Adsorption of Zn2+ ion by macadamia nut shell biochar modified with carboxymethyl chitosan and potassium ferrate

Abstract

A series of biochars and modified biochars were prepared by using macadamia nut shell (MNS) as raw material at different calcination temperatures and further using carboxymethyl chitosan (CMC) and K2FeO4 as the modifying agent, respectively. These biochar and modified biochars were used as adsorbents for adsorbing Zn2+ ion in aqueous solution. It is found that the adsorption behaviors of modified biochars BC-CMC and BC-K2FeO4 are consistent to the pseudo second-order kinetics model and the Langmuir equation. The maximum adsorption capacities for these adsorbents are increased in the following order: BC-CMC > BC-K2FeO4 > > BC-700. Among these biochars, BC-CMC exhibits the highest adsorption capacity of 97.09 mg/g, which may be mainly due to that BC-CMC has more amino, hydroxyl and carboxyl functional groups. The BC-CMC also exhibits better desorption performance and reusability. Furthermore, BC-CMC also shows higher adsorption capacity for Cu2+ and Pb2+. Based on the results, the adsorption mechanism of BC-CMC for Zn2+ was also proposed.