Understanding the adsorption of heavy metals on oxygen-rich biochars by using molecular simulation

Abstract

The adsorption of heavy metals on biochars derived from Carya illinoinensis biomass was studied using molecular simulation tools to understand the adsorption mechanism. The experimental conditions to obtain the best performing biochar were determined using a L16 orthogonal array of the Taguchi method and considering the removal of heavy metals from water as response variable. The studied factors were the mass of precursor, drying temperature, heating rate, maximum temperature of thermal treatment and holding time. Particularly, it was possible to obtain samples of biochar that were very efficient for the removal of Al3+, Pb2+, Cd2+, Cu2+ and Zn2+ from water, using relatively low temperatures of carbonization (200–350 °C) and low processing times (20–50 min). The most influencing factor in the final properties of biochar was the maximum temperature of the thermal treatment. The biochars obtained were rich in oxygen functional groups (carboxylic and phenolic), which favored the removal of heavy metals from water by complexation and ionic exchange mechanisms. According with the data obtained by molecular simulation, the adsorption mechanism of heavy metals was controlled by the dipolar moment of the metallic cations, with Pb2+ being adsorbed more efficiently.