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By Raymond F. Dalton

Despite the ready availability of numerous zinc sources, the process of solvent extraction- electrowinning (SX-EW) has as yet found little favour in the zinc industry. It is suggested that this is largely due to the previous lack of availability of suitable selective reagents having the particular features required to enable them to fit in to a solvent extraction-electrowinning based process for zinc, particularly with regard to strength and selectivity for zinc over iron. This paper describes work on the development of new selective extractants for the recovery of zinc from both sulfate and chloride aqueous solutions and suggests how they might be integrated into new zinc processes.

Jan 1, 1994

By Michael L. Sorokin

The various methods of converter slag cleaning operation are analysed from the thermodynamk point of view: cleaning using coal, cleaning using combustion products of natural gas and cleaning in presence of matte. All calculations were done, applying the developing computer procedure based on the free energy minimisation algorithm. Three-suffix Margules equations were used to calculate thermodynamic properties of melts; The calculations resulted in recommendations for the practical appliance.

Jan 1, 1995

By Joon H. Jang

At a selected pH, hydrothermal oxidation of chalcopyrite was carried out under controlled F+,, at elevated pressures and temperatures (172-200°C) by balancing the rate of oxygen injection against the rate of consumption. Chalcopyrite was converted to covellite (CuS) and digenite (CU1.8S) with rejection of iron and sulfur to the solution. Covellite forms in the first stage, followed by nucleation and growth of digenite in the second stage. The effects of rapid and slow injection of stoichiometric quantities of oxygen are compared. Both the covellite and digenite form a porous layer occupying the same volume as the original chalcopyrite grain. An electrochemical kinetic model is presented to correlate the observed results.

Jan 1, 1993

By D. Majuste

This paper describes an experimental approach to evaluate the effect of organic impurities or even additives on metal electrowinning and product quality. In addition to electrowinning tests and electrochemical measurements, the approach includes organic analysis by Fourier Transform Infrared spectroscopy and gas chromatography; video monitoring of the reaction interface; and product characterization by using scanning electron microscopy, crystallographic texture and bending tests. The mechanical behavior of metal cathodes was assessed with a customized bending device that is able to bend the cathodes up to angles similar to that of the stripping machine. In this work, the effect of a potential organic impurity, lubricating oil, on the production of electrolytic zinc is taken as a case study. The findings of the investigation allowed a better understanding on the role of this organic on energy consumption and product quality and a qualitative prediction for the behavior of Zn cathodes during the stripping operation. Simple control and optimization procedures resulted in significant energy savings.

By John M. Gaines

Lead concentrates from the Viburnum Trend in the Southeast Missouri Lead district are sintered prior to smelting to bind the particles together homogenize the feed, and reduce the sulfur content. Good sinter forms competent masses about 4 to 6 inches across, that hal!e about 15% porosity and good mechanical strength to withstand transport and the weight of the overlying load in the smelter. Bad sinter has poor mechanical strength and forms fine fragments that retard the circulation of reducing gases in the furnace and lengthen the time required for reduction. The productivity of the lead smelter depends on good sinter feed. Because some lead sinter plants produce bad sinter about 20% of the time, this applied mineralogy study has been undertaken to determine the mineralogical and microtextural differences between good and bad sinter. A reflected light microscopic study of 130 polished sections has shown that good and bad sinters differ distinctly in their mineralogy, tex1ure. and character of, porosity. Good sinter consists of hardystonite, franklinite. lead-zinc-bearing magnesium-calcium silicate, lead silicate matrix, and large crystals of calcium-magnesium-iron silicate, together with minor amounts of lead oxides, lead-zinc silicate, metallic lead, specular hematite, magnetite, lead-iron-bearing zincite and zinc-Iead-magnesium-bearing wustite in a tightly intergrown mesh of crystals and with an evenly distributed porosity of 15% to 20%. Electron microprobe analyses show that the principal phases contain lead (or zinc): hardystonite (4-20% Pb) franklinite (2-14% Pb) and lead silicate matrix (65-74% Pb). Bad sinter differs from good sinter in the greater abundance of lead silicate matrix, galena metallic lead, and lead oxides and the lesser abundance of hardystonite, franklinite and calcium-magnesium-iron silicate. Bad Sinter is characterized by a lack of an intimate intergrowth of the constituent phases. Its porosity is much lower commonly 0 to 5% and those pores are concentrated in local areas rather than distributed evenly throughout the sinter.

Jan 1, 1991

By I. J. Moon

The reduction behavior of hematite by H2 and H2-CO gas mixtures was investigated to elucidate the reduction mechanism at 800-950 °C. The hematite compacts were made by Cold Isostatic Pressing to produce compacts of uniform shape and size. The compacts were sintered at 1000° C for 30min, and showed a contraction of 29%. Mercury pressure porosimeter was used for measuring the total porosity, pore size distribution and pore surface area of the compacts. Reduction was measured by means of weight-loss technique using Cahn Balance (Model : TG-171, capacity log, accuracy f 10pg). Microscopic examination and X-ray analysis were used to correlate the structure of reduced compacts with the mechanisms of reduction. Neither chemical reaction control nor diffusion control is adequate in describing the complete course of reduction of the hematite compact. The reduction of hematite compacts was initially controlled by the chemical reaction at oxidelmetal interface. The reaction goes through a transition phase .where it is undergoing a mixed control, followed by the diffusion control towards the end of the reduction. The values of apparent activation energies for chemical reaction control were 3.48-8.43 kcal/mol depending on the gas compositions.

Jan 1, 1997

By Satu Jyrkönen

A single-particle laminar-flow technique was used to study reactions of sulfidic nickel particles. The studied materials were three natural nickel concentrates and four synthesised nickel mattes. The variables of the experiments were the gas preheating temperature (500 - 1300°C), the composition of the reaction gas (N2 + 0 - 75 vol-% 02) and the ,particle size of the feed. Chemical analysis of the particles was used to determine the oxidation degree of the materials, and optical and scanning electron microscopy were used to detect alteration in their morphology, internal composition and structure. General reactivity of the materials was monitored by the extent of sulfur removal. The reaction mechanism of the studied materials was found to depend primarily on the materials composition as well as oxygen content of the reaction gas.

Jan 1, 1998

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

By S. Seetharaman

A mathematical model has been developed to evaluate the viscosities of melts at high temperatures. The viscous flow in liquid is described by the equation, {n = Aexp(AG*/RT)} based on the absolute reaction rate theory. The Gibbs energy of activation,{ AG* } is considered to be a function of the temperature as well as the composition of the melt. The model has been applied successfully to various metallic and slag systems from unary to quaternary. On the basis of this model, a relationship has been suggested to relate the Gibbs activation energy of viscosity to the Gibbs energy of mixing in binary metallic melts. The viscosities predicted from available thermodynamic data in the case of a number of binary metallic systems using this correlation show satisfactory agreement with the reported experimental values.

Jan 1, 1994

By I. D. Reznik

On blowing nickel matte in a converter without quartz, first the oxidation of metallic iron and a part of FeS occurs without evolving sulfur dioxide, the formed FeO dissolves in a sulphide smelt and form a homogeneous oxysulphide smelt. On further increasing the FeO content, the oxysulphide separates into 2 layers. Based on the laboratory investigation of FeO-(FeS+Fe°) - (Ni3S2+Ni°) ternary phase diagram we have identified the separation region at 1250°C. The boundaries of the separation region have the form of an arc and the composition of the separated oxysulphide layers is defined by the canodes. In the nickel or copper-nickel matte - silicacalcium oxide slag system at 1250°C three layers, namely sulphide, oxysulphide, and slag may be formed. A high slag basicity due to the presence of CaO can serve to enhance the activity of FeO; a low nickel content in the matte corresponds to a high concentration of FeS therein; FeO from slag and FeS from the matte form a homogeneous FeO-FeS solution, i.e. an oxysulphide layer. The investigation on the "Camebaks" apparatus and by the nuclear gamma-ray resonance spectroscopy method of the phase composition in a slowly cooled oxysulphide layer has shown the presence of four phases: wustite, troilite, ferronickel grains, and calcium oxide-silica inclusions. Knowledge of regularities in the oxysulphides formation makes it possible to use them in pyrometallurgy of nickel and cobalt or preventing their formation.

Jan 1, 1997

By Ljiljana Solujic

The need for the removal of mercury from the precious metals extraction circuits may be influenced by process, environmental, as well as by occupational hazard reasons. In these circuits mercury is mainly present as cyanide complexes. The effectiveness of any stabilization method will be influenced by the high thermodynamic stability mercury-cyano species exhibit in an aqueous solution. In this study, we have investigated the utility of the trisodium salt of trimmercapto-s-triazine (TMT) for precipitation of mercury from the corresponding cyano-complexes. The influence of pH molar ratio of TMT to Hg, coagulant and flocculant additions, excess of free cyanide, as well as the presence of other metal-cyano species on the effectiveness of mercury precipitation were investigated in detail. Also, a "teal world" precious metals mill effluent initially containing ~7 ug/mL (ppm) of Hg was treated and A was found that greater than 99.8% of the mercury was removed from the solution as am insoluble Hg/TMT complex.

Jan 1, 1996

By Yuan She, Qihang Liu, Keng Wu, Hailiang Ren

By observing different coal char’s microstructures and microscopic morphologies during the coking process, the characteristics of COREX coal char’s microstructure and properties were analyzed. MCRI and MCSR were used to respectively describe the reactivity and the strength after reaction of coal char, with those of BF’s coke for reference, and then the physical meaning of MCRI and MCSR were given. MCRI and MCSR were determined by the composition of coal char. For the two kinds of COREX coal, the formula to forecast the hot performance of coal char was set up by making a multiple linear regression between the hot performance and microstructure of the coal char at 1100℃, and the predictive values of coal char’s hot performance at 600℃, 800℃ and 1000℃ coincided well with the measured values.

Jan 1, 2015

By Junfu Chen, Jiann-Yang Hwang, Yong Zhou, Lijun Lu, Likun Lia, Jixiong Liu

The sheet-like NiS-ZnS heterostructured composites were prepared by the microwave hydrothermal. The fabrication of the heterojunctions broadened the range of light response of ZnS. The photoexcited electrons of ZnS migrated to the redox potential of NiS/Ni2S under visible light irradiation, which can facilitate the effective separation of photogenerated electrons and holes in space. The visible photocatalytic activity towards hydrogen production for NiS/ZnS nanosheet heterostructed composites without co-catalyst achieved 0.28 mmol h–1, and the quantum efficiency was up to 18.6% under the wavelength with 420 nm visible light irradiation.

Jan 1, 2015

By Kimio Itagaki, Makoto Ohtsuka, Kouki Chiba, Minoru Matsumoto

"The properties of Ni-Mn-Ga films such as chemical composition, crystal structure, microstructure and transformation temperature were investigated with respect to sputtering conditions in the present study. The Ni-Mn-Ga films were deposited on a polyvinyl alcohol substrate with a radio-frequency magnetron sputtering apparatus using the NisoMn2sGa2s and Nis2Mn:«1Ga24 targets. After separating from the substrates, the films were annealed at the temperature between 873 and 1273 K for 3.6 ks. The chemical composition of the films depended on the radiofrequency generating power, however, there was no dependence on the heat treatment temperature. Each deposited film had a columnar grain structure. After heat treatment, the width of columnar grains widened and then became indistinct with increasing heat treatment temperature. The Heusler type cubic crystal structure of the fi4n with heat treatment at 1073 K changed to the tetragonal one through the martensitic structural transformation during cooling. The martensitic structural transformation temperature increased with increasing nickel content of films, while the Curie temperature decreased. The film obtained at 200 W using the Nis2Mn24Ga24 target after heat treatment at 1073 K showed one-way shape memory effect through the reverse martensitic structural transformation during heating.IntroductionThe ternary intermetallic compound NiiMnGa has a Heusler-type crystal structure and is an intelligent material, which has a shape memory effect and a ferromagnetic property. The martensitic structural transformation occurs within the ferromagnetic temperature region. The cubic crystal structure of L21 at high temperature changes to a tetragonal one through the martehsitic structural transformation during cooling. The films of this compound can be applied for an actuator of micro-machines."

Jan 1, 2000

By Pier-Lorenzo Solari, Philippe Moisy, Michel Schlegel, Stephane Pellet-Rostaing, Eric Mendes, David Bengio, Richard Husar, Thomas Dumas

Ionic liquids (ILs) are molten salts composed of an organic cation that are liquid below 100 °C. They demonstrate unique physico-chemical properties such as good conductivity, negligible vapor pressure and non-flammability. As a consequence, they are often regarded as green solvents and could become an alternative to the use of both high-temperature molten salts and volatile organic solvents in rare-earth elements processing and recycling. The diversity of interactions existing in an ionic liquid allows the solubilization of both polar and apolar compounds. Moreover, coordinating functions on their composing ions can lead to stabilization of some species. For instance, in non-aqueous media, europium exists in the (II) oxidation state which is not stable in aqueous solutions. Understanding the mechanism of Eu(III) electrochemical reduction to Eu(II) and the stabilization of Eu(II) species in IL media could be of major interest for the development of innovative recycling processes. Using transient electrochemistry and UV-Vis spectroscopy we could get valuable information on the redox behavior of the Eu(III)/(II) couple in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([EMIm][NTf2]). Reduction of Eu(III) to Eu(II) and stability of Eu(II) was also studied thanks to a XAS-spectroelectrochemistry set up used to follow in situ the evolution of the XANES spectrum around the L3 edge of Eu during electrolysis.

Mar 1, 2018

By Sue Xue, Carl C. Nesbitt

A project was completed which investigated the efficacy of recycling lead or lead monoxide from various fire assay wastes including crucibles, cupels and slag. The scope of the project was to determine optimal hydrometallurgical parameters so that direct separation and recovery of lead salts was economically feasible. A process was developed from the study which could use either acetic acid or nitric acid as a leachant, followed by several precipitation processes which could directly recover litharge (PbO) or other lead salts, such as lead carbonate or lead sulfate. The economics of the process is discussed. Analytical equipment such as the atomic absorption spectrophotometer and x-ray diffractometer supplied much of the information required for the study. However some novel analytical approaches using these instruments had to be developed to help in the determination of leaching kinetics and process quality control which are discussed.

Jan 1, 1999

By Liu Zhonghua

Hydrogen reduction of cobalt sulfide (Co9S8) was experimentally investigated in the temperature range 813-1053 K. The results revealed that the reaction kinetics can be described by the shrinking core mod¬el in chemical control regime at low temperatures, it is of first order with respect to hydrogen concentration, and the reaction activation energy is 67.4 kJ/mol. The SEM second electron images of the samples before and after experiments showed that the swelling of the sample above 973 K is due to the formation of metallic cobalt whiskers.

Jan 1, 1992

By Qiang Guo, Zongliang Zuo, Mengqi Wei, Qingbo Yu, Qin Qin

Activated carbons, derived from waste ion-exchange resin by CO2 physical activation, were applied to separate CO2 from flue gas against global warming. The BET specific surface areas of activated carbons at different activation temperatures and times were investigated. The CO2 adsorption capacity was tested under non-isothermal and isothermal conditions. The experimental results show that when keeping the activation temperature constant, the specific surface area increases firstly and then decreases with increasing activation time. For the given activation time, the specific surface area rises firstly and then declines with increasing activation temperature. The adsorption capacity decreases with increasing temperature. The maximum adsorption capacity is 51.46 mg/g under the condition of 298 K and pure CO2. Fractional order kinetic model is the best one to describe the kinetics of CO2 adsorption. The activated carbons show the potential to be an effective adsorbent for the removal of CO2 from flue gas.

Mar 1, 2018

By Adam J. Gesing

Eddy current separators are increasingly used by the auto shredder operators to produce higher grade of nonferrous metal concentrate for recycling. While this increases the unit price of the concentrate, metal losses through inefficient metal recovery quickly offset the price differential. We show how to optimize the eddy current separation system at the shredder to maximize mate- rial throughput, nonferrous metal recovery and grade of the nonferrous metal concentrate.

Jan 1, 1998

By T. DebRoy

In recent years rapid technological advances have been achieved in the application of high energy density heat sources such as lasers and electron beams in diverse metals processing operations such as metal refining, fabrication, coating, surface modification and alloying. However, our phenomenological understanding of these new and emerging processes has not kept pace with the technological achievements. Inadequate understanding of plasma-metal interactions, the complexity of the component physical processes, and the scarcity of thermophysical data at temperatures much higher than the melting points of metals are the main difficulties in the comprehensive analysis of these processes. Several unique contemporary issues related to metals processing with high energy density beams such as rapid evaporation of alloying elements during processing and the role of plasma in influencing vaporization rate interfacial tension and species solubility in metals are discussed in this paper.

Jan 1, 1993