Removal of dye modified metal ions with low-cost adsorbents from aqueous solution

In this study, the use of natural low-cost adsorbents was investigated as a replacementfor current costly methods of removing metals from aqueous solution. For this aim, differentnatural adsorbents such as shells of raw wheat (HF), modified wheat (MF), raw hazelnut(HB), and modified hazelnut (MB) was used. The removal of Cu(II) by these adsorbents fromaqueous solution was investigated using parameters such as contact time, temperature and pH.The adsorption process attained equilibrium within 60 min. The extend of Cu(II) removalincreased with increasing contact time, temperature and pH and also increased withmodification by reactive orange 122 of adsorbents. Optimum pH value for Cu(II) adsorptionwas determined between 4-5. The experimental data were analysed by the Langmuir andFreundlich models of adsorption. It was found that the Langmuir equation fit better than theFreundlich equation. The maximum adsorption capacities for Cu (II) onto HF, MF, HB, andMB at 298, 308 and 318 K temperature were found to be 3.95, 4.65, and 4.74; 7.00, 8.12, and7.61; 9.51, 9.63, and 11.78; 15.22, 15.29, and 17.42 mg g-1, respectively. In addition, theadsorption data obtained at different temperatures of Cu(II) by adsorbents were applied topseudo first-order, pseudo second-order and Weber-Morris equations, and the rate constantsof first-order adsorption (k1), the rate constants of second-order adsorption (k2) andintraparticle diffusion rate constants (k3) at these temperatures were calculated, respectively.The rates of adsorption were found to conform to pseudo second-order kinetics with goodcorrelation ( R2 0.991). The data obtained from adsorption isotherms at differenttemperatures have been used to calculate some thermodynamic quantities such as free energyof adsorption (Go), enthalpy (Ho), and entropy (So). It is expected that Go is negative,indicating that the nature of adsorption process for Cu(II) is spontaneous. The positive valueof Ho indicates that the adsorption of Cu(II) onto adsorbents is an endothermic process.Thepozitive value of So reflects the affinity of the adsorbent for Cu(II). In the result, the formsraw and modified of shells of hazelnut and wheat, being a cheap, and easily availablematerial, can be an alternative for more costly adsorbents used for removal of Cu(II) fromaqueous solution