Molecular Design And Synthesis Of Sulfoxides And Their Application In The Recovery Of Palladium And Platinum From Secondary Resources

Platinum group metals (PGMs) are precious metals, and their waste are significant valuable secondary resources in recovery industry that have been highlighted in many countries. Solvent extraction (SX) technology has been widely used in the recovery of PGMs from secondary resource, and sulfoxide extractants are emphasized in SX of PGMs due to their strong extraction and separation ability. In order to develop a good efficient sulfoxide extractants, quantum chemical molecular modeling methods were used to explore the structure-extraction property relationship. Based on the theoretical results, Benzyl iso-octyl sulfoxide (BSO) had be designed and synthesized successfully. The experimental results indicated that BSO exhibited excellent extraction property to PGMs. The main contents of this thesis are as follows.1. The substituent effect of sulfoxides di-n-hexyl sulfoxide (DHSO) and diphenyl sulfoxide(DPSO) in SX of palladium was investigated theoretically by using di-n-hexyl and diphenyl sulfoxide-palladium (II) adducts as model complexes. Various methods had been used in geometry optimization of free sulfoxides and their palladium (II) complexes at 6-31G* level (for metal Pd (II), 3-21G* basis set was used). It is showed that BHandH method can give adequate accuracy for both free sulfoxides and their Pd (II) complexes from geometry optimization results.2. Calculation results showed the binding energy (BE) of trans-PdCl2(DHSO)2 is more favorable by -76.154kJ/mol than trans-PdCl2 (DPSO)2. DHSO has larger binding affinity towards Pd (II) as compared to DPSO. The HOMO of DHSO is much localized on S and O atoms, while HOMO of DPSO contains aπbond located at the phenyl, and thus it lowered composition of S and O orbitals. The change of S atom charge indicates that DHSO could provide more electron density to the metal-sulfur bond than DPSO does, so the sulfur atom of DHSO is"softer"than that of DPSO. It is also found that the energy of all coordination bonds of trans-PdCl2 (DHSO)2 is lower than that of trans-PdCl2 (DPSO)2, but theπBack-Bonding interaction is the reverse.3. 2- Butyl- tetrahydrothiophene- 1- oxide (BTHTO) and three isomeric Pd (II) model complexes had been calculated. The calculated energy of model A complex with O-coordination is the highest among the three isomeric model complexes, and model B complex with S-coordination has the lowest energy. The molecular energy of model C complex with mixed S- and O-coordination is slightly higher than that of model B. O atom is preferable in coordination due to the less steric hindrance. In the SX process, BTHTO and Pd (II) form C mode complex firstly. the complex changes gradually into model B that is the thermodynamic steady state, this is evidenced by IR spectroscopy of cyclic sulfoxide-Pd (II) adduct.4. The new approach of unsymmetrical sulfoxide molecular design is presented. It is called the unsymmetrical sulfoxide molecular design; that is one substituent of sulfoxide is an alkyl with benzene ring which may improve the extraction of Pd (II) in O coordination mode, while the other one is an alkyl with side chain to increase the solubility in kerosene. It is found the extraction and back-extraction of Pd (II) is strengthened with O coordination fastly through the systemic analysis on some sulfoxide extractants. According to theoretical work, the alkyl with benzene ring could disperse orbital distribution of HOMO, weaken S coordination, and strengthen O coordination in SX process. Benzyl isooctyl sulfoxide was designed to verify above effects. Theoretical investigation of benzyl isooctyl sulfoxide (BSO) and di-isooctyl sulfoxide (DBESO) showed that BSO has a lower orbital distribution of HOMO in S atom and larger polarity in its protonated species, this suggests that extraction performance of BSO is superior to DBESO.5. Benzyl isooctyl sulfoxide, benzyl isoamyl sulfoxide and benzyl butyl sulfoxide had been synthesized based on the molecular design. These compounds were well characterized by FAB-MS, EI-MS, 1H NMR, 13C NMR and IR spectroscopy. Dibenzothiophene sulfoxide was also synthesized. S=O bond in dibenzothiophene sulfoxide is weaker than that of other sulfoxides because it has longer bond length. By using kerosene as the diluent, extraction of palladium (II) and platinum (IV) with BSO were studied. Extraction of palladium (II) is above 99% with 0.3mol/L BSO between 0.1 to 4.0mol/L [HCl], and extraction of platinum (IV) is above 99.5% with 0.6mol/L BSO in 4.0mol/L [HCl]. Aqueous phase containing 10.873g/L of Pd(II) and Pt(IV) 33.114g/L were extracted with 10% and 50% BSO, and the extraction achieve 98.0% and 98.2% respectively. Mixed S and O coordination is confirmed at low acidity and ion-pair formed at high acidity by IR spectrum of BSO Pd (II) extraction complexes. Furthermore, Pd (II) and Pt (IV) could be extracted and separated by BSO with high efficiency. In the co-extraction of Pd(II) and Pt(IV), the separation coefficient is 4.96×103 at high acidity, and in extraction of Pd (II) from Pt (IV) the separation coefficient is 2.23×105 at low acidity. Extraction behavior of benzyl isoamyl sulfoxide and benzyl butyl sulfoxide has not studied because their poor solubility in kerosene.6. BSO has been applied to extraction separation of PGMs from secondary resource. Extraction of palladium is 99.6 % from the solution of waste wire in 2.0mol/L[HCl] using 0.5mol/L [BSO], and the separation coefficient between Pd(II) and Cu(II) is 5.82×103. Palladium is stripped well by ammonium chloride-ammonia solution with 96% percentage of recovery. Thus palladium could be separated from the solution of waste wire containing copper and nickel metals successfully with high selectivity by BSO extractant.