Preparation Of Azo Compound Modified Chitosan For Separation And Determination Of Noble Metal

Preparation of azo compound modified chitosan for separation and determination of noble metalIn this paper, common methods for the separation and determination of precious metal ions, and preparation of chitosan derivatives for the separation of noble metal are summarized. Two kinds of azo crosslinked chitosan 4'-nitro-4-amino azobenzene crosslinked chitosan and 3'-nitro-4-amino azobenzene crosslinked chitosan are synthesized, which are abbreviated as CS-PANAB and CS-MANAB, respectively. The noble metal ions are determinated using FAAS. The adsorbents are characterized by FT-IR and SEM. The adsorption behaviors of noble metal ions from chloride medium with the modified chitosan have been studied. Various parameters such as pH. initial concentration, contact time, adsorption isotherms and kinetics, desorption have been investigated. Additionally, the national standard ore sample analysis has been carried out to check up the feasibility of this method. The main points of the experiment are as the follows:(1) The adsorption of Au(â…¢) and Pd(â…¡) by CS-PANAB is best at pH 3.0 for Au(â…¢) and at pH 2.0 for Pd(â…¡), where maximum adsorptions are 69.9300 mg/g. 58.5800 mg/g. The optimum pH values are 5.0 for Au(â…¢).4.0-6.0 for Pd(â…¡) and 3.0 for Pt (â…£) for the adsorption of Au(â…¢). Pd(â…¡) and Pt(â…£) by CS-MANAB,corres-ponding maximum adsorptions are 35.7142 mg/g,29.3255 mg/g and 43.1034 mg/g.(2) The relevant experimental data are fitted with Freundlich and Langmuir isotherm models. The adsorption isotherms of CS-PANAB obey the Langmuir equation in case of Au(â…¢). and the Freundlich and Langmuir equations in case of Pd(â…¡). That of CS-MANAB obey the Langmuir isotherm models for the adsorption of Au(â…¢). Pd(â…¡) and Pt(â…£).(3) The adsorption kinetic data are analyzed in the light of pseudo-second-order kinetic equation and intraparticle diffusion model. The adsorption kinetics follow a pseudo-second-order model for the adsorption of Au(â…¢) and Pd(â…¡) by CS-PANAB. and the adsorption process is greatly influenced by initial concentration. The degree of fitting by pseudo-second-order model is higher for the adsorption of Pd(â…¡) and Pt(â…£), while the straight line has passed through the orgin using intraparticle diffusion model for the adsorption of Au(â…¢) by CS-MANAB.(4) This new adsorbent shows high affinity for Au(â…¢),Pd(â…¡) and Pt(â…£), while the adsorption is negligible for a small minority of base metal ions or non-adsorbing of the other metal ion.(5) Various concentrations of thiourea and thiourea-HCl are used to study the desorption behaviors of noble metal ions from adsorbents. It is found that 1.00 mol/L thiourea and 0.50 mol/L thiourea are suitable eluents for the desorption of Au(â…¢) and Pd(â…£) from CS-PANAB. the corresponding desorption ratios are 82.97% and 87.73%. 0.20 mol/L thiourea-0.50 mol/L HC1 solution provides effective desorption of Au(â…¢), Pd(â…¡) and Pt(IV) from CS-MANAB,and the elution ratios are 92.21%, 90.40% and 93.38%. respectively.(6) The relative standard deviation (n=6) values are 2.76% for Au(â…¢) and 4.33% for Pd(â…¡) in the analysis of ore samples using CS-PANAB. With respect to CS-MANAB,the relative standard deviation(n=6) values are 5.10% for Pd(â…¡), 3.76% for Pt(â…£).3.64%(GBW(E)070015) and 4.63%(MG-1) for Au(â…¢), respectively. The limits of detections of Au(â…¢). Pd(â…¡) and Pt(â…£) are 0.010 mg/L 0.015 mg/L and 0.024 mg/L. respectively.The experimental results incidate that these adsorbents of CS-PANAB and CS-MANAB exhibit many desirable characteristics such as high selectivity, excellent ability to resist interferences and good reproducibility towards Au(â…¢), Pd(â…¡) and Pt(â…£). which is successfully applied to the determination and separation of Au(â…¢). Pd(â…¡) and Pt(â…£) in aqueous samples and ore. It is of theoretical and practical significance in the separation and extraction of precious metal ions.