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Isothermal and kinetic adsorption behaviour of Pb²⁺ ions on natural silicate minerals

¹ Chemistry Department, The Hashemite University, P.O. Box 150459, Zarqa 13115, and ² Department of Chemistry, University of Jordan, Amman, Jordan

^* E-mail: aldegs{at}hotmail.com

(Received 20 October 2002; revised 24 May 2003)

Four different types of natural clay were tested as potential adsorbents for toxic Pb²⁺ ions. Based on the preliminary screening studies, the adsorbents were effective at retaining Pb²⁺ ions from solution. A strong correlation was observed between the cation exchange capacity of clay samples and their function as adsorbents of Pb²⁺ ions. An adsorption isotherm of Pb ions on Petra clay was measured at 30°C and at a concentration range of 0–200 mg dm^–3. Over the entire concentration range, the Langmuir isotherm gave a good representation of adsorption data, which confirms the formation of one molecular layer of adsorbate on the clay surface. Two variables were investigated to elucidate the rate-limiting steps of adsorption: the effect of initial concentration of Pb²⁺ and the effect of solution temperature. It is concluded that external diffusion was the only mechanism in operation in the adsorption process. It has been noted that adsorption of Pb²⁺ by natural clay is a fast process, where 80% of equilibrium capacity was established within the first minutes of interaction.

KEYWORDS: clay deposits, heavy metals, adsorption, diffusion and rate-limiting steps

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