Kinetic and adsorptive characterization of biochars in zinc, copper and lead metal ions removal using batch and continuous systems -

Abstract

Spent mushroom compost biochar (SMCB) and coconut shell biochar (CB) were prepared by carbonisation and tested for the removal of heavy metals: Zn(II), Cu(II) and Pb(II) by adsorption. They were characterized to determine their physical and chemical properties. The adsorption of heavy metals was evaluated by studying several factors, such as the initial solution pH, contact time, temperature and competitive adsorption. The effect of initial solution pH was initially studied and it was found that at a pH of 6 the highest metal removal took place for the adsorption using both biochars. Kinetic and equilibrium studies were carried out to determine the mechanism involved during adsorption. Pseudo-second order and Langmuir model most accurately described the adsorption process, showing that chemisorption takes place on a monolayer, homogenous and energetically-equivalent adsorption sites. The Weber-Morris model demonstrated the significance of intra-particle diffusion on the adsorption process. In addition, thermodynamic studies showed that the process is endothermic, favorable, with good affinity of metals to the biochar. SMCB and CB were used as adsorbent in a continuous fixed-bed column. The breakthrough curve was obtained for each heavy metal and the Thomas and Clark models were fitted to further understand the breakthrough behavior. When all three metals co-exist, competitive adsorption took place in both batch and continuous systems, showing that Pb has higher affinity to SMCB than Cu and Zn.