In this study, the removal of Cu(II), Zn(II) and Co(II) ions from aqueous solutions using the adsorption process onto natural bentonite has been investigated as a function of initial metal concentration, pH and temperature. In order to find out the effect of temperature on adsorption, the experiments were conducted at 20, 50, 75 and 90°C. For all the metal cations studied, the maximum adsorption was observed at 20°C. The batch method has been employed using initial metal concentrations in solution ranging from 15 to 70 mg L −1 at pH 3.0, 5.0, 7.0 and 9.0. A flame atomic absorption spectrometer was used for measuring the heavy metal concentrations before and after adsorption. The percentage adsorption and distribution coefficients (K d ) were determined for the adsorption system as a function of adsorbate concentration. In the ion exchange evaluation part of the study, it is determined that in every concentration range, adsorption ratios of bentonitic clay-heavy metal cations match to Langmuir, Freundlich and DubininKaganer-Radushkevich (DKR) adsorption isotherm data, adding to that every cation exchange capacity of metals has been calculated. It is shown that the bentonite is sensitive to pH changes, so that the amounts of heavy metal cations adsorbed increase as pH increase in adsorbent-adsorbate system. It is evident that the adsorption phenomena depend on the surface charge density of adsorbent and hydrated ion diameter depending upon the solution pH. According to thȩ adsorption equilibrium studies, the selectivity order can be given as Zn 2+ > Cu 2+ > Co 2+ . These results show that bentonitic clay hold great potential to remove the relevant heavy metal cations from industrial wastewater. Also, from the results of the thermodynamic analysis, standard free energy G 0 , standard enthalpy H 0 and standard entropy S 0 of the adsorption process were calculated.

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Langmuir, Freundlich, DKR, Temkin, BET, Harkins-Jura, Elovich, Fowler-Gugenheim, Hill de Boer, Frumkin, Halsey, Henderson, Smith, Jovanovic and Scatchard isotherm equations.

Inverse gas chromatography has been used to evaluate the adsorption parameters ( H a , H st , S a and G a ) of some probe molecules, each representing a class of organic (n-hexane, cyclohexane, benzene, n-octane, 1-octene and isooctane) on bentonite and chemically treated-bentonites. The adsorption parameters of the probes on the bentonite samples were determined in infinite dilution region. Adsorption of the organic species was investigated in the temperature range of 200-275 • C, using a flame ionization detector, and nitrogen as a carrier gas. The net retention volumes (V n ) of the probes were determined by the help of the retention times (t R ) observed on gas chromatograms for each probe. Injection was made at least three times for each probe, obtaining reproducible results of ±0.5%. It was found that benzene exhibits more negative H than for n-hexane and cyclohexane on all of the adsorbents. In addition, it was found that 1-octene exhibits more negative H than for n-octane and isooctane on the chemically treated-bentonites, whereas n-octane exhibits more negative H than for 1-octene and isooctane on the natural bentonite. Also, interactions of benzene with the natural-and chemically treated-bentonites were found to be stronger than those of n-hexane and cyclohexane with the same carbon number. Again, interactions of the 1-octene with the chemically treated-bentonites were found to be stronger those of n-octane and isooctane with the same carbon number. On the contrary, interactions of n-octane with the untreated-bentonite were found to be stronger than those of 1-octene and isooctane.

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