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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.

The extraction of gold from thiosulfate solutions with a mixture of neutral reagents and amines was studied. A combination of the primary amine N 1923 and the neutral donor reagents, such as alkyl phosphorus esters, was found to be the most effective solvent for the extraction. Using slope analysis, the compositions of the gold extraction species in mixed organic solvents with N 1923 and tributyl phosphate (TBP) were investigated. The effect of N 1923 and TBP in the mixed organic phase on the extraction is not the same for different ranges of aqueous pH. It may be proposed that with an equilibrium pH 1923 is the main extractant with TBP as a synergistic reagent; while with an equilibrium pH>9, N 1923 shows a synergistic effect on the extraction of gold with TBP.

The extraction of gold from thiosulfate solutions with alkyl phosphorus esters was studied. The experimental results showed that the gold can be extracted only in alkaline thiosulfate solutions. The gold recovery increases with the increase in concentrations of thiosulfate in the aqueous phase and of alkyl phosphorus esters in the organic phase respectively. Compared with aliphatic hydrocarbon diluents, aromatic hydrocarbons tested are unfavorable to the gold extraction. The addition of ammonia to thiosulfate solutions has a strong influence on the mechanism of the extraction of gold.

Studies on the synergistic extraction of phosphorus, arsenic and silica as impurities from sodium tungstate and molybdate solutions with a solvent mixture of primary amine and tributyl phosphate (TBP) were made. The experimental results indicate that phosphorus, arsenic and silica can be extracted and separated very effectively from weakly alkaline sodium tungstate and neutral molybdate solutions. The extraction behavior of phosphorus and arsenic for molybdate systems is quite different from that for tungstate systems. For molybdenum systems, the optimum separation of phosphorus and arsenic can only be obtained in a narrow range of equilibrium pH values of about 6-7; outside this pH range the extraction of these two elements decreases sharply. However, the extraction of phosphorus, arsenic and silica for tungsten systems and silica for molybdenum system increases with decreasing pH. Phosphorus, arsenic and silica cannot be extracted without the presence of tungsten and molybdenum in the aqueous phase. The loaded organic phase can be stripped with dilute sodium hydroxide solution quantitatively. The alkaline crude leaching solutions of sodium tungstate and ammonium molybdate were tested and the results were in agreement with those obtained from solutions prepared by mixing sodium salts of the elements concerned.

The mechanism of the removal of phosphorus, arsenic and silica from tungstate or molybdate solutions by synergistic extraction with primary amine and tributyl phosphate (TBP) was investigated. Phosphorus, arsenic and silica were considered to be extracted into the organic phase as heterotungstic or heteromolybdic acids. The composition of the extracted species is strongly dependent on the concentration of tungsten and molybdenum and equilibrium pH values of the aqueous phase, An extraction mechanism based on the formation of hydrogen bonding between the primary amine, TBP and heteropoly acids is proposed. The loaded organic phase was characterized by UV and IR spectra and by molar conductance, It is proposed from the experimental results that the proton transfer from the heteropoly acids to the primary amine in the extracted species occurs intramolecularly, resulting in the formation of ion-associated species, because the primary amine is a weak base and heteropoly acids are strong acids. The mechanism of proton transfer is also proposed.

Metallic membranes with minipores have been used in the rotating disc diffusion cell (RDC) for the quantitative study of the effect of diffusion on the kinetics of solvent extraction. A study of the mass transfer of KCI through the membrane at different rotational speeds showed that the hydrodynamic conditions on the both sides of the membrane are reproducible. A kinetic study of iron(III) extraction from sulfate solutions with primary amine N-1923 and TBP (tri-butyl phosphate) was performed with the modified RDC after cell calibration. The results showed that the rate-limiting step in the extraction process is chemical reactions at the interfaces. The effects of various parameters on the rate of extraction suggested that the reaction order may be 1, 1, - 1 and 0 with respect to the concentrations of iron(III), amine sulfate, hydrogen ion and TBP, respectively. Due to the change in the reaction mechanism, the rate of extraction increased by one order of magnitude with the addition of TBP to the primary amine system.

The conversion of galena into lead carbonate in ammonium carbonate solution through which oxygen was bubbled was found to be a slow process whose rate could be significantly enhanced in the presence of cupric ions. A kinetic and electrochemical investigation was carried out on this system. It was found that, except at the beginning of the reaction, the kinetic results could be well described by an empirical equation alpha = (Klog(t)) + B, where alpha is the fraction of conversion, t is the reaction time and K and B are constants. The catalytic effect of cupric ions was due to the Cu(NH3)42+ complex facilitating the transfer of electrons from PbS into oxygen. The electrochemical results supported this mechanism, and the Stem-Geary method was used to evaluate the increase in the conversion rate in the presence of cupric ions. A higher conversion could be achieved with high concentrations of both cupric ions and ammonium carbonate.

The extraction of Fe (III) in sulfate solution by a mixture of tertiary amine and alkylphosphonic acid monoalkyl ester or dialkylphosphinic acid as solvent was studied. The stripping of iron extracted into the organic phase with sulfuric acid was also investigated. Synergism was found to be present in the extraction of Fe (III) with these two types of solvent mixture. The extraction and stripping of iron with HEHEHP as solvent with and without the addition of tertiary amine to the organic phase were compared. It has been indicated that with the addition of tertiary amine not only are the rates of extraction and stripping increased but also the concentration of sulfuric acid required for the stripping of iron in the organic phase is reduced. Satisfactory separation was obtained with this solvent mixture for removal of Fe (III) in aluminium sulfate and zinc sulfate leaching solutions.

The stripping of Fe(III) extracted by di-2-ethylhexyl phosphoric acid (HDEHP) in kerosene as organic phase with sulfuric acid was studied. Results indicate that whether it is easy or difficult to strip Fe(III) in the organic phase using H2SO4 depends mainly on the species of iron extracted into the organic phase. When the iron was extracted from solutions with pH of 1.5–2.5 as hydroxyferric complexes into the organic phase, it was stripped rather easily with dilute sulfuric acid. When it was extracted from solutions with pH ∼ 1.0 as unhydrolyzed iron, a high concentration H2SO4 was required for stripping. When iron was extracted from highly acid solution by solvation, it cannot be stripped, even with highly concentrated sulfuric acid.