This work evaluates phosphate and nitrate ion adsorption from aqueous solutions on calcined adsorbent substrates of variable charge, prepared from three granulometric fractions of an oxidic lithological material. The adsorbent material was chemically characterized, and N2 gas adsorption (BET), X-ray diffraction, and DTA techniques were applied. The experimental conditions included the protonation of the beds with HCl and H2SO4 and the study of adsorption isotherms and kinetics. The lithological material was moderately acidic (pH 5) with very little solubility (electrical conductivity 0.013 dS m−1) and a low cation exchange capacity (53.67 cmol (+) kg−1). The protonation reaction was more efficient with HCl averaging 0.745 mmol versus 0.306 mmol with H2SO4. Likewise, the HCl-treated bed showed a better adsorption of PO4−3 ions (3.296 mg/100 g bed) compared to the H2SO4-treated bed (2.579 mg/100 g bed). The isotherms showed great affinity of the PO4−3 ions with the oxide surface, and the data fit satisfactorily to the Freundlich model, suggesting a specific type of adsorption, confirmed by the pseudo-second-order kinetic model. In contrast, the nitrate ions showed no affinity for the substrate (89.7 µg/100 g for the HCl-treated bed and 29.3 µg/100 g bed for the H2SO4-treated bed). Amphoteric iron and aluminum oxides of variable charges present in the lithological material studied allow for their use as adsorbent beds as an alternative technique to eliminate phosphates and other ions dissolved in natural water.

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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.