Sorption behavior of malachite green onto pristine lignin to evaluate the possibility as a dye adsorbent by lignin

Abstract

The objective of this study was to evaluate the adsorption characteristics of malachite green (MG) on pristine lignin as a dye adsorbent. The adsorption capacity of MG on lignin (31.2 mg/g) was described by Langmuir isotherm and pseudo second order models, and were higher than humic acid (6.4 mg/g). The adsorption of MG by lignin was rapid occurring within 15 min of the reaction, and then equilibrium was reached. The adsorption of MG by lignin based on an intraparticle diffusion model indicated that it was dominated by external boundary. Removal of MG by lignin can be applied at a wide range of pH’s (2–5), and optimal lignin dosage for MG removal was 3 g/L. In addition, the desorption efficiency of MG adsorbed on lignin was highest in methanol + acetic acid (95:5%, v/v) mixture of all solutions tested. The peaks attributed to the hydrogen-bonded stretching vibrations and sulphonyl groups in lignin before MG adsorption, were assigned at about 3400 and 620 cm−1, while the peaks in lignin after MG adsorption were attenuated or reduced. This result indicates that the adsorption of MG by lignin is closely related to the O–H and S–O bonds. Finally, this study suggests that pure lignin, which excludes active processes, can also be used as an adsorbent for dyes. However, in order to utilize the dye-adsorbed lignin repeatedly, further studies will be needed."