S Martínez

Gold extraction equilibrium in the system Cyanex 921-HClAu(III)

Abstract The partition of gold from hydrochloric acid solutions by the phosphine oxide Cyanex 921 has been studied. The extraction system is exothermic (ΔH° = −44.6 kJ/mol), the extraction being influenced by several variables. Maximum gold extraction is obtained in the HCl concentration range 5–7 M. Experimental data were analyzed numerically using the program LETAGROPDISTR. The results showed that the extraction can be explained assuming the formation of the species HAUCl4L (log K° = 1.99) and HAuCl4L2 (log K° = 6.68) in the organic phase, where L represents the organic extractant. From the experimental data the interaction coefficients for (AuCl4−1, H+) were estimated. Gold stripping is achieved effectively with water and the reaction is endothermic (ΔH°= 16.9 kJ/mol). Results on the extraction of HCl by Cyanex 921 are also presented.

The phosphine oxides Cyanex 923 and Cyanex 925 as extractants for gold(I) cyanide aqueous solutions

Abstract The behaviour of the phosphine oxides Cyanex 923 and Cyanex 925 in the recovery of gold(I) from cyanide solutions is described. Extractions are studied as a function of several variables such as temperature, diluent aromaticity, ionic strength and extractant concentration. Gold(I) stripping can be accomplished effectively with low aqueous ionic strength solutions and at high temperatures. From the experimental results it is seen that Me+-Au(CN)2−·3R3PO, where Me+=Li+ and R3PO=the phosphine oxide, is extracted into the organic phase. The extracted species is probably solvated by water.

The extraction of gold(I) from cyanide solutions by the phosphine oxide Cyanex 921

Abstract The extraction of gold from cyanide solutions by the commercially available phosphine oxide, Cyanex 921, is described. The effect of several variables, such as equilibration time, temperature, diluent aromaticity, extractant concentration and the ionic strength of the aqueous phase is discussed. An IR spectroscopy study showed that the Au (CN) 2 − complex and the extractant did not form a discrete compound, supporting a solvating mechanism of extraction. Results showed that the phosphine oxide could effectively extract gold(I) cyanide from alkaline solutions. Stripping was accomplished by low ionic strength aqueous solutions and enhanced by high temperatures.

Solvent extraction of gold (III) by the chloride salt of the tertiary amine Hostarex A327. Estimation of the interaction coefficient between AuCl4− and H+

Abstract The equilibrium distribution of gold (III) between hydrochloric acid and the chloride salt of the amine Hostarex A327 in n -decane was studied. The extraction reaction is exothermic (Δ H °=−22.9 kJ/mol). Gold (III) is extracted by the reaction: R 3 NH + Cl − org +AuCl − 4 aq ⇄R 3 NH + AuCl − 4 org +Cl − aq The extraction equilibrium constant depends on the ionic strength. From this dependency it was estimated that the interaction coefficient (AuCl 4 − ,H + ) is 0.26.

Extraction of gold from cyanide or chloride media by Cyanex 923

This work was Ðnancially supported by the DGICYT (Spain), Project PB89-0021. Authors would also like to acknowledge Mrs M. I. Cuenca for her collaboration.

Permeation of iron(III) by an immobilised liquid membrane using Cyanex 923 as mobile carrier

A study of iron(III) transport through an immobilised liquid membrane using the phosphine oxide Cyanex 923 as carrier has been carried out using batch experiments. A model is reported describing the transport mechanism which consists of (i) a diffusion process through a feed aqueous diffusion layer, (ii) a fast interfacial chemical reaction and (iii) a diffusion of HFeCl4·2L through the membrane. The mathematical equations describing the rate of transport are derived which correlate the membrane permeability coefficient to diffusional and equilibrium parameters as well as the chemical composition of the system, such as carrier concentration in the membrane phase and hydrochloric acid in the feed phase. The experimental data are explained with the derived equations and the diffusion resistances to mass transfer are evaluated. The influence on the transport of stirring speed in the feed phase and the nature of the diluent have also been discussed.

Cloning of a gene encoding a DNA polymerase-exonuclease of Streptococcus pneumoniae

A procedure was developed for cloning and characterizing genes that encode proteins with nuclease activity in the Streptococcus pneumoniae [pLS1] host/vector system. Clones are screened for nuclease activity by a DNase colony assay and the nucleases that they produce are characterized by detection of enzyme activity after sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The method was used to clone the gene encoding a DNA polymerase (Pol)-exonuclease of S. pneumoniae. The activity of this enzyme, the predominant DNA Pol of S. pneumoniae, is tenfold greater in cells carrying the multicopy recombinant plasmid than in cells without the plasmid. The enzyme corresponds to a 100-kDa polypeptide, and its properties are similar to PolI of Escherichia coli. A restriction map of the pSM22 plasmid containing the pneumococcal polA gene was obtained. The gene was transferred into Bacillus subtilis and E. coli, and it was expressed in both species. Its direction of transcription was determined by placement of the gene in both orientations in an E. coli hyperexpression plasmid. In one of the orientations the pneumococcal PolI enzyme was produced at a level 50-fold greater than normally found in S. pneumoniae, and it comprised 5% of the total protein.

The solvent extraction system Au(III) — HCl-Cyanex 471X

Abstract The effectiveness of Cyanex 471X as extractant of gold(III) from hydrochloric acid solutions is demonstrated. The extraction system is endothermic and experimental variables, such as extractant concentration, organic diluent and hydrochloric acid concentration, influence it. Maximum gold extraction is obtained in the range of 1–3 M HCl concentrations. Equilibrium loading isotherms showed that the [Cyanex 47lX]/[Au (III)] molar relationship in the organic phase is near l.5, which is the probable stoichiometry of the extracted species defined by HAUCl 4 L (log K ext ° = 3.79) and HAUCI 4 L 2 (log K ext ° = 6.34), L representing the organic extractant. The system seems to be suitable for the selective extraction of gold. Stripping of the metal can only be accomplished using sodium thiosulphate solutions, the corresponding reaction also being endothermic.

Complementation of Bacillus subtilis polA mutants by DNA polymerase I from Streptococcus pneumoniae

SummaryThe polA gene of Streptococcus pneumoniae cloned in the recombinant plasmid pSM22 is expressed in Bacillus subtilis. Extracts of B. subtilis polA mutants containing pSM22 showed 6 times more DNA polymerase activity than extracts of wild-type cells without the plasmid. Complete complementation of the B. subtilis polA5 and polA59 mutations with respect to in vivo resistance to UV irradiation and methyl methanesulfonate was observed when four copies of the pneumococcal polA gene were present in each cell. Ectopic integration of the polA gene together with a cat marker into the chromosome of B. subtilis gave chromosomal insertions containing single and double doses of the pneumococcal polA gene. Correlation with gene dosage was observed for both chloramphenicol acetyltransferase and DNA polymerase activities measured in vitro. Depending on the number of copies of the S. pneumoniae polA gene present, restoration of DNA repair functions in polA mutants of B. subtilis was either partial or complete.

Solvent extraction of zinc from acidic calcium chloride solutions by Cyanex 923

The reaction of zinc chloride with Cyanex 923 (phosphine oxide) in Solvesso 100 has been studied from acidic calcium chloride solutions. The distribution coeffient of zinc is independent of equilibrium pH, thus, suggesting a solvation extraction mechanism. Experimental data indicate that the reaction is exothermic (ΔH° = −55.2 kJmol−1). Slope analysis for the system at various Cyanex 923 concentrations reveals the formation in the loaded organic phases of species which probable 1:2 (Zn: Cyanex 923) stoichiometries. The stoichiometric factor of water in the extraction reaction was found to be 0, 1 or 2, whereas experimental data indicated that two chloride ions are involved for each metal extracted.