Preparation of Waste‐Derived Biochar Materials and their Application in Adsorptive Removal of Inorganic Phosphorus from Aqueous Solutions

Coconut coir (agricultural waste) and clam shells (seafood waste) are natural resources, and the comprehensive utilization of these wastes is an important aspect of environmental protection research. This study presents a circular‐economy strategy to valorize coconut coir and clam shells into CaO‐doped biochar (CCB) for phosphorus (P) removal and sustainable agriculture, addressing environmental pollution and waste management challenges. CCB was synthesized via pyrolysis at 650 °C using a 1:1 raw material mass ratio. scanning electron microscopy, Fourier transform infrared spectroscopy, and X‐ray diffraction characterize its morphology, chemistry, and structure. Batch experiments evaluate P adsorption at pH 6 (0.4 g L −1 dosage), modeled by pseudo‐second‐order kinetics and the Freundlich isotherm to assess mechanisms. CCB achieves a high P adsorption capacity (171.547 mg g −1 ), with chemisorption and heterogeneous interactions as dominant mechanisms. Beyond water treatment, CCB offers potential for slow‐release fertilizers, soil structure improvement, and fertility enhancement, demonstrating a dual‐purpose solution for waste recycling and sustainable nutrient management in agriculture.