Comparison Adsorption of Cd (II) onto Lignin and Polysaccharide-Based Polymers

Abstract

Given the predominantly negative impact of heavy metals on living organisms, the present study proposed to evaluate the adsorption performances under static conditions of Cd (II) from aqueous solutions on unmodified Sarkanda grass lignin compared to the adsorption performances of polysaccharide polymers chemically functionalized, obtained by synthesis and in their native state, but which, although effective, have a cost price that does not allow for large-scale expansion. To improve the retention of Cd (II) on this aromatic component of the biomass resulting from the processing of lignocellulosic materials, different experimental conditions (pH, concentration, dose and contact time) were followed. The Freundlich and Langmuir isotherms were used to describe the equilibrium conditions. Adsorption kinetics were assessed using the Lagergren I and Ho and McKay II kinetic models, furnishing informative insights into the process mechanism. Lignin adsorption capacity was also analyzed by performing biological tests on tomato seeds (Lypercosium esculentum), since heavy metals are known to be a stress factor for seeds by disturbing the osmotic equilibrium. Through the prism of the investigated parameters and under precisely established experimental conditions, unmodified Sarkanda grass lignin—an aromatic biopolymer—can be recommended as a promising adsorbent for the retention of Cd (II) from aqueous solutions, successfully replacing polysaccharide, especially cellulose-based polymers.

Adsorption of Ni(II) from Aqueous Media on Biodegradable Natural Polymers—Sarkanda Grass Lignin

“…Main chemical materials: Unmodified Sarkanda grass lignin supplied by Granit Récherche Development S.A., Lausanne, Switzerland [20], and NiSO 4 •6H 2 O supplied by ChimReactiv S.R.L., Bucharest, Romania.…”

“…To reduce pollution, it is necessary to not only decrease the amount of pollutants in the air, water, and soil but also explore options for recovering waste from industrial activities. The literature suggests various alternatives, Crystals 2024, 14, 381 2 of 17 including the use of low-cost materials such as cellulosic and lignin biomass fractions for different purposes, as adsorbent materials for the retention of pollutant species [14][15][16][17][18][19][20], in gasification processes; as precursors in organic syntheses [21]; or as bio-cyde substances for the preservation of natural composite structures [22].…”

“…This facilitates the formation of stable donor-acceptor and ligno-complex bonds [25,26]. As a result, different types of lignins have been tested as substrates for heavy metal ion adsorption [15,[18][19][20][21]27].…”

“…The most commonly used models are Freundlich and Langmuir [28,29]. These models indicate the mass of the solute retained by a given adsorbent under specific experimental conditions, such as the initial pH of the aqueous solution, sorbent dosage, initial concentration of the metal ion, and contact time between the two phases [20,30]. Studies on the kinetics of the adsorption process provide information on its mechanism [2,21].…”

“…However, the adsorption kinetics depend on both the adsorption process and the solute diffusion from the solution to the active centers on the adsorbent surface, and the level of relative humidity [31]. The two most commonly used kinetic models for approximating the mechanism of pollutant adsorption from aqueous solutions are the first-order Lagergren kinetic model and the second-order Ho-McKay kinetic model [20,32,33].…”