Ultrasound-assisted removal of malachite green from aqueous solution by dead pine needles

The dead needles of Aleppo pine (Pinus halepensis) were tested as a possible sorbent for the removal of malachite green from aqueous solutions in the absence and presence of ultrasound. Batch process was employed for sorption kinetic and equilibrium studies. Sorption experiments indicated that the sorption capacity was dependent of operating variables. Both the rate and the amount of malachite green sorption are markedly increased in the presence of the ultrasonic field. The dye removal with the assistance of ultrasound was enhanced with the increase of sorbate initial concentration and temperature, and with the decrease of sorbent dosage and ionic strength. The combination of stirring and ultrasound leads to an improvement of the removal of dye. The sorption kinetics was controlled by the intraparticle diffusion. The intraparticle diffusion coefficient increased 1.7 times in the presence of ultrasound and up to 3.6 times in the combined process. The sorption capacity, estimated according to the Freundlich model, indicates that ultrasound enhanced the sorption properties of the sorbent. The effect of ultrasound on the improvement of dye sorption is due to a variety of physical and mechanical effects as well as to thermal properties. The combination of ultrasound and stirring for the sorption process was shown to be of interest for the treatment of wastewaters contaminated with malachite green.