Comparative biosorption efficiency of Agaricus bisporus mushroom and spent mushroom compost for cobalt and manganese removal from aqueous solution: Equilibrium, kinetic and thermodynamic analysis

The search for affordable and environmentally friendly adsorbents has become a top priority for the effective removal of heavy metals to mitigate their harmful effects using waste residues. In this direction, the present study investigates the effectiveness of Agaricus bisporus mushroom (ABM) and its spent mushroom compost (SMC), a waste, as potential adsorbents for removing cobalt Co(II) and manganese, Mn(II) from aqueous solutions. The optimal conditions for the maximum removal of these metals were found to be at pH 5, 0.5 g of biosorbent, 6 h of equilibrium time, and initial concentrations of 24 μg/mL for Co(II), while 15 μg/mL for Mn(II). A pseudo second order kinetic model with R² > 0.991 for both the metals, and Freundlich's isotherm model with R² > 0.997 for Co(II) and R² > 0.985 for Mn(II) provided good correlation with the data. Thermodynamic analysis indicated the spontaneous and endothermic nature of the biosorption process for both metals. Characterization techniques including FTIR, XRD, SEM, and EDX confirmed the accumulation of Co(II) and Mn(II) on the biosorbent surfaces with the involvement of hydroxyl, carboxyl, amine, phosphate, and amide groups in metal uptake. The results indicated that SMC has higher biosorption efficiency than ABM for both the metals, accompanied by higher biosorption of Co(II) than Mn(II). Furthermore, both ABM and SMC have shown remarkable regeneration and recyclability up to seven adsorption-desorption cycles with significant adsorption of both the metals.