Preparation and Characterization of Cattail-Derived Biochar and Its Application for Cadmium Removal

Biochars produced from aquatic plants have attracted increasing attention for the removal of heavy metals from the environment. Therefore, biochars derived from the roots (CBR), stems (CBS) and leaves (CBL) of cattail were investigated in this paper for their higher adsorption capacity, particularly for Cd(II). The adsorption characteristics and the leaching of alkali (soil) metals within biochars obtained from the different tissues of cattail were also discussed. The results showed that the specific surface area of cattail root biochar reached 15.758 m2 g−1. Langmuir, Freundlich and D-R isotherm equations were used to fit the experimental data, and the last equation revealed the best fitting result. The adsorption kinetics for Cd(II) removal were determined by using two different models. The experimental data for CBR and CBS were in good agreement with the pseudo second-order model, whereas the pseudo first-order model provided a better fit for CBL. The amount of leached K reached 73.214 mg g−1 in CBS (55.087 mg g−1 in CBL), which was almost an order of magnitude higher than those of Mg and Ca. The experimental data showed that the leached Mg and Ca metals in CBL had maximum levels of 6.543 and 10.339 mg g−1, respectively. The mechanism of Cd(II) sorption by the biochar is complex and probably involves a combination of mass transfer, ion exchange, and mineral precipitation through the macropores and micropores of the biochar in the sorption process.