The contamination of soil and water bodies with mercury from anthropogenic sources such as mining and industry activities causes negative effect for living organisms due to the process of bioaccumulation and biomagnification through the food chain. Therefore, the need for remediation of contaminated areas is extremely necessary and very desirable when it is cost-effective by using low-cost sorbents. This paper compares the sorption abilities of natural and iron-modified zeolite towards Hg(II) ions from aqueous solutions. The influence of pH, solid/liquid ratio (S/L), contact time, and initial concentration on the sorption efficiency onto both zeolites was investigated. At the optimal pH = 2 and S/L = 10, the maximum amount of sorbed Hg(II) is 0.28 mmol/g on the natural zeolite and 0.54 mmol/g on the iron-modified zeolite. It was found that rate-controlling step in mass transfer is intraparticle diffusion accompanied by film diffusion. Ion exchange as a main mechanism, accompanied with surface complexation and co-precipitation were included in the Hg(II) sorption onto both zeolite samples. This is confirmed by the determination of the amount of sorbed Hg(II) and the amount of released exchangeable cations from the zeolite structure as well as by the scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDS) of saturated zeolite samples. In a wide pH range, 4.01 ≤ pH ≤ 11.08, the leaching of Hg(II) was observed in the amount of only 0.28–0.78% from natural zeolite and 0.07–0.51% from iron-modified zeolite indicating that both zeolites could be used for remediation purposes while the results suggest that modification significantly improves the sorption properties of zeolite.

The kinetics of removal of lead ions from aqueous solutions using the column method with a fixed bed of natural zeolite clinoptilolite has been examined. Experimental results are presented as breakthrough curves, and tested according to the kinetic equation developed by Clark by means of the linear and non‐linear regression analysis. Both mathematical methods attain the same values for parameters A and r of the Clark equation. These parameters are used for the calculation of the sorption rate coefficient k and the removal capacity q. The removal capacity obtained from the experimental results and the capacity calculated using the Clark kinetic equation have shown excellent agreement. The Clark kinetic equation has been found suitable for description of removal of lead on zeolite for different experimental conditions. Based on the calculated parameters, the theoretical breakthrough curves have been plotted and compared with the experimental ones. Applicability of the kinetic equation used has been additionally confirmed by the good fit of experimental and modelled breakthrough curves. Based on the parameters calculated, the behavior of modelled breakthrough curves was predicted for different depths of fixed bed of zeolite.