Separation And Enrichment Of Au(Ⅲ), Pd(Ⅱ) And Pt(Ⅳ) By Synthesizing Chitosan Derivatives

The application of chitosan and its derivatives in the field of separation and enrichment of precious metals in recent years was reviewed. Furthermore, by synthesizing novel adsorbents, the precious metal ions such as Au(III) , Pd(II) and Pt(IV) were determined with FAAS after adsorption.A new chemically modified chitosan bead with 2,5-dimercapto-1,3,4-thiodiazo- le (CTS-DMTD) has been synthesized after crosslinking glutaraldehyde to improve its strength and acid resistance. The structure of CTS-DMTD was confirmed by elemental analysis and FTIR. A series of adsorption-desorption experiments as well as anti-interference ion experiments were carried out to explore the nature of the sorbent. It was found that adsorption capacities were significantly affected by the pH of solution and contact time, with optimum pH values of 3.0 for Au(III), 2.0 for Pd(II) and Pt(IV). The saturated adsorption capacities were 198.5 mg/g for Au(III), 16.2 and 13.8 mg/g for Pd(II) and Pt(IV), respectively. The recovery experimental data showed that CTS-DMTD had a higher affinity toward Au(III), Pd(II), and Pt(IV) in the coexistence system containing Cu(II), Fe(III), Cd(II), Ni(II), Mg(II), and Zn(II) and the recovery of standard addition was 90%~101%. The studies of desorption were carried out using various reagents and the optimum effect was obtained using thiourea. Langmuir and Freundlich isotherm adsorption models were applied to analyze the experimental data. The results showed that adsorption isotherms of Pd(II) and Pt(IV) could be well described by the Langmuir equation while adsorption isotherms of Au(III) fitted in with Freundlich The adsorption kinetic investigations indicated that the kinetic data correlated well with the pseudo-second-order model.A new chemically modified chitosan bead with L-Cysteine (CTS-Cys) has been synthesized after crosslinking epichlorohydrin to improve its strength and acid resistance. The structure of CTS-Cys was confirmed by FTIR. A series of adsorption-desorption experiments as well as anti-interference ion experiments were carried out to explore the nature of the sorbent. It was found that adsorption capacities were significantly affected by the pH of solution, with optimum pH values of 2.0 for Au(III) and Pd(II). The saturated adsorption capacities were 12.68 mg/g and 18.2 mg/g for Au(III) and Pd(II), respectively. The recovery experimental data showed that CTS-Cys had a higher affinity toward Au(III) and Pd(II) in the coexistence system containing Cu(II), Zn(II), Fe(III), Co(II) and Ni(II) and the recovery of standard addition was 92%~102%. The studies of desorption were carried out using various reagents and the optimum effect was obtained using thiourea-HCl. Langmuir and Freundlich isotherm adsorption models were applied to analyze the experimental data. The results showed that adsorption isotherms of Au(III) and Pd(II) could be well described by the Langmuir equation. The adsorption kinetic investigations indicated that the kinetic data correlated well with the pseudo-second-order model for Au(III) and pseudo-first-order model for Pd(II). Moreover, according to Vant Hoff equation to explore the thermodynamic adsorption process, it is an endothermic reaction and can occur spontaneously.