Abstract
Ph.D. (Chemistry)
Due to the continued global demand for silver and gold, there is constantly a need for more efficient and cost-effective methods to recover these precious metals from industrial aqueous solutions. The recovery of these metals is not easy owing to their presence in complex matrices. As selective recognition elements materials, molecularly imprinted polymers (MIPs) have been attracting great attention for their application in metals extraction. In this research, the performance of imprinted polymers as an adsorbent for the selective recovery of precious metal ions from mining and metallurgical wastewaters was investigated. The imprinted polymers were prepared using various functional monomers (vinylated monomers) and modified chitosan-biopolymers. Various techniques were used to characterize the prepared polymers and to elucidate their interaction mechanisms with the studied precious metal ion. The study also investigated the adsorption behavior of these materials in single and co-adsorption metal ions systems.
In the first part of the study, ion-imprinted polymers (IIPs) were prepared by bulk polymerization method using three coordinating monomers namely: 4-vinyl pyridine (4-VP), N-(4-vinyl benzyl) ethylenediamine (EDA) and N-(allyl)-N-diethylthiophosphate (ADT), and ethylene glycol dimethacrylate (EGDMA) as a cross-linker. Comparative studies on the adsorption performance of these IIPs for gold ion were conducted. The results obtained indicated that IIPs containing 4-VP had superior adsorption capability and selectivity towards gold compared to the other IIPs. Molecular modeling, using a Gaussian software package, was used to understand this difference in the adsorption ability. The results obtained indicated that the interaction between gold ion and 4-VP monomer is the strongest (ΔG = -4143.75 kcal mol-1) than its interaction with the other two monomers, suggesting that the adsorption process is more feasible for the IIP derived from 4-VP. FTIR and XRD analysis were done in order to understand and elucidate the adsorption mechanisms. It was proposed that gold ion adsorbed onto IIPs 4-VP and EDA by coordination and ion exchange mechanisms, while complexation – reduction mechanism was the one that accounted for its adsorption onto ADT produced polymeric material.
In another attempt, IIPs synthesized from two functional monomers, 4-VP and 1-vinyl imidazole (1-VID), and N, N-ethylene bisacrylamide (EBAm) as the crosslinker via a precipitation polymerization method were found to be suitable for Ag(I) extraction...