In this thesis, a novel concept for the development of a polysulfone (PS)-biomass composite fiber as a high-performance and acid-tolerant adsorbent for the recovery of precious metals from acidic solutions is reported. Polyethylenimine (PEI)-coated polysulfone-Escherichia coli biomass composite fiber (PEI-PSBF) was prepared by spinning biomass-PS blends into water, coating with PEI and cross-linking with glutaraldehyde (GA). Polysulfone fiber (PSF), polysulfone-biomass composite fiber (PSBF), and PEI-modified PSF (PEI-PSF) were also prepared and their sorption capacities were compared with PEI-PSBF. Pt(IV) was used as model precious metal ion. The results of SEM and FTIR analyses revealed the presence of PEI on the surface of PEI-PSBF. The maximum Pt(IV) uptake of PEI-PSBF was 6.6 times higher than that of PSBF. However, the PSF showed negligible sorption capacity toward Pt(IV). Pt(IV) ions were completely recovered from loaded PEI-PSBF by 0.1 M thiourea in 1 M HCl solution. The PEI-PSBF was also stable in 0.1 M and 1 M HCl solutions.
In preparation of PEI-PSBF, the solution pH in the PEI coating step was a key factor affecting the sorption performance of PEI-PSBFs of precious metal Pd(II), which was used as a model precious metal. The optimum pH for coating was around pH 9 where the Pd(II) uptake was 101.35 ± 5.88 mg/g. The effect of pH on the sorption performance was able to be explained with pH-dependent speciations of the E. coli biomass and PEI and their electrostatic attraction. The pH for the maximum electrostatic attraction was calculated to be pH 9.2 which was similar to experimentally observed optimum pH. Furthermore, an enhanced PEI-coating efficiency was achieved by removing the electrostatic repulsion through succination of amine groups on the E. coli biomass which. The PEI-coating efficiency of PEI-PSSBF was dependent on pH. In addition, the use of succinated biomass made the applicable pH range wide, which was another evidence to support that electrostatic repulsion was eliminated.
The Pd(II) and Pt(IV) sorption performances of developed sorbents were evaluated in single Pd(II), Pt(IV) and Pd(II)-Pt(IV) bimetal solutions to test selective sorption behaviors. The comparison of Pd(II) selectivity was carried out by using ion exchange resins with different types of amine groups. In the single metal systems, the sorption capacities of PEI-PSBF for Pt(IV) and Pd(II) were found to be 237.33±18.64 and 158.70±12.59 mg/g, respectively. Meanwhile, in the bimetal system, the sorption capacities for Pd(II) and Pt(IV) were 102.85±1.87 and 70.97±2.78 mg/g, respectively, which corresponded to 1.7 times of selective adsorption toward Pd(II). The Pd(II) selective adsorption behavior of PSBF was higher than PEI-PSBF. In order to understand the underlying reason, ion exchange resins (TP214 and Amberjet 4200) with different amine types were compared with the PEI-PSBF and PSBF. As a result, it was found that the sorbents containing primary amine groups could selectively adsorb Pd(II) more easily in the binary mixture. Based on the selective binding property and mechanism the selective separation of Pt(IV) and Pd(II) was achieved by chromatography method with PEI-PSBF and various desorption eluants.