Adsorption of Cu2+, Cd2+ and Zn2+ in a modified leaf fixed-bed column: competition and kinetics

Modified waste phoenix tree's leaf was prepared to improve its adsorption capacities for metal ions: Cu2+, Cd2+ and Zn2+. Batch adsorption isotherm and kinetics in one-component system were conducted. Dynamic adsorption experiments especially the kinetics and competition of the three metal ions in one-component, binary and ternary systems were carried out in the modified leaf fixed-bed column. Results showed that there was an antagonistic effect in the competitive adsorption process under the binary and ternary system. The modified leaf displayed a high selectivity toward one metal ion with an affinity order of Cu2+ > Cd2+ > Zn2+. Due to the difference in the adsorption affinity, the whole process in the complicated systems could be divided into three phases: complete adsorption phase, separation phase and saturation phase. Yoon-Nelson and a modified Yoon-Nelson model were used to predict the adsorption kinetic curves. Results showed that the data fitted the models well and the obtained values of the breakthrough time and adsorption capacity at time t were very close to the experimental values. The modified leaf fixed-bed column could be regenerated efficiently and used repeatedly, and it had great potential in treating the industrial wastewater containing heavy metal ions.