Matthew J. Shaw

Leaching and recovery of gold using ammoniacal thiosulfate leach liquors (a review)

A review is presented summarising the leaching of gold with ammoniacal thiosulfate solutions, and evaluating the current use and development of ion exchange resins for the recovery of gold and silver from such leach liquors. Comparisons are also made with other recovery processes, including carbon adsorption, solvent extraction, electrowinning and precipitation. Thiosulfate leaching chemistry is compared with cyanide leaching, and the problems associated with obtaining a high yield of recovered gold using the former process are discussed. The present limitations of using Resin-in-Pulp (RIP) and Resin-in-Leach (RIL) systems with thiosulfate liquors are indicated and possible solutions discussed.

Developments in suppressor technology for inorganic ion analysis by ion chromatography using conductivity detection.

A review is presented detailing the development and use of suppression devices for the conductimetric detection of inorganic ions by ion chromatography (IC). An overview of the general response equation for conductivity detection is also given. Topics of discussion include the role and function of suppressors, the development of early suppressors including packed column and membrane devices from 1975 to 1990 and the subsequent progression towards present day commercially available suppressors and recent innovations. Post-suppression devices for signal enhancement are also discussed.

Chromatographic and electrophoretic separation of inorganic sulfur and sulfur–oxygen species

A review is presented of the use of chromatographic and electrophoretic methods for the separation of inorganic sulfur species in aqueous matrices, with particular emphasis on ion chromatographic methods. The species considered are elemental sulfur, sulfide, polysulfides (Sx2−), sulfite, sulfate, thiosulfate, dithionate, polythionates (SxO62−) and metal–thiosulfate complexes. A brief introduction to sulfur anion chemistry is given, followed by a discussion of the separation and determination of sulfur species using ion chromatography, capillary electrophoresis and other separation-based techniques. Difficulties inherent in the analysis of complex sulfur anion mixtures are indicated and the procedures that have been used to overcome these difficulties are also examined.

Selectivity behaviour of a bonded phosphonate--carboxylate polymeric ion exchanger for metal cations with varying eluent compositions.

The chromatographic behaviour of a commercially available ion-exchange stationary phase (the Dionex IonPac CS12A column) is described for a wide range of transition and heavy metal ions with nitric acid eluents containing chloride and nitrate potassium salts. The separation selectivity was found to arise from simultaneous ion-exchange interactions and chelation with the attached carboxylic and phosphonic acid groups. These interactions were investigated by altering the ionic strength and pH of the eluent and also the column temperature. Strong affinity of the stationary phase towards heavy metal ions, in particular bismuth and the uranyl ion was observed at low pH under chelating ion-exchange conditions, with high efficiency separations of other ions including cadmium and lead being possible with short analysis times (approximately 5-15 min). Examples are given of separations obtained using 4-(2-pyridylazo)resorcinol or Arsenazo III as the post-column chromogenic reagents, demonstrating the potential versatility and utility of this stationary phase for heavy metal ion analysis.

Variation within and between Eucalyptus nitida Hook. f. and E. coccifera Hook. f

Morphometric analyses of adult and seedling characters indicate that a phenetic continuum exists between E. coccifea and E. nitida on several mountains in the central south-west of Tasmania. On these mountains there is a transition in adult form from stands typical of E. nitida at the base to forms approximating E. coccifera at the summit. However, these clines are not as marked in the seedling characters. Flowering time does not appear to be a major bamer to gene exchange between the different forms, and estimates of the variability of both the adult and juvenile characters indicate that there is no consistent pattern of increased variability in any of the populations from these mountains compared to allopatric populations of either taxon. A comparatively high level of intraspecific variation is apparent within E. coccifera. This species has a disjunct distribution, occumng as the tree-line species on many isolated mountains in the centre and south-east of the island, whereas E. nitida has a more continuous distribution, mainly in the west of the island. Some of the outlying E. coccifera populations occur on hills at relatively low altitude and it is argued that they may represent genetic relics left after up-slope migration following the last glacial. The restricted distribution of E. coccifera in the west may be due to limited migration of this species from a south-eastern refuge since the last glacial. The possible origins of the clines between E. coccifera and.E. nitida are discussed in terms of the significance of both historical and ecological factors.

Retention characteristics of lanthanide ions on a mixed phosphonic acid–carboxylic acid cation exchanger

The chromatographic behaviour of lanthanide ions on a dual phosphonate- and carboxylate-functionalized ion-exchange resin (Dionex IonPac CS12A and CG12A) was studied using various mobile phase compositions. By suppressing ion-exchange interactions through increasing the ionic strength of the eluent, the column selectivity changed to that of a chelation mechanism via the phosphonate functional groups. Retention was based on the varying conditional stability constants of the lanthanide ions with the phosphonate groups. Eluent pH was additionally found to exert a strong influence on analyte retention, but no further changes to the column selectivity occurred. The inclusion of small concentrations of organic solvents could also be used to manipulate retention to a more minor extent, as could altering the column temperature. Examples of separations are given, especially the separation of gadolinium and europium, which are often co-eluted when using nitrogen–oxygen-chelating groups such as iminodiacetic acid.

High-performance chelation ion chromatography of transition and heavy metal ions on polystyrene–divinylbenzene resin dynamically modified with 4-chlorodipicolinic acid

A neutral polystyrene–divinylbenzene column, combined with 4-chlorodipicolinic acid present in the mobile phase, has been developed as a chromatographic system for the high efficiency isocratic separation of transition and heavy metal ions. Retention arises from the formation of a stable dynamically coated chelating stationary phase, the capacity of which is dependent upon both the pH and ligand concentration in the eluent. The results obtained illustrate the increased loading and selectivity of this chlorinated chelating molecule in comparison with unsubstituted dipicolinic acid, exemplified by the separation of 7 metals in under 8 min. The column also displayed a strong affinity for CdII and an unusual retention for NiII, which showed a good symmetrical peak shape.

Fabrication of an Aurin Tricarboxylic Acid Immobilized Chelating Polymer for the Ion Chromatographic Determination of Trace Metal Ions in Highly Mineralized Waters

Abstract A high efficiency 7 µm neutral polystyrene divinylbenzene resin, impregnated with the chelating dye aurin tricarboxylic acid (ATA), was investigated for the separation and quantitative determination of Cd(II), Pb(II) and Cu(II) in high ionic strength matrices including mineral waters, by chelation ion chromatography. The fabricated ATA substrate demonstrated a unique selectivity pattern for transition and heavy metal ions, being more selective towards the environmental pollutants Cd(II) and Pb(II) in particular, in comparison with dyes containing iminodiacetate groups which have been extensively investigated recently. A development of the dye impregnation procedure, using ultrasound, siginificantly increased the capacity of the chelating column by a factor of four. Utilising a developed pH gradient elution, in an eluent of 0.1 M potassium nitrate to suppress ion exchange interactions, allowed Cd(II), Pb(II) and Cu(II) to be baseline resolved from other transition metals and the alkaline earths within 30 min. Detection limits were considerably improved by buffering the 4-(2-pyridylazo)resorcinol post column reagent with borate instead of ammonia, resulting in a threefold increase in sensitivity for Cd(II) and near twofold for Pb(II) at 520 nm. The developed procedure was applied to the determination of these metals in highly mineralised water and high ionic strength matrices. The calibration curves produced good linearity (>0.994), with excellent detection limits of 1 µg L−1 for Cd(II) and 5 µg L−1 for both Pb(II) and Cu(II), respect vely.

New conductivity detection response equation for anions eluted with fully and partially ionised eluents in non-suppressed ion chromatography.

A response equation for conductivity detection in ion chromatography has been derived. This equation is applicable to non-suppressed ion chromatography using both fully ionised and partially ionised eluents. A prime assumption of this equation is that when partially ionised eluents are used (such as benzoic acid), both the ionised and neutral components of the eluent species contribute to the detector response of anionic analytes. Experimental evidence is provided to support this assumption in that pH changes accompanying the elution of an analyte have been measured. These pH changes are proportional to the concentration of analyte injected onto the column, in accordance with predictions from the response equation. Furthermore, it is shown that protonated eluents (such as benzoic acid) give more sensitive detection than equivalent ionised eluents (such as potassium benzoate) and the signal enhancement achieved using a protonated eluent species is in accordance with theory.

Separation of polythionates and the gold thiosulfate complex in gold thiosulfate leach solutions by ion-interaction chromatography

A method for the separation of the polythionates (SxO6(2-), x = 3-5) in gold thiosulfate leach solutions using ion-interaction chromatography with conductivity and ultraviolet (UV) detection is described. Polythionates were eluted within 18 min using an eluent comprising an acetonitrile step gradient at 0.0 min from 15% v/v to 28% v/v, 3 mM TBAOH, and 2.5 mM sodium carbonate, operated using a Dionex NS1-5 micron column with guard. The developed method was capable of separating the gold thiosulfate complex ion in standard solutions, but quantification of this species in realistic leach solutions proved impractical due to a self-elution effect that caused the gold peak to be eluted as a broad band. Detection limits for polythionates using a 10 microL injection volume ranged between 1-6 mg L(-1) (5-23 microM) for conductivity and 0.8-13 mg L(-1) (4-68 microM) for UV detection, based on a signal-to-noise ratio of 2. Calibration was linear over the ranges 5-2000, 10-2000 and 25-2500 mg L(-1) for trithionate, tetrathionate and pentathionate, respectively. The technique was applied successfully to leach liquors containing 0.5 M ammonium thiosulfate, 2 M ammonia, 0.05 M copper sulfate and 20 % m/v gold ore.