Adsorption of Pb (II) ions on variable charge oxidic calcined substrates with chemically modified surface

Abstract

Background: The adsorption process is an alternative method for treating natural and waste waters, with heavy metals. Oxidic lithological materials, rich in iron and aluminum amphoteric oxides, with pH-dependent surface charges, are a reliable medium for ionic adsorption. Being thermally resistant, these materials can be used to prepare a calcined substrate which is chemically treated in an acid or alkaline solution to enlarge surface positive or negative charge density, making it possible anion as well as cation adsorption reactions from aqueous solutions. Oxidic lithological materials use is a low-cost alternative for filtering system because of its availability and ease of preparation and application. Methods: Present paper shows results of the adsorption reaction of Pb+2 ions on calcined substrates prepared with oxidic lithologic material. The study was performed on the substrate with chemically modified surface in alkaline medium as well as on non-treated surface. Results: Results show L-type isotherms for the adsorption on the activated substrate, indicative affinity between adsorbate and adsorbent. Average value of adsorption capacity (k) for activated substrate is around 3.7 times greater (1791.73±13.06) compared to the respective average k value for the non-activated substrate (491.54±31.97), during the adsorption reaction, 0.35 and 0.26 mmolH+ of proton are produced on the activated and non-activated substrate respectively using a 1 mM Pb+2 solution and 72.2 and 15.6 mmolH+ using a 10 mM Pb+2 solution. This acidification agrees with the theoretic model of transitional metals chemisorption on amphoteric oxides of Fe, Al, Ti and Mn present in lithological material used for the preparation of adsorbent substrates confirming the information given by the L-type isotherms. Conclusions: Results suggest that these oxidic lithologic materials show great potential as an alternative technique for water treatment and heavy metal retention from contaminated waters using a low-cost and reliable adsorption system.