Equilibrium and kinetics of colour adsorption from textile wastewater by a novel adsorbent

Abstract

Activated carbons were produced from a local variety of mango seed by carbonizing the inner seed before activation with ZnCl₂ using an  impregnation ratio of 1:4. Laboratory batch studies were conducted in order to generate data for kinetic and equilibrium modelling of adsorption of colour by the produced mango seed endocarp activated carbon (MSEAC) for the purpose of determining the mechanism and rate controlling steps of the adsorption process. Langmuir, Freundlich and Tempkin Isotherms were adopted. While the kinetic models used were pseudo first order kinetic, pseudo second order kinetic, Intra-particle diffusion and Elovich models. The pseudo second order model gave the highest coefficient of  determination (R₂) of 0.999 (indicating goodness of fit) compared to other  kinetic models tested. This suggests that chemisorption is the rate-limiting step in this biosorption system. Langmuir isotherm fitted experimental data better compared with the other tested models(R₂=0.9987), implying that the adsorption process is based on a monolayer adsorption. Chi-squared test performed on all the models confirmed the goodness of fit of the generated data to the Langmuir and pseudo-second order over the other isotherm and kinetic models because they had the least caculated Chi- squared (χ² Cal) values of 5.2 and 3.2 respectively. It was recommended
that these two models are reliable tools for predicting the mechanism and rate of adsorption of colour from textile wastewater by the produced MSEAC.

Keywords: Mango seed endocarp, activated carbon, colour, kinetics,  isotherms, Textile wastewater.