Valorisation of Lignocellulosic Wastes, the Case Study of Eucalypt Stumps Lignin as Bioadsorbent for the Removal of Cr(VI)

Abstract

The main objective of this work was to assess Eucalyptus globulus lignin as an adsorbent and compare the results with kraft lignin, which has previously been demonstrated to be an effective adsorbent. Eucalypt lignin was extracted (by the dioxane technique), characterised, and its adsorption properties for Cr(VI) ions were evaluated. The monomeric composition of both types of lignin indicated a high content of guaiacyl (G) and syringyl (S) units but low content of p-hydroxyphenyl (H), with an H:G:S ratio of 1:50:146 (eucalypt lignin) and 1:16:26 (kraft lignin), as determined by Py-GC/MS. According to elemental analysis, sulphur (2%) and sodium (1%) were found in kraft lignin, but not in eucalypt lignin. The adsorption capacity of the eucalypt lignin was notably higher than the kraft lignin during the first 8 h, but practically all the ions had been absorbed by both the eucalypt and kraft lignin after 24 h (93.4% and 95%, respectively). Cr(VI) adsorption onto both lignins fitted well using the Langmuir adsorption isotherm model, with capacities of 256.4 and 303.0 mg/g, respectively, for eucalypt and kraft. The study’s overall results demonstrate the great potential of eucalypt lignin as a biosorbent for Cr(VI) removal from aqueous solutions.

Clean Forest—Project Concept and Early Results

“…Forest residues from Acacia melanoxylon (chips-wood and bark; crown residuesleaves and branches; and a mixture of both) were collected and characterized by pyrolysis analysis (PY-GC/MS). The extractive-free samples were milled into a fine powder and pyrolyzed at 550 • C for 1 min according to the literature [14]. The content of carbohydrates ranged from 42.6% (crown) to 52.4% (mixture), while lignin ranged from 19.6% (mixture) to 24.0% (chips).…”