Highly Selective Separation and Recovery of Metal Ions Using Highly-Functionalized Chitosan Derivatives

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  • BABA Yoshinari
    Department of Applied Chemistry, Faculty of Engineering, Miyazaki University

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  • 天然多糖類キチン・キトサンの高機能化と金属イオン交換技術を活用した高度分離・回収技術の開発
  • 受賞論文(平成20年度[日本イオン交換学会]学会賞) 天然多糖類キチン・キトサンの高機能化と金属イオン交換技術を活用した高度分離・回収技術の開発
  • ジュショウ ロンブン ヘイセイ 20ネンド ニホン イオン コウカン ガッカイ ガッカイショウ テンネン タトウルイ キチン キトサン ノ コウキノウカ ト キンゾク イオン コウカン ギジュツ オ カツヨウシタ コウド ブンリ カイシュウ ギジュツ ノ カイハツ

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Abstract

This article reviewed author's studies on the selective adsorption and separation of valuable metals based on ion exchange or chelate formation using chitin and chitosan. In order to develop the new adsorbents and processes for recovery and separation of precious metals, valuable or harmful metal ion, the authors have synthesized new ion exchangers and chelating resins using chitin and chitosan. Fist of all, some kinds of chitosan derivative were synthesized by chemically modifying chitosan. To protect the amino groups of chitosan from the attack of cross-linking reagents, the authors have developed a new synthesis process via the Schiff's base formation as an amino protective group. New chitosan derivatives exhibited the high selectivity for gold (III), palladium (II), and platinum (IV) over base metals in hydrochloric acid. In addition, the chitosan derivative containing pyridyl groups exhibited the high selectivity for copper (II) over iron (III) in 1 M aqueous ammonium nitrate solution. The adsorption capacities of these chitosan derivatives for palladium (II) were found to be about 2-4 times greater than those of the cross-linked original chitosan and commercial chelating resins.<br> Highly-porous chitosan microspheres(OWOC) were prepared by coexisting the O/W/O emulsion containing chitosan and the W/O emulsion containing high concentrations of NaCl through the difference in their osmotic pressures. In addition, cross-linking and introduction of functional moieties to OWOC were simultaneously performed using the activated OWOC with chloromethyloxirane and bifunctional reagents for recovery of metals. Thus, the 1,2-dithioethane-containing OWOC chitosan derivative (EDTSC) was synthesized to examine the selectivity for precious metals. EDTSC exhibited the high selectivity for precious metals from hydrochloric acid. The adsorption rate of palladium (II) on EDTSC was measured to elucidate its adsorption mechanism. In the adsorption of palladium (II) on EDTSC, it was found that the intraparticle-diffusion process is not the rate-determining step, but the chemical reaction of PdCl3− with EDTSC is the rate-determining step owing to through-pores in EDTSC. EDTSC can be expected as an adsorbent for a perfusion chromatography.<br>

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