Produção e caracterização de biocarvões obtidos de bagaço de cana-de-açúcar modificado para remoção de manganês de efluentes aquosos

Abstract

Manganese is one of the most common contaminants in mine water and mining effluents in Minas Gerais, often neglected because it is an essential micronutrient. However, when improperly disposed of in the environment, Mn can contaminate aquatic systems, generating unsuitability of water for various uses, compromising the life and health of several species. Although several treatment methods can be used for remediation of aqueous effluents containing Mn, the removal of this metal in aqueous media is still an important issue for treatment technologies and environmental management that aim to meet the parameters established by legislation. In this context, adsorption using carbonaceous materials, such as biochar (BC), for decontamination of aqueous media has been proposed as an alternative of high efficiency, low cost and easy implementation. However, the use of different biomass pretreatment conditions and pyrolysis temperature (TP), which play an important role in modulating the properties of biochars by increasing their adsorption performance, has been little explored in the removal of Mn from aqueous effluents of mining. Therefore, this study evaluated the effects of chemical pre-treatment of sugarcane bagasse (using NaOH or H3PO4) and pyrolysis temperature in the syntesys of BC for Mn(II) adsorption. BC were synthesized in a muffle furnace, in the partial presence of oxygen, at temperatures of 400 and 500 °C and characterized by different techniques (FTIR, conductometric analysis, SEM, EDS and TGA). Studies evaluating the effect of pH and ionic strength, as well as studies of kinetics and balance of metal ion adsorption were evaluated in synthetic aqueous solutions, for later application of BC with better performance in real mining samples. The different types of pre-treatment of biomass and TP affected the yields of the materials, their functional groups of surface and pHPCZ values. Adsorption studies showed that Mn(II) removal can be applied over a wide initial pH range (4 - 8) and that adsorption equilibrium is achieved in a short contact time. Adsorption isotherms showed that the material obtained at 400°C by treating the biomass with NaOH (BC400TB) had the highest adsorptive capacity (about 22 mg g−1). However, some effects such as increased of the ionic strength and the addition of another chemical species such as iron in the system caused the removal percentage to reduce. Finally, BC400TB was used as an adsorbent in mining effluents and showed high potential for Mn removal from these systems.