Phosphate adsorption by different clay minerals modified with lanthanum and iron for application in aquatic eutrophic environments

Excessive supply of phosphorus in aquatic environments from urban areas, mainly from domestic and industrial sewage leads to eutrophication. Modified clay minerals have been explored for remediation of eutrophic areas because of the better adsorption properties and functions of these materials1. The objective of this work was the modification of two smectites clays with lanthanum and iron aiming their application in the removal of phosphate in aquatic eutrophic environments. The materials Bent and PetBent were modified as described in Table 1 and characterized by X-ray diffraction, X-ray fluorescence, physical adsorption of N2 and scanning electron microscopy. The degree of lanthanum and iron incorporation in the clays was dependent on their pore diameter but the chemical composition of the materials governed the adsorption capacity for phosphate. The adsorption of phosphate by the clay minerals was directly related to the percentage of incorporated lanthanum. Adsorption and kinetic models were evaluated, being better described by Lagmuir model and pseudo-second order, respectively. The materials were selective for phosphate adsorption in the presence of Cl-, NO3 - and SO4 2- anions. In addition the most promising material was evaluated in the laboratory with a sample of real water from the Jacarepaguá Lagoon (Brazil). The water characteristics were: suspended particulate material: 93.25±2.47 mg.L-1; Cl-: 2.68±0.3 g.L-1; SO4 2-: 383.85±4.45 mg.L-1; NO3 -: 5.37±0.08 mg.L-1; PO4 3- inorganic: 0.41±0.01 mg.L-1. The modified clay adsorbed the amount of 69.84 mg PO4 3-/g from the water, which represents 86% of adsorption yield, remaining only 0.06 mg.L-1 of inorganic phosphate in solution.