Influence of pyrolysis temperature and feedstock biomass on Cu2+, Pb2+, and Zn2+ sorption capacity of biochar

Abstract

Biochar has attracted significantly growing attention due to its effectiveness in terms of both cost and environmental safety in removing trace metals from soil and water. Its metal sorption capacity depends on its properties, which are in turn governed by pyrolysis temperature and type of biomass. Therefore, this study examines the role of pyrolysis temperature and biomass in biochars sorption capacity of Pb2+, Cu2+ and Zn2+. Biochars produced by pyrolysis of maize (Zea mays L.) cobs at different temperatures were used to assess the effect of temperature, whereas evergreen oak (Quercus ilex L.) pyrolyzed at 500 °C was used to assess the effect of biomass. Sorption isotherms were constructed by batch method and compared with Langmuir and Freundlich models. Most of the sorption isotherms displayed irregular curves and not all of the isotherms fitted the models. Therefore, sorption distribution coefficients and metal removal percentages were used to determine sorption capacities biochars for studied metals. Accordingly, Quercus ilex L. was most effective in sorbing all studied metals, which indicates the role of biomass. The maize biochar pyrolyzed at 500 °C was most effective among maize cob biochars, which revealed the influence pyrolysis temperature. The concentrations of added sorption solutions also played significant role in sorption, and consequently biochar pyrolyzed 350 °C was least effective. The targeted metals also affected the sorption as they compete for sorption sites. Thus, their selective sequence was in the order of Pb2+ ˃ Cu2+ ˃ Zn2+.