A novel dynamic biosorption kinetic model based on reactions on the biosorbent surface for biosorption of heavy metal copper by non-living biomass waste tea leaves

A novel dynamic biosorption kinetic model was developed by taking account of reactions occurring on the biosorbent surface and applied to quantify the biosorption process of heavy metal copper (Cu) using non-living biomass biosorbent waste tea leaves. The proposed kinetic model is based on the surface complexation mechanism on the surface of waste tea leaves, which consists of two steps, i.e., Step 1: the deprotonation of functional groups and Step 2: the formation of biosorbate complexes with deprotonated functional groups, and the surface precipitation mechanisms. Batch experiments of Cu(II) removal using waste tea leaves were conducted to examine the effects of operating parameters such as initial Cu(II) concentration and solution pH on the dynamic biosorption kinetics of Cu(II). The biosorption capability was found to be relatively low at highly acidic solution pH and intensified with increasing pH. After the Cu(II) removal reached the maximum biosorption capability at pH 5, it was suppressed at a higher solution pH. With increasing solution pH, the number of negatively charged active sites increased due to the facilitation of the deprotonation of functional groups on the surface of waste tea leaves. As a result, the biosorption of Cu(II) through the surface complexation mechanism was further promoted. When the solution pH exceeded 5, the proportion of Cu^2 + in the solution decreased and the contribution of surface precipitation of Cu(OH)₂ dominated. The proposed biosorption kinetic model based on surface complexation and surface precipitation mechanisms could reasonably simulate the dynamic kinetic of Cu(II) biosorption by waste tea leaves.