No abstract

A B S T R AC TNatural adsorbents such as shells of unmodifi ed wheat (RW), and modifi ed wheat (MW) were assessed for Cu(II) adsorption from aqueous solutions. The removal of Cu(II) by these adsorbents from aqueous solution was investigated by using several parameters such as modifi ciation, contact time, temperature and pH. The extent of Cu(II) removal increased with increasing contact time, temperature and pH and also with modifi cation by Reactive Orange 122 of adsorbent. The experimental data were analysed by the Langmuir and Freundlich models of adsorption. It was found that the Freundlich equation fi ts better than the Langmuir equation. In addition, the adsorption data obtained at different temperatures of Cu(II) by adsorbents were applied to pseudo fi rst-order, pseudo second-order and Weber-Morris equations, and the rate constants of fi rst-order adsorption (k 1 ), the rate constants of second-order adsorption (k 2 ) and diffusion rate constants (k 3 ) at these temperatures were calculated, respectively. The rates of adsorption were found to conform to pseudo second-order kinetics with good correlation (R 2 ≥ 0.989). The data obtained from adsorption isotherms at different temperatures were used to calculate some thermodynamic quantities such as free energy of adsorption (ΔG°), enthalpy (ΔH°), and entropy (ΔS°). It is found that ΔG° is negative, indicating that the nature of adsorption process for Cu(II) is spontaneous. The positive value of ΔH° indicates that the adsorption of Cu(II) onto adsorbents is an endothermic process. The positive value of ΔS° refl ects the affi nity of the adsorbent for Cu(II). As a result, the present work indicates that the wheat shells MW chemically by Reactive Orange 122, possess more effi ciency in adsorbing Cu(II) ions than the unmodifi ed one (RW).

ab s t r ac tThe influence of reactive dye modification on the efficiency of adsorption capacities of hazelnut shells was investigated. To that end, natural adsorbents such as shells of unmodified hazelnut (RH), and modified hazelnut (MH) were used. The removal of Cu(II) by these adsorbents from aqueous solution was investigated by using several parameters such as modification, contact time, temperature and pH. The adsorption process attained equilibrium within 60 min. The extent of Cu(II) removal increased with increasing the contact time, temperature and pH and also with modification by Reactive Orange 122 as the adsorbent. Optimum pH value for Cu(II) adsorption was determined between 4-5. The experimental data were analysed by the Langmuir and Freundlich models of adsorption. It was found that the Langmuir equation fited better than the Freundlich equation. The maximum adsorption capacities for Cu(II) onto RH and MH at 298, 308 and 318 K were found to be 3.95, 4.65, and 4.74, 7.00, 8.12 and 8.61 mg/g, respectively. In addition, the adsorption data obtained at different temperatures of Cu(II) by adsorbents were applied to the pseudo first-order, pseudo second-order and Weber-Morris equations, and the rate constants of the first-order adsorption (k 1 ), the rate constants of the second-order adsorption (k 2 ) and intraparticle diffusion rate constants (k 3 ) at these temperatures were calculated, respectively. The rates of adsorption were found to conform the pseudo second-order kinetics with good correlation (R 2 ≥ 0.991). The data obtained from the adsorption isotherms at different temperatures were used to calculate some thermodynamic quantities such as free energy of adsorption (∆G o ), enthalpy (∆H o ) and entropy (∆S o ). It is expected that ∆G o is negative, indicating that the nature of the adsorption process for Cu(II) is spontaneous. The positive value of ∆H o indicates that the adsorption of Cu(II) onto adsorbents is an endothermic process. The positive value of ∆So reflects the affinity of the adsorbent for Cu(II). As a result, the hazelnut shells (both modified and unmodified), inexpensive and easily available material, can be an alternative for more costly adsorbents used for Cu((II) removal from wastewater.