Adsorption and chromatographic separation of rare earths with EDTA- and DTPA-functionalized chitosan biopolymers

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Abstract

Dysprosium is enriched in comparison with neodymium at low pH values on EDTA- and DTPA-functionalized chitosan. The observed differences in selectivity are used to separate mixtures of rare earths by column chromatography.

Abstract

Chitosan, which is derived from chitin by deacetylation, is one of the most promising biopolymers for adsorption of metal ions from diluted waste streams. By functionalization of chitosan with ethylenediaminetetraacetic acid (EDTA) or diethylenetriaminepentaacetic acid (DTPA) groups, it is possible to obtain a material that is much less soluble in acidic aqueous solutions than native chitosan. The coordinating EDTA and DTPA ligands are very efficient for binding of rare-earth (lanthanide) ions. The functionalization was achieved by reaction of chitosan with EDTA bisanhydride or DTPA bisanhydride. The binding of lanthanide ions to functionalized chitosan was investigated by FTIR (binding of Nd ³⁺) and luminescence spectroscopy (binding of Eu ³⁺). Comparison of the luminescence decay times of the europium( iii) coordinated chitosan complexes swollen in water and in heavy water allowed determination of the hydration number of the coordinated Eu ³⁺ ion. Batch adsorption tests for the uptake of neodymium( iii) from aqueous nitrate solutions were performed for EDTA-chitosan and DTPA-chitosan. Different experimental parameters such as the adsorption kinetics, loading capacity and pH of the aqueous feed were investigated. The modified chitosan materials are much more effective for adsorption of rare earths than unmodified chitosan. It was shown that adjustment of the pH of the aqueous feed solution allows achieving selectivity for adsorption of rare-earth ions for mixtures containing two different ions. After stripping of the metal content, the modified chitosans could be reused for new adsorption experiments. Medium pressure liquid chromatography (MPLC) with DTPA-chitosan/silica as the stationary phase and a dilute nitric acid solution as eluent was used for the separation of the following mixtures of rare-earth ions: Nd ³⁺/Ho ³⁺, Pr ³⁺/Nd ³⁺ and Pr ³⁺/Nd ³⁺/Ho ³⁺. The experiments show that separation of the rare-earth ions is feasible with DTPA-chitosan/silica, without the need for using solutions of chelating agents as eluents.

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Majeti N.V Ravi Kumar (2000)

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Low-cost adsorbents for heavy metals uptake from contaminated water: a review.

Sandhya Babel, Tonni Kurniawan (2003)

In this article, the technical feasibility of various low-cost adsorbents for heavy metal removal from contaminated water has been reviewed. Instead of using commercial activated carbon, researchers have worked on inexpensive materials, such as chitosan, zeolites, and other adsorbents, which have high adsorption capacity and are locally available. The results of their removal performance are compared to that of activated carbon and are presented in this study. It is evident from our literature survey of about 100 papers that low-cost adsorbents have demonstrated outstanding removal capabilities for certain metal ions as compared to activated carbon. Adsorbents that stand out for high adsorption capacities are chitosan (815, 273, 250 mg/g of Hg(2+), Cr(6+), and Cd(2+), respectively), zeolites (175 and 137 mg/g of Pb(2+) and Cd(2+), respectively), waste slurry (1030, 560, 540 mg/g of Pb(2+), Hg(2+), and Cr(6+), respectively), and lignin (1865 mg/g of Pb(2+)). These adsorbents are suitable for inorganic effluent treatment containing the metal ions mentioned previously. It is important to note that the adsorption capacities of the adsorbents presented in this paper vary, depending on the characteristics of the individual adsorbent, the extent of chemical modifications, and the concentration of adsorbate.