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By E. L. C. Martins, M. J. Nicol, D. Majuste, A. D. Souza

The effects of organic compounds on the current efficiency (CE), morphology, crystal structure and mechanical properties of the metal deposited during the electrowinning of zinc are described. A flotation collector and lubricating oil were selected based on observations made during the industrial production of zinc from silicate ores, in Brazil. The analysis by Fourier transform infrared spectroscopy of these compounds, which may be present in minor amounts in the electrolyte solution, indicated the presence of a polar amine group in the collector, while the lubricating oil is a non-polar compound. The average CE value obtained from organic-free industrial solution was 91.15 ± 0.26 %. The CE dropped to 54.35 ± 0.73 % in the presence of 100 mg·L-1 of collector in the solution, and a negative effect was also observed in the presence of similar amounts of oil (88.84 ± 0.61 %). The characterization of the deposits by scanning electron microscopy and X-ray diffraction revealed the formation of pores in deposits obtained from solutions containing the oil, while a different growth pattern (perpendicular zinc platelets) was identified when the flotation collector was added to the industrial solution. In the presence of these contaminants in the solution, guided-bend tests revealed that the deposits have a higher resistance to deformation, but lower ductility, properties that may affect the performance of the stripping stage. As a result of this work, simple control and optimization actions were applied in the industrial plant, which resulted in important improvements in the electrowinning process.

Jan 1, 2014

The mechanism of thiosulfate decomposition and the products formed were investigated in the presence of pyrite or pyrrhotite in copper-ammonia solutions used for leaching gold. The presence of the sulfides significantly increased the decomposition of thiosulfate. The sulfide-surface-catalyzed oxidation of thiosulfate to tetrathionate by dissolved oxygen or the cupric tetra-ammine complex was proposed to be the dominant thiosulfate decomposition mechanism. The catalysis of the sulfides in this reaction could originate from their strong affinity for aqueous sulfur species and their semiconducting properties. Oxygen was found to be the initial driving force for thiosulfate decomposition in the absence of cupric ions and the driving force for the continuous decomposition of thiosulfate in the presence of cupric ions. Under an oxygen free atmosphere, the decomposition of thiosulfate was limited to reduce the cupric ions and the catalytic effect of the sulfides was also marginal. The dominant oxidative product of thiosulfate was trithionate in alkaline solutions especially in an oxygen rich or cupric ion rich environment. Tetrathionate was found in relatively smaller amounts in an oxygen and cupric ion deficient environment. Tetrathionate was not stable and would further decompose after extended periods. Trithionate concentrations increased almost linearly with time.

Jan 1, 2005

By M. A. Tomlinson, A. Di Feo, T. C. Cheng

"Goldcorp is evaluating the potential for economic reprocessing of historic tailings at several sites, including the Aunor A facility located in Timmins. The overall project is investigating the ability to recover value, remove sulphide minerals and alternative tailings re-deposition strategies. Desulphurization of tailings will eliminate potential acid generation while improved tailings re-deposition could reduce long-term liabilities and closure costs. Through a task-share project between CanmetMINING and Goldcorp, tailings obtained from Aunor A site have been characterized using mineral association analysis and diagnostic separation techniques. The selected tailing samples contain about 2 g/t of gold. Mineralogical analysis has identified coarse agglomerates bound with gypsum and significant free gold, confirmed by high recoveries in cyanide leach tests. However, despite no evidence of surface passivation on the minerals, conventional flotation techniques were found to be ineffective in concentrating gold or sulphides due to the high fines content and highly agglomerated particles.INTRODUCTION Aunor Mine is one of the historic mines that belongs to Porcupine Gold Mines (PGM) in Timmins, Ontario. PGM has undertaken an extensive mine closure program to remediate the legacy and closed mines with the funding supported by operating mines since 2006. Over the course of 100 years of operation in the Porcupine camp, it is estimated (Stevens et al., 2013) that about 130 million tonnes of tailings have been generated. Aunor Mine produced 2.5 million troy ounces of gold between 1940 and 1984, while processing over 7.6 million tons of ore. The original gold grade of Aunor Mine ores was about 10 g/t. With 95% gold recovery at the time, an estimate of 0.5 g/t of gold remains in the Aunor Mine tailings. Aunor Mine has two tailings impoundment areas: designated as Aunor A and Aunor B. The two sites are similar in size, about 7 hectares each. The amount of tailings in the Aunor A site alone is about 3.2 million tonnes. In 2017, bulk tailings were sampled from five designated locations in Aunor A. They were characterized using mineral association analysis and diagnostic separation techniques. The bulk tailings samples contained about 10% total sulphur, 10% iron, 2% arsenic and 2 g/t of gold. The prime objective of this collaborative work between CanmetMINING and Goldcorp is to facilitate the timely development and deployment of innovative tailings reprocessing solutions, specifically in the areas of desulphurization, and recovery of metals. This work targeted specific tailings of interest to Goldcorp which goals are to improve its environmental footprint and to reduce long-term liability. Thus, it is imperative to look for innovative reprocessing options that can overcome not only technological challenges but also achieve economic benefits to offset the costs associated with reprocessing the tailings. Moreover, the greater goal is to demonstrate and deploy tailings reprocessing solutions to solve one of the industry’s most difficult challenges for a sustainable mining industry in Canada."

Jan 1, 2019

By Pierre Pelletier, Christian Pichetie, Dany Pelletier

"IntroductionDuring 1994, Barrick Gold Corporation, or American Barrick at that period, acquired Lac Minerals Ltd. properties. One of them was the Bousquet Complex. The Bousquet Complex is divided into three distinct sites: one mine (Bousquet 2), one mill (Est-Malartic Division) and one analytical chemistry laboratory (Les Terrains auriferes).The Bousquet 2 orebody was discovered in 1986. An extensive drilling program was initiated during 1987. Its purpose was to define the orebody extent. At the end of 1997, gold production from Bousquet 2 mine reached 1 290 000 oz of gold from a cumulative tonnage processed of 4 175 000 M t.From 1980 to 1990, the Est-Malartic mill was used for the treatment of ore from the following mines: Bousquet 1, Doyon, Francoeur (Richmont mines), Buckshot and 1-20 stope. At present, the mill receives ore from the Bousquet 2 mine.HistoryThe Est-Malartic mill is located close to the town of Malartic in northwestern Quebec. The mill has been in production since the mid-1930s processing mainly clean, free mill gold ore. Active mining from the Est-Malartic mine ceased in 1979 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 it would be economically more attractive to modify the existing Est-Malartic mill than building a new facility on site. The Est-Malartic mill modifications for processing the high-copper/gold ore from the Bousquet 2 mine began in late 1989 and 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 leaching circuit continued to operate on the copper flotation tailings with some minor modifications to the solution handling systems. A S02/Air cyanide destruction circuit was also added at that time."

Jan 1, 2000

By R. T. Jones

"Technical publications in the field of mining and metallurgy have existed for a long time. Recent developments in electronic publishing on websites make it possible to disseminate information more widely and cost effectively than before. Professional societies have an opportunity to serve their members and their industry by publishing high-quality peer-reviewed papers on their websites as well as in printed form. Older publications can be scanned, and optical character recognition can be used to provide searchable text. Various business models exist around this process. This paper outlines the approach used by the Southern African Institute of Mining and Metallurgy (SAIMM) to provide free open access to their journal papers and conference proceedings, as well as the work being done by OneMine.org to collect technical papers from a number of international societies and make them available to subscribers via a large database. An approach is outlined that should be of benefit to authors, readers, and society at large.INTRODUCTIONGeorgius Agricola (1494-1555) was not the first writer on the subjects of mining and metallurgy, but is well known as the author of De Re Metallica (‘of things metallic’ or ‘on the nature of metals’), a book that documents and illustrates the observations he made in the course of his extensive travels in the 1500s. Agricola wrote extensively about mining methods and metallurgical processes that were in place in the Middle Ages. The original Latin version of De Re Metallica was published in 1556, the year after Agricola died. It was translated into English by Herbert Hoover, a mining engineer and later President of the United States, and his wife Lou Henry Hoover, a geologist and classicist. The English version of De Re Metallica was published in 1912."

Jan 1, 2012

By F. Baerhold

Recycling of hydrochloric acid from the pickling of mild steel using pyrohydrolysis is a state-of-the-art technology. Recent developments have focused on the production of a high value iron oxide by-product, where the chemical purity and physical properties are the main issues. New processing routes, especially for TiO2 and Ni production, use leaching operations with hydrochloric acid. The feasibility of those processes depends on the availability of an economic and reliable process for the recovery of the acid. Depending on the level and type of impurities and the required specification of the by-product, pyrohydrolysis in a fluid bed or in a spray roast reactor can be the ideal solution. In stainless steel annealing and pickling lines, a mixture of nitric and hydrofluoric acids is used to remove the scale from the surface after heat treatment. Nitrate emissions from the pickling and the rinsing processes have to be avoided because of more stringent environmental regulations. An annealing and pickling line that is totally wastewater-free was developed, where not only the nitric/hydrofluoric acid but also the rinse water, is completely recycled. New developments to increase the HNO3-recovery rate and to obtain a metal oxide by-product that is easier to recycle are presented.

Jan 1, 2006

By A. L. Mackie

Mine water from base metal mines is generally characterized as having high concentrations of heavy metals and low pH, resulting in the need for treatment prior to discharge to receiving waters. In this study, two high-rate clarification processes were evaluated at bench-scale: the high density sludge (HDS) process and sand-ballasted flocculation. High-rate clarification processes generate larger, denser flocs which settle more quickly than those formed in conventional flocculation processes. The HDS process uses recirculated sludge in order to seed floc formation, whereas ballasted flocculation uses microsand. Both of these high-rate processes require the addition of quicklime or hydrated lime to increase pH and allow for the formation of insoluble metal hydroxides, which can then be removed in the clarification stage. Previous research has shown that cement kiln dust (CKD) can effectively replace quicklime in conventional sedimentation processes for metals and acidity reduction to meet discharge guidelines (Mackie & Walsh 2012). CKD is an alkaline by-product of cement manufacture that has fine particle sizes and varying free lime concentrations depending on the manufacturing process. The lower solubility (i.e., free lime content) of CKD requires larger doses of material to be added to reach treatment pH targets for metals precipitation. The purpose of this study was to evaluate the treatment efficacy of high-rate clarification processes for mine water treatment, compared with conventional sedimentation, at bench-scale with conventional (i.e., lime) and novel (i.e., CKD) pH adjustment additives. Results of the study showed that all treatment processes (i.e., HDS, ballasted flocculation, and conventional sedimentation) were able to reduce target metal concentrations to well below Canadian guidelines (i.e., total zinc and total nickel < 0.5 mg/L, total copper < 0.3 mg/L) using either CKD or lime. Additionally, mine water samples treated with CKD generated lower sludge volumes than those treated with lime (i.e., 50 versus 100 mL for conventional sedimentation and 100 versus 200 mL for HDS) even with increased concentrations of solids introduced during treatment. This is most likely due to slower neutralization rates when using CKD, due to its lower solubility, as well as finer particle size. The sand-ballasted flocculation process was able to reduce final turbidity in CKD-treated samples while the HDS process did not when compared to conventional sedimentation, making the ballasted flocculation process preferable for reducing final solids concentrations in CKD-treated mine water.

Aug 1, 2013

By T. C. Cheng, G. P. Demopoulos

It is the object of this paper to discuss various options for improving the hematite process in terms of increased throughput hence lower capital cost and production of saleable quality hematite. With reference to increasing the throughput of the process, it has now been determined via the analysis of Akita Zinc Co&apos;s continuous industrial autoclave performance data that the process kinetics is limited by the rate of the hydrolytic precipitation reaction. By correlating the hydrolytic precipitation rate to supersaturation ratio, it is shown that accelerated kinetics can be achieved via the following measures: (1) in-situ neutralization with addition of zinc calcine; (2) elevation of temperature; and (3) dilution of feed; of which, the first one was retained for further evaluation. According to presented estimates, addition of calcine, amounting to only 2.6% of the total zinc calcine processed, can allow for shortening the retention time by at least 50%. Such drastic shortening of retention time may be either used to increase the throughput of a given autoclave circuit or alternatively to release autoclave capacity for clean hematite production. Hydrothermal treatment of the crude hematite product proved effective in producing clean hematite as according to laboratory tests, hence allowing the sulphur content of hematite to be reduced from around 4% to less than 1%. A conceptual flowsheet incorporating in-situ neutralization for accelerated kinetics with hydrothermal upgrading of crude hematite without sacrificing production capacity and with minimum upset of the plant&apos;s water balance is described.

Jan 1, 2004

By G. B. Harris

In recent years, increasing attention has been focused on the hydrometallurgical treatment of base metals feeds, especially nickel laterites and polymetallic sulphides. One approach that has received some attention is the use of high?concentration chloride solutions (brines), which are now showing some promise after initial setbacks. Iron is usually the major component in the base metal feed to such processes, and if physical means cannot be used to remove it, then the iron concentration in the pregnant leach solution is always significant. This paper presents some of the background theory on the hydrolysis of iron in high-strength (>3M) chloride brines, and discusses the roles of temperature, solution concentration and free acidity. It is shown that the system is complex, but that crystalline and readily-filterable hematite can be generated, and that the system has a low energy requirement.

Jan 1, 2006

By H. Arima, Y. Kudo

In general, the iron content of zinc leach residue produced by sulphuric acid leaching from calcine is disposed as jarosite or goethite into a tailing dam. More recently, these iron residues have been treated pyrometallurgically to avoid waste disposal. The Iijima refinery selected a different zinc leach residue treatment process for iron control when it was established in 1971. The Iijima refinery is the only plant in the world that has processed a zinc leach residue by the combination of SO2 pressure leaching and O2 pressure hematite precipitation. The process enhances zinc recovery and recovers gold, silver, copper, lead and rare metals in saleable by-products. This paper focuses on the two stages of autoclave application in the zinc leach residue treatment process. The detailed flowsheet and recent advancements to improve the quality of by-products are discussed.

Jan 1, 2004

By W. B. Timm

Introduction In preparing this paper on Recent Developments in Gold Milling Practice, the idea occurred to me that possibly the best way to deal with the subject would be to take you in thought on a visit to the principal gold mining camps of the Dominion, starting at the east and finishing up in the west, and noting, as we go, the outstanding improvements that have been made in the last few years in the practice of gold milling. Before beginning this tour, I desire to emphasize the debt this country, and particularly our mining industry, owes to that body of trained and experienced men, little heard of, but who, working quietly on their problems, are responsible for these improvements. The metallurgists, to whom I refer, have solved many difficult problems for the mining industry, in connection with the treatment of our complex ores; for instance, the silver-cobalt ores of the Cobalt district, the gold ores of the Porcupine district, the gold-telluride ores of the Kirkland Lake? district, the copper-gold ores of Noranda, the arsenical-gold ores of the Beattie mine, the copper-zinc ores of Flin Flon, and the lead-zinc ores of Kimberley. In doing so, they have maintained the high technical standards of the profession, and the practices thus evolved are noteworthy for their high degree of efficiency. When the price of gold increased from $20.67 to $35.00 an ounce, what had formerly been thought to be a low tailing became almost an ore, so that the metallurgists are now busily engaged upon the problem of putting this railing back in its proper place of being a tailing once more, or from its value, at the present price, of anywhere from 50 cents to a dollar or so per ton, to a few cents per ton. Owing to the changing prices of the metals in the world&apos;s markets, still greater improvements in metallurgical practices are imperative. An important contributory factor towards improvement in ore dressing is the aid furnished by the microscope in the examination of ores and mill products. By making possible the determination of the mineral constituents of the ore, their association, and grain size, it gives the investigator a knowledge of his problem, before he does any actual test work. In the Mines Branch laboratories at Ottawa, its use has enabled us to predict how an ore should respond to various methods of treatment.

Jan 1, 1935

By L. Vollert

"The application of pneumatically-assisted fluidized bed flotation, specifically the ERIEZ HydroFloatTM technology, has found widespread use in non-sulphide processing (particularly phosphate, potash and coal) for the recovery of coarse particles. In gold processing, centrifugal gravity circuits and flash flotation cells are typically employed for the recovery of coarse and near-size liberated gold which tends to accumulate in recycled grinding streams due to bypass to the classifying cyclone underflow streams owing to the higher specific gravity of these gold particles. Early removal of this gold from the grinding circuits contributes toward the reduction of downstream processing losses as a result of overgrinding and particle shape deformation in the case of flotation processing, longer leach residence times in the case of extractive processing, and surface occlusions in the case of both flotation and extractive processing. Furthermore, recovery to bullion attracts higher payment terms by way of comparison to concentrate sales in the case of copper-gold concentrators. This paper assesses the application of pneumatically assisted fluidized bed flotation for the recovery of coarse liberated gold through the analysis of piloting data generated from the operation of a continuously operated 16 inch ERIEZ HydroFloatTM unit treating a sized coarse grinding circuit stream. The paper presents the stage recovery by size performance of the ERIEZ HydroFloatTM unit together with quantitative gold deportment analysis to demonstrate the efficiency with which gold was recovered during this pilot campaign and then compared to more conventional processing units – centrifugal gravity and conventional flotation.INTRODUCTION Newcrest Mining Limited (NML) has identified that an opportunity exists for improving the recovery of coarse composite particles at its current operations, both as a means for improving overall recovery and as an opportunity for early gangue rejection. As such, Newcrest Mining Limited has taken an interest in the application of pneumatically-assisted, fluidized-bed flotation i.e. ERIEZ HydroFloatTM technology. This interest dates back to 2011 with sighter testwork carried out on their Australian-held ore bodies (Kohmuench et al, 2013). Newcrest continues to assess ERIEZ HydroFloatTM potential for coarse composite recovery and, in the case of the topic of this paper, coarse gold recovery based on examples in the literature which demonstrate the efficiency of this technology in this regard (Carmona Franco et al., (2015); Miller et al., (2016); and Kohmuench et al, 2013)."

Jan 1, 2017

By C. J. Brown

Regeneration of hydrochloric acid steel pickle liquors has traditionally been accomplished by pyrohydrolysis. However, a number of factors have recently conspired to reduce the attractiveness of this approach. Moreover, the process is not amenable to small-scale operations. On the other hand, the standard technique for regeneration of sulfuric acid pickle liquors, which is the low-temperature crystallization of ferrous sulfate is applicable to any size operation. A similar technique has recently been developed to regenerate hydrochloric acid. Sulfuric acid is added to the ferrous chloride-bearing spent HCl pickle liquor. The temperature is then reduced to below 0°C, resulting in the crystallization of ferrous sulfate heptahydrate and liberation of free hydrochloric acid. Depending upon the crystallization temperature, variable concentrations of sulfate are left in the regenerated acid. Although this residual sulfate has an impact on the pickling characteristics of the regenerated acid, tests have shown that by adjusting the conditions, pickling rates will be at least equal to those using pure HCI, and an acceptable surface finish will be produced.

Jan 1, 2006

By Zhou Yanwen, Fudong Wang, Shing Liu

Mixed CrB2 and MoS2 powder (Cr:Mo=1:1 atomic %), without any further process, were used as the targets to be sputtered and deposited onto stainless steel and silicon substrates by pulsed DC power supply. The structures and properties of the CrBMoS films were then analyzed by using SEM, XRD, micro-hardness tester. The SEM morphology of the films showed dense, defect free structure, and the preferred orientations of the films were CrB2 (111) and MoS2 (200) according to XRD spectra. The thicknesses of the films were measured and the relationship between the deposition rates and pulsed factors was determined. The films, with the micro-hardness as high as 19GPa and friction coefficient as low as 0.02, could be considered to be the hard solid lubricant films.

Jan 1, 2015

By W. Beres, R. E. Miller, B. Shiari, L. R. Zhao

A dynamic multiscale simulation method has been developed to study the material scratching processes on nanoscale single crystals. The model simultaneously captures the atomistic mechanisms near the free surface and the long range mobility of dislocations and their interactions, without the computational cost of full atomistic simulations. The method also permits the simulation of system sizes that are approaching experimentally accessible systems, albeit in 2D. Simulations are performed on single crystal aluminum to study the atomistic details, surface evolution, and generation and propagation of dislocations for a variety of scratching depths at room temperature. Simulations demonstrate the power of the developed method in capturing both long-range dislocation plasticity and short-range atomistic phenomena during tool advance. Variations of scratching normal and tangential forces are investigated and related to plastic deformation and dislocations generation during the simulation process.

Jan 1, 2006

By P. Fossi

This report describes a pilot-scale study of a hydrometallurgical process to treat high-grade nickel matte or a nickel-cobalt sulphide precipitate to produce high-purity electrolytic nickel. The first step of the process is the oxidative leaching of the nickel-bearing material by nitric acid; the nitrous gases generated during leaching are reconverted to nitric acid. The crude nickel sulphate nitrate solution is purified and is then subjected to a denitrification step. Nitrate separation is effected either by the crystallization of nickel sulphate or by precipitation of basic nickel carbonate. The electrolyte is prepared from the nitrate-free material and nickel is then recovered by electrolysis of the sulphate solution using insoluble anodes. Some technical and economic problems encountered with this processing route are discussed and the method is compared to the "all-chloride" process developed by Société Le Nickel.

Jan 1, 1977

By D. Ling, Santos. R. M., T. Van Gerven, M. Guo

The valorization of alkaline waste materials from thermal processes utilizing intensified mineral carbonation routes is investigated. The principal advantages of this approach are the chemical stability and storage safety of mineral carbonates, the opportunities for process integration presented by the technology, and the potential for conversion of low-value materials into useful products. Treatment and disposal of steel slags are a costly burden on steel plants. Sustainable solutions for Argon Oxygen Decarbonisation (AOD) and Continuous Casting (CC) stainless steel slags and Basic Oxygen Furnace (BOF) steel slag are desired. An integrated on-site mineral carbonation approach is envisaged as a favourable solution.

Jan 1, 2011

By S. Caron

From the early 70?s, ?Centre de Recherche Minérale? (CRM) has conducted and co-ordinated Research and Development activities for the mineralurgical and metallurgical industries. Since 1999, CRM has continued its mandate through COREM which is a consortium of 13 members that uses the benefits and advantages of collaborative pre-competitive industry / university research. In particular, COREM?s ?In-Situ Optimization Group? is involved in the implementation of modern optimization and control tools. The POP Project was launched in order to increase and consolidate the use of modern optimization and control tools and methods for mineralurgical and metallurgical processes. To ensure a successful transfer in the industry, there are a number of essential activities that have to be undertaken. These activities have been identified by COREM?s members and are grouped into three main modules: - R&D Module: Research and Development in universities, research centres and other partners; - Technology Transfer Module: integration of new tools and methods into the POP Software, industrial applications and technical support; - Training Module: education of new engineers in universities, continuing education of plant personnel through on-site workshops and resource networking by specific information exchange tools. This paper outlines the opportunities that led to the definition of the POP Project and describes its main modules. The main features of the POP Software are presented, the first application is described and finally, future developments are discussed.

May 1, 2001

By Zhan Zhang, Hiromi Nagaumi, Zhen Li

"Recently, the remarkable strengthening effect of ??-Al(Mn, Fe) Si dispersoids at both ambient temperature and elevated temperature were found by several researches. A large amount of dispersoids can be formed by applying special heat treatments and within a suitable range of chemical composition of AA3xxx alloys. In the present work, the influences of Cr addition on the mechanical properties and microstructures of the Al-Mn-Mg-Si alloys were investigated. The mechanical properties at ambient and elevated temperatures were evaluated by micro-hardness and yield strength. Moreover, the microstructures in as-cast and heat-treated conditions were quantitatively analyzed by optical and electron microscopes. Results revealed that Cr also had effect on the number density and volume fraction of dispersoids. Micro-hardness and yield strength at ambient temperature increased with the increasing content of Cr, and the Cr addition increased the yield strength at elevated temperature as well. Moreover, the creep resistance at 300°C improved dramatically with the increasing content of Cr.INTRODUCTION Traditionally, AA3xxx aluminum alloys were widely used in packaging, automobile and architecture industries, because of its good formability, excellent corrosion resistance and weldability. And AA3xxx alloys were considered as non-heat-treatable alloys. However, the strengthening effect of dispersoids in AA3xxx alloys was discovered recently (Li & Arnberg, 2003;Li, Muggerud, Olsen, & Furu, 2012; Li, Zhang, & Chen, 2016; Liu & Chen, 2015).Alarge amount of dispersoids could precipitate by a proper heat treatment.In order to further improve AA3xxxalloys, the composition of the alloys should be optimized. A few previous studies were reported to investigate the influence of compositions on AA3xxx alloys. Adding Mn element could enhance the precipitation of ??-Al(Mn, Fe)Si dispersoids and improve the yield strength(Muggerud, Mørtsell, Li, & Holmestad, 2013), as long as the concentration of Mn was under the solid solution limit. Fe decreased the solubility of Mn and accelerated the precipitation rate of ??-Al(Mn, Fe)Sidispersoids(Li & Arnberg, 2003), the yield strength and creep resistance at elevated temperature could increase with an optimized content of Fe(Liu & Chen, 2016). Mg element would affect the nucleation process of ??-Al(Mn, Fe)Sidispersoids by forming metastable Mg2Si(Hirasawa, 1975; Li, Zhang, & Chen, 2017a; Lodgaard & Ryum, 2000), metastable Mg2Si precipitated during heating process and promoted the precipitation of ??-Al(Mn, Fe)Sidispersoids, moreover, Mg provided solid solution strength for AA3004 alloys(Li et al., 2016). Si increased the volume fractionof ??-Al(Mn, Fe)Sidispersoids(Muggerud et al., 2013)and decreased the size of ??-Al(Mn, Fe)Sidispersoids(Li, Zhang, & Chen, 2017b). With the addition of Mo, the size of dispersoids became finer with a higher volume fraction, the volume percentage of dispersoid free zones was reduced. Elevated temperature yield strength and creep resistance improved due to Mo addition (Liu, Ma, & Chen, 2017).However, the effect of Crelements on microstructure and mechanical properties of AA3xxx alloys were rarely reported."

Jan 1, 2018

By Ahmad Ghahreman, Lin Li

"In this study, the Fe(II)/Fe(III) redox reaction kinetics on the surface of pyrite, have been investigated in a 0.5 mol L-1 sulfuric acid solution for a temperature range of 22 to 65°C. Based on mixed potential theory, chronoamperometry is introduced to study the Fe(II)/Fe(III) kinetics by subtracting the current density of pyrite oxidation in an iron-free acidic solution from that in an iron-containing solution at the same applied polarized potential. Tafel behavior was established by this method to analyze the kinetics of the Fe(II)/Fe(III) redox reactions. The results showed that exchange current densities increased slightly with temperature, however remained on the order of 10-5 A cm-2. The activation energy for Fe(II) oxidation and Fe(III) reduction on the pyrite surfaces was calculated to be 102.0 and 32.7 kJ mol-1, respectively. Anodic transfer coefficients also increased, from 0.24 to 0.39, with increasing temperature, which indicates a weakened n-type semiconductor property at higher temperatures. Electrochemical impedance spectroscopy measurements have indicated that at lower anodic over potentials the charge transfer is the rate determining step of pyrite oxidative dissolution in sulfuric acid solution. In the presence of Fe ions, the major contribution of the total current density comes from the Fe(II)/Fe(III) redox reaction. INTRODUCTION Pyrite, an abundant sulfides mineral in the nature, is commonly considered a valueless gangue mineral frequently associated with other valuable sulfide minerals such as chalcopyrite, or metals such as gold, or coal (Lin & Say, 1999). Pyrite oxidation has been the subject of extensive research in view of gold metallurgy, as oxidation of pyrite is the initial step to break down the pyrite lattice and expose the encapsulated fine gold particles (Gasparrini, 1983). Fe(III) ion and dissolved oxygen (DO) have generally been considered as the two most important oxidants with respect to pyrite oxidation, having been studied extensively in previous research (Zheng, Allen, & Bautista, 1986; King Jr & Lewis, 1980). The process of pyrite oxidation can be viewed as a series of reactions amongst pyrite, ferrous, ferric and oxygen in which pyrite is initially oxidized by the dissolved oxygen in water forming ferrous (Eq. 1), and then the ferrous also is oxidized by he dissolved oxygen to form ferric (Eq. 2). The ferric, produced by reaction 2, then could potentially oxidize pyrite (Eq. 3) and convert to ferrous."

Jan 1, 2017