Adsorption of phosphate ions from aqueous solution using malted sorghum mash-derived hydrochar

The excessive use of phosphorus-based fertilizers has led to elevated concentrations of phosphate ions (PO₄ 3− ) in aquatic systems, contributing to eutrophication. This study investigates the potential of malted sorghum mash-derived hydrochar (MSMDH) to adsorb PO₄ 3− from aqueous solutions. Hydrochar produced at 210 °C exhibited a bulk density of 276.95 ± 1.0 kg/m 3 and a yield of 72.06 ± 0.25%. The adsorbent (MSMDH) was characterized by a pH of 4.01 ± 0.006, a point of zero charge (pHpzc) of 2.5, electrical conductivity of 193.30 ± 1.69 μS/cm, fixed carbon content of 20.74 ± 0.58%, and cation exchange capacity of 27.688 cmol/kg. Scanning Electron Microscopy (SEM) and Fourier Transform Infrared (FTIR) analyses revealed a porous structure with hydroxyl, carboxylate, and carbonyl functional groups. Adsorption experiments evaluated the effects of pH, dosage, temperature, initial concentration, and contact time. Optimal PO₄ 3− removal occurred at pH 6 with 1.0 g/L of adsorbent, achieving a maximum adsorption capacity of 95.69 mg/g. Isotherm data conformed to the Langmuir model, indicating monolayer adsorption. Kinetic studies showed that adsorption followed a pseudo-second-order model rather than intraparticle diffusion. Thermodynamic parameters confirmed the endothermic nature of the process, with physisorption and spontaneous ion exchange mechanisms. Compared to other adsorbents, MSMDH demonstrated superior performance, suggesting its viability for efficient phosphate removal from contaminated water.