Removal of Fe and Mn ions from groundwater using activated carbon obtained from waste products of Brazil nut and andiroba cultivation in the Amazon region

Brazil nut (Bertholletia excelsa Bonpl.) biomass waste and andiroba (Carapa guianensis Aubl.) biomass waste were used as precursors in the production of activated carbons for removing Fe and Mn ions from groundwater. Activated carbon materials were prepared via carbonization and chemical activation using KOH and exhibited high specific surface areas of 1121 m2 g−1 (activated carbon from Brazil nut shells) and 2411 m2 g−1 (activated carbon from andiroba). These samples were modified by treatment with HNO₃ under microwave heating. The increase in surface acidity was confirmed through measurements of the pH at the point of zero charge and Boehm titration analyses, which identified the presence of phenolic, carboxylic, and lactonic groups. The modified activated carbons showed good adsorption capacity for the tested metal ions regardless of the precursor used. The achieved removal rates were greater than or equal to 85%, reaching values close to 100% for Fe removal using the carbon prepared from andiroba biomass waste. The antimicrobial activity assay indicated that the modified activated carbon impregnated with Ag+ ions exhibited antibacterial activity against Escherichia coli bacteria. The results are promising and suggest the feasibility of using the investigated residues as precursors for activated carbons and have good physicochemical properties.