Eco-friendly utilization of phosphate-modified oyster shell for efficient arsenic adsorption

Abstract

Arsenic contamination in aquatic systems, especially from acid mine drainage, poses severe environmental and health risks due to the toxicity and mobility of arsenate (As(V)). In this study, oyster shell waste was valorized into phosphate-modified oyster shells (PMOS) as an eco-friendly and low-cost adsorbent for As(V) removal. PMOS was prepared through thermochemical treatment followed by phosphate functionalization, and its adsorption behavior was systematically investigated under different conditions. The results showed that As(V) removal efficiency strongly depended on pH, contact time, initial concentration, and adsorbent dosage, with optimal performance (~95% removal) achieved at pH 3÷ 7, a dosage of 1.0÷ 1.5 g/L, and equilibrium reached within 100 min. Kinetic analysis confirmed that the process followed a pseudo-second-order model, indicating chemisorption as the dominant mechanism, while isotherm studies revealed the Freundlich model provided the best fit, with a maximum adsorption capacity (qmax) of 46.34 mg/g. Structural characterization confirmed the successful incorporation of phosphate groups, enhancing affinity for arsenate through electrostatic attraction, ion exchange, and surface complexation. Importantly, reusability tests demonstrated that PMOS maintained more than 80% of its removal efficiency even after five adsorption–desorption cycles, confirming its regeneration stability. These findings highlight PMOS as a promising, sustainable, and cost-effective material for arsenic remediation in acid mine drainage-impacted waters while simultaneously contributing to circular economy strategies through aquaculture waste valorization.