Thermodynamic Profile of Some Heavy Metal Ions Adsorption Onto Biomaterial Surfaces

The adsorption of Co²⁺, Zn²⁺, Pb²⁺ and Hg²⁺ onto dried non-living biomass (NB) of different Pseudomonas strains has been investigated in detail. Maximum adsorption of these cations is achieved at optimum pH values from 3.5 to 4.5 to avoid hydrolysis, polymerization and precipitation of metal cations in the treatment solutions. The experimental data obtained at different temperatures were fitted to the Langmuir model at different temperatures from 283 to 323 K. Metal ions adsorption occurs in multi detectable steps (i=A, B, C). Binding of Pb(II) to NB occurs in one detectable step labeled A, where two detectable binding steps were observed for the other cations; A and B for Zn(II), A and C for Co(II), B and C for Hg(II), respectively. Site capacities, υ_i are found to be temperature-independent in the whole investigated temperature range. The thermodynamic parameters (ΔH_i, ΔS_i and ΔG_i) for the adsorption processes were calculated for each binding step i and the results suggest that the nature of adsorption is endothermic and the process is spontaneous and favorable. Thermodynamic data pairs (ΔH_i, ΔS_i) for metal binding are linearly correlated for all sites in the investigated biosorption systems.