Equilibrium, kinetics, and thermodynamic evaluation of mercury (II) removal from aqueous solutions by moss (Homalothecium sericeum) biomass

In the present research, Homalothecium Sericeum was utilized for the first time as an effective and readily available adsorbent in removal of Hg(II) ions from aqueous solutions through a batch adsorption technique. The effects of initial solution pH, contact time, initial Hg(II) and adsorbent concentration, temperature, and ionic strengths were evaluated on the removal efficiency of Hg(II) ions, after being characterized of H. sericeum by different techniques. The maximum Hg(II) adsorption was obtained as 128.2 mg g-1 at initial pH 6.0 with an equilibrium time of 60 min, adsorbent dosage of 5.0 g L-1 and initial Hg(II) concentration range of 50-750 mg L-1. The adsorption behaviors of Hg(II) ions onto H. sericeum were investigated in terms of kinetics (pseudo-first order, pseudo-second order, and intraparticle diffusion models), isotherms (Langmuir, Freundlich, and Dubinin Radushkevich models), and thermodynamics evaluation. Both the Langmuir and Freundlich isotherm models were found to be suitable to describe the adsorption equilibrium while the adsorption kinetics followed by the pseudo-second order model. Thermodynamic parameters including the Gibbs free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) changes indicated that the adsorption of Hg(II) ions onto H. sericeum was feasible, spontaneous, and endothermic in nature.