Adsorption mechanism of basic blue-9 onto quartz mineral: kinetics, isotherms and thermodynamic

Abstract

Adsorption of basic blue-9 (BB9) by natural quartz mineral was tested. The quartz mineral was characterized by FTIR, SEM, DRX, zeta potential and Sear’s surface area measurements. The quartz mineral contains 99.13% of SiO₂ and has a specific surface area of 0.6 m²g⁻¹. The zeta potential measurements of quartz showed a zero point charge (ZPC) at a pH of 2.12. Adsorption experiments results of basic blue-9 showed an excellent achievement after 15 min, for 100 μm sorbent particles seize, 1.0 g l⁻¹ sorbent mass, pH of 5.0, agitation speed of 200 rpm and Temperature of 60 °C. Moreover, the BB9 concentration and temperature were directly related to increase in adsorption capacity and the highest adsorption capacity of 27.78 mg g⁻¹ was achieved for 30 mg l⁻¹ at 60 °C. Langmuir isotherm and pseudo-second-order kinetics (R² > 0.99) were found to be the most appropriate models to describe the removal of metylen blue dye by quartz mineral. The apparent diffusion parametres were estimated to be between 3.24 × 10^–6 and 3.67 × 10^–6 cm² s⁻¹, indicating an adsorption process controlled by the external mass transfert on the quartz surface. The calculated thermodynamic parameters and Dubinin–Radushkevich adsorption free energy (E_ads = 0.28 kJmol⁻¹) showed that adsorption of BB9 onto quartz was spontaneous, endothermic and a physisorption reaction. FTIR spectroscopy and semi empirical RM1 calculations established an adsorption mecanism by electrostatic attraction. The regeneration tests after four runs showed that natural quartz could be an alternative material for cationic dyes removal.