Adsorption kinetics and isotherm of methylene blue and its removal from aqueous solution using bone charcoal

Abstract

This study aims at describing the removal of methylene blue (MB) from aqueous solution using bone charcoal (BC) as an adsorbent material. The effects of dye concentration, pH, contact time and the adsorbent dose were investigated. The chemical composition and solid structure of BC were analyzed using X-ray diffraction (XRD) and scanning electronic microscopy (SEM). The surface area was measured via the Brunauer–Emmett–Teller (BET) isotherm. The experimental data were analyzed with Langmuir, Freundlich and Temkin isotherm models. The results show that the main component of BC is calcium hydroxylapatite (Ca5(PO4)3OH). The BETSuface area of BC is approximately 100 m2/g. The experimental adsorption isotherm complies with Langmuir equation model (R2 = 0.99) and the maximum amount of adsorption (qmax) was 5 mg/g. The elevation of BC dose led to a decrease in qmax, however, increasing the pH led to the elevation of dye adsorption. The kinetic studies revealed that the adsorption of MB is rapid and complies with the pseudo second-order kinetic (R2 > 0.99). Apart from R2, four error functions have been used for the validation of data. Analysis of data with Dubinin–Radushkevich isotherm showed that the energy of MB adsorption process onto BC was 2.65 kJ/mol, which implies that the adsorption of MB with BC is a physical adsorption.