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By B. D. Pandey, M. S. Kim, B. S. Kim

The recovery of Sn from used Pb-free solder (Sn, 3~4 % Ag, < 0.9 % Cu, < 1.2 % Pb) has been investigated by electrorefining in sulfuric acid solutions containing small amount of hydrochloric acid. This involved preparation of the anode material by melting and casting the used solder followed by refining. During electrorefining, dendritic tin was deposited on stainless steel cathode. Increasing the amount of hydrochloric acid up to 0.3 mol /L in the electrolyte enhanced the current efficiency to 92.2 % and the enrichment ratio of silver to 94.3 % in the anode slime which was otherwise 84.7% and 81.6 % in absence of HCl, respectively. The electrolyte containing hydrochloric acid has also prevented the precipitation of tin oxide in the bath. In the scale-up experiment using 1.6 kg anodes, 84.3 % current efficiency and close to 100 % Ag enrichment ratio were obtained, while the purity of electro-refined tin was over 99.9 %. The energy consumption of the winning process was found to be 0.151 kWh /kg-Sn which is competitive as compared to commercial tin electrorefining processes.

Jan 1, 2014

By W. J. Przybylowicz, V. M. Prozesky, D. de Bruin

"The common style of gold mineralization in the Basal Reef and other auriferous conglomerates of the Witwatersrand Supergroup comprises clusters of gold grains occurring interstitially to quartz and pyrite pebbles as well as gold accumulations attached to the surface of and infilling hairline cracks and fractures in round, compact, detrital pyrite. The latter textural association is generally interpreted as a result of remobilization of originally detrital gold during regional metamorphism and related hydrothermal fluid circulation. There is general agreement that, although gold solubility was low, ore modification occurred during the metahydrothermal event, but uncertainty exists about the magnitude and scale of gold remobilization.Micro-textural and chemical investigation of compact round pyrite and associated gold accumulation has established that gold is preferentially deposited on chemically heterogeneous pyrite surfaces. Combinations of alternating high- and low-As zones in pyrite result in mixed np-type conductivity accompanied by electron exchange and the reduction-driven deposition of gold at the cathode. This model does not explain gold accumulations which are not immediately linked to chemical heterogeneities and it is inferred that an additional control on the deposition of gold was exerted by physical defects which lead to zones of increased charge density and/or areas of focussed conductivity. The inferred precipitation mechanisms suggest that submicrocopic physical and chemical controls are the important factors that determined the sites of gold nucleation and that precipitation mechanisms based on physicochemical changes of the hydrothermal system were not involved. The Basal Reef contains on average close to 5OJo of round, detrital, chemically zoned pyrite which provides a large number of electrochemically active pyrite surfaces. The extremely effective electrochemical precipi- . tation mechanism together with the low solubility of gold in Witwatersrand fluids is the main reason for the spatially restricted remobilization of gold in the conglomerate reefs."

Jan 1, 1994

By G. R. MANSON

The Brisco Barite Mine lies 70 km south-southeast of Golden, British Columbia. Barile mineralization occurs in a northstriking brecciation zone within Ordovician-Silurian Beaver/ oot dolomites and quartzites. Brecciation was caused by faulting related to the Mount Forster-Steamboat Fault. The main barite vein occupies a fault zone and is up to 12 m wide and over 250 m long. It is light grey to white, fine grained and compact; BaSO4 content is 9/. 70 per cent. Production started in 1945 and has continued to the present. Barile originally was removed from an open pit; later, an adit, begun in 1957, reached more than 240 m along the vein, 15 m below the pit floor. Today ore is hoisted from a decline resting some 37 m below the pit floor.

Jan 1, 1984

By D. Zagidulin

Short term electrodeposition experiments (up to 80 min.) at two current densities 220 and 275 A/m2 with varying concentrations of thiourea and glue were performed to determine the optimum levels of glue, thiourea and current density for industrial copper electrorefining. White Light Interference Microscopy was used to acquire digital images of the morphology of the electrodeposited copper. Scaling analysis was employed to pa-rameterize the morphological information encoded in the images. The limiting rough¬ness, *, the critical scaling length, Lc, and the aspect ratio, 4*/ Lc, were determined as a function of the deposition time and the amount of organic additives. These parameters were used to calculate the dynamic exponent, B, the roughness exponent, 1/z, and the as¬pect ratio exponent, y, plotted as a function of glue and thiourea concentrations. These 3D plots allowed us to find conditions corresponding to the minimum of B and y, at which the deposited copper is characterized by a small roughness and a dense structure.

Jan 1, 2007

By J. A. E. Bell

"Inco has shifted part of its traditional extractive research effort at its J..Roy Gordon Research Laboratory in Mississauga toward new, value-added products. Most of the effort is being expended on new Ni powders for batteries and new Ni-coated products which will be produced in Inco&apos;s carbonyl nickel refineries. New products under development are Ni-coated powders, Ni-coated fibres and ultra-fine Ni powders. Other new products for advanced material applications include controlled expansion composites, NiGOLD strip, Thermal barrier coatings on Inco alloys, and plasma coatings.Research and Corporate Strategic ThrustsThe newest strategic thru st of the company is to increase the value of the primary metal products. These new products are to be in addition to any new alloys or downstream alloy fabrication.Historically Inco has had the highest research expenditures in the extractive metallurgy field in North America. This has resulted in many new processes including flash smelting , matte separation, fluid bed roasting, pressure carbonyl refining and cobalt electrowinning which have contributed to establishing Inco as the lowest cost nickel producer. The recession of the 1980s caused a restructuring of Inco research and corporate goals .As shown in Figure I, from 1975-1982, i.e. pre-recession, Inco spent around 33 million dollars per year on research. Some 48070 of that sum was spent in Corporate Laboratories in Sterling Forest in the United States and in the United Kingdom , mostly on alloy associated research. A further 10% was spent on alloy research at the alloy production facilities in Hunting- ton, West Virginia, and Birmingham and Hereford in the United Kingdom. On extractive research, 13% was spent by process technology groups at the plant s, 20% at the pilot plants in Port Colborne and 9% at the J. Roy Gordon Research laboratory.The relative research expenditures (Fig. 2) have decreased so that today they are at the same level as 1975-80. The research as a per cent of sales has been cut from 2.2% to 1.2% of normalized sales. A normalized sale price of $4.00/lb Ni was used in the 1988 figures. This was partly achieved by closing Corporate Laboratories. Most of the essential alloy research was moved to producing plants and total alloy research is now 27%.A new thrust initiated in the 80s was mining research which now accounts for 20% of research expenditures. Over a period of the past five years this research has doubled the mining productivity in Inco. The pilot plant expenditures have been cut in half. One entire research station at Port Colborne was converted into a platinum group metals intermediate refinery. The decrease in pilot plant expenditures has been compensated by full scale plant trials devoted to the S02 abatement program at Sudbury."

Jan 1, 1990

By Otto Engel

"A multipurpose program for a hand-held programmable TJ-59 calculator and PC-100C printer facilitates the evaluation of various mineral processing tests and the calculation of mass and metal balances. Its application is demonstrated by some example problems. Detailed user instructions are given for each application.IntroductionThe program listed in Appendix I is written for a programmable Texas Instruments TI-591 PC-100C calculator I printer combination. The program is applicable for the evaluation of:1) screen analyses;2) flotation test s; and3) mass and metal balances.Each application is demonstrated by an example problem and corresponding detailed user instructions. The ""measured"" data in the examples are fictitious and do not represent a real operation.The steps in using the program are the same for each of the three types of application, viz.:1. Enter the number of product fractions and press ""A"".2. Enter the measured weights (0) of each fraction and press ""RIS"" each time. After the last fraction has been entered, the printer automatical1y displays the total weight.3. Press ""B"" to calculate the weight distribution (Y). Once ""B"" is pressed, the printer automatically displays the weight distribution of all fractions.4. If the accumulated weight distribution (EV) is also needed, press ""RIS"". The printer now displays these data. This step is optional and may be bypassed.5. Press ""2nd A"" to prepare for entering of the measured metal assay (M).6. Enter the measured metal assays of each fraction and press ""RIS"" each time. If analytical data exist for more than one metal, each data set has to be entered separately in one sequence.7. Press ""C"" to determine the ""calculated"" head assay (MA) of all fractions.8. Press ""RIS"" to calculate the metal distribution (R). Once ""RI S"" is pressed, the printer automatically displays the metal distribution of all fractions. This operation is optinal and may be bypassed if desired.9. Again press ""RIS"" to obtain the accumulated metal distribution (ER). This operation is optional and may be bypassed.10. Press ""D"" to calculate the gangue distribution in the concentrate (W). One ""D"" is pressed, the printer automatically displays the data for all fractions. This operation is optional and may be bypassed.11. Press ""RIS"" to obtain the accumulated gangue distribution (EW). This operation is optional and ma y be bypassed.12. For more than one metal, press ""E"" to clear the memory for storing the assays of the next. Then press ""2nd A"" and start entering the assays of the next metal as described previously (6 to 11). Steps 5 to 12 may be repeated as many times as desired."

Jan 1, 1982

By Michel Carreau

Presentation topic Introduction to Renewable Power in Remote Mining Industry Trend What are the Challenges and How to address them Acceptability (Management Buy-in) ? RP not core business to mining company Significant upfront costs Project Risks - Technological and Delivery Wind and solar power variability Operating hybrid power (Operator Buy-in) Conclusion Introduction ? RP at Remote Mining Sites Mining Project Cost Energy represents 25% of mining project CAPEX Energy represents 25% of OPEX Diesel, HFO, ? cost : 30+ cents/kWh RP - Proven technology - Excellent track record ?Wind (20 years), Solar PV (10+ years)? Hundreds of GW installed ?Reliable, High availability, very small OPEX. ?Wind/Solar cost : 15 to 22 cents/kWh (with good resource) ?Potential 10% to 20% Reduction in net cost of energy ?Price certainty for 20 to 25 years

May 1, 2013

By Ken Steele, Pam Sangster, Myra Gerow

Ontario leads Canada in production of structural materials and ranks third in production of non-metallic minerals. The total value of industrial mineral production in 1997 was $1.6 billion. The province is the leading producer of nepheline syenite, salt, talc, clay products, cement, lime, sand and gravel, stone and a major producer of gypsum and silica. Barite, sulphur in smelter gas, elemental sulphur, tremolite, serpentine, gemstones and peat are also produced. Table 1 shows recent actual industrial mineral production levels in Ontario. Other industrial minerals, including phosphate, petalite, diamonds, wollastonite, vermiculite, kyanite, garnet, graphite, silica, kaolin, dimension stone and anorthosite, have been the target of exploration and development projects. Investment opportunities exist at all levels from grass-root prospect through to production level.

Jan 1, 2001

By Yi-Chun Lin

Mechanical/Electrical/Piping (MEP) systems, due to their complexity and diversity, are the most intricate part of building construction. This being the case, Combined Services Drawings (CSD) and Structure, Electric and Mechanic(SEM) drawings can ensure that all coordination issues are resolved prior to construction. Construction companies attempt to apply Building Information Modeling (BIM) to manage and integrate engineering information and solutions efficiently into the CSD and SEM processes to enhance the accuracy of design and the efficiency of review. There are several powerful commercial tools, such as Bentley Navigator, Autodesk Navisworks, and Tekla BIMsight, that can review the integrated BIM model and detect conflicts in systems, and allow planners to correct the conflict issues one at a time. However, for increasing numbers of conflicts, this may be inefficient, and requires them to be arranged in a list according to impact and seriousness before solving them. For this reason, this research implements a module for conflict impact assessment based on rule-based reasoning to classify and weigh conflict impact and seriousness, and highlight the conflicted objects in the BIM system in different colors depending on their conflict type and seriousness during the analysis. This system not only detects and lists possible conflicts and errors, but also sorts them according to the severity of impact and conflict type. Planners can effectively modify the BIM models according to these conflicts as they are listed and visualized in the BIM system. If these conflicts, such as pipeline interference and problems of insufficient space, can be avoided in the early stages of planning, it facilitates the achievement of project objectives in quality, scheduling, and cost.

Aug 1, 2013

By J. M. Skeaff

"The main solution, ore and residue pulp streams in the Rio Algom Quirke I uranium mill at Elliot Lake have been sampled and analyzed for radium-226. Analysis of the ore and leached residues indicates that Ra-226 dissolves and precipitates within the first pachuca tank. A maximum of approximately 0.2% of the Ra-226 in the ore remains in solution during leaching.IntroductionConcern over the acid drainage and radionuclide dissolution problems associated with uranium tailings disposal sites in Canada has prompted investigation into methods for improving current uranium processing practice.Present commercial practice usually involves leaching of the uranium ore with sulphuric acid, ion-exchange separation of the uranyl sulphate complex from the leach liquor and"" precipitation of the uranium as yellowcake. Daughter products of U-238, such as Th-230, Pb-21O and Ra-226 remain with the tailings and undergo long-term dissolution.Table I summarizes the probable behaviour of the radionuclides during milling. The concern here is with Ra-226, because it will deposit in the bones if ingested and is ""thus considered a serious health hazard(1), Similarly, Po-218 and Bi-214, which are daughter products of Rn-222, can be retained in the lungs and are considered to be the principal sources of radiation dosage(2) arising from the inhalation of Rn-222. Previous investigations(3-9l indicate or imply that Ra-226 undergoes redistribution during milling. However, detailed published information on the behaviour of Ra-226 in the uranium milling process appears to be lacking. A knowledge of the behaviour of Ra-226 in uranium mills, particularly during leaching, could lead to improved methods for its control.This paper reports the occurrence of Ra-226 in the Rio Algom mill. The main objectives of the study were to determine (1) the distribution of Ra-226 within the solids, (2) at what point, and how rapidly, redistribution occurs and (3) whether there are high concentrations of Ra-226 in solution."

Jan 1, 1981

By Yu-Min Cheng

Over the past two years, the construction industry has increasingly recognized the benefits and capabilities of building information modeling (BIM) for information integration, visualization and parametric design, reducing the duplication of work and complexity of interface integration, while significantly saving both time and cost. However, due to the variety of participants in engineering projects, the differences between data definition, data format, and data storage increase the difficulty of integrating data from diverse sources. Therefore, buildingSMART has developed a common data schema, called Industry Foundation Classes (IFC), that makes it possible to hold and exchange relevant data between different software applications, to increase the efficiency of BIM work and to ensure a consistent and high-quality output. This paper presents a novel methodology that assists in facilitating the import and export process for parametric BIM objects between heterogeneous BIM systems. This methodology is based on the IFC data schema and includes graphical and non-graphical description data. The objective is to retain the geometry, parameters, unit, texture and links of an object during exchange and sharing to ensure that data integrity is maintained. To sum up, this research addresses the issues of transferring parametric BIM objects between heterogeneous systems to increase data integrity and reduce transfer and integration times.

Aug 1, 2013

By A. L. Rutledge, R. S. Nichols

"Waste dump development at the Fording River Operation s in British Columbia began in 1971. In 1981, several unique as well as unplanned situations provided an opportunity to study water flows through waste dumps.The key to the drainage is naturally segregated rock sizes .created by end dumping from the crest of a pile. The largest size material accumulates at the toe. Flow rates along the base of the studied dumps varied from 2,800 to 13,500 m3/day or 0.032 to 0. 156 m3/s (1.2-5.5 cfs}. Sediment concentrations in the water ranged from 1 to 1,800 mg/I.This paper describes water flows through dumps of varied lithology and maturity. The results suggest that neither long-term water flow nor contained sediments in small streams are jeopardized when crossed by end-dumped fills.IntroductionThe Fording River Operations are located in southeastern British Columbia approximately 115 km north of the United State s and 10 km west of Alberta, within the medial range of the Rocky Mountains. All production is carried out at elevations ranging between 1,600 and 2,200 m above sea level.The property is within a continental climatic zone, with temperature extremes of - 40°C in January to +35°C in July. The average annual precipitation of 335 mm of rainfall and 390 cm of snowfall feeds the numerous seasonal, small drainage courses along the Fording River valley.Since start-up in 1971, 149 million bank cubic met res of waste from truck-shovel and dragline mining have been placed in numerous dumps or ""spoils"". The dumps were developed to the point that several unique situations could be studied. During the peak run-off period of May-June 1981, water flow studies were performed on dumps of varied lithology and maturity. This paper describes the results of the study."

Jan 1, 1982

By James Tuer, John R. Goode, Jim Cambon

"Hudson Resources Inc. (Hudson) has defined a major resource of high purity anorthosite (calcium feldspar) assaying about 30% Al2O3 at the White Mountain (Naajat) deposit in Western Greenland. Extensive beneficiation and evaluation testwork has shown that the material can be simply beneficiated to produce a feed material ideal for the production of low-alkali E-glass used for making glass fibre. An offtake agreement is in place with a major US fibreglass manufacturer and, subject to the mine construction schedule, shipments are scheduled for late 2016 or early 2017. In parallel with the E-glass program, Hudson has completed an initial program of metallurgical testwork which shows that the White Mountain anorthosite can be processed by hydro- and pyro-metallurgical processes to yield either smelter-grade alumina (SGA), suitable for conversion to aluminium metal, or a high purity, chemical/specialty-grade alpha-alumina (CGA) commanding a premium price. The process includes dissolution of the anorthosite in hydrochloric acid, HCl sparging to precipitate aluminium chloride hexahydrate (ACH), recycle of the ACH filtrate to leaching with a bleed stream processed for HCl regeneration from CaCl2, and two-stage calcination of the ACH to regenerate HCl and produce SGA and/or CGA. Calcium silicate and amorphous silica are marketable by-products. This paper discusses the White Mountain anorthosite deposit; the process testwork completed to develop production processes for SGA and CGA; production plans, and indicative economics.INTRODUCTIONHudson Resources Inc. (Hudson) holds a 100% interest in the Naajat Exploitation Licence in Western Greenland that cover the White Mountain high-calcic anorthosite deposit. Anorthosite is a calcium aluminosilicate of slightly variable composition but generally containing about 30% Al2O3. The alumina content is similar to that in bauxite and anorthosite has long been studied as a feedstock for the production of alumina. Other potential uses include feedstock for the high-end fiberglass (E-glass) industry and as a filler for use in paint and plastics."

Jan 1, 2016

By Xiaoxing Hu, Guibing Zheng, Yangge Zhu, Xingrong Zhang

"In China, more than 90 percent of titanium resources are reserved in vanadic titano-magnetite deposits. In this type of ore, the same elements such as Ti, Fe, Ca, Mg exist on surface of both ilmenite and titanaugite (the gangue mineral) because of isomorphism, which makes selective flotation difficult. Therefore, how to enlarge the floatability difference between these two minerals has always been a research emphasis and still needs to be studied further. In this paper, the pre-treatment methods using ultrasonic wave were proposed. The results indicate that ultrasonic treatment shows beneficial effect to enlarge the floatability difference, and the effect will be strengthened by extending the ultrasonic treatment time or increasing the ultrasonic power. The mechanism was investigated through infrared spectroscopic (FT-IR) analysis. Collector interacts with Ca and Mg which results in titanaugite flotation, after ultrasonic treatment, the dissolution of Ca and Mg is intensified, which leads to the lack of active points on mineral surface, so the floatability of titanaugite is depressed. Meanwhile, collector mainly interacts with Fe which results in ilmenite flotation, and the present of ultrasonic might promote its oxidation (Fe2+ to Fe3+), so the floatability of ilmenite after sonication is increased.INTRODUCTIONUltrasonic is the sound wave with frequency of 2 × 10-4 Hz~2 × 10-9Hz. Since the first International Symposium of Sonochemistry in 1986, the application of ultrasonic wave is more and more extensive. In researches about mining and metallurgy, various investigators have shown that intensive acoustic fields can modify the state of a mineral, leading to chemical or dispersive effects. Generally, the effect of ultrasonic vibration depends upon the nature of the mineral and also the way ultrasonic wave is applied (Celik, 1989; Ozkan, 2002). In addition, ultrasonic treatment usually plays roles of removal of reagents adsorbed layer from minerals and emulsification of flotation reagents when it is used in flotation (Nicol, Engel, & Teh, 1986; Slaczka, 1987; Djendova & Mehandj, 1992; Farmer, Collings, & Jameson, 2000; Gurpinar, Sonmez, & Bozkurt, 2004)."

Jan 1, 2016

By Jacob Wood, Robert Matusewicz

The Outotec® Ausmelt Top Submerged Lance (TSL) Process has achieved widespread commercial acceptance over the past 40 years for the processing of copper, nickel, lead, tin, zinc and precious metal bearing feeds. The continual development and evolution of the technology during this period has resulted in a more intense smelting process with higher energy efficiency and lower operating costs. More recently, considerable effort has been invested in decarbonisation of the process through improvements such as increased oxygen usage, dry feed injection and use of low-carbon auxiliary fuels. This paper covers a number of these recent advances to the technology and highlights their impacts on energy consumption and CO2 emissions for a range of non-ferrous smelting flowsheets. INTRODUCTION Relentless demand for improvements in the profitability, safety and environmental performance of non-ferrous smelting plants has driven a continual development and evolution of processing technologies in this industry. In response to these demands, a number of bath smelting technologies have emerged over the past 40 years and have been implemented for the treatment of primary and secondary feedstocks. The Outotec® Ausmelt Top Submerged Lance (TSL) Process (henceforth Ausmelt Process) is one such bath smelting technology which has been widely adopted in a large number of greenfield projects and brownfield plant modernisations (Wood & Hughes, 2016). Emissions of CO2 from the production of non-ferrous metals represent approximately 4-5% of global totals (Rankin, 2012), comparable with the almost 10% attributed to iron and steel production. Despite significant improvements in the energy efficiency of modern smelting technologies (Coursol, Mackey, Kapusta & Cardona Valencia, 2015), primarily through increased oxygen usage, further innovation and development is still required to address their reliance on fossil fuels such as coke and coal. Transformation of the non-ferrous smelting industry to low-carbon technologies and process flowsheets is lagging behind the power and transport sectors, which have witnessed significant growth in clean/renewable energy technologies to reduce CO2 emissions and address the issue of anthropogenic climate change (IRENA, 2018; IEA, 2018).

Jan 1, 2019

By B. A. McKee, T. Adamcewicz

For a capital expenditure of only $46,000, Caland Ore Company has successfully converted its three dry grinding center peripheral discharge rod mills to dry grinding ball mills. The conversion has resulted in a significant capacity increase, operating cost reductions and in-plant environmental improvements. This paper describes why and how• the conversion was made.

Jan 1, 1972

By G. H. Hope, D. Green

"Recent process advances at Lac Minerals Est Malartic Division are discussed. The Est Malartic mill treats massive sulphide, copper/gold ore from the Bousquet 2 mine, to produce a gravity gold product, a copper flotation concentrate and a gold precipitate. The mill operation has been improved by the application of Knelson concentrators to replace jigs, the application of Outukumpu high grade tank cells and optimizing the cyanide leach to minimize cyanide consumption.IntroductionThe Est Malartic mill is located near the town of Malartic in the Abitibi Region of north western Quebec. The mill has been in production since the mid- J 930's processing mainly clean, free milling gold ore. Active mining from the Est Malartic mine ceased in 1980 and the mill was switched to custom processing of ore from La Mine Doyon located some 45 km to the west. This custom processing arrangement continued until 1987 when the expanded mill at Doyon became available to process all of the Doyon production. In 1987, Lac Minerals commenced development of a second mine at the Bousquet site located 40 km west of Malartic. This mine, Bousquet 2, is the down dip extension of the La Ronde mine developed by Agnico Eagle. During pre-feasibility evaluations, it was determined that modification of the Est Malartic mill to handle this new ore source was economically more attractive than building a new facility on site. Modifications to the mill to process the high copper/gold ore from the Bousquet 2 mine began in late 1989 and the new circuits were commissioned in mid-1990. Modifications included the addition of both gravity and flotation concentration circuits to recover coarse, free gold and the copper. The existing leach circuit continued operating on the copper flotation tailings with some minor modifications to the solution handling systems. An SO,/air cyanide destruction circuit was also added at this time."

Jan 1, 1993

The most expensive unit operation in the beneficiation of ores is grinding. The correct design of the grinding circuit is crucial to prevent unnecessary use of energy. Proper design and evaluation of SAG grinding circuits require the specific grinding energy, which is determined experimentally. The most common tests in SAG grinding are the Drop Weight Test, from the Julius Kruttschnitt Mineral Research Center (JKMRC) in Australia, and the SAG Power Index, from MinnovEX Technologies in Canada. The application of these tests to the same ore sample commonly produces different results. The work reported here aims at comparing the application of these two tests in the determination of the specific grinding energy for sulfide copper ores from Sequeirinho and Sossego deposits, Sossego Project, Companhia Vale do Rio Doce - CVRD, in Para state, Brazil.

Jan 1, 2007

By Jeremy D. Glennon

A number of exciting challenges, opportunities and unanswered questions remain concerning the chemistry, geochemistry, medical, industrial and analytical applications of gold and its compounds.1 Among the challenges presented is the need for extraction methods for gold, at process and indeed analytical scales, that avoid the use of organic solvents or hazardous reagents. Extensive environmental contamination has occurred in the Brazilian Amazon from the mercury-gold amalgamation process. Major problems with the cyanidation process are the relatively slow dissolution kinetics and the health and environmental problems associated with it. With innovation and technical changes, a cleaner way for solubilising and extracting this versatile precious metal can be found. This cleaner future may lie in supercritical fluid science. Interestingly, geochemical studies of gold solubility and speciation in hydrothermal solutions have highlighted the importance of supercritical conditions and sulphur species in the deposition of gold in natural environments. Gold solubility in supercritical brines is far higher than previously supposed while interest in the high content of carbon dioxide in the mineralizing fluids is growing. 2,3 In recent years, also, there has been a tremendous amount of attention paid in analytical chemistry and in industry, to the area of supercritical fluid extraction (SFE) of organic and metallic species. 4 This interest has been fuelled by the introduction of more stringent environmental control and the subsequent need for cleaner solvents and processes to replace established ones. Carbon dioxide is the substance of choice for SFE because of its moderate critical parameters (Tc = 31oC, Pc = 73atm), inertness and availability in pure form. It is an excellent extraction medium for non-polar and moderately polar species, and with careful ligand design, it can be used for analytical and process scale metal extraction from solution and solid phases. In general, the dissolution of a metal in supercritical CO2 (sc-CO2) requires that the charge on the metal ion be neutralised on complexation by the ligand or through a form of ion pairing (analogous to the situation where metal ions are extracted into organic solvents, such as methyl isobutyl ketone or toluene). In this way, then, many chelating agents such as dithiocarbamates and hydroxamic acids have been utilised to extract metal ions such as Cu and Fe into sc- CO2, the process greatly enhanced by the use of fluorinated ligand derivatives. 5-7 In this review paper, we show that supercritical conditions and complexation with sulphur donor atoms, important in the natural deposition of gold, can form the basis of a clean, eco-friendly chemistry for gold extraction. Analytical scale extractions of gold from a variety of matrices can be conveniently used to assess the efficiency of any new proposed ligand.

Oct 1, 2003

By Peter J. Barnard

Mitochondria play a key role in the regulation of apoptosis (cell death) and in diseases characterised by abnormal apoptotic responses such as cancer. Mitochondrial membrane permeabilisation (MMP), regulated by the mitochondrial permeability transition pore complex, is widely accepted as being central to the process of cell death. As a result there has been considerable recent interest in targeting mitochondrial cell death pathways in the development of new chemotherapeutic agents.(1) There is potential to overcome the two overriding problems in cancer chemotherapy?the common occurrence of drug-resistant tumour cells and the lack of selectivity of cancer drugs in differentiating between tumour cells and normal tissues. Significantly, carcinoma cells have an elevated mitochondrial membrane potential relative to normal cells and lipophilic cations are concentrated within mitochondria in response to mitochondrial membrane potentials. There is potential for the selective targeting to tumour cells with compounds having optimal lipophilic-hydrophilic character. Research stemming from the early 1980?s points to two distinct classes of Au(I) phosphine antitumour agents where an antimitochondrial mode of action has been implicated: (i) neutral linear two-coordinate Au(I) complexes such as triethylphosphinegold(I) chloride and the tetraacetylthioglucose gold(I) phosphine complex, Auranofin; (ii) cationic tetrahedral bis-chelated Au(I) phosphine complexes related to [Au(dppe)2]+.(2) Recently it has been reported that Auranofin, at submicromolar concentrations, induces MMP observed as mitochondrial swelling and dissipation of membrane potential.(3, 4) Both events are completely inhibited by cyclosporin-A, the specific inhibitor of MMP. The permeability changes were shown to occur at concentrations associated with the selective inhibition of mitochondrial thioredoxin reductase.(3) Auranofin is a potent and specific inhibitor of this enzyme due to Au(I) binding to the active-site selenol group.(5) The redox state of mitochondrial thiols may be critical in the control of MMP.(3) In general, swelling is stimulated by thiol blocking or oxidising agents and is prevented by thiol reducing agents.(1) Mitochondrial thioredoxin reductase may play an import role in the redox control of the permeability of mitochondrial membranes.(3) Our interest is in investigating the antitumour potential of Au(I) phosphine compounds using a number of different approaches. In recent work we have evaluated a series of hydrophilic analogs of [Au(dppe)2]+ containing pyridylphosphine ligands which have demonstrated greater tumour selectivity than the parent compound. To investigate the possible antimitochondrial mode of action we are studying the effect of [Au(dppe)2]+ and related compounds on isolated rat liver mitochondria. To assess whether the lipophiliccationic nature of the compounds determines the antitumour activity, we have synthesized a series of novel Au(I) complexes based on heterocyclic carbene rather than phosphine ligands. The similar chemistry and structural features of the two classes of complexes allow us to assess whether the phosphine ligands are essential for the antitumour properties.

Oct 1, 2003