Hongcheng Gao

Extraction and separation of gold (I) cyanide in polyethylene glycol-based aqueous biphasic systems

Abstract The extraction of gold (I) cyanide in polyethylene glycol-based aqueous biphasic systems has been investigated. Almost all of gold (I) cyanide (>96%) was transferred from salt-rich phase into the polyethylene glycol (PEG)-rich phase without addition of any extractant. No significant influence of solution pH on gold (I) cyanide extraction was observed. The aqueous biphasic systems have high capability of extraction. The gold (I) cyanide in the PEG-rich phase can be easily reduced by addition of zinc. The PEG-rich phase could be reused for extraction of gold (I) cyanide without decrease of extraction capability. The PEG/salt aqueous biphasic systems may provide a potential new technique for gold separation from cyanide solutions because all components of systems are virtually nontoxic and nonflammable.

Extraction of gold from alkaline cyanide solution by the tetradecyldimethylbenzylammonium chloride/tri-n-butyl phosphate/n-heptane system based on a microemulsion mechanism

The mechanism of extraction of gold by tetradecyldimethylbenzylammonium chloride (TDMBAC)/tri-n-butyl phosphate (TBP)/n-heptane solution from an aqueous alkaline cyanide solution was studied by means of extraction equilibrium, Karl Fischer titration, electrical conductivity, FTIR spectroscopy and dynamic laser scattering (DLS). When the gold concentration is lower than 3 g L−1 and the volume percentage of TBP is less than 10%, the plots of the extraction percentage of gold against the molar ratio of [TDMBA+] to [Au(CN)2−] and logD–log[TBP](o) plot indicated that the stoichiometry of the extracted species is a 1 ∶ 1 ∶ 4 complex, TDMBA+ ∶ Au(CN)2− ∶ TBP. Karl Fischer titration showed that 4 H2O molecules participate in the formation of such a species. Electrical conductivity measurements confirmed its ionic character. Fourier self-deconvolution of the O–H stretching bands revealed 4 different kinds of water molecules contained in the organic phase, some of which were bound to TBP via hydrogen bonding. A supramolecule [TDMBA+] · [Au(CN)2−] · 4H2O · 4TBP is proposed for the extracted species. Two TBP molecules are bound to [Au(CN)2−] by two H2O bridges through hydrogen bonding, forming a [(RO)3PO⋯H–O–H⋯NC–Au–CN⋯H–O–H⋯O = P(OR)3]− moiety. Two hydrated TBP molecules, (RO)3PO⋯H–O–H, surround [TDMBA+] by ion–dipole interaction. The bulky anion and cation form a lipophilic supramolecule. The possible structure of the supramolecular anion was calculated with an ab initio molecular orbital (MO) method. The DLS study showed that mixing of TDMBAC and Au(CN)2− in the aqueous phase led to the formation of micelles. When an organic phase containing TBP was added to this aqueous phase, the complexes transferred into the organic phase and reversed micelles or a microemulsion (W/O) were formed when the gold concentration reached a certain limiting value.

Solvent Extraction of Gold from Alkaline Cyanide Solution with a Tri‐n‐octylamine/Tri‐n‐butyl phosphate/n‐heptane Synergistic System

Abstract Solvent extraction of KAu(CN)2 from alkaline cyanide solution by using the pre‐acidified tertiary amine, tri‐n‐octylamine(TOA) as extractant with the addition of tri‐n‐butyl phosphate (TBP) as a synergist has been studied. The influence of several variables such as the molar ratio of TOA to KAu(CN)2 (n r ), the volume percentage of TBP (ϕ TBP ), the phase ratio of the organic phase to the aqueous phase and the pH value of the aqueous phase were investigated. The results indicated that, at a certain pH range, while ϕ TBP is above 20%(v/v) and n r is bigger than 1, the organic phase can extract gold from the aqueous phase completely. The relationship between the extraction percentage of gold (E) against n r and the logD − logϕ TBP plot indicate that the stoichiometry of the extracted species is a 1:1:3 complex, namely, [TOA · H+] · [Au(CN)2 −] · 3TBP. Dynamic laser scattering (DLS) method reveals that the organic phase tends to self‐assemble to form aggregations when the concentration of gold in the organic phase reaches a certain limiting value. The stripping of the loading organic phase by NaOH and inorganic salts, such as NH4SCN, NaClO4 and potassium halides, has also been investigated.

Photoluminescence Phenomenon during the Formation of Silver Nanoparticles

Silver nanoparticles were synthesized by the method of γ-irradiation in the water-in-oil (w/o) microemulsion composed of SDS (sodium dodecyl sulfate), n-hexanol, cyclohexane and aqueous solution. Light emission in different formation stages was observed, and we found that in our case it was mainly the clusters but not nanoparticles that caused the photoluminescence, with the proof from the absorption spectra and transmission electron microscope (TEM). And it was also suggested that electron and/or hole states can be perturbed by surface states, as indicated by the dependence of the emission spectrum on the nature of the surface. Silver nanoparticles can self-assemble to form the superlattics due to the very narrow size distribution.

FTIR and EXAFS investigations of microstructures of gold solvent extraction: hydrogen bonding between modifier and Au(CN)2-

The microstructures of loaded organic phases of three quaternary amine solvent extraction systems for gold, which were N263–xylene, N263–tributyl phosphate (TBP)–dodecane and N263–2-ethylhexanol (isooctanol)–dodecane (N263-trialkylmethylammonium chloride; alkyl=C8–C10), were studied by Fourier transform infrared (FTIR) spectroscopy and extended X-ray absorption fine structure (EXAFS) spectroscopy. According to the EXAFS results, it was found that the gold coordination environment was the same before and after extraction. However, the C3N stretching vibrations of Au(CN)2- in the three systems differed greatly. The second derivative spectra of C3N stretching bands of Au(CN)2- were also found to be different. In order to explain the differences in the IR characteristics of C3N in the three extraction systems, three microstructure models are proposed. For the N263–xylene system, the model is a simple ion pair. For the other two systems with a modifier (TBP and isooctanol), the models are two supramolecular structures based on hydrogen bonding between the modifier and Au(CN)2-. Some related work such as on the hydration of acetonitrile and the fine structure of C3N in solid KAu(CN)2 was also performed in order to offer additional supporting evidence for the reliability of the proposed models.

Solvent extraction and stripping of gold(I) cyanide in the tetradecyldimethylbenzylammonium chloride system

Abstract The solvent extraction of KAu(CN) 2 from alkaline cyanide solutions by using quaternary ammonium tetradecyldimethylbenzylammonium chloride (TDMBAC) as extractant with the addition of tri- n -butylphosphate (TBP) has been investigated with the 198 Au radioactive tracer method. The influence of several variables such as agitation time, volume percentage of TBP and the molar fraction of TDMBAC in the aqueous phase ( x TDMBAC ) were investigated. The results indicated that the organic phase has a high extraction capacity. Almost all of the Au(CN) 2 − (>95%) was transferred from the aqueous phase into the organic phase. Most of the Au(I) in the organic phase can be stripped with 2,2′-thiodiethanol, glycol or ammonium thiocyanate aqueous solutions, from which elemental gold could potentially be recovered by the addition of reducing agents, such as NaBH 4 and zinc. The extraction mechanism can be explained based on a microemulsion mechanism while the mechanism of stripping by inorganic salts follows the perchlorate effect.

FT-IR Study Of Rare Earth Naphthenates In The Extract Phase

The FT-IR spectra and subtraction spectra of fifteen rare earth naphthenates in the extract phase have been studied with the following results: (1). The symmetrical stretching vibration band 04) of the carboxylate ion in the extracted rare earth naphthenates can not be found in the used FT-IR spectra, but we have found them in the subtraction spectra. (2). Then the differences between j),ms (asymmetrical frequency of COO ) and y can be obtained from which the coordination structure of rare earth naphthenates may Be discussed. (3). By this way, the effect of coordination of the secondary octyl alcohol (ROH) with the rare earth naphthenates was observed.

FT far-IR investigation of rare earth nitrates in non-aqueous solution

The Fourier far infrared spectra of 14 lanthanide and yttrium nitrates in ethyl alcohol, dimethyl formamide and propylene carbonate have been investigated. From the subtraction spectra, a new broad band in the range of 190–260 cm−1 was observed for each solution, these bands are assigned to Re3+-O (solvent oxygen) stretching vibration.