Adsorption Kinetics and Mechanism of some Metal (II) Ions from Aqueous Solution using Activated Carbon prepared from Star Apple (<i>Chrysophyllum albidum</i>) Pericarp

Abstract

In this research white star apple Chrysophyllum albidum, an agricultural product, available in large quantity in south region of Nigeria, were used as low-cost adsorbent for removal of metal ions such as Ni(II), Cd(II), Co(II) and Cu(II) from aqueous solution. Batch operation was used to study the equilibrium behaviour of Chrysophyllum albidum pericarp. The effects of solution pH, and contact time of adsorbent for the heavy metal ions were evaluated. To study the kinetics of adsorption of Ni(II), Cd(II), Co(II) and Cu(II), pseudo-first-order, pseudo-second-order, Elovich, Macky and Poot and liquid film Models were evaluated. The removal of these metal ions by the biosorbent was found to be dependent on contact time and pH solution. Results showed that the adsorption process was fast and that equilibrium was achieved at 120 min for Ni(II), Cd(II), Co(II) and Cu(II) ions. Results further showed that the optimum solution pH for the study occurred at pH 6.0 with maximum quantity adsorbed of 12.05 mg/g, 12.24 mg/g, 12.43 mg/g and 12.50 mg/g for Co(II), Ni(II), Cd(II) and Cu(II) ions respectively. Adsorption process fitted pseudo-second-order kinetic based on the high correlation coefficient (R² values) when compared to other kinetic models. Moreover, maximum adsorption capacities at pH 6.0 for Ni(II), Cd(II), Co(II) and Cu(II) ions are 12.4688 mg/g, 12.3456 mg/g, 12.4224 mg/g and 12.4378 mg/g respectively. The transport mechanism of the process was found to be a combination of intraparticle diffusion and liquid film controlled. In addition, the results will serve as a parameter to consider in the design of wastewater treatment plant for Pb(II), Cd(II) and Ni(II) ions detoxification using Chrysophyllum albidum.