Effects of macromolecular humic/fulvic acid on Cd(II) adsorption onto reed-derived biochar as compared with tannic acid.

In this work, the adsorption of Cd(II) on reed-derived biochar (BC) as affected by dissolved organic matter (DOM), i.e., tannic acid (TA), macromolecular fulvic acid (FA) and humic acid (HA), was investigated through batch experiments. Results showed that a promotive effect of DOM on Cd(II) removal was demonstrated at pH < 6, whereas an inhibitory effect appeared at pH > 6. The maximum Cd(II) adsorption capacities were found to be 206.18 mg/g based on the Sips model. The order of addition sequences was found to exert a significant influence on Cd(II) adsorption. Addition of DOM (100 mg/L) to a Cd(II)-BC pre-equilibrated system led to 1.3%-7.4% enhancement for Cd(II) adsorption than other addition sequences. The surface properties of BC before and after Cd(II) adsorption were studied systematically, which implied that the effective adsorption of Cd(II) on BC was primarily ascribed to the cation exchange, formation of precipitation with CO32-, and surface complexation with oxygen-rich functional groups. Our findings will not only benefit the further utilization of reed-derived BC for aqueous Cd(II) removal but also aid in a better understanding for the roles of TA and macromolecular HA/FA in influencing the physicochemical behavior of heavy metals in natural environment.