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Recovery of rare-earth metal neodymium from aqueous solutions by poly-γ-glutamic acid and its sodium salt as biosorbents:Effects of solution pH on neodymium recovery mechanisms

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Journal of Rare Earths 2018年第5期36卷 528-536页

作者： Misaki Hisada Yoshinori Kawase Research Center for Biochemical and Environmental Engineering Department of Applied Chemistry Toyo University

For recovery of metals from low-concentration sources, biosorption is one of promising technologies and poly-γ-glutamic acid（γ-PGA） has been known as a potential biosorbent for recovery of heavy metals from aqueous solutions. Effects of solution pH on recovery of rare-earth metal Nd are systematically examined to clarify mechanisms of Nd recovery by y-PGA and its sodium salt（y-PGANa）. The recovery efficiency of Nd by y-PGA increases from 2.4 to 19.6% as pH increases from 2 to 4. Subsequently the Nd recovery efficiencies for y-PGA and y-PGANa remain almost constant in the range of pH from 4 to 7. For pH 〉 7 the increase in Nd recovery is significant and 100% recovery of Nd is achieved at pH 9. The pH dependency on Nd recovery by y-PGANa is similar to that by y-PGA. Contributions of adsorption and precipitation/coagulation to Nd recovery process are quantified. Whereas the adsorption dominates Nd recovery at lower pH（〈～4）, the precipitation/coagulation controls Nd recovery process for pH 〉 7. At higher pH, purple gel precipitates are observed. The maximum adsorption capacities for γ-PGA and yPGANa are 215 mg-Nd/（g-γ-PGA） at pH 4 and 305 mg-Nd/（g-y-PGANa） at pH 3, respectively. From the spectra of FT-IR and XPS, the biosorption of Nd onto y-PGA and y-PGANa via electrostatic interaction with carboxylate anions at pH 3 is verified. The Nd complexation with amide and carboxylate anion groups on γ-PGA and γ-PGANa may also contribute to the Nd recovery. The biosorption isotherms for Nd recovery by γ-PGA and γ-PGANa can be satisfactorily fitted by the Langmuir model. The thermodynamic studies suggest that the biosorptions of Nd by γ-PGA and γ-PGANa are endothermic. The utilization of γ-PGA and γ-PGANa as potential and eco-friendly biosorbents for the highly effective recovery of Nd from aqueous solution is confirmed.

关键词： Rare-earth metal Nd recovery Poly-y-glutamic acid Biosorption Precipitation coexisting cations

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