Adsorption of cyanide from aqueous solution using calcinated eggshells: Equilibrium and optimisation studies

Abstract

Eggshells were calcined and used to adsorb cyanide from its aqueous solution. X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier Transform Infra-red (FTIR) and Scanning Electron Microscope (SEM) were used to characterize both raw and calcined eggshell (CE) while UV spectrophotometer was used to monitor the cyanide concentration. The XRD and FTIR showed the conversion of CaCO3 to CaO. Batch adsorption experiments were carried out using 10ml each of 0.01mol/L to 0.05mol/L cyanide solutions at different contact times, and adsorbent dosages. To establish optimum adsorption conditions, Central Composite Design (CCD) in Response Surface Methodology (RSM) was employed using the time, concentration and adsorbent dosages as variables at a fixed pH of 7. Adsorption efficiency of 84.53% was obtained with 0.01mol/L, 8.98g of calcined eggshell at 26.58min contact time using RSM. Pseudo second order kinetic model best fitted the experiment. The coefficients of determination of Langmuir and Freundlich isotherms were 0.988 and 0.650 respectively, with Langmuir isotherm giving a better fit for the adsorption. The maximum monolayer adsorption capacity from Langmuir isotherm was 3.27mg/g at pH 7 and a temperature of 30°C