Adsorption of Phosphate and Nitrate Ions on Oxidic Substrates Prepared with a Variable-Charge Lithological Material

Abstract

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.

Seasonal impact of constructed wetlands on nitrogen and phosphorus in sediments of flood control lakes with pollution assessment

“…The unusual results in the area without vegetation growth in this study are likely attributed to the high TP content in the sediments, induced by the substantial input of P at the water inlet (J. Chen et al., 2019). The retention of TP in sediments is primarily achieved through biological fixation and particle adsorption sedimentation, however, few wetland plants existed in areas B and C. This indicates that TP in the constructed wetland area is predominantly reliant on sediment adsorption, which includes the non‐specific adsorption of phosphate anions through electrostatic attraction to positively charged iron and aluminum oxides, as well as the exchange of structural hydroxyl groups of hydrogen phosphate ions with iron, aluminum oxides, and clay surfaces caused by chemical reactions, to form the specific adsorption of inner layer complexes (Prato et al., 2022). The P content in the sediment does not decline with increasing depth but exhibits the initial decrease followed by an increase.…”

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

“…However, some of these materials behave as arid soils basically composed by refractory aluminum and iron oxides among other crystalline phases as quartz and clays, they are called “Oxidic Lithologic Material”, OLM. 1 , 2 The two most important properties of these kinds of materials are the thermal resistance and their amphoteric behavior. 2 , 3 In alkaline medium the oxides deprotonate, to create surface negative charges while in acidic medium the oxides protonate, to create surface positive charges.…”

“…1 , 2 The two most important properties of these kinds of materials are the thermal resistance and their amphoteric behavior. 2 , 3 In alkaline medium the oxides deprotonate, to create surface negative charges while in acidic medium the oxides protonate, to create surface positive charges. In the first case it favors the cationic adsorption while the second one it favors the anionic adsorption.…”

“…In previous studies some oxidic lithologic materials, OLM have been characterized with the purpose of preparing calcined adsorbent substrates for ionic adsorption from aqueous solution. 1 , 2 , 25 , 26 The high content of amphoteric iron and aluminium, as well as titanium and manganese oxides, with p H dependent variable charges surfaces, make them suitable for ionic adsorption. 2 , 5 , 7 As a consequence of this particular property, these OLM materials are versatile for preparing a calcined adsorbing substrate using thermal treatment of calcination.…”

“…1 , 2 , 25 , 26 The high content of amphoteric iron and aluminium, as well as titanium and manganese oxides, with p H dependent variable charges surfaces, make them suitable for ionic adsorption. 2 , 5 , 7 As a consequence of this particular property, these OLM materials are versatile for preparing a calcined adsorbing substrate using thermal treatment of calcination. Positive or negative charges density is achieved by alkaline or acid treatment, alkaline treatment causes oxide deprotonation creating a negative charge density while acid attack causes oxide protonation, creating a positive charge density on the oxide surface.…”