Enhanced biosorptive recovery of Mn2+ from low-grade ore leachate using naoh activated mangifera indica kernel biomass kinetics isotherms and desorption studies

Sustainable recovery of critical metals like manganese (Mn 2+ ) from low-grade resources is essential for advancing circular bioeconomy and integrated bioprocessing strategies. Conventional physicochemical methods often suffer from poor selectivity, high energy demand, and secondary waste generation. Agro-waste-derived biosorbents, such as Mangifera indica kernel biomass ( Mi KB), a low-cost and widely available by-product of mango processing, offer an environmentally benign alternative. However, their application in real hydrometallurgical systems remains underexplored. This study investigates NaOH-activated Mangifera indica kernel biomass (NaOH– Mi KB) as a functional biosorbent for selective Mn 2+ recovery from low-grade manganese ore leachate. Selective reductive leaching produced a pregnant leach solution (PLS) with a high Mn : Fe selectivity ratio (259.5:1), enabling targeted biosorption. Process optimization identified pH 5, 90 min contact time, initial 20 mg/L of Mn 2+ concentration, and 0.5 g dose of adsorbent as optimal conditions, achieving a maximum removal efficiency of 98.9%.Equilibrium studies revealed the best agreement with the Langmuir model ( \(\:{R}^{2}\approx\:\) 0.98385), supporting a monolayer coverage mechanism over relatively uniform active sites, resulting in the highest adsorption potential (qₘ) of 43.84 mg/g. Although the Freundlich model also showed satisfactory agreement, the comparatively better Langmuir fitting suggested limited multilayer adsorption. The kinetic modelling verified that the sequestration of Mn 2+ conformed to the pseudo-second-order model ( \(\:{R}^{2}\:\) ≈ 0.997), which indicates chemisorption is the dominant mechanism. FTIR, XRD, SEM, and pHₚzc analyses confirmed that hydroxyl and carboxyl functional groups participated in ion exchange and surface complexation, leading to Mn–O bond formation. The biosorbent maintained high adsorption efficiency over repeated regeneration cycles, while retaining nearly 90% desorption efficiency up to three successive adsorption–desorption cycles, demonstrating strong structural stability and reusability. This study demonstrates the sustainable coupling of agro-waste valorization and hydrometallurgical manganese recovery under a biorefinery concept. The findings revealed that NaOH – Mi KB possesses high adsorption capacity, strong selectivity, definite chemisorption mechanism, and great reusability potential, thus laying a foundation for exploitation of multi-metal biosorption as well as optimization of operation parameters and into the develop process of industrial low-carbon recovery in circular bioeconomy.