Sustainable biosorptive recovery of Mn2+ from low grade manganese ore leachate using NaOH activated Artocarpus heterophyllus seed derived biosorbent

Sustainable recovery of manganese from low-grade ores requires efficient and environmentally compatible approaches for treating ore-derived leachates. This study investigates Mn 2+ recovery from an actual manganese-rich pregnant leach solution (PLS) using NaOH-activated Artocarpus heterophyllus Lam. seed biomass (NaOH – Ah SB), an agro-waste-derived biosorbent. Batch adsorption experiments were conducted to evaluate the effects of pH, contact time, adsorbent mass, and initial Mn 2+ concentration, followed by equilibrium, kinetic, thermodynamic, mechanistic, and regeneration studies. Under optimized conditions (pH 6, 60 min contact time, 20 mg L⁻¹ initial Mn 2+ concentration, and 0.5 g adsorbent), NaOH – Ah SB achieved 97.70% Mn 2+ removal. Alkali activation substantially enhanced Mn²⁺ removal compared with raw biomass (38.40%). The Langmuir model provided the best fit to equilibrium data (R² = 0.9860), with a maximum adsorption capacity of 34.30 mg g⁻¹, while adsorption kinetics followed the pseudo-second-order model (R² = 0.9989). FTIR, SEM–EDX with elemental mapping, XRD, and pH p zc analyses indicated the involvement of hydroxyl and carboxyl groups through electrostatic attraction, ion exchange, and surface complexation. Thermodynamic analysis indicated spontaneous and endothermic adsorption, with ΔH° = +54.60 kJ mol⁻¹ and ΔS° = +193.47 J mol⁻¹ K⁻¹. The biosorbent retained stable Mn 2+ removal performance over seven adsorption–desorption cycles, demonstrating its potential for sustainable Mn 2+ recovery from ore-derived leachates while valorising agricultural waste. Integrating agricultural waste valorization with critical metal recovery supports a circular bioeconomy and advances SDGs 6, 9, and 12 through resource efficiency, clean water, and sustainable industry.