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By J. E. Dutrizac, J. M. Zinck

Ferrihydrite is often the initial precipitate resulting from the rapid neutralization of Fe(III) sulphate solutions, and it seems to be a major constituent of zinc plant neutral leach residues. The most important parameters affecting ferrihydrite precipitaton are temperature, solution pH and the neutralization rate. Low temperatures and rapid neutralization rates yield poorly filterable ferrihydrite, whereas higher temperatures and slower neutralization rates produce readily filterable precipitates; in all instances, however, the precipitates are two-line ferrihydrite. Significant amounts of Zn are incorporated in the ferrihydrite precipitates, and the Zn contents increase with increasing Zn concentration, pH or temperature. Generally, the sulphate contents of the precipitates decrease as the Zn contents increase, and this may indicate that the Zn is adsorbed on the ferrihydrite. Discrete Zn phases were not detected. Neither Cd nor Tl is precipitated with ferrihydrite, although thallium jarosite co-precipitates with ferrihydrite at high Tl concentrations and elevated temperatures. Virtually all of the Sn added to the solution precipitates with the ferrihydrite, but the tin is believed to be present as intimately admixed amorphous SnO2.nH2O. Although selenite extensively precipitates with the ferrihydrite, selenate remains mostly in solution, likely because of the close similarity of the SeO4 2- ion to the SO4 2- ion which is present in high concentrations and saturates the available sites for anion adsorption.

Jan 1, 1998

By Chunlin Chen

Published data on thermodynamics of tin in liquid copper, matte and slag have been reviewed, assessed and used in development of thermodynamic solution models of melts. The developed model/database was applied in modelling the Sn deportment in primary copper smelting and e-waste melting processes. The results show that Sn can be removed from the matte through evaporation of various volatile Sn species (with SnS the most volatile) and slagging during copper smelting. The Sn removal increased with increasing matte grade due to the increased gas and slag volume. In the e-waste smelting process, fluxing strategy was developed for smelting e waste to produce a slag with reasonable liquidus and viscosity. Modelling results show that very low amounts of Sn reported to the gas phase due to low S, hence low SnS partial pressure in the system. The black copper produced could contain a few percent of Sn depending on the oxygen potential. The Sn in the black copper could be removed to the slag phase during anode refining. INTRODUCTION Tin is an impurity element commonly found in copper ores, which will be dispersed into various solid, liquid, and gaseous streams during the pyrometallurgical processing of copper. Tin alloy is widely used in electronic soldering due to its low melting point. The growth in treatment of recycled e-waste through primary and secondary copper smelting has led to an increased tin input to the smelting system. Therefore, the deportment of tin between phases is of great interest to the operators of modern smelters. Multi-Phase Equilibrium (MPE) is a thermodynamic package developed by CSIRO for simulating reactions between phases in multi-component and multi-phase systems (Zhang et al., 2002). Over the years the capability of the MPE model has been extended to cover the behavior of a large number of elements in high temperature system (Chen, Zhang, Wright, & Jahanshahi, 2006). In the present paper, the thermodynamic data on tin in liquid copper, matte and slag have been reviewed, assessed and used in the development of a database for Sn slag, alloy and matte phases. The model/database was applied in modelling the tin deportment in primary copper smelting and e-waste smelting processes. The aim of this study is to provide a better understanding of the chemical behaviours of tin in high-temperature copper processing and e-waste smelting.

Jan 1, 2019

By J. F. Henderson

Stable mining operations commenced in the Northwest Territories in 1933. Pitchblende from Great Bear lake and gold from the Yellowknife district are the main minerals produced. The value of pitchblende products produced from 1933 to 1941 was nearly $6; 000; 000; data on subsequent production are not available. The first gold was produced from the Con mine at Yellowknife in 1938. Other properties that later came into production include the Negus; Slave Lake; Thompson Lundmark; and Ptarmigan mines. The annual gold production reached $3; 862; 000 in 1942 but due to the war and consequent labour shortage fell to $333; 218 in 1945. The only producing mines at present (May; 1947) are the Con and Negus; but several promising properties are under development; including that of Giant Yellowknife Gold Mines where large tonnages of ore are being blocked out. With the reopening of former producing mines and new production from properties now being developed; gold production should rapidly increase and exceed its former peak within the next few years.

Jan 1, 1954

By I. C. Christopher

Introduction The geology of the Cochen-our Willans gold mine has been described in reports by the late Dr. H. C. Horwood (1) in 1940 and by Dr. J. P. Nowlan (2) in 1947. Information from these and other (unpublished) reports has been incorporated in the present paper, together with some recent ideas regarding structural features which are at present being used to locate ore shoots. Location and History The mining claims of Cochenour Willans Gold Mines, Limited, occupy 705 acres in Dome township, on the east shore of Red lake opposite McKenzie island. Adjoining properties are those of McKenzie Red Lake Gold Mines on the west, Boymar Gold Mines on the north, Marcus Gold Mines on the east, and Martin-McNeely Gold Mines on the south. The claims of the original group were staked by W. M. Cochenour, Dan Willans, and H. G. Young, and the Cochenour Willans Syndicate was formed in 1928. Work was carried out by the Syndicate and several other companies during the next eight years with inconclusive results, due to the irregular occurrence of the ore. In 1936, Cochenour Willans Gold Mines, Limited, was incorporated and production was finally started late in 1939.

Jan 1, 1951

By H. Nouranian, M. Askari

GOLGOHAR Mining & Industrial Co., with annual production of 16 million tons, is one of the largest pelletizing and iron ore supplier in Iran that recently this year, because of using mineral processing techniques and extraction of ore body positioning between the metamorphic rocks, about 150 million tons of dry tailings has been created as a result of concentrate production. On the other hand, many environmental issues such as groundwater pollution have been developed by sulfide and silicate gangue minerals, which containing heavy metals such as mercury and arsenic. In this study, a new product with high added value has been introduced for the company by identification and extraction of industrial minerals in dry tailings. Also, by removing large masses of dry tailings, environmental pollution sources were gradually eliminated. This method can be used as a modern waste management approach in the world.

Jan 1, 2017

By V. Schenk

Dust exposure resulting from the exploitation and winning of natural resources below ground has presented a serious health problem since the beginning of mining. The boom phase of the German hard coal mining industry after World War II with at times up to 500,000 employees saw an increase of dust exposure of miners below ground as the mechanization of road heading and mining increased significantly. More and more miners were diagnosed with coal-workers-pneumoconiosis (CWP), a chronic and irreversible lung disease resulting in a significant impairment of pulmonary function. This realization led to a reduction of CWP in the German hard coal mining industry in the 1960s. The successful fight against CWP began with the introduction of technical dust prevention measures. By infusing the coal seam with water before mining, sprinkling and spraying of heading and mining machines as well as canopies with water, aspiration in places with high amounts of dust and the suppression of dust with chemical substances it is possible to significantly reduce the miners? dust exposure. All operating points below ground are checked and measured regularly with regard to dust exposure. Through the combination of these values together with the individual shift data a relatively precise profile of individual dust exposure can be obtained. This profile allows the targeted work assignment when certain predetermined limits have been reached, moving the miner to a work place with less dust exposure and thus reducing the chronic dust exposure. The state of health of the individual is known because since about 60 years ago extensive occupational health checks have been carried out regularly at least every two years which means that work restrictions can be imposed depending on the findings. Since the beginning of the 1980s more value has been attached to not only situational but also behavioral prevention. Given the comprehensive provision of protective masks, having a protective effect as well as the required comfort when being worn, each miner has the opportunity to protect his respiratory organs depending on the specific dust exposure. Through a combination of all these measures the German hard coal mining industry has succeeded in beating the classic coal miner?s disease CWP. For mines in the Ruhr valley this means that a miner who started work after 1978 will no longer develop CWP.

Aug 1, 2013

By M. S. Moats, F. Elnathan

"The effect of current reversal on two commercially manufactured electrodes (RuO2-TiO2 and IrO2-Ta2O5 coated Ti) in a chloride bearing electrolyte was evaluated. Accelerated lifetimes were found to decrease with increasing current density and increasing reversal frequency. Ru: Ti coated electrodes exhibited longer lifetimes than Ir: Ta coated electrodes even though they had one-third as much precious metal content. Chloride concentration did not affect lifetime in the range examined. Using energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS), the failure mode of the electrodes was determined to be coating dissolution leading ultimately to passivation by the presumed growth of a highly resistive oxide at the coating/substrate interface.INTRODUCTIONCatalytic titanium anodes (CTAs) were developed in the 1960’s to replace graphite anodes in chlor-alkali cells. CTAs exhibited much better dimensional stability than graphite leading to lower operating potentials by promoting smaller electrode gaps and better operational efficiencies as they had to be replaced less often. CTAs are simply Ti substrates coated with precious metal oxides (such as IrO2 and RuO2) mixed with other components (such as TiO2 and TasO5) (Trasatti, 2000).CTAs are used in many other electrochemical industries, including water disinfection, wastewater treatment, cathodic protection and metal plating. RuO2 based coatings are typically used for chlorine evolution. IrO2 based coatings are for the most part utilized for oxygen evolution (Comninellis & Nerini, 1991; Forti, Olive, & De Andrade, 2001; Kotz, Stucki & Carcer, 1991; Trasatti & Lodi, 1981)"

Jan 1, 2016

By L. Fernandes

A factorial study was performed to investigate the relative effects of temperature, copper concentration and meso-2,3-dimercaptosuccinic acid (DMSA) concentration on the performance of thiosulfate leaching of gold. A total of 24 leaching experiments were performed representing eight unique combinations of high-low levels of the three factors performed in triplicate. All investigations were performed in an electrochemical cell with an electrolyte composed of 0.1 M sodium thiosulfate with a combination of copper (either 0 mM or 1 mM) and DMSA (either 0???or 1µM). All leaching investigations were conducted under open circuit while the electrolyte, which was open to the atmosphere and mechanically stirred, was maintained at either 25°C or 50°C. After 1.5h of leaching the amount of gold in solution was quantified using ICP-MS analysis from an aliquot of the electrolyte. Results indicate that DMSA addition improved gold leaching performance, most notably at 50°C and with addition of copper. Under this unique condition, the quantity of gold in solution was reproducibly and significantly above the average response of all other factors studied.

Jan 1, 2014

By D. E. M. Plaumann

"The wet grinding of asbestos has attracted the attention of engineers for many years as a means of improving fibre liberation from the ore. Today, added impetus for wet grinding has resulted from a need to minimize worker exposure to asbestos dust in conventional dry mills using air, as well as a need to provide a cleaner, technically superior fibre for use by product manufacturers. However , high viscosities of asbestos slurries create transport and grinding difficulties which have been a factor impeding use of a wet grinding process.Laboratory evaluation of reagents to reduce viscosities of asbestos slurries found that one reagent, XFS-4272.00, reduced the viscosity of a 35% (by weight) slurry by 75%. The impact of XFS-4272.00 on actual grinding parameters were evaluated using a pilot plant rod mill. Slurries containing 78% solids and XFS-4272.00 were successfully milled and asbestos fibres from that milling compared favourably in liberation and relative surface area to asbestos fibres obtained from milling a 4% slurry without additives.IntroductionAlthough the use of asbestos has been declining over the last few years, the large deposits of chrysotile in eastern Canada (Quebec in particular) remain very important. Asbestos production in Canada stands ninth in volume for mineral production with over 740 000 tonnes produced in 1985. Of this quantity, 722000 tonnes were exported with a value of $446 million . Canada is second in world production of asbestos behind the U.S.S.R ."

Jan 1, 1988

By G. R. Heffernan

"In the early 1970ssteelmakers worldwide were looking forward to many years of expansion and profitability. Huge government investments in Europe, the United Kingdom, Japan, Brazil, and Venezuela were committed in anticipation of growing market s based on long-term OECD forecasts. In 1973 the first OPEC oil shock occurred. Steel demand shrank. Restructuring became the buzz word of the day as billions of dollars in taxpayers' money was poured into eliminating excess capacity and labour. In the United States, where government help was not available, inefficient companies went bankrupt; capacity was cut to 100 million tons from 155 million tons. The industry throughout the industrialized world shrank. By 1979the world economy seemed back on track and a modest degree of optimism could be detected in the international steel fraternity. Then came the second oil shock. By 1982 the industry was in the midst of another shakeout. More bankruptcies, more rationalization, and fewer jobs resulted. In Canada some well-known companies came close to the brink as low prices and high interest rates took their toll. In the light of the turmoil in the steel market over the past 20 years an attempt to forecast the trends through to 2001 is intimidating.However, there are good reasons to be optimistic today about both markets and technology.An economic super power is emerging in western Europe as 1992 draws near. The creation of a single market of 320 million well educated and economically ambitious people has major positive implications for steel demand. The mega projects of the channel tunnel, a European network of high speed railways, and the London docklands are the forerunners of greater things. Still to come is another $200 to $300 billion by the year 2001 in identifiable major projects for highways, railways, airports, water and sewage systems. Add to that the demands of an increasingly affluent population for automobiles, appliances and housing. On top of all that place large increasing demands for electric power and you have a potential beyond anything seen during the 1970s and 1980s. In 1988 the EEC steel industry operated at 90% and in 1989 at 92% of effective capacity. A surge in spot prices indicated that 92% was close to the ceiling. This pace moderated in early 1990 but any slack will probably be taken up rather quickly."

Jan 1, 1990

By R. K. Collings

Mineral wastes from the mining, metallurgical and chemical processing industries in Canada amount to about 800 million tonnes annually. Such wastes often are largely non-metallic in composition and are of interest for traditional non-metallic mineral uses and applications. Mineral waste disposal and maintenance are costly; furthermore, these wastes may pollute groundwater, rivers and lakes. These factors and an increased appreciation of the potential utility of some mineral wastes have stimulated research in this area.

Jan 1, 1984

By Richard Dawson

Increasing global demand for coking coal has initiated several new coal mine developments in northeast BC. These developments are able to take advantage of the currently under utilized infrastructure that was put in place during the 1970?s and 1980?s for the Quintette and Bullmoose coal mines; which includes the Town of Tumbler Ridge, a 1,000km rail line to the coal terminal at Prince Rupert and a road system providing highway access to the town site. Coal within the two foothills regions of BC (north-east and south-east) is mined by open pit truck/shovel methods. Optimized mine plans require a thorough understanding of Rocky Mountain structural geology, attention for access in steep terrain, and a related understanding of the geotechnical conditions that control the stability of pit slopes and waste dumps. Thus there is a requirement to properly integrate mine planning with geotechnical engineering considerations. Many of the technical issues are well understood from experience during the past 30 years of Western Canadian coal mining. The challenge is to ensure that the mine plans are able to take full advantage of these lessons learned. The paper will focus on mine planning and geotechnical design issues to do with high angle-of-repose waste dumps and steeply bedded footwall slopes to illustrate the advantage of properly recognizing the important stability control issues during the early stages of engineering evaluations. Case histories from the existing and planned coal mining operations will be presented.

May 1, 2006

By C. W. Chao, M. Melashvili, F. Hilário

The processing of a bulk concentrate containing copper as chalcocite, enargite, bornite and chalcopyrite along with pyrite and precious metals of silver and gold was studied. A leaching study was undertaken to examine the application of the atmospheric acid leaching process to a bulk copper concentrate for copper recovery followed by cyanidation or thiosulfate leaching for gold and silver recovery. The extraction of copper exceeded 90% under some conditions and the recovery of gold and silver reached a maximum of 44 and 45%, respectively. A sample of bulk concentrate was roasted in air to oxidize the sulfides with release of sulfur dioxide followed by acid leaching of the roaster calcine and cyanidation of the acid leach solution. The copper extraction reached over 92% and the gold extraction exceeded 88%. The sulfur dioxide may be captured for acid production. INTRODUCTION The processing of a large primary copper deposit in Indonesia is under investigation. One of the possible routes for processing involves flotation of a bulk copper-gold concentrate followed by treatment by an atmospheric leach/SX-EW process for copper recovery. The atmospheric leach residue would then be leached for recovery of gold and silver. A second route involves roasting of the concentrate followed by acid leaching and SX-EW for copper recovery. The leach residue from the roaster calcine would then be leached for recovery of gold and silver. The roaster off-gases could be used for sulfuric acid manufacture, enabling the production of a valuable by-product. The Cobre Las Cruces (CLC) process (Munoz, Garcia, & Delgado, 2017) was designed to treat a resource of copper discovered close to Seville, Spain. The process was developed by Outotec with MK Gold (original project owner). INMET Mining subsequently purchased the deposit from MK Gold and built the copper processing facility. The CLC process is similar to the Mt. Gordon Copper process; except that OKTOP reactors have been installed instead of a low temperature, low pressure autoclave process. The plant was designed to treat 1.3 mtpa of ore at a grade of 6.2% Cu to produce 72,000 tpa of cathode copper over a 15 year project life. The main gangue mineral at Cobre Las Cruces was pyrite. The Cobre Las Cruces ore is therefore similar to a rougher flotation concentrate containing copper minerals and pyrite. The roasting of a rougher flotation concentrate can be designed to produce hematite, basic copper oxides and sulfur dioxide off gas. The acid leaching of the basic copper oxides may produce soluble copper for SX-EW recovery of copper. The sulfur dioxide off-gas may be used to make sulfuric acid.

Jan 1, 2019

By R. B. Kaunda

One fundamental requirement for surface and underground rock engineering is the ability to characterise the rock mass. An accurate characterisation of the rock mass allows rock engineers to optimize designs safely and economically. A number of classification systems have been developed in the past 50 years to help characterise rock masses such as RMR, Q system, Rmi, and several others. The challenge in developing rock characterisation schemes is often practicality, i.e. creating systems with relatively simple inputs for the everyday practitioner. A second challenge is the degree of subjectivity often inherent in commonly used classification systems. These challenges are especially exacerbated in weak rock or densely jointed rock masses. This paper introduces a new approach to characterise densely jointed rock mass using artificial neural networks and principal component analysis, based on principles commonly used in the geotechnical engineering of rock fills and waste rock dumps. Thirteen input parameters are dimensionally compressed using principal component analysis. Using a global database with more than 100 case histories, an artificial neural network is developed to conduct the rock mass characterisation. The advantage of this approach is less subjectivity as commonly used engineering (quantitative) terms are put to use. A further advantage is that given that the method is site-data dependent, it allows for ‘fine tuning’ of the model for a specific site.

Jan 1, 2015

By Z. Pilecki

This work concerns the identification of weak zones in the structure of a rock mass endangered by outburst of gases and rocks in the Rudna copper ore mine at greater depths (approximately 1200 m). A special methodology has been undertaken for the recognition of that threat in the wake of an outburst in the mine in 2009. No similar phenomena have been previously recorded in KGHM Polska Miedz copper ore mines. The research described in this paper was carried out in the new part of the deposit prepared for mining. Geophysical methods were used: seismic tomography and borehole ground penetrating radar (BGPR), along with particular identifications using geological engineering methods. In the researched area, Permian layers of sandstone and shale clay (Weissliegendes formation) and of Zechstein dolomite (top of Rotliegend formation) and anhydrite occur in the copper ore deposit. The rock layers are characterized by variable thickness and intensity of mineralization, varying internal structure, and local fracturing containing different gases and water. It is assumed that accumulation of gases occurs in the tectonically fractured dolomite. The study was focused on the recognition of the structure and properties of the dolomite layer lying directly within the roof of excavations. The first tests were performed with seismic tomography for the recognition of anomalous changes in the elastic properties of the rock mass. The results of these studies were used to design a control borehole for a detailed geological engineering assessment and BGPR surveys with 100MHz antennas. Seismic tomography enabled the identification of changes in Pwave and S-wave velocity, the Vp/Vs ratio, dynamic Poisson's ratio and dynamic Young's modulus. It was clear that seismic anomalies required verification by other methods. The BGPR survey was performed in a specially designed borehole, passing through the selected seismic anomalies. While the borehole was being drilled, the outflow of gases was identified, with varying amounts of CH4, CO2, and H2S detected, as well as water outflow. The results of BGPR confirmed the location of a reservoir of water and gases, about 30 m in length, found in layer of dolomite. The direct cause of the BGPR anomaly was assumed to be intensive fracturing, a greater content of clay material in the dolomite, and the presence of water in the fractured zone. The BGPR image was correlated with information on lithology, fracturing based on the RQD index and additional information acquired during drilling about water and gases surveys and other symptoms. The achieved results also showed a very strong correlation between the location of the zone containing gases and water and the anomalous S-wave velocity and field of dynamic Poisson?s ratio, and to a lesser extent other seismic parameters. It was found that the other measured seismic anomalies may be of the same nature as those identified in the control borehole and accordingly will require the implementation of detailed identification. The performed tests have also shown the usefulness of geophysical methods to identify geodynamic hazards under the geological and mining conditions of the copper ore deposit in the Rudna mine.

Aug 1, 2013

By Chris M. Healey

"Perhaps the single most significant variable in the evaluation of a mining project is the reserve estimate. Many parameters are considered when estimating reserves, among them geology. This paper examines the link between the quality of a reserve estimate and a good understanding of the geological controls for the deposit. A clear understanding of the geometry is essential to the accurate definition of the shape and size of the deposit. This includes the definition of any structural controls as well as the proper interpretation of the stratigraphy. Further when the distribution of grades is erratic and there is consequently a high nugget effect, there are significant problems in estimating the true grade of the deposit.Two Saskatchewan examples are presented, one with good knowledge of the controls and therefore good estimates of reserves, and the other with a poor understanding of the geology and resultant problems in deriving good estimates. In both cases the reserve estimates at various stages in the project development are compared to actual results from underground work. The first example is the Star Lake Mine where just about all the estimates were within 10070 of the actual on both tonnage and grade. The Laurel Lake deposit is discussed to show how problems in interpreting the geological data make reserve estimation very difficult. Laurel Lake has the additional problem of erratic grade distribution."

Jan 1, 1992

By Stephen Hardcastle

Personnel Heat Exposure Issues In Canada?s Deep Mechanized Mines ?Project developed in 2004 ?Base/precious metal industry identified heat stress/management as a major challenge affecting productivity and operating costs ?Project started in 2005 ?Current research nearing completion ?Guidelines, further data analysis and ?Communicating the Science? will continue into 2011

Oct 1, 2010

By Gema Ribeiro Olivo

The hydrothermal Au-Pd deposits are hosted by the jacutinga in the Lake Superior-type iron-formation of the Itabira Group, Minas Supergroup. Jacutinga is a highly sheared, metamorphosed, hydrothermally altered iron-formation composed of hematite, magnetite, quartz, talc and phlogopite (Cauê) or muscovite (Conceição) and minor tourmaline, palladian gold, arsenopalladinite, mertierite II and palladeisite (hydrothermal) and native gold, native palladium Pd-Cu-oxides, and kaolinite (weathering products). The highest concentrations of Pd-Au occur in quartz and hematite veins parallel to the S1 foliation (Corpo Y, CorpoX, Aba Leste and Central orebodies, at Cauê and a single orebody at Conceição) or parallel to the S2 foliation (Aba Norte). The average ore grade is 30-40 g/t Au+Pd. The characteristics of the Au-Pd ore favor an epigenetic model for gold and palladium concentration in the iron-formation. During the D1 deformation and peak metamorphism, the oxiziding, acid and hot hydrothermal fluids transported Au and Pd preferentially as chloride complexes. The reaction of the fluid with the dolomitic carbonate (the probably protolith of the jacutinga) would have dissolved carbonate and K-feldspar to form muscovite or phlogopite and tourmaline, resulting in an increase in solution pH and a decrease of Cl concentration and subsequent deposition of gold and palladium minerals.

May 1, 2003

By Kazutoshi Haga, Batnasan Altansukh, Atsushi Shibayama, Ryuji Oinuma

"Recently, the arsenic grade in copper ores has been increasing year by year. Arsenic bearing minerals (enargite (Cu3AsS4) and tennantite (Cu12As4S13)) coexist with typical copper minerals such as chalcopyrite (CuFeS2). The removal of arsenic from copper ores that contain relatively high arsenic content is essential due to its adverse impact on the environment and the resulting economic consequences. In this study, arsenic removal and dissolution behaviour of Cu and As from enargite (Cu3AsS4) were investigated using ferric sulphate (Fe2(SO4)3) solutions containing sodium chloride under high pressure oxidation conditions. The effects of numerous parameters including the concentration of Fe2(SO4)3 and NaCl, temperature, total pressure, leaching time and particle size were studied while other variables such as pulp density and stirring speed were fixed at 100 g/L and 750 rpm. The results showed that more than 60% of the copper was dissolved in a 0.1 M ferric sulphate solution under the high pressure oxidative conditions, whereas the leaching rate of arsenic was less than 20%. SEM observation revealed that elemental sulphur was deposited on the surface of enargite forming a passivation layer and the residue was agglomerated. Those phenomena may cause a decrease in the copper leaching rate. It was found that more than 80% of copper was dissolved in the ferric sulphate solution in the presence of 0.34 M sodium chloride under the conditions optimized, whereas the dissolution of arsenic in the mixture did not exceed 2%. XRD analysis of the solid residues from the leaching experiments used ferric sulphate and mixtures of ferric sulphate and sodium chloride showed arsenic to be present as scorodite (FeAsO4).INTRODUCTION In recent years, there has been an increase of the arsenic (As) content of copper ores due to the gradual depletion of high grade copper ores. In some copper deposits, arsenic occurs in the form of minerals such as enargite and tennantite. The removal of arsenic in ores containing copper is critical to the production of pure copper and the management of the environmental challenges caused by the smelting process. Due to the environmental risk caused by arsenic emission and the deteriorated quality of the copper product, smelting of enargite concentrates is not an effective method for the extraction of copper (Padilla et al., 2010; Safarzadeh et al., 2014; Long et al., 2012). Therefore, a number of studies have been carried out to develop arsenic removal technologies from copper ores using various methods such as hydrometallurgy (Curreli et al., 2009; Tongamp et al. 2010), pyrometallurgy (Dalewski., 1999; Padilla. et al, 2012) and bio-oxidation (Ehrlich, 1964; Sasaki et al., 2010). Several hydrometallurgical leaching processes like sulphuric acid, alkaline sodium sulphide and sodium sulphate and ferric sulphate leaching have been developed to treat enargite ores and concentrates. The alkaline sodium sulphide leaching process has been developed for the removal of arsenic from enargite (Anderson, & Twidwell, 2008; Parada et al., 2014). The mechanism of the dissolution of arsenic from enargite in sodium sulphite solution is"

Jan 1, 2016

By Aalbert Zwijnenburg

One of problems connected with the use of gold/titania-based catalyst systems is the low yield in propene oxide (up to 2 wt %). It is shown that the low propene oxide yield is due to product inhibition. New options for propene epoxidation with hydrogen and oxygen are discussed. INTRODUCTION The direct gas-phase synthesis of propene oxide (PO), by the use of molecular oxygen, is still aimed for. Agbased catalysis is in principle possible, but selectivity at present is not promising. Highly dispersed gold on titanium containing catalysts show an extraordinary selectivity in the oxidation of propene to the corresponding epoxide (> 99 %), using a combination of H2 and O2 as oxidation mixture [1]. Additional studies of the epoxidation reaction have indicated several drawbacks of the Au/TiO2 catalyst. Firstly, the low conversion (1- 2 %) obtained under typical reaction conditions (atmospheric pressure, 323 - 423 K) cannot be increased by increasing the reaction temperature, because this leads to extensive by-product formation. Secondly, the low efficiency of hydrogen (relatively large amounts of water are formed) is hard to prevent. Finally, significant deactivation of Au/TiO2 catalysts within several hours on stream has been observed. Deactivation can be almost completely prevented by using dispersed TiO2 supports, such as TiO2/SiO2 and Titanium-Silicalite-1 (TS-1) [2]. In recent literature [2,3] a hydroperoxide-like intermediate has been proposed to be responsible for the selective epoxidation. This oxidising species is said to be formed over gold and subsequently used for epoxidation over the Ti-containing support. The support is responsible for the slow desorption of PO. One of the problems for future industrial application might be the low yield in propene oxide. Furthermore, the presence of minor amounts of by-products, not detected on lab-scale catalyst testing, might complicate the separation unit in an industrial process. The reason for the low PO yield over Au/TiO2-based catalysts will be discussed in this paper. Temperature Programmed Desorption (TPD) and micro-flow experiments have been carried out to study PO desorption and catalyst performance, respectively. A catalytic cycle is proposed together with its consequences for the maximum yield in PO. Finally, several process and catalyst options are discussed in view of potential future industrial application.

Oct 1, 2003