Sorption parameter evaluation of copper and zinc from aqueous solutions using natural lake sediment as a low-cost adsorbent: feasibility of application

Natural lake sediment (NLS) was evaluated as a low-cost and environmentally sustainable adsorbent for the removal of Cu (II) and Zn (II) from aqueous solutions. XRD, FTIR, SEM and EDX revealed a heterogeneous structure dominated by silicate and aluminosilicate phases, together with oxygen-containing surface functional groups (–OH, Si–O and –COOH). FTIR bands confirmed the involvement of these groups in surface interactions and coordination processes. The experimentally observed adsorption capacities reached 30.5 mg g−1 for Cu (II) and 26.3 mg g−1 for Zn (II), demonstrating appreciable uptake of both divalent metal ions. Nonlinear kinetic analysis showed that the pseudo-second-order model provided a better description than the pseudo-first-order model for both metal ions, although the Elovich model also provided an excellent fit for Zn (II), consistent with adsorption on heterogeneous sites. The nonlinear Langmuir model provided the highest R2 for Cu (II), whereas the nonlinear Freundlich model provided the highest R2 for Zn (II), indicating that the equilibrium behavior was described differently for the two metal ions. The values of ΔH° were 89.77 ± 12.0 kJ mol−1 for Cu (II) and 41.96 ± 3.61 kJ mol−1 for Zn (II), confirming the endothermic nature of the adsorption process and the enhanced uptake at elevated temperatures. Overall, the adsorption behavior is consistent with multiple concurrent surface interactions on the heterogeneous sediment matrix, with possible contributions from ion exchange and reduced proton competition. Overall, NLS represents a promising natural sediment-based adsorbent for the sustainable removal of potentially toxic elements from contaminated waste water streams.