Activated carbon manufacturing via alternative Mexican lignocellulosic biomass and their application in water treatment: Preparation conditions, surface chemistry analysis and heavy metal adsorption properties

Abstract

The preparation and functionalization of activated carbons from different biomass of Mexico and their application in the adsorption of heavy metal ions is reported in this paper. Jacaranda seeds, guava seeds, grape pomace and sugarcane bagasse were utilized as lignocellulosic precursors to obtain activated carbons via the chemical activation of biomass and its pyrolysis. The best conditions to prepare the activated carbons were identified with ZnCl2, NaOH, HNO3 and H3PO4 as activating agents. A systematic analysis of the biomass chemical activation and thermochemical transformation via pyrolysis was performed to maximize the Hg2+, Zn2+ and Pb2+ adsorption properties of activated carbons. These adsorbents showed maximum adsorption capacities from 0.014 to 0.84 mmol/g at 25–40 °C where the best adsorbent was obtained from the Jacaranda fruit activated with 0.5 M ZnCl2 for 2 h and pyrolyzed at 800 h for 4 h. This adsorbent was effective for the Hg2+ removal in single, binary and ternary systems thus suggesting its potential application for industrial wastewater treatment where several heavy metal ions could be present. The removal of these heavy metal ions with all tested activated carbons was endothermic where the oxygenated functional groups were involved in the adsorption mechanism. Isotherm data modeling with statistical physics indicated that Hg2+ and Pb2+ adsorption was mono-ionic, while the Zn2+ adsorption was multi-ionic. Antagonistic adsorption of these heavy metal ions occurred in multi-metallic solutions where Hg2+ affected significantly Zn2+ and Pb2+ removal. Regeneration of the best activated carbon was feasible with HNO3. These results contribute to valorize alternative agricultural and biomass wastes to satisfy the demand of activated carbons for water cleaning in Mexico applying a circular economy approach to reduce the production costs and to minimize the solid waste generation.