Copper ions biosorption onto bean shells: kinetics, equilibrium, and process optimization studies

The removal of copper ions from aqueous solutions using bean shells as an adsorbent is presented in this paper. The influence of the solution solution pH on the biosorption capacity was investigated. The biosorption capacity increased with the increase in the solution pH. The pseudo-second order kinetic model showed the best agreement with the analyzed experimental data, indicating that chemisorption could be a possible way of binding the copper ions to the surface of the bean shells. The Langmuir isotherm model best fitted the analyzed isotherm data. The SEM-EDS analysis was performed before and after the biosorption process. The change in the morphology of the sample after the biosorption process was evident, whereby K, Mg, Si, and Ca were possibly exchanged with copper ions. Response Surface Methodology (RSM) based on the Box-Behnken design (BBD) was used to optimize the biosorption process, with the selected factors: the solution pH, initial copper ions concentration, and contact time. The optimum biosorption conditions were determined to be: pH = 3-4, initial copper ions concentration 100 mg dm-3, and contact time 10-30 minutes.