Removal of malachite green using ultrasound-assisted and conventional batch adsorption based on Paracentrotus lividus shells as biosorbent

The purpose of this investigation is the evaluation of the Paracentrotus lividus shells (PLS) as a new inexpensive non-conventional biosorbent for the removal of malachite green (MG) from water by mechanical agitation or ultrasonic irradiation under various operating conditions in a batch process. The PLS have been characterized by scanning electron microscope and Fourier-transform infrared spectrometer. The findings revealed that the adsorption rate of MG was improved when ultrasound was used; equilibrium time is reduced in half when using ultrasound instead mechanical stirring. The influence of operating conditions such as initial dye concentration (2–10 mg/L), adsorbent dose (0.2–0.8 g), particle size (850–2,000 μm), stirring speed (0–200 rpm), temperature (21°C–50°C), ionic strength (0–5 g/L) and initial solution pH (2–9) on the removal of MG was investigated. Basic pH conditions are more propitious for the adsorption of MG. The equilibrium time decreases from 420 to 60 min when the temperature increases from 21°C to 50°C. Biosorption kinetics obtained at different biosorbent doses were analyzed using Lagergren pseudo-first-order, Blanchard pseudo- second-order, Elovich and intraparticle diffusion models. The kinetic data are excellently fitted by the pseudo-second-order kinetics model for the stirring method and sonication method. For adsorption by stirring, experimental equilibrium data were best represented by Temkin model followed by form 1 of the Langmuir model followed by the Freundlich model. Additionally, the adsorption by sonication is better described by the Harkins–Jura model followed by form 2 of the Langmuir model and the Freundlich model. The results in this study indicated that PLS was an attractive candidate for removing cationic dyes from the dye wastewater and the use of ultrasonic radiation instead of mechanical agitation seems to be a very interesting technique to speed up the biosorption process.