Synthesis Of Polymeric Ester Thiourea Resin And Its Adsorption And Separation Properties For Noble Metal Ions

Based on the quantum chemistry calculation and bonding features of noble metal ions and its ligands, a new chelating resin, polymeric ester thiurea resin, was designed and synthesized and applied to adsorption and separation for Au³⁺, Ag⁺, Pt⁴⁺ and Pd²⁺.Quantum chemistry calculation of common ligands was performed in the framework of density functional theory with Gaussian 03 software at B3LYP/6-31G(d) level, and bonding features of noble metal ions and ligands were studied with the help of hard and soft acids and bases theory. The result indicates that the energy ofσ-type HOMO of ester thiourea group is very high, that ofÏ€-type LUMO is low relatively and is negative, so it has strong strong coordinating ability with noble metal ions. According to theoretical analysis and experimental results, polymeric ester thiurea resins have good adsorption ability and selectivity to noble metal ions.Reverse synthesis method was employed to design the synthesis route of polymeric ester thiourea resin and their intermediates, and a novel polymeric ester thiourea resin was invented. Bischloroformates were prepared by the reaction of diols and triphosgene, catalyzed by N,N-dimethyl aniline (DMA); bischloroformates reacted with KSCN by solid-liquid phase transfer catalysis, also catalyzed by DMA, from which diisothiocyanatidates were synthesized; at last, diisothiocyanatidates reacted with polyamine to obtain polymeric ester thiourea resins. Synthesis technologies of bischloroformates, diisothiocyanatidates and polymeric ester thiourea resins were studies systematically by experimental research, and optimal conditions were as follows: molar ratio of triphosgene to doils 2.2:3, molar ratio of DMA to doils 0.035:1, reaction temperature 5℃, and reaction time 10 h for preparation of bischloroformates; molar ratio of bischloroformates to KSCN 1:2.5, reaction temperature 5℃, and reaction time 3.5 h for preparation of diisothiocyanatidates; molar ratio of amino groups and isothiocyanatidate groups 1.25:1, reaction temperature 5℃, and reaction time 5 h for polymerization reactions. Five series and 20 kinds of polymeric ester thiourea resins, polymaric ethyl ester thiurea resins (PE), polymaric butyl ester thiurea resins (PB), polymaric diethyl ether ester thiurea resins (PD), polymaric hexyl ester thiurea resins (PH), polymaric diethoxyethane ester thiurea resins (PT), were prepared. Yields of PB and PD are all above 90%, and higher than others. Element analysis, FTIR, XRD, SEM and TG, etc. were adopted to characterize their structures and properties.Adsorption properities of polymeric ester thiurea resins for Au³⁺, Ag⁺, Pt⁴⁺ and Pd²⁺, etc. were investigated systematically. The relationship of structure of resins and adsorption properities were studied by batch test, and according to effects of the kind of resins and molar ratios of monomers on adsorption capacities for Au³⁺, PB and PD were selected for farther studies. PB and PD have higher adsorption capacities for Au³⁺, Ag⁺, Pt⁴⁺ and Pd²⁺, for example, adsorption capacities of PB1 for Au³⁺, Ag⁺, Pt⁴⁺ and Pd²⁺ are 4.55, 4.32, 1.60 and 3.00 mmol·g^-1 respectively, and those of PD1 are 4.90, 4.50, 1.85 and 3.41 mmol·g^-1 respectively. Adsorption capacities of PB1 and PD1 for Au³⁺, Ag⁺, Pt⁴⁺ and Pd²⁺ increase with the increases of adsorption time and initial concentrations of nobel metal ions; With the increases of acidities, adsorption capacities increase for Au³⁺ and Pt⁴⁺, keep invariant for Pd²⁺, increase firstly and decrease successively for Ag⁺. In dynamic adsorption experiments for Au³⁺ and Ag⁺, adsorption rates of PB1 and PD1 decrease with the increase of flow rates and increase with the increase of the amounts of resins. Breakthrough curves were also determined, and the adsorption rates are high at penetrative points.Adsorption kinetics, thermodynamics and coordination mechanism of resins were revealed by analyzing adsorption data and FTIR and XPS data of resins fore-and-aft adsorption. The adsorption data of PB and PD fit Boyd's diffusion equation of liquid film, indicating the adsorption is controlled by liquid film diffusion. The isothermal adsorption of PB 1 and PD1 obey Langmuir and Freundlich equation, especially the former equation, indicating that the adsorption is a monolayer one;â–³H,â–³G andâ–³S were calculated by thermodynamic formulas. According to FTIR and XPS, functional groups of the resins coordinated with noble metal ions in the adsorption. S, N and O atoms donate electrons to Au and Ag atoms in the adsorption of Au³⁺ and Ag⁺; S and O atoms donate electrons to Pt and Pd atoms in the adsorption of Pt⁴⁺ and Pd²⁺.Separation properities and regeneration technology of polymeric ester thiurea resins for noble metal ions were studied. PB and PD have higher adsorption capacities for noble metal ions, those for Cu²⁺, Zn²⁺, Fe³⁺, Co²⁺, Ni²⁺ and Pb²⁺ are lower relatively, and those for Ca²⁺, Mg²⁺, Na⁺ and K⁺ are the lowest. Separation factors of noble-base metals binary metal ion systems are above 1300, 110, 90 and 80 for Au³⁺, Ag⁺, Pt(4+) and Pd²⁺ respectively, indicating that adsorption selectivity for noble metal ions is excellent. In dynamic adsorption experiments, adsorption capacities of Au³⁺ and Ag⁺ in mixing solutions are still very high, so it can be concluded that the resins could be applied to separation of noble and base metal ions. Acidic thiourea solutions were applied to desorption of noble metals on PB1 and PD1, and the results indicate that elution and regeneration properties are very good.Active carbon fiber cloth (ACFC) and polyethylene terephthalate (PET) nonwoven cloth support polymeric ester thiurea resin composite absorbents were prepared, and their adsorption properities were also investigated. Polymeric ester thiurea resin composite absorbents, ACFC-PD1 and PET-PD1, were prepared by impregnation, polymerizing diethyl ether diisothiocyanate and diethylene triamine on ACFC and PET nonwoven cloth. They were characterized by FTIR, SEM, element analysis and TG, etc. Batch testes were adopted to investigate adsorption property of composite absorbents for Au³⁺. The adsorption data fit Boyd's diffusion equation of liquid film, Langmuir and Freundlich isotherm equation. Adsorption capacities decrease with the increases of temperatures, indicating that the adsorption is an exothermic process. The physical and adsorption properities of absorbents are improved by modification, and the composite absorbents are hopeful to be put into practice.