Kinetic, sorption isotherms, pseudo-first-order model and pseudo-second-order model studies of Cu (II) and Pb (II) using defatted Moringa oleifera seed powder

Abstract

In the recent decades, there has been a concern on heavy metals in waste water and high cost of conventional methods of removing heavy metals, for this reason search on adsorbents of biological origin which is low cost and efficient is necessary. In this work defatted Moringa oleifera seed powder was studied as a potential alternative adsorbent for removal of Cu(II) and Pb(II) from aqueous solution. Physicochemical parameters such as pH, contact time, adsorption kinetics and initial ions concentration adsorption capacity using sorption models were evaluated. The results showed that the optimum pH for biosorption of Cu(II) was 6.5 while that of Pb(II) was 5.5. Contact time for Cu(II) was observed to occur after 30 min while that of Pb(II) occurred after 40 min. FTIR analysis revealed that defatted Moringa oleifera seed biomass had presence of amino, carboxyl, hydroxyl and carbonyl groups, these groups were responsible for biosorption of Cu(II) and Pb(II) from aqueous solution. Biosorption kinetic data fitted well with pseudo-second-order kinetic model (r2 ≤ 0.9997) giving equilibrium rate constant (k2) of 0.0350±0.0275 g mg−1 min−1 for Cu (II) loaded biomass and 0.0206±0.0114 g mg−1 min−1 for Pb (II) loaded biomass; the biosorption isotherms for the biosorbent fitted well with Freundlich isotherm model than with Langmuir isotherm model. However, the separation factor RL of Langmuir model was between 0 and 1 indicating favourable sorption process and the low value of mean sorption energy of 9.19×10-2 kJ from D-R model showed that the forces of attraction involved were Van der Waal forces indicating the process of adsorption was physical adsorption. In conclusion, the study revealed that defatted Moringa oleifera seed is an efficient biosorbent for removal of Cu(II) and Pb(II) from aqueous solution.