Influence of Pre‐Pyrolysis Drying Methods on the Physicochemical Properties of Conocarpus erectus Biochar and Its Adsorptive Performance for Heavy Metal Removal

ABSTRACT

This study investigated the effect of pre‐pyrolysis drying methods on the yield, physicochemical properties, and heavy metal adsorption performance of biochar produced from Conocarpus erectus woody biomass. Biomass was subjected to oven drying (100°C, 24 h), sun drying (7 days), and indoor air drying (14 days), followed by slow pyrolysis at 350°C–400°C. Sun‐dried biomass produced biochar with the highest yield (22.17 ± 1.26%), porosity (80.00 ± 1.45%), surface area (60.95 ± 1.34 m ² /g), cation exchange capacity (20.85 ± 0.38 mol/kg, and water‐holding capacity (24.90 ± 0.36 g/g), whereas air‐dried biochar exhibited the most compact structure and lowest functionalization. Batch adsorption experiments using showed strong pH dependence with maximum adsorption capacities for sun‐dried biochar at pH 6.0 of 22.7, 21.5, and 17.1 mg/g for Pb (II), Cu (II), and Cd (II, respectively at 5 g/L adsorbent dose, removal efficiencies reached approximately 100% for Pb(II), 92%–95% for Cu(II), and 77%–81% for Cd(II). Equilibrium data were best described by the Langmuir isotherm, with maximum monolayer capacities for sun‐dried biochar at 40°C of 20.1, 18.6, and 16.6 mg/g for Pb(II), Cu(II), and Cd(II), respectively, while adsorption kinetics followed the pseudo‐second‐order model. Thermodynamic analysis revealed negative ΔG° and positive ΔH° and ΔS°, confirming that adsorption was spontaneous, endothermic, and entropy‐driven. Overall, pre‐pyrolysis sun drying emerged as an effective, low‐cost strategy to enhance both agronomic and environmental functionality of Conocarpus ‐derived biochar for use in tropical and arid regions.