Potential of using green adsorbent of humic acid removal from aqueous solutions: equilibrium, kinetics, thermodynamic and regeneration studies

The natural organic matter in water resources poses many problems, such as unpleasant taste and colour in the water, and is one of the most important precursors to the formation of disinfection byproducts (DBPs) during water treatment. This study was performed to evaluate the efficiency of activated carbon (AC) and activated carbon coated with nZVI nanoparticles (AC-nZVI) to remove humic acid from aqueous solutions. To end this, the effect of some operational factors including pH, contact time, humic acid concentration and adsorbent dose was studied in removal of humic acid from aqueous solutions in the presence of AC and AC-nZVI. The structure of the adsorbents and their morphology were characterized by FTIR, BET, SEM and XRD analyzes. The adsorption isotherm was determined using Langmuir, Freundlich and kinetic adsorption models by studying quasi-first-order and quasi-second-order models. The thermodynamic parameters of the adsorption system such as changes in enthalpy (ΔH0), entropy (ΔS0) and free energy of Gibbs (ΔG0) were also measured and evaluated. The results showed that the removal efficiency is directly associated with the dose of adsorbent and has a reverse association with pH and humic acid concentration. The optimal removal of humic acid at the adsorbent dosage of 1.6 g/L, the humic acid concentration of 50 mg/L and the contact time of 45 min was found 84.7% and 95.68% for AC and AC-nZVI, respectively. The SBET and total pure volume for the AC-nZVI were 821.52 m2/g and 0.631 cm3/g respectively. The removal rate by AC-nZVI as significantly high, indicating the effective role of nanoparticle stabilisation on activated carbon. As a result, it is possible to find an effective and highly efficient adsorbent by stabilising the nanoparticles on activated carbon that can be used to remove humic acid.