Thermodynamic and kinetic studies for the adsorption of malachite green on diatomite

Abstract

Pollution by dyes is one of the main pollutions of industrial effluents. This research examined Moroccan diatomite as a low-cost adsorbent to remove one of the dangerous dyes, malachite green (MG). Brunauer–Emmett–Teller analysis, scanning electron microscopy, pHpzc and X-ray diffraction were used to characterise diatomite. The studies were carried out at different levels of pH, diatomite masses and MG concentrations at a temperature of 25°C. Equilibrium, kinetics and thermodynamic characteristics were also studied. The results show that the diatomite consisted of an integrated and nearly circular sieve plate with many small ordered pores, giving it a high specific surface area of 17.36 m2/g. The ideal pH was found to be 7, with a saturation period of 90 min. The results indicate that MG removal increased accordingly as the pH increased and also as the adsorbent mass increased. The results of the isotherms showed that the Langmuir model is the most adequate, while the adsorption of MG is better characterised as monolayer adsorption. The maximum adsorption capacity obtained from the Langmuir model is about 22.17 mg/g at 25°C. Kinetic studies indicated the pseudo-second-order model as the most adequate model. It was also revealed that intraparticle diffusion is not the only rate-controlling step. From the thermodynamic data, it was concluded that the adsorption is endothermic – that is, the adsorption is more favourable at high temperatures. The research confirmed the applicability of diatomite as an effective and inexpensive adsorbent for removing hazardous materials.