Comparison of column adsorption processes by downflow and upflow for removal of cupric (Cu2+) ion solutions using non activated and activated charcoal from rambutan (Nephelium lappaceum L.) stems

Abstract

The escalating environmental threat of heavy metal pollution particularly copper ions emphasizes the importance of wastewater treatment methods. A practical approach is adsorption using plant biomass. This study used column adsorption by comparing the downflow and upflow processes to remove cupric (Cu²⁺) ion from solution by adsorbent from rambutan stems charcoal that not activated and activated using nitric acid. The adsorbent size was 50 mesh, 70 mesh, and 100 mesh, the feed flow rates was 5 mL/min and 10 mL/min, initial concentrations of Cu²⁺ ion was 50 mg/L and 150 mg/L. The Cu²⁺ ion solution was pumped by upflow and downflow after the activated rambutan stem charcoal was inserted into the column. Fourier Transform Infra-Red carried out for analysis the functional group of the adsorbent before and after the activation. Changes in pore structure and chemical composition were verified by Scanning Electron Microscopy-Energy Dispersive X-Ray analysis. The modelling with breakthrough curve and modeling of Bohart-Adam model, Yoon-Nelson model and Thomas model are determined to fit the both column adsorption processes. Based on the results, the highest removal efficiency was 82.71 % obtained at Cu²⁺ ion concentration of 50 mg/L by upflow adsorption at flow rate of 5 mL/min using 100 mesh of activated charcoal of rambutan stem achieved of 2.87 min loading time. The result of this study describe the increase in removal efficiency occurred at lower Cu²⁺ ion concentrations with lower flow rate while using of larger adsorbent size. Longer loading times achieved at the increasing of Cu²⁺ ion concentration, decreasing of flow rate, and increasing of adsorbent size led to. Compared to downflow adsorption, upflow adsorption has a longer loading time. The breakthrough curve has "S" shaped profile for both upflow and downflow adsorption. However, the upflow adsorption breakthrough curve is more reliable as well as other modeling fittings showed higher coefficient of determination than the downflow.