Low temperature sulfonated biochar from Macauba’s endocarp for lead adsorption from wastewater

Abstract

Lead is a heavy metal that can be present in different types of effluents. This toxic ion is harmful both to human health and to other species. Therefore, it is necessary to study materials that can be used to remove lead from aquatic environments. In this context, the use of modified biomass residues for the production of efficient adsorbents for this purpose stands out. In this work was synthesized a new type of adsorbent material, sulfonated carbon, from macauba oil extraction residue for application in the removal of lead ions from aqueous media. The sulfonated carbons were produced from the reaction of macauba endocarp with concentrated sulfuric acid at 100 °C at 1, 2 and 4 h. The materials were characterized by XRD, MS-TG, Raman and infrared spectroscopies, SEM, potential titration, elemental analysis and by N2 adsorption/desorption. All synthetic conditions were efficient to produce functionalized carbonaceous materials with amorphous characteristics and good thermal stability. Although the material carbonized for 4 h had a low specific surface area (2 m2.g−1), it showed the higher efficiency for the removal of lead ions from aqueous solution. The adsorption occurred due to interactions of these ions with the functional groups present on the surface of the coal. The greatest lead removal occurred at pH 5.0 (83.8%), where –COOH and SO3H groups are in the deprotonated form, what favors the electrostatic attraction of Pb2+ ions. The experimental results were fitted using pseudo-first-order and pseudo-second-order models. A high concentration of lead ions was removed in the first 40 min, and the removal percentage was 97.5% for the less concentrated solution (10 mg·L−1) and 55.0% for the solution with the highest concentration (100 mg·L−1). The increase in the concentration of adsorbent provided an increase in the removal of this contaminant. The isotherm of adsorption was adjusted by Langmuir and Freundlich models. The better adjust was obtained by Langmuir and the maximum adsorption capacity by this model was 104.2 mg·g−1. The best lead removal conditions were: adsorbent concentration: 0.5 g.L−1; pH 5; Pb2+ concentration 80 mg.L−1 and time 2 h.