Hidróxidos duplos lamelares com substâncias húmicas: perspectivas de aplicações ambientais

Abstract

The search for alternative methods for the removal of contaminants through the adsorption process has been intensively studied in recent years. Phosphate species can affect aquatic ecosystems, since excess of this nutrient can cause eutrophication, generating environmental impacts. In addition, due to the harmful effects of potentially toxic metals and organic residues on the environment and human health, it is necessary to develop and improve effective technologies for the removal of these species from wastewater in order to reduce the impact of the disposal of these matrices on the environment. Layered double hydroxides have shown promise in this regard, and humic substances (the main component of natural organic matter) have a strong influence on the availability of contaminants in the environment. In this context, layered double hydroxides intercalated with three types of materials, humic substances, nitrate and carbonate, were synthesized with the aim of applying them as adsorbents of phosphates, organic contaminants and potentially toxic metals present in the environment. The characterization of the materials, performed by X-ray diffraction, showed the presence of characteristic peaks of layered double hydroxides and the thermogravimetric analysis showed the decomposition behavior of the layered structure, confirming the structure of layered double hydroxides. The adsorption capacity reached equilibrium in approximately 30 min, being more efficient for layered double hydroxides with NO3. The maximum adsorption capacity of phosphate ions presented results of 35.03 and 44.20 mg g-1 for layered double hydroxides with humic substances and layered double hydroxides with NO3, respectively. The complexation capacity showed that the influence of pH is directly related to complexation, being greater for layered double hydroxides with humic substances at pH 6.5. Regarding the adsorption study, the isotherm for Pb metal fitted best to the pseudo-first order model and for Zn, it was found to fit both the pseudofirst order and the pseudo-second order models, suggesting that adsorption can occur with rapid and reversible multilayer formation. Thus, nanostructured materials with humic substances are promising for use in contaminant remediation and adsorption can be a fast and efficient technique for use in water.