5.5 and 8.5, respectively while the Freundlich equilibrium constant (K_f) values were 4.67 and 4.36 mg/g at pH 5.5 and 8.5, respectively. The rate of adsorption confirmed to follow pseudo-second order kinetics with a better correlation. The thermodynamic parameters predicted that the adsorption process is an endothermic and spontaneous process.