N-(2-(2-Pyridyl)ethyl)chitosan (PEC) for Pd(II) and Pt(IV) sorption from HCl solutions

Abstract

Chitosan was modified by grafting 2-pyridyl-ethyl moieties on the biopolymer backbone for the synthesis of a Platinum Group Metal (PGM) sorbent. The sorbent was tested for Pd(II) and Pt(IV) sorption from HCl solutions. Stable for HCl concentrations below 0.5 M, the sorbent reached sorption capacities as high as 3.2 and 2.6 mmol metal g -1 for Pd(II) and Pt(IV), respectively. Metal sorption mainly proceeds by electrostatic attraction in acidic solutions, though a contribution of complexation mechanism cannot be totally rejected. The resistance to intraparticle diffusion is the main controlling mechanism for uptake kinetics. While agitation speed has a limited effect on kinetics, metal concentration and sorbent dosage have a greater effect on the kinetic profiles. The intraparticle diffusivity varies between 3 9 10 -11 and 4.5 9 10 -10 m 2 min -1 . Thiourea (combined with HCl solution) is used for Pd(II) and Pt(IV) desorption. The resin could be desorbed and recycled for a minimum of five cycles maintaining high efficiencies of sorption and desorption.

Chitosan and Its Derivatives as Highly Efficient Polymer Ligands

“…In general, this synthesis method is distinguished by simplicity of a single stage modification without usage of organic solvents and unstable and toxic hydride reducers. Crosslinking of the 28N derivative (Figure 2) is provided by glutaraldehyde [80] or epichlorohydrin [78].…”

Ion Exchange Recovery of Palladium(II) from Acidic Solutions Using Monodisperse Lewatit SR-7

“…As given in the literature, thiourea solutions of different concentrations will be promising in the regeneration of many palladium(II) loaded sorbents. The following selected examples of regeneration efficiency confirmed the usefulness of thiourea or acidic thiourea in Pd(II) desorption: thiourea–0.1 M HCl, Pd(II) desorption efficiency 91%, desorption from N -(2-(2-pyridyl)ethyl)chitosan (PEC); 0.4 M HNO 3 –1.0 M thiourea, Pd(II) desorption efficiency 97.3%, Pd(II) desorption from magnetic cross-linking chitosan nanoparticles modified with ethylenediamine; 0.1 M thiourea, Pd(II) desorption efficiency 93–96%, desorption from imidazole containing resin; 0.5 M thiourea, Pd(II) desorption efficiency 81%, Pd(II) desorption from chitosan derivatives …”

“…Moreover, ammonia solutions at different concentrations of 0.5–3 M have been also tested and the above half amount of Pd(II) sorbed was desorbed from the resin (55–61%). A much lower, less than 10%, desorption yield of palladium(II) from N -(2-(2-pyridyl)ethyl)chitosan (PEC) by means of ammonia solutions (0.5–3 M) was obtained by Santos Sopena et al Also, a lower Pd(II) desorption yield (<4%) by ammonia solutions was observed in the case of the weakly basic anion exchange resin Purolite A-830. An 82.2% Pd(II) desorption from magnetic cross-linking chitosan nanoparticles modified with ethylenediamine was obtained by Zhou et al using 5 M NH 4 OH.…”

“…Varying HCl concentrations may affect palladium(II) sorption through the effect of both chloride and hydrogen ions. Depending on the pH and their total concentrations in solutions, the speciation of palladium(II) can be different (see Figure S2 in the Supporting Information) and, in turn, it can control the affinity of palladium(II) for the binding sites . In the case of solutions under consideration, palladium(II) in the chloride solutions forms the chloride complexes of negative charge PdCl 4 2– .…”

“…Additionally, only a monolayer adsorbate coverage of the adsorbent surface is assumed and the desorption rate is independent of the neighboring sorption sites occupancy. The Langmuir isotherm can be represented using the following equation: , …”