Chemical Modifications of Douglas Fir Bark, a Lignocellulosic By‐product—Enhancement of Their Lead(II) Binding Capacities

Abstract

Chemical modification of Douglas fir bark and its subsequent utilization in adsorption of Pb²⁺ from aqueous solutions was investigated. We developed a new solvent‐free approach to enhance the natural properties of bark by utilizing polyfunctional groups covalently attached at their surface. The hydroxyl groups of their polysaccharide moiety were functionalized by periodate oxidation and derivatized via reductive amination in presence of aspartic acid or 4,4′‐diamino‐2,2′‐stilbene disulfonic acid. The degree of substitution of derivatized bark was estimated by the means of pH titration. Adsorption isotherms of Pb²⁺ on derivatized barks were determined and compared with the performances of crude bark. Adsorption was characterized using the noncompetitive Langmuir adsorption model in terms of affinity (b) and maximum binding capacities (q _max). Derivatization resulted in enhancements of both q _max (×4–7) and b (×1.5–10). These experimental data are discussed in the context of the Hard and Soft Acid and Base theory.

Keywords:

• Douglas fir bark
• Chemical modifications
• Biosorption
• Adsorption isotherms
• Langmuir
• Lead

Acknowledgments

The authors gratefully acknowledge the “Direction Régionale Agriculture et Forêt du Limousin” for financial support.