Adsorção de íons metálicos em alga marinha Lithothamnium calcareum

Abstract

Due to the acceleration of global development and industrialization, the contamination of water bodies resulting from the discharge of industrial effluents is one of the main threats to the environment and human health. Adsorption is considered an auxiliary process in the treatment of effluents that have a high concentration of metal ions in their composition. In this sense, due to their high availability, regeneration capacity and low cost, marine algae have been considered as promising adsorbents for the removal of metallic ions from industrial effluents. Given the above, the objective was to evaluate the adsorption capacity of the metallic ions Lead (Pb), Chromium (Cr), Manganese (Mn) and Zinc (Zn) to the marine algae Lithothamnium calcareum, submitted to thermochemical treatment, through kinetic tests adsorption, batch adsorption and mobility in a fixed bed column filled with Lithothamnium calcareum and sand, with a view to developing a simple technique for the treatment of effluents with a high concentration of metal ions. In the adsorption kinetics, 0.2 g of alga was weighed, amount transferred to 125 mL Erlenmeyer flasks, to which 15 mL of solution at a concentration of 5 mg L-1 of the metal ion was added. The vials were shaken at 60 rpm for 2, 5, 10, 20, 60, 120, 180 and 240 minutes. In batch adsorption, 0.2 g of alga was weighed, the amount transferred to 125 mL Erlenmeyer flasks, to which 15 mL of solution was added in concentrations of 5, 10, 20, 50, 100, 250 and 500 mg L-1 of the metallic ion. The flasks were shaken at 60 rpm for 24 hours. In both assays, after shaking, the collected supernatant solutions were centrifuged at 2000 rpm for 5 minutes, and the remaining concentrations of the metal ions under study were determined by atomic absorption spectrometry. The data obtained in the adsorption kinetics tests were fitted by the Pseudo-first order, Pseudo-second order and Elovich models and the data obtained in the batch adsorption tests were fitted by the linear Freundlich, potential Freundlich, Langmuir and Sips models. The fixed bed column was built in PVC tube, 20.02 cm high and 4.42 cm in diameter, filled with Lithothamnium calcareum and sand in a proportion of 1:1 by mass. Mobility tests were conducted with constant hydraulic load and upward flow. The elements Pb, Cr, Mn and Zn were evaluated individually, at initial concentrations equal to 576.00; 668.15; 500.00 and 718.35 mg L-1, respectively. The adsorptive capacity was evaluated by constructing elution curves, analyzing the delay factor, the partition coefficient and the mass balance of the elements in the column. The elution curves were integrated by applying the Gompertz, Logistic, Ratkowsky, Morgan-Mercer-Flodin (MMF) and Weibull models. The results obtained in the adsorption kinetics and batch adsorption tests showed that the marine algae Lithothamnium calcareum submitted to thermochemical treatment presented itself as a potential material to be used in the adsorption of Pb, Cr, Mn and Zn. The results obtained in the mobility tests in a fixed bed column showed that the Lithothamnium calcareum and sand mixture presented high adsorptive capacity for Pb and low adsorptive capacity for Cr, Mn and Zn.