Low-cost biosorbent derived from <i>Hermetia illucens</i> larval shells for competitive removal and adsorption mechanisms of lead(II), copper(II), and iron(III) ions

Industrial wastewater containing a mixture of various heavy metals requires an adsorption technology capable of selective and efficient operation.This study examines Hermetia illucens larval shells (H.illucens LS) as unactivated biosorbents, characterizing their physicochemical properties and evaluating adsorption performance in a multi-metal batch system.XRD analysis indicates the dominance of CaCO phases with contributions from chitinbased biopolymers; FTIR reveals changes in functional group vibrations associated with surface complexation and ion exchange mechanisms after metal interaction; BET analysis shows a specific surface area of 8.464 m/g with mesoporous characteristics, and SEM-EDX confirms pore narrowing and the presence of lead (Pb), iron (Fe), and copper (Cu) after adsorption.Selectivity tests involving seven metal ions demonstrate that Fe(III), Pb(II), and Cu(II) are preferentially adsorbed, forming the basis for mechanistic interpretation and the novelty of this study.The adsorption affinity follows the order Fe(III) > Pb(II) >> Cu(II), reflecting differences in charge density, coordination behavior, and competitive binding strength in multi-metal systems.Kinetic analysis indicates that adsorption follows a pseudo-first-order model which in this case is dominated by rapid initial interactions.Isotherm modeling shows that Fe(III), Pb(II), and Cu(II) are best described by the Freundlich model (R > 0.99), confirming heterogeneous adsorption involving multilayer coverage.Thermodynamic parameters indicate that Fe(III) and Pb(II) adsorption is spontaneous and exothermic, whereas Cu(II) adsorption is less favorable due to weaker surface affinity.Overall, these findings demonstrate the intrinsic selectivity of H. illucens larval shells governed by surface chemistry rather than surface area, and support their potential as a cost-effective and sustainable biosorbent, with economic considerations discussed in this study, for multi-metal wastewater treatment.