Investigation of Isotherms of Competitive and Non-competitive Zinc Adsorption Using Gel-E-Sarshour in Presence and Absence of Copper and Humic Acid

Zinc (Zn) is one of the micronutrients that is toxic in high concentrations. One of the best ways for removing heavy metals (HMs) from water and waste water is the adsorption of HMs by using different adsorbents. The main component of Gel-E-Sarshour (GES) is a Di-octahedral smectite with high layer charge. Therefore it can be used for removal of Zn from contaminated water. In order to study the competitive and non-competitive retention characteristics of Zn onto GES, a trial with 7 different concentrations of Zn in the absence or the presence of humic acid (HA) was conducted. Zn adsorption data onto GES the best fitted to the Freundlich model, followed by Langmuir and Redlich-Peterson models. Although, the Zn adsorption data showed a highly significant fit to the Langmuir isotherm, the fit of data to a two-surface Langmuir isotherm proved to be more desirable. In all treatments, bonding energy of the first surface criterion (KL′) was several times greater than bonding energy of the second surface criterion (KL′′), while, adsorption maxima for the second site (b′′) were higher than that of the first site (b′). This means that although, the first site had a much greater tendency for Zn adsorption, it was rapidly saturated with Zn. Since, GES has a low price, being natural and abundant in Iran and due to its high adsorption capacity for the removal of HMs, application of this substance is promising for the removal of HMs.