1. Rada Petrović, Tehnološki fakultet Univerziteta u Banjoj Luci,
Republic of Srpska, Bosnia and Herzegovina
2. Dragana Gajić, Prirodno-matematički fakultet Banja Luka, Republic of Srpska, Bosnia and Herzegovina
3. Darko Bodroža, Tehnološki fakultet Univerziteta u Banjoj Luci, Republic of Srpska, Bosnia and Herzegovina
4. Zora Levi, Republic of Srpska, Bosnia and Herzegovina
5. Darija Kičić, Prirodno-matematički fakultet Banja Luka, Republic of Srpska, Bosnia and Herzegovina
This paper studies the possibility of chromium(VI) ions removal from aqueous solutions using green and white tuff as adsorbents.
Initially, the influence of various parameters (mass of adsorbent, contact time, pH value of solution, temperature and initial concentration of chromium(VI) ions in the solution) was examined. Optimal experimental conditions found to be: mass of adsorbent m=2 g; contact time t=90 min; pH value pH=2; temperature t=30oC and the highest efficiency of hexavalent chromium removal were at the concentration of 2 mg/L. The point of zero charge of green tuff was determined at different sodium chloride solution concentrations, and results showed that point of zero charge was not affected by the ionic strength of the solution and in all three cases was approximately 7,4.
Equilibrium data were analyzed with three linear adsorption isotherm models: Langmuir, Freundlich and Temkin, and experimental data were the best described by Langmuir model.
The thermodynamic study showed that adsorption process was unspontaneous, since positive value of Gibbs free energy. The negative value of enthalpy indicates an exothermic process and physical adsorption. There is an increase in disorder at solid/liquid boundary, which is indicated by positive value of entropy.
Experimental data showed that adsorption of chromium(VI) ions on both green and white tuff is in better agreement with pseudo second order kinetic model.
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