Study On Recovery Of Precious Metals-Gold, Palladium, Platinum From Secondary Resourcse By Solvent Extraction

The industrial rejectamenta containing spent noble metals are valuable secondary resources for obtaining noble metals. Extraction using sulfoxides as extractant is considered as the most important method to get the noble metals from waste materials. Sulfoxides are viewed as the most promising extractant due to their good stability in acid or base solution and excellent extracting selectivity.Two kinds of cyclic sulfoxide are prepared in this work. The TMSO is prepared by oxidation of THP with hydrogen peroxide in acetone solution, the productivity is about 80.5%,and then cyclic sulfoxide derivative, α -dodecyl-tetrahydrothiophene-o-oxide(DTMSO), is prepared by the alkylation of tetrahydrothiophene-o-oxide. The influences of molecular ratio of raw materials, reaction time and temperature on the productivity are discussed in detail. DTMSO is separated and purified with a silica gel columnThe structure of DTMSO is characterized with FT-IR, ^H-NMR, ¹3C-NMR and MS spectra. It is showed that the prepared extractant is a mixture of Cis- and trans-isomers. The effect of solvent on structure of DTMSO is discussed and the difference of ¹H-NMR of DTMSO separated from silica gel column with different solvent is explained.On the basis of study of DTMSO, two new kinds of extractant, OTMSO and BTMSO, are synthesized. Both of them are yellow liquid and their structures are characterized.The behavior and mechanism of extraction of Au (III) with Cyclic sulfoxide derivatives are investigated. It is found that the extraction percentage increases with the raise of the concentration of DTMSO. The extraction percentage can reach 98% under the condition of C_dtmso=0.1 mol L^-1,C_Au=0.89 g L^-1 and C_HCl =0.1 mol L^-1. The extraction of Au is a rapid exothermic reaction. The back-extraction of Au loaded in the organic phase can be carried out by using Na₂SO₃ solution as back-extractant. The stripping percentage of gold can get up to 92% when the 12.5% Na₂SO₃ solution is used. The mechanism of extracting gold is also studied in this work, the results indicate that gold is extracted as the coordination compound which exists in the form of oxygen-metal coordination in low acidity, and the reaction is a neutral solvent complexing extraction. In the high acidity, the extraction is an acid association one, intercoordination transfer occurs within complex, because the conversion of configuration occurs before extraction, the complex with single configuration is formed, and Au is coordinated with oxygen atom in >S=O group.The relation between structure of sulfoxides and their behavior in extraction of gold is investigated. The order of the ability of extracting gold with sulfoxides is obtained as follows: E_Dtmso>E(otmso)>E(btmso)The mechanism of extracting Au (III) with DTMSO and OTMSO having longchain is neutral solvent complexing extraction at low aqueous acidity, theirmechanism of extracting Au( III )is acid association extraction at high aqueous acidity.Au is coordinated with oxygen atom in >S=O group. The mechanism of extracting Au(III) with BTMSO having short chain is neutral solvent complexing extraction, andAu is coordinated with oxygen or sulfur atom in >S=O group 0Furthermore the extraction of Palladium with Cyclic sulfoxide derivatives is also investigated. The extraction percentage can reach 98% under the condition of Cdtmso=0.3 mol L"1, Chci=0.1⁴ mol L"1 . The extraction of Pd is a rapid exothermic reaction. The stripping of Palladium from the organic phase is achieved using aqueous solutions of Na2SC>3 and Stripping percentage can get up 87.5%. The structure of complex and its change are discussed by slope method, UV spectra, FT-IR spectra,'H-NMR spectra and 13C-NMR spectra ,and the mechanism of extracting Palladium with DTMSO is deduced: the reaction is neutral solvent complexing extraction and acid association extraction at low aqueous acidity, Palladium is coordinated with oxygen or sulfur atom in >S=O group, the complex of Palladium being coordinated with oxygen atom in >S=O group will change into the complex of Palladium coordinated with sulfur atom in >S=O group after a long time through a transition condition and the reaction is acid association extraction at high aqueous acidity. In complex, intercoordination transfer occurs between sulfoxide and PdCU2" and the complex coordinated with S atom is formed. The ability of some sulfoxides for extracting Palladium can be described as following order: Edtmso>Eotmso>Ebtmso- The order of ability of coordination of oxygen atom is BTMSO>OTMSO>DTMSO. The mechanism of extracting Palladium with DTMSO and OTMSO is the same. The mechanism of extracting Palladium with BTMSO is also a neutral solvent complexing extraction.The extraction of platinum is studied, it is found that the extraction percentage can get up to 91% under the condition of Cdtmso=0-6 mol L"1, C hci= 4 mol L"1. The extraction of Pt with DTMSO is also a rapid exothermic reaction. The loaded organic phase of platinum can be stripped with 2%Na2SO3 solution and stripping percentage of platinum is 68%. Back-extraction percentage increases with increasing the concentration of Na2SO3. The structure of complex is discussed by slope method, UV spectra, FT-IR spectra, 'H-NMR spectra and 13C-NMR spectra. The extracting reaction is acid association extraction. Composition of complex is (H+- H2O- 2DTMSO)2PtCl62\ platinum is coordinated with S atom in >S=O group.The extraction of Palladium from electroplating wastewater containing a large quantity of Na, Sn, Cu is studied, concentration of Palladium is smaller than 5mg L"1 in aqueous after extractions with 0.2mol L^OTMSO repeated three times, Extraction percentage of Palladium can reach 99.6% and Stripping percentage of Palladium from the loaded organic phase can reach 97%, therefore, percentage of recovery of Palladium can get up to 96.6%, it can match the requirements of recovery noble metals industrially.