Production of magnetic biochar-steel dust composites for enhanced phosphate adsorption

In this study, a new low-cost magnetic composite comprising biochar-steel dust wastes was fabricated by the facile co-pyrolysis method at different proportions of steel dust wastes. The performance of the magnetic composite was investigated for the adsorption of phosphate from water. The physicochemical characteristics of the magnetic composite indicate an effective coupling of the steel dust into a biochar matrix leading to improved crystallinity, surface heterogeneity, and functional groups (C[dbnd]O, C[dbnd]C, and metal oxides). The proportion of the steel dust significantly influenced the adsorptive characteristics of the magnetic biochar-steel dust composite. The synergistic effect of the biochar and steel dust facilitated enhanced phosphate adsorption compared to the pristine biochar and steel dust. Pseudo-second order model well-described the kinetics of the phosphate adsorption, while the isotherm results showed better fitting with the Redlich Peterson model (R² > 0.999). The maximum monolayer adsorption capacity of 175.23 mg/g was achieved at pH 4, 240 min, and 25 °C, higher than many other similar magnetic adsorbents. The magnetic biochar composite exhibited excellent phosphate removal with just ~10% reduction in the presence of co-existing ions (SO₄²⁻, CO₃²⁻ and HCO₃⁻). The high reusability performance of the magnetic composite for up to five cycles implies that the composite possessed great potential for low cost and sustainable remediation of phosphate from water streams.