Avaliação do potencial de biossorção do íon metálico Cr (VI) utilizando biomassa do fungo Lasiodiplodia theobromae MMPI como adsorvente

Abstract

Electroplating consists of the coating of parts with different types of metals in order to protect them from corrosion, thus increasing their useful life. However, effluents rich in metal contaminants are generated in this process and may cause serious environmental risks as regards the disposal of the water body. Biosorption is a technique of removing metals from aqueous solutions that have shown relevant results using microorganisms as a biosorbent. The objective of this study was to evaluate the potential of Cr (VI) removal from synthetic and real effluents using the biomass of the fungus Lasiodiplodia theobromae MMPI dried in heating chamber (BSE) and by freeze drying (BSL) as biosorbent. The dried biomass samples were characterized by scanning microscopy, which indicated the presence of long and thin micropores on their surface, which were confirmed by the determination of the texture characteristics that presented surface area of ≈1 for BSE and <1 for BSL for particles of 0, 59 and 1.00 mm, respectively. In the infrared spectra, the presence of carboxylic acids, amines and amides, as well as phosphate groups and CNinteractions was observed, referring to the surface polysaccharides of the samples. Using a 2² full factorial design, it was possible to identify the best working conditions, optimizing the process and directing it to the best contaminant removal index at pH 5.5 of the synthetic effluent and 0.59 mm of granulometry of the biosorbent. However, assays at pH 8.5 were performed in parallel in order to reproduce the characteristic of the actual effluent. The results of the kinetic study showed reaction equilibrium in approximately 30 minutes for both biomasses and the best mathematical fit was observed in the pseudo-second order model. The Langmuir isotherm model satisfied the mathematical conditions for the Cr (VI) biosorption conditions compared to the fungal biomass with the two types of drying, although unfavorable to the biosorption process studied. The thermodynamic parameters were determined at different temperature ranges, indicating the process as spontaneous for higher temperatures, endothermic and of chemical nature for the BSE assays. For the use of BSL, the results indicated no spontaneity for the process, being exothermic and with the presence of chemisorption. In addition, a kinetic study of the biosorption process was carried out with both biomasses in real gross effluent (before treatment) and treated in an electroplating industry. The Cr (VI) removal was highly efficient for the treated effluent, presenting 95.41 and 97.49% for BSE and BSL, respectively. On the other hand, for the raw effluent, the removal was 36.55% for BSE and 37.58% for BSL. An FT-IR analysis of the biosorbent after the kinetics in real effluent corroborated the presence of chemisorption and the change in the surface chemical structure of the same after the removal of the metal ion, besides reducing characteristics of the biomass. The use of the dried biomass of the Lasiodiplodia theobromae MMPI fungus in the removal of Cr (VI) from the synthetic and real electroplating effluents showed higher efficiency at low concentrations and could be indicated as a complementary treatment for effluent recovery in this segment before its disposal.