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By Chris Harris, Kamal Adham

The use of HCl acid is gaining momentum among hydrometallurgical processes. However, the issue of environmentally efficient and economically viable ways to regenerate HCl acid (from various metal chloride intermediate products) remains a technology and operational challenge. The authors provide a state-of-technology review based on Hatch’s years of testing, design and commissioning experience with high-temperature units (fluid bed and spray roasters), plus the recent efforts in the area of low-temperature HCl regeneration.

Jan 1, 2014

By P. A. Gonzalez Contreras

Scorodite is considered as a secondary mineral formed from the product of weathering of primary minerals by chemical or biological reactions. In the case of biological scorodite formation, microorganisms mimic and accelerate what in nature takes a very long time, i.e. biocrystallisation. The goal of the biological scorodite formation is to form very stable arsenic crystals suitable for long-term and safe disposal. The biological formation of scorodite is a novel combination of biological oxidation, biocrystallisation, and proper bioreactor design to achieve the biological formation of scorodite crystals in one step. We have explored simultaneous biological arsenic and iron oxidation at 30ºC and at 70ºC leading to arsenic-jarosite phases and scorodite, respectively. As biologically formed scorodite crystals are very stable (TCLP < 1 mg/L As (V)), the risk of arsenic toxicity is minimized when leaching takes place. This process is suitable for arsenic concentrations above 0.5 g/l As achieving up to 20 mg/l As in the effluent. This biological scorodite formation system is a selfsufficient bio-oxidation system and therefore many new applications can be explored such as reprocessing of arsenic trioxide, orpiment or calcium arsenate to scorodite crystals for a stable and safe disposal.

Jan 1, 2014

By K. Peake, A. Dalvi, V. Hernandez, S. Chang, M. Oliazadeh

"Ironstone Resources Ltd. is developing the Clear Hills oolitic iron ore deposit in northwest Alberta, Canada. Sources of oolitic iron ore worldwide are abundant and ubiquitous, but there is currently no commercial technology to extract iron from oolitic iron ores. Mineral processing of the ore to generate a commercial iron ore concentrate is very challenging due to the nature of these ores. Accordingly, Hatch and Ironstone are developing a new pyrometallurgical process (Hatch Ironstone Chloride Segregation) to produce metallic iron from high silica and high phosphorus oolitic iron ores. Following the chloride segregation process, the treated ore is subjected to fine grinding. The iron is then separated by magnetic separation. The iron grade and phosphorus content of the final product shows a strong dependence on the separation methodology and the grind size. The pyrometallurgical process has been developed and tested at a lab-scale pilot plant. The commercialization of this technology could provide an opportunity for the development of a new alternate iron making technology. This paper presents the results of test work done on the raw iron ore to create a concentrate and also on the products of the pyrometallurgical process for the production of a high grade 90% metallic iron product.INTRODUCTION Oolite is a sedimentary rock formed from ooids – spherical particles with concentric layers. There are a number of large oolitic iron deposits where the mineralogical form features a low iron content and high concentration of impurities making them presently impossible to exploit on either a technical or economic basis. The fifteen largest oolitic iron ore deposits in the world are estimated to contain approximately 337 billion tonnes of iron ore, which would be a significant source of supply for worldwide steel production. A viable process that can economically recover iron from these oolitic iron ore deposits could become an important new technology to meet future demand in the steel industry. Hatch and Ironstone have demonstrated that oolitic iron ores can be exploited to produce direct reduced iron (DRI). Direct reduction ironmaking is a method for producing solid metallic iron using different techniques compared to the blast furnace process, which is the more conventional ironmaking route. The demand for the construction of direct reduction ironmaking plants has increased in response to the increasing demand for crude steel. It is viewed as a method of providing low-residual iron sources to scrap-based steelmaking in electric arc furnaces."

Jan 1, 2014

By George P. Demopoulos

In this paper the author will provide an overview of over 20 years of research & developments in the area of hydrometallurgical arsenic immobilization that culminated recently in the industrial implementation of the atmospheric scorodite process. The paper will consider various aspects of arsenic fixation in the non-ferrous metal industry from the iron-arsenic co-precipitation process employed to arsenic-bearing effluent solutions; to autoclave processing of arsenical copper and gold feedstocks and the fate of the in-situ formed iron sulphato-arsenate precipitate phases; the precipitation and stability of scorodite; the possible stabilizing role of mineral phases like yukonite, and the development of "scoroditeplus" processes employing novel encapsulation strategies. Emphasis is placed on the characterization and long-term stability of the various forms of arsenic-immobilized phases under either oxic or anoxic conditions over a wide pH range and the establishment of critical links between process parameters and hazardous material stability, contributing thus to advancement of new generation safe and sustainable waste management technologies.

Jan 1, 2014

By Fathi Habashi

New technology first introduced by Nippon Steel Corporation at Kitakyushu in Japan in 1976 now used at a number of plants in other countries, known as dry quenching of coke, uses nitrogen in a closed circuit to avoid environmental emissions. In addition, heat is recovered in the form of steam, from the red-hot coke. In steel plants oxygen is used extensively and therefore by-product nitrogen from air liquefaction can be effectively utilized in this way.

Jan 1, 2014

By M. E. Moraes Castanho de Almeida, A. Ribeiro Cotri

Recovery of cobalt to produce high grade cobalt sulfate from cobalt concentrate by leaching and solvent extraction was investigated. The PLS typically contains Co 10g/l, Mg 2g/l, Fe < 10ppm, Mn < 200ppm, insolubles <100ppm and is extracted with 20wt% Cyanex??272. The typical strip solution contains Co 60g/l, Mg 0.03g/l, and was sent to the current process for the production of cobalt sulfate heptahydrate. The cobalt yield of the plant with two extraction steps was 92%, with three steps was 97% and with four steps 99%. The extraction stage used the concept of "scrubbing" in a countercurrent system. In the first stage of extraction pH was 4.8, and in the last stage of extraction pH 5.5 to promote the exchange of magnesium in the organic with cobalt contained in the PLS. Following the extraction, when using two scrubbing stages, Co/Mg selectivity between of 2,000-3,000 was obtained, and with three scrubbing stages, selectivity was greater than 6,000. The desired selectivity was reached when using a scrubbing configuration with O/A ratio of 10:1. The typical cobalt sulfate heptahydrate had the following composition: Co 20wt%, Mg < 0.01wt%, Fe < 5ppm, Mn < 0.01wt%, Cu < 0.01wt%, Zn < 0.01wt%.

Jan 1, 2014

Of the many organic impurities present in Bayer liquor, sodium oxalate is known to have one of the most detrimental effects on the Bayer process. Because of its limited solubility, it will co-precipitate with gibbsite during the precipitation stage which results in many operational challenges for the refinery. Despite the importance of this phenomenon, the interaction mechanism between gibbsite and sodium oxalate is not well understood. In this study, the growth of sodium oxalate on three main morphologies (random agglomerates, prims and hexagons) of water-washed and caustic-washed gibbsite was observed under synthetic Bayer conditions using in situ optical microscopy. After a short induction period, oxalate started to nucleate on gibbsite crystals, and grew with a needle-shaped morphology which eventually developed into oxalate bundles. In addition, the results indicated that caustic washing was able to partly decompose gibbsite crystals and thus make the gibbsite surface rougher, which provides more potential sites for oxalate nucleation and growth. The growth rate of oxalate crystals on the basal (001) face of water-washed gibbsite was 1.33 µm/min determined by the time-lapse imaging of in situ optical microscope.

Jan 1, 2014

By Jon R. Maki

"EVTAC, an iron ore mine in Minnesota, had trouble meeting the customer’s pellet silica requirements. In addition, the mine plan was moving towards a lower grade ore and funding was not available for plant improvements to compensate for the change in ore or improving quality. Small changes to optimize various processing equipment resulted in significant improvements in both quality and productivity; for example, productivity on one mill line increased by 10% while producing lower silica concentrate. This paper will provide the methodology that allowed EVTAC to improve quality and productivity through process optimization with little capital investment.INTRODUCTION EVTAC, an iron ore mine in Minnesota, had trouble meeting the customer pellet silica requirements. In addition, the short-term mine plan was changing to a lower ore grade. Because of limited funds, EVTAC did not have the capital for investing in the plant to compensate for the ore change or to make improvements to lower product silica levels. Small changes to optimize process equipment resulted in significant improvements in quality and productivity; for example, one mill line feed rates increased by 10% while also producing a higher quality concentrate. These changes were sufficient enough to allow the mine to lower the target ore grade beyond their initial goal. At one time, a $3M flotation facility was considered as a way to meet quality with the new ore grade. However, the process changes were able to accomplish the same silica reduction with roughly a $50,000 investment in VFDs for sump controls. This paper will discuss some of the modifications that allowed EVTAC to meet the quality and production objectives with little capital investment. It also discusses the methodology used to make these process improvements."

Jan 1, 2014

By T. -W. Hong, Y. Son, S. -J. Hong, D. Choi

The characteristics of indium-tin-oxide (ITO) nanoparticles recovered from TFT-LCD panel scraps were investigated. The ITO was separated from TFT-LCD panel scraps by dissolving the color filter layer located between the ITO layer and the glass substrate. The solution was filtered to separate the ITO from the color filter component, and the filtered ITO was dissolved in the acid solution. ITO nanoparticles were then precipitated with ammonium hydroxide and organic dispersing agent, followed by heat-treatment at 600 °C. HRTEM, EDX and XRD analyses revealed that the 20 nm sized particle were composed of 90 % In and 10 % Sn, and were well crystallized to in the (222) preferred orientation.

Jan 1, 2014

By F. M. Doyle, G. Sidhu, A. J. Dussault, A. Raygani

There is a growing demand for rare earth metals for use in high strength permanent magnets, most notably Nd2Fe14B. Rare earth metals are extremely reactive, with reduction potentials around -2.5V SHE, and are conventionally produced by molten salt electrolysis. The current work was done to investigate an earlier report of electrodeposition of a neodymium ferroalloy from aqueous solution, to determine whether this approach could be an environmentally and economically competitive commercial approach for producing feedstock for permanent magnets. Such a process would be analogous thermodynamically to the Castner- Kellner process, in which aqueous sodium chloride brine is electrolyzed in cells with mercury cathodes. Metallic sodium forms an alloy (amalgam) at the cathode, thereby lowering the activity of the metallic sodium significantly below unity and making the reduction potential of sodium significantly less negative than the standard reduction potential. Here we report the effects of Nd/Fe ratio in the electrolyte, current density, temperature and two different complexing agents, glycine and cysteine, on the composition and morphology of the electrodeposits, along with current efficiency. The energy needed to produce neodymium as Nd:Fe alloys by aqueous electrodeposition was compared with values estimated for production by molten salt electrolysis and the thermodynamic energy requirement.

Jan 1, 2014

By Cz. Mora, A. Pawelczyk, D. Hreniak, P. Nowak, A. Dyonizy, S. Strek, W. Strek, K. Grabas, A. Ostrowski

Globalization and a growing demand for limited raw material resources have forced changes in the approach to the supply chain. This is particularly true in the case of rare earths, which are regarded as one of the most important development indicators of modern technologies. To ensure a secure supply of commodities, the European economies have been prompted to investigate REE recovery from sources which until recently, for technical or economic reasons, were considered not sufficiently attractive. An interesting example is apatite phosphogypsum waste dumps. The REE content in these waste dumps averages around 0.5-1 %. One of the most important phosphogypsum locations in Poland is the Lower Silesia region where a phosphoric acid Chemical Plant "Wizów" operated for several dozen years. In this work, rare earths are leached from the phosphogypsum crystalline structure by a chemical treatment and can then be separated into individual chemical compounds. The technology used in these recovery tests, matches up to a coherent European raw materials policy supporting effective management of resources and promoting waste materials recycling.

Jan 1, 2014

By Kosuke Hosoda, Shuji Owada, Hiroyuki Tokuichi, Hirobumi Ohta, Chiharu Tokoro, Moto-o Sato, Katsushi Okumura, Hiroto Ogawa, Hideaki Umezawa

The Japanese government enforced the "Small Domestic Appliances (SDAs) Recycling Law" in 2013. The law targets metals such as Ta, Nd, Dy, Co, and W to be recycled. Considerable amounts of these minor rare metals are mounted on printed circuit boards (PCBs) of the SDAs and/or e-scrap (electric and electronic scraps). Although precious metals and copper can be recovered from the e-scrap in non-ferrous metals smelters, most of the minor rare metals report to the slag in these smelters in non-recoverable forms. These metals are often used in particular types of devices, and therefore it is possible to concentrate them by separating such devices before feeding to the smelters. In previous work we developed technology for "Device Separation" to concentrate several minor rare metals, but some problems remained, such as how to remove the PCBs from e-scrap bodies, and how to detach devices from PCBs after their removal from escrap bodies. This paper proposes a two-stage crushing process in which, firstly, PCBs are removed from the e-scrap body with various crushers, and secondly, devices are detached from the PCBs involving the application of elevated temperatures. It was found that in the first stage, crushers with physically flexible rotating media such as chains, which provide high collision probability with the sample and consume relatively low energy, can quite effectively separate the PCBs from the e-scrap bodies non-destructively. In the second stage, heating was found to be remarkably effective in helping to detach mounted devices from PCBs, also non-destructively. This paper will also discuss the detailed mechanism of the heating effect on the detachment of devices from PCBs.

Jan 1, 2014

By Guy Brouillard

A bow-tie analysis is a safety review methodology that uses a structured approach that can be qualitative or quantitative to document the potential risk of safety incidents. The bowtie diagram itself provides a powerful graphical representation of the threats barriers, events, and recovery measures which are readily understood by the "non-specialist". This presentation will discuss how mining operations can use this valuable tool within their operations to understand the risks and apply the appropriate safeguards toward reducing these risks to acceptable levels.

Jan 1, 2014

By Linlin Tong, Xiangling Song, Guobao Chen, Zhenan Jin, Hongying Yang

Biooxidation of a high arsenic-bearing refractory gold ore was investigated to determine the arsenic removal efficiency by the cultured bacteria and to examine the effect of biological pretreatment on subsequent gold cyanidation. The biooxidation pretreatment process utilizes the ability of adapted acidophilic bacteria to oxidize pyrite and arsenopyrite and release the encapsulated gold. The released gold can be efficiently extracted by the subsequent cyanidation process. The biooxidation experiments were conducted with cultured bacteria using various sizes of agitation tanks. Leaching results showed that over 96.26 % arsenic extraction could be obtained from this ore after 6 days of bioleaching with continuous stirred tank reactor (CSTR). Gold extraction during the cyanidation process was increased from 29.35% to 96.71% after biological pretreatment. The content of arsenic in the biooxidation residue was reduced to below 0.3%. The transformation process of As was considered as [AsS]2- ? As (?) ? As (?) during the biological pretreatment.

Jan 1, 2014

By C. Van Den Heuvel, C. B. Van Buuren

BIOX® has been successfully demonstrated over the past 2 decades for the recovery of gold from refractory sulphide concentrates. To date 12 successful BIOX® plants have been installed in 8 countries spanning 4 continents with the 13th installation currently nearing completion in the Philippines. In 2010 BIOMIN introduced the ASTER™ process for improved water balances in commercial BIOX® applications by supporting tightening environmental legislation on water usage and availability in both arid and tropical regions. Previously, a common challenge for BIOX® plants was the inability to recycle thiocyanate containing water due to the low tolerance of the organisms. ASTER™, a biological thiocyanate and cyanide destruction process, renders a non-toxic solution for re-use in BIOX®. Two commercial ASTER™ plants are in operation with the 3rd ASTER™ plant under construction in the Philippines. A 3rd BIOMIN technology, specifically developed for double refractory ores is available for implementation. The HiTeCC process has shown considerable success on ores where competition from disseminated carbon has rendered ineffective gold recoveries. Through HiTeCC, gold is desorbed from the carbonaceous matter by manipulating the ionic strength and temperature of conventionally treated CIL product. One Australian commercial plant utilises HiTeCC while a 2nd installation is set for commissioning 4th Quarter 2014. BIOMIN’s premier solutions for refractory gold processing are described herein.

Jan 1, 2014

By Bernard Tougas, Franco Chiesa, David Levasseur, Bernard Duchesne

"In the present paper, the optimization of a tilt poured permanent mold will be carried out using filling and solidification modeling. This exercise resulted in 3 modifications of the initial mold design which was based on the foundry experience. The optimization provided a 20% improvement in the yield while increasing the output from 10 to 15 castings per hour.In a subsequent study, the value of the critical fraction solid of AlSi7Mg (A356) alloy was verified by radiographic analysis of the castings produced in the first 5 cycles of a run, which are necessary to bring the mold to a dynamic thermal equilibrium."

Jan 1, 2014

By V. A. Leão, A. M. Silva, S. M. Bertolino, B. C. S. Ferreira, D. Guimarães

Although not considered a high risk pollutant as compared to toxic metals and acidity, environmental agencies worldwide are proposing regulations to control sulphate in effluents and drainages by setting a threshold value varying between 250 mg/L and 500 mg/L. The aim of this study was thus to compare four different techniques for removing sulphate ions from mining/metallurgy effluents. The first alternative studied was sulphate removal by precipitation as ettringite. Treating a synthetic solution containing 1650 mg/L sulphate at 22±1 ºC resulted in removals close to 85% during continuous precipitation. Sulphate sorption was also investigated using three different ion exchange resins as well as limestone. Fixed bed experiments produced sulphate loadings of up to 70 mg SO4 2-/L resin, at pH 2.0. In neutral wastewaters, limestone is also a potential adsorbent producing a maximum particle loading of 19 mg/g. Sulphate sorption on limestone seems to be an alternative to treating mine waters with sulphate concentrations below the 1200-2000 mg/L range, where lime precipitation is not effective. Subsequently, sulphate removal by sulphate reducing bacteria was also investigated and it was observed that reactor’s hydrodynamic conditions and the choice of substrate are important factors for the process. The different technical aspects of each technology are addressed.

Jan 1, 2014

By G. W. Norval, V. G. Papangelakis, G. A. Moldoveanu

Smelting has been the primary method of treatment for refractory copper sulfide concentrates such as enargite (Cu3AsS4), but the pyrometallurgical processing generates elevated levels of volatile arsenic. The present research investigates a novel hydrometallurgical process of oxidative dissolution of enargite at ambient conditions in the presence of chlorine dioxide (ClO2), a very powerful oxidant generated in solution by the reaction between a strong acid (HCl or H2SO4) and sodium chlorite (NaClO2). The effects of initial oxidant concentration, particle size, agitation speed and temperature on dissolution kinetics and copper extraction were investigated. It was found that a stoichiometric ratio of ClO2:Cu3AsS4 = 9:1 were needed to completely and congruently dissolve the mineral with fast kinetics (<15 minutes) under ambient temperature. The dissolution extent (metal extraction) increases with increasing ClO2 concentration and decreasing particle size of solids, but is not influenced by temperature or agitation speed.

Jan 1, 2014

By M. Celikin, M. Isac, R. I. L. Guthrie, S. Ge

Horizontal Single Belt Casting (HSBC) is a near-net-shape casting process in which molten metal is directly cast into thin strips, at high cooling rates (order of several 100°C/s), with the potential for high volume, friction-free, continuous production of metal strips. This casting process was used in the present work to produce strips of Al-Mg alloys in the AA5000 series, with additions of Sc and Zr. Such aluminum alloys show exceptional potential as a structural material for transportation/aerospace applications. To demonstrate the suitability of the HSBC process to manufacture competitive strip products of Al-Mg-Sc-Zr, the mechanical properties and microstructures of the strips produced using the HSBC process were compared with conventionally cast products. The effects of annealing on the mechanical properties of the strip-cast Al-Mg-Sc-Zr alloys were also investigated.

Jan 1, 2014

By Denilson Coutinho, Euler Soares, Paulo de Tarso, Jordana Ferreira, John R. Goode, Andreas Sprecher, Alexandre Rocha

The Serra Verde Project is located in the northern part of Goiás state, Brazil, and comprises 49 mineral claims covering an area of 69,814 ha. The Serra Verde deposit is a rare earth element (REE) enriched weathered granite comparable to the weathered granite, or ionic-clay, deposits found in southeastern China. The Mineral Reserves of the Serra Verde Project total 388 Mt (Measured and Indicated) at an average grade of 1,484 ppm of REE oxide (REO). Several hundred agitated leach and column leach tests have confirmed recovery of about 40 to 55% of the REE, except for Ce, using simple desorption techniques. Present plans call for a heap leach operation followed by precipitation of impurities and precipitation of a pure REE carbonate suitable for refining and separation. The project plan includes initial production of 5,000 t/a of REO, with a high content of heavy and critical REO, rising to 10,000 t/a of REO. This production rate will be obtained by mining of the Mineral Reserves over a 22-year mine life at an initial rate of 6 Mt/a for the first four years with the mining rate thereafter increasing as required by grade and production targets.

Jan 1, 2014