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By Tomás Vargas

The catalytic role of Thiobacillus ferrooxidans in the dissolution of chalcopyrite was studied by leaching pure massive samples of this sulfide with a pure strain of Thiobacillus ferrooxidans (ATCC 19859). Monitoring of the bacterial activity showed that an important fraction of the total bacteria generated during leaching remained attached to the chalcopyrite surface. Bacteria grown in the system, which were the offspring of bacteria adhered to chalcopyrite, was well explained as the result of the utilization of ferrous ion and sulfur as energy sources. The potential for indirect and direct action was fully utilized by the existing bacteria and the leaching process was controlled by the kinetics of chalcopyrite dissolution.

Jan 1, 1990

By C. B. Catanach

The development and in place leaching of a chalcocite ore body at Mountain City, Nevada is described. Block caving was used to induce permeability while ore removed during development was leached in heaps on the surface. Copper was recovered by precipitation on iron. Excess ground water which seeped into the mine was pumped into a deep disposal well. A parallel system was used to purify water by lime neutralization. Copper extraction was at an annualized rate of 11% during the first six full months of underground leaching and totalled approximately 30% during six months of heap leaching. Leach solution flow and distribution had a major effect on extraction rate. Enrichment of leach solutions with ferric sulfate did not produce conclusive results until analyzed with the aid of a leaching model.

Jan 1, 1976

By Fumitaka Tsukihashi

Increasing amounts of steel scrap are being used as resources for steelmaking. Therefore. there has been a growing interest in the removal of handful tramp elements such as antimony, zinc, tin, arsenic, bismuth, lead and copper from the molten steel. The problem that should be solved is the economic removal treatment of residual tramp elements in the steelmaking processes and the production of high quality steel by reducing the effect of the contaminated tramp clements and satisfying the environmental regulations. In this paper, the available thennodynamic data of the residual tramp elements in the molten steel are summarized and the possibility of the removal of residual tramp elements from the molten steel is thcnnodynamieally estimated.

Jan 1, 2003

By Jim A. King

The total pressure oxidation of copper concentrates is a potentially viable option for treating copper concentrates that are either low grade or contain significant impurities. Both concentrate types are heavily penalized in smelter contracts. The total pressure oxidation process involves autoclaving the copper concentrate at temperatures of 200-220 C under oxygen pressure. The autoclave discharge can be separated into a solid (oxidation residue) and a liquid (oxidation solution) product. The oxidation solution can be treated for copper recovery by solvent extraction - electrowinning or by direct electrowinning. The direct electrowinning recovery of copper requires prior removal of selenium and tellurium by cementation on finely divided scrap copper. The oxidation residue is washed thoroughly to remove acid and dissolved copper prior to precious metals recovery by conventional cyanidation in the presence of lime. The results of a benchscale investigation involving a number of copper concentrates are reported. Copper recoveries in autoclave oxidation and gold recoveries by cyanidation of the oxidation residue exceeded 99%. The results of benchscale experiments to demonstrate copper recovery are described. Various flowsheet options are presented.

Jan 1, 1993

By Eric J. Beckman

Recovery of metals from dilute solution, whether the matrix is solid, or liquid, remains a considerable technical and financial challenge. Methods currently exist whereby metals can be extracted from either type of matrix, yet these methods consume significant quantities of reagents and can also generate multiple waste ,streams in the process. Technology developed in our lab allows efficient application of environmentally-benign CO2 to a number of separation problems involving metals. For example, we have employed biphasic mixtures of C02 and water as a green acid leach medium. Metals have been extracted from a steelmaking process residue and then recovered as metal carbonates through depressurization. In this process, metals are extracted and recovered without the use of reagents other than CO2 and water, and CO2 is sequestered as a solid. In addition, through synthesis of Cal-miscible phase transfer agents, we have shown that CO2 can replace the organic solvent currently used in refining of precious metals, The sensitivity to pressure of phase behavior in a CO2-mixture may allow significant streamlining of the process as well. Finally, CO2 soluble chelating agents have been used to extract toxic metals from acidic effluent such as that found in plating facilities.

Jan 1, 1999

By Jerome P. Downey

In the thermal treatment of electric arc furnace (EAF) dusts, zinc is reduced, volatilized, and ultimately recovered either as liquid metal in a splash condenser or as solid zinc oxide in bag filters. During the process, the duet's chlorine and fluorine content also enters the gas phase and condenses as dross in the splash condenser or as salts which contaminate the zinc oxide product. Pretreatment of EAF dust by pyrohydrolysis appeared to offer a means of minimizing the duet's halogen content. The primary research objectives were to experimentally verify the technical viability of pyrohydrolysis and delineate the process parameters requisite for efficient halogen removal. To this end, representative EAF duet samples were secured and characterized by x-ray diffraction, scanning electron microscopy, and Mössbauer analyses. Specific- experimentation focused on the response of halogen extraction to variations in temperature, retention time, water vapor partial pressure, and various additives. The experimental results proved that 97 to 99 percent chlorine extraction and 80 to 85 percent fluorine extraction are consistently achieved when EAF dusts are blended with silica and roasted at temperatures of 850°C or greater in a furnace atmosphere of 75% steam (diluted by air). A statistical analysis further established that more than- a single optimal point exists, thus affording flexibility in parameter selection (e.g., by increasing temperature, the necessary retention time and additive concentrations are decreased). The findings substantiate the feasibility of pyrohydrolysis roasting in reducing the chlorine and fluorine in the EAF dust to a level that will obviate industrial concerns about halogen contamination. The end-product of the pyrohydrolysis procedure is a de-halogenated, self-fluxing calcine which can be directly charged to a plasma or flame reactor. The paper includes design parameters and flow diagrams illustrating the pyrohydrolysis process integrated with the plasma and flame reactor technologies.

Jan 1, 1992

By Florian Kongoli

Slags and fluxes are important interchangeable dimensions of pyrometallurgical processes. They can increase the efficiency of the smelting, converting and refining processes and improve the quality of the final products. A good slag should have appropriate physicochemical properties such as low liquidus temperature, optimal viscosity, maximum ability to attract undesirable elements, minimum potential of attracting valuable elements, etc .. A good flux, on the other hand, when properly used, can considerably improve the physicochemical properties of the slag since by modifying its chemical composition it could decrease the liquidus temperature, improve viscosity etc.. Consequently, the choice of a good slag and the corresponding fluxing strategies has become indispensable in most of industrial processes. However, the properties of multicomponent slags as well as the effect of several fluxes are known only empirically and confusion exists in the literature and in the industrial practice. In today's reality of frequent changes in the composition of raw materials and that of the fluxes themselves, in the existing or new developing technologies, the quantification of the thermophysicochemical properties of multicomponent slags and the effect of fluxes becomes indispensable. This paper reviews some of the work carried out by the author's group during the last ten years on the quantification of the thermophysicochemical properties of multicomponent slags and on the effect of fluxes in several smelting and converting processes in close relation to their individual characteristics. Several examples have been given in order to demonstrate the fact that when taken outside the context some fluxes can become in fact anti-fluxes.

Jan 1, 2003

By William K. Tolley

The U.S. Bureau of Mines (USBM) is investigating hydrometallurgical processing techniques to recycle metals from semiconductors and other advanced materials. Cadmium and tellurium were recovered from mixed CdTe/CdS scrap produced in the manufacture of thin-film photovoltaic devices. Cadmium and tellurium dissolution was achieved using hydrogen peroxide in dilute sulfuric acid. Leaching the scrap in 2.2 N H2SO4 yielded 99% Cd extraction and 98% Te extraction. Sulfur remained in the leach residue primarily in the elemental form. Elemental tellurium was precipitated from the leach liquor by adding Na2S2O5. Cadmium sulfate was recovered by evaporation. A preliminary process evaluation suggests that the process may have economic potential. Alternative recovery schemes are discussed.

Jan 1, 1995

By Binxu Zhaug, Mark Jolly, Xiaojun Dai

"In conventional investment casting process of aluminium alloys for the application of the aerospace industry, to assure the quality of the final casting, usually the foundry uses large runner system which results in low yield, high energy consumption and high GHGs emission. In one case of this investigation, the yield is between 5 ~ 10% which means that the current casting process wastes large amount of energy and generates lots of scraps. By applying a new casting method, the bulky runner system and the melting/holding time are significantly reduced, the quality of the casting is improved, and in the meantime the related energy consumption and GHGs emission are significantly decreased. In the investigation, the energy efficiencies and GHGs emission between the current and traditional processes are calculated and compared.1. IntroductionAs one of the conventional casting process, Investment Casting Process (ICP) and its applications can be traced to thousand years ago [l]. In current casting industry, ICP still plays an important role in the production of small and precious castings with high quality requirements in automobile and aerospace industries. Both casting quality and manufacturing costs which mainly consist of energy costs have crucial effects on the competitiveness of castings in the market. In the production of aluminium alloy castings using ICP, the energy cost and energy efficiency of a casting facility depend mainly on the efficiency of its melting and heat treating performance. In association with the two performances, more than 60 % of the total process energy costs are symbolised in a typical casting facility [2]. Additionally, in conventional ICP of aluminium alloys for the application of the aerospace, to assure the quality of the final casting, typically the foundry uses huge runner system including big risers/feeders which cause low yield, creates lots of scraps and generates high energy consumption. Consequently, there are huge opportunities for casting industry to choose the best practices for potential energy saving. Furthermore, the reasons such as the stringent limitation of environmental legislation in Europe and the pressure of the rising energy price force the casting industry to reduce the energy consumption and greenhouse gases (GHGs) em1ss10n."

Jan 1, 2012

By Jorge Alberto Soares Tenório, Denise Crocce Romano Espinosa, Luciana Harue Yamane

"The present work investigated the effect of inoculums volume on bioleaching to recover metals from printed circuit boards using Acidithiobacillus ferrooxidans-LR. Printed circuit boards from obsolete computers were mechanically processed by comminution followed by magnetic separation, and the obtained non-magnetic fraction was used in the bioleaching experiments. A shake-flask study was carried out on the non-magnetic fraction samples using a rotary shaker at 30°C, 170 rpm and different volumes of oxidized culture solution as inoculums (%v/v): 5, 10, 20, 30, 40, 50 e 60. The oxidized culture solution was prepared inoculating pre-adapted bacteria Acidithiobacillus ferrooxidans-LR (5%v/v) in 200mL T&K medium. Leaching in acidic ferric sulphate was also performerd. The analyzed parameters were pH, ferrous iron concentration and metals analysis (AAS). The results showed that using 10%v/v of inoculums were extracted 99,2% of copper and 60% of aluminum by bioleaching. Zinc, lead and tin extraction were not influenced by bacterial leaching and extractions rate were obtained by chemical leaching promoted by acid medium. Ferric iron leaching extracted less copper (35%) than bioleaching. SEM analysis shown surface difference between samples of non-magnetic fraction before treatment and after bioleaching, showing corrosion pits formed by the bacteria contact.IntroductionWaste of electrical and electronic equipments (WEEE) has been target of discussion due to environmental, political and economical issues involved. Around 17 million of computers are discarded annually in the world due to malfunctioning equipment or because technologies become obsolete [1,2]. In contrast, only the central processing unit (CPU) of computers weights around 3kg. From this data, it can be calculated that 51 million kilograms of CPU waste are discarded yearly. This calculation was performed considering only the CPUs, disregarding the cathode ray tubes and liquid crystal displays of monitors [3,4]. Because of the amount that has been accumulated, e-waste has become a global problem but also can be an alternative source to recover valuable materials [5,6]."

Jan 1, 2012

A novel process is being developed for metal recovery from waste electrical and electronic equipment involving a leach reactor coupled to an electrochemical reactor. Metals such as Ag, Au, Cu, Pb, Pd, Sn etc. are dissolved from shredded electronic scrap in an acidic aqueous chloride electrolyte by oxidising them with aqueous dissolved chlorine species. In the electrochemical reactor: (i) chlorine is generated at the anode for use as the oxidant in the leach reactor, and, simultaneously, (ii) at the cathode, the dissolved metals are electrodeposited from the leach solution. The extended Butler-Volmer equation was used to provide predictions of the electrode potential dependences of partial current densities and, hence, total current densities, current efficiencies and alloy compositions for acidic aqueous chloride electrolytes containing Ag(I), Au(III), Cu(II), Pb(II), Pd(IV) and Sn(IV) species, together with dissolved chlorine. With judicious choice of kinetic parameters, the predicted total current density ? electrode potential behaviour of such solutions was in good agreement with experimental data for a rotating Pt disc electrode. Reduction of dissolved chlorine at a Pt rotating disc electrode exhibited mass transport controlled behaviour, in agreement with Levich?s equation over the potential range 0.3-0.9 V (SHE). This could form the basis of a linear sensor, possibly using a microelectrode for measurement and control of the dissolved chlorine concentration in the efflux of leach reactors and inlet to electrowinning reactors in the envisaged process.

Jan 1, 2003

By Joseph Goodwill

1. PURPOSE The objective of this paper is to summarize a study undertaken by the EPRI Center for Metals Production (CMP). The overall purpose of the study was to identify electrolytic opportunities that might merit consideration for joint development by industry and EPRI. 2. SCOPE The electrolytic technologies of interest to this study include: Electrorefining, Electrowinning, and Fused-salt electrolysis. Recovery from primary, secondary, and waste materials were included in this effort; however, we excluded from consideration: Plating and coating operations, such as electrogalvanizing; Mining and milling operations in which electric energy is predominantly used for comminution; Electrothermal processes in which submerged-arc, open electric-arc, and plasma-based smelting processes use electric energy largely to provide a melting or refining ("heating") capability; and Aluminum electrotechnologies since these were the subject of a separate study (CMP 86-2). We recognize that there may be some "gray areas" between these excluded areas and the electrolytic sectors of interest. For this reason, a secondary criterium was used, namely, if the major use of electric energy was to extract or refine the

Jan 1, 1990

By David Cocke

Study of surface and subsurface interfacial chemistry of metallic and similar systems has its enormous technological importance. Copper, for example, is a common component of many alloys and bulk amorphous systems. It is being increasingly studied today because of its use for electronic interconnect systems where processing is done below 200 ºC. Since several types of copper oxides exist, and the degree of their formation is dependent on temperature, perhaps characterization by EDS-SEM depth profiling and EIS might delineate one type of oxide from another. In this paper, we described our work on transformation of copper oxides with temperature ranging from 70 to 350 °C and their characterization by SEM, EDS, and XRD. We also showed the use of the phase angle portion of the impedance as a means to identify the predominant structure and the transition through Cu3O2 between the predominant stable CuO and Cu2O.

Jan 1, 2009

By Y. K. Rao

In the carbonyl process for the refining of crude nickel CO(g) reacts with nickel in the 310-370K range producing nickel tetracarbonyl, Ni(C0)4(g). Iron and cobalt impurities also form gaseous carbonyls but their partial pressures are low. The carbonyl is led to a decomposer plant wherein the gas disproportionates in the 500-600K range depositing pure metal on nickel pellets that move countercurrent to the gas-flow. This system serves to illustrate the fundamental principles involved in the vapor phase mass transport of elements, against temperature-gradient, under the influence of chemical potential gradient. Unlike in the crystal growth, the source is at a lower temperature (say 350K) whereas the seed is in the hot-zone (say 550K) of the closed ampoule-type reactor. By assuming virtual gas-solid equilibria in the end zones, with diffusion of gaseous species between them acting as a slight perturbation, the quasi-steady- state mass-transport rates are computed for a range of CO-pressures and temperatures.

Jan 1, 1993

By Beate Ina Jenssen

Ferric iron removal from the nickel electrolyte at Glencore Nikkelverk AS in Kristiansand, Norway, is achieved by precipitation of iron hydroxide followed by filtration, and it is desirable to improve filtration properties of the precipitated iron hydroxide in order to decrease the filtration time. The effect of increasing the residence time from the current 45 min to 75 min and temperature from 65 °C to 90 °C on the filtration properties of the precipitated iron hydroxide (akaganéite) was studied by simulating the industrial process conditions in a continuous reactor setup operating at steady state, using ferrous-containing process solution as feed material. It was possible to decrease the filter cake resistance by both increasing residence time and temperature, but temperature gave the most pronounced effect and reduced the filter cake resistance by one order of magnitude.

By K. Yamada, T. Takaoka, A. Ozeki, M. Yamaga, Y. Kawai, S. Nishioka, Y. Kikuchi

"Recently, smelting reduction of chromium ore in BOF has been actively investigated as a key unit process for an innovative future stainless steelmaking. The prominent feature of this new process route is energy and process saving, and production cost saving. The development is already in the midst of application to the commercial production, however there still remain the following key technologies to be established for the full use of the process. One is a speed up of the reduction of chromium ore to match with sequential continuous casting, and the other is efficient combustion of carbonaceous materials in BOF to reduce their consumption, and hence to assure the steel quality. High degree of post combustion technology and new charging technology, i.e., ore-coal-flux-oxygen mixed injection, could be effective for those two subjects. In 2000 or beyond, the new process would have become quite popular owing to the establishment of those key technologies.Introduction Since stainless steel was invented, its production has continued to expand because of its attractive combinations of functions of excellent corrosion resistance, good formability, a pleasing appearance, and a wide range of strength levels. New types of stainless steels as well as new applications are continually being developed.Compared to the production of ordinary steels (1), stainless steel production (2,3) shows steady growth worldwide, while the former production remains on the same level, as Figure 1 shows. It can be estimated that future production would show further growth since materials consumer demands are more fashionable, or more functional, which could be satisfied by stainless steels.Thus market needs would be met, if it could be produced with reasonable production cost. The emergence of an innovative production technology is then potentially requested as VOD and AOD processes have emerged, which has saved substantial production cost. This paper describes a possibility of a future stainless steelmaking process, which uses the in-bath smelting reduction of chromium ore in BOF, and which would save production as well as energy cost."

Jan 1, 1988

By P. M. Prasad

The last two decades have witnessed the emergence of numerous hydrometallurgical and direct processing techniques for the extraction of some metals from pocketed/lean/complex sulfide ore deposits. A new approach with some inherent technological merits, investigated in recent years, is the lime-enhanced reduction of metal sulfides. Thermodynamic aspects relevant to the lime-enhanced reduction of metal sulfides by H2,C0 and C are discussed. A survey of the researches on the basic features of and factors influencing the lime-scavenged reduction of selected sulfides and sulfide concentrates reveals that lime tremendously enhances the sulfide reduction rates (up to 100 times) and drastically reduces the sulfur emission into off-gas to negligible levels. Further successful practice of lime-enhanced reduction requires only a moderate temperature of reduction (characteristic of each sul¬fide) and, in the case of gaseous reduction, relatively low gas flow rates. Relevant kinetic aspects of the concerned reactions that have a bearing on process development and its understanding are also briefly discussed. A conceptual scheme of general applicability for the processing of sulfide concentrates by the lime-enhanced reduction technique consists of three main steps: (0 lime-enhanced reduction by a suitable reagent (e,g., H,2, CO, gasified coal, water gas), (ii) separation of the product metal from the dry slag (CaS + unused CO) by mechanical separation, magnetic/gravity concentration or flotation and (iii) melting and refining by standard procedures. This novel approach, which is patently less complex, is expected to employ basically simpler flow sheets at comparatively lower operational temperatures and aid in pollution abatement. Potential for developing such a route for the small scale extraction of metals like copper, molybdenum and antimony is indicated. Possibility of utilizing this technique for the production of fibers/ filaments of some metals is also outlined.

Jan 1, 1983

By M. Moinpour, E. Liao, C. Y. Aw, D. J. Brown, P. W. Cheung

"Currently, silicon-based insulated-gate field-effect devices are being widely developed as the basic structural elements in a new generation of chemical microsensors. In this paper, we discuss some of the process considerations related to the fabrication of the Chemically Sensitive Field-Effect Transistor (CHEMFET). This ion-sensitive CHEMFET (or ISFET as it is often called) can be used for pH measurements (i.e., as a pH sensor) when the gate insulator of the electrolyte/insulator interface is made of Si3N4 obtained by the LPCVD method. Effects of processing parameters such as the Si3N4 deposition rate, gas composition, total flow rate, annealing treatment, etc. on Si/Si02, Si/Si3N4 and Si/Si02/Si3N4 structures are discussed in relation to the CHEMFET fabrication. Their effects on the electrical characteristics and chemical response of the sensor are also examined. Capacitance-Voltage (C-V) measurements and ESCA analysis have been used to interpret the results. The Si3N4/Si02 double dialectric layer provides improved ion blocking for the gate insulator in electrolyte solutions with enhanced pH sensitivity over time. The stability and performance of the fabricated CHEMFET sensors were tested by measuring the pH sensitivity in various storage conditions. The SEM analysis was used to evaluate the hydration effect at the ISFET's gate insulator with respect to different storage conditions.IntroductionThere has been a continuous interest in the development and fabrication of various chemical microsensors for chemical and biomedical applications over the last fifteen years. The application of semiconductor (particularly silicon) technology to the area of sensor fabrication has led to an emergence of a new generation of miniaturized, microelectronic, solid-state chemical sensors. There are numerous clinical situations where continuous monitoring of body electrolytes concentrations such as Na+, K+, Ca+2 , etc. and blood gases (pH, Po2 , and PC02) would be essential for the effective diagnosis and management of patients under critical conditions. Solid- state microsensors can be used for direct and continuous in vivo measurement of the above parameters in most instances."

Jan 1, 1988

Mineralogical and metallurgical scoping testwork were carried out to investigate the production of separate, marketable gold and platinum concentrates. The study utilized a flotation concentrate assaying approximately 5 wt% gold and 5 grams per tonne platinum. The gold-platinum mineralization was recovered from a placer deposit. Optical microscopy and scanning electron microscopy with energy dispersive x-ray analysis identified gold as zoned Au- Ag and Au-Ag-Cu alloys. Platinum primarily occurred as weakly zoned, variably magnetic Pt- Pd-Fe alloys. A combination of gravity and magnetic separations resulted in a gold concentrate grading 86.9 wt% Au (and 9.lwt% Ag) and a separate platinum concentrate grading 400 g/t Pt with recoveries of 94.5% and 96.7%, respectively. Magnetohydrostatic separation (MHS) using the Magstream 200 Separator indicated promising results.

Jan 1, 1994

By Pekka Taskinen

The converter-less nickel matte smelting technology (DON) adopted more than 20 years ago in Boliden Harjavalta smelter has been since that applied successfully to the processing of large number of nickel sulphide concentrates of various Ni-to-Cu ratios and MgO contents. The operational point of the technology is far from the conventional primary nickel smelting in the smelting-converting route. Therefore, a careful scouting of distribution equilibria of the base and trace elements in the smelting conditions of DON process has been conducted, in order to obtain quantitative information about the equilibria and thermodynamic properties of the nickel mattes at low iron concentrations, less than 10 wt% [Fe] in matte. The series of investigations has included novel experimental and analytical techniques for increasing the reliability and sensitivity of the phase equilibria as well as the element distribution observations carried out in typical high-grade nickel matte smelting conditions.