Nonlinear sorption of phosphorus onto plant biomass-derived biochars at different pyrolysis temperatures

Aside the characterization of feedstocks and biochars (BCs), the nonlinear sorption of phosphorus (P) onto corn cob (CC), rice husk (RH), cocoa pod husk (CP) and palm kernel shell (PK) BCs charred at 300, 450 and 650 °C were investigated using series of batch experiments. Conversion of feedstock to BC resulted in a higher pH, C content, ash, fixed C, surface area (SA) and lower volatile matter, moisture, H, N, O and S contents. Increasing pyrolysis temperature proportionally decreased the polarity (O/C, O+N/C, and O+ N+ S/C), volatile matter, moisture content, readily labile organic C and potentially unstable C vis-à-vis an increased in C content, fixed C, stable C and aromaticity (H/C). The nonlinearity index (n) as well as P sorption capacity (K_F) increased with temperature and were highly dependent on BC properties. Significant linear relationships were observed between P sorption parameters (n and K_F) and O content, polarity, aromaticity, fixed C, stable C, readily labile organic C and SA. The low polarity and high aromaticity and SA resulted in the high nonlinear sorption of P at 650 °C. Findings of this study provides insight into P sorption behaviour, thereby serving as a theoretical basis for biochar application either agronomically or environmentally.