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By Alex I. Kociubczyk, Wilky Desrosin, Lucía Mabel Boycho, Alicia E. Ares, Carlos E. Schvezov

In the present research, commercially pure Sn and Zn, and Sn-Zn alloys (Sn-1wt.%Zn, Sn- 2wt.%Zn, Sn-4wt.%Zn, Sn-8wt.%Zn and Sn-8.9wt.%Zn, weight percent) were obtained by a horizontal directional solidification process with two opposite senses and heat extraction. The solidification process was realized using a horizontal furnace with two heat extraction systems at both ends. The temperature was measured using eight K-type thermocouples and an electronic recorder of temperature data. The resulting structures were analyzed using optical microscopy. From the solidification process the thermal and metallographic parameters were determined in all samples. The presence of defects in the solidified pieces was observed. Internal defects pretended to be dependent not only on the composition of the alloys under consideration but also on the size of the structures formed, also, on the velocities and accelerations of interphases, and on the variation of thermal gradients. A model of the phenomenon from the first principles is presented.

Jan 1, 2015

By Ralph P. Hackl

Bacterial leaching of the Doe Run Company?s cobalt/nickel-containing copper concentrate at low pH (pH 1.0-1.2) and high redox potential (>750 mV vs. SHE) enabled the cobalt and nickel to be preferentially dissolved over copper and iron due to the rapid passivation of the chalcopyrite component. Selective leaching of the cobalt and nickel was achieved with a mesophilic culture comprised mainly of Leptospirillum-like bacteria and Acidithiobacillus thiooxidans. This finding led to the conception of a novel hydrometallurgical process for passivating chalcopyrite and recovering the cobalt and nickel. The bacterial leaching process was tested extensively at the bench and pilot plant scales during 1997-1998. A pilot plant containing four leaching stages processed 30-40 kg/day of chalcopyrite concentrate continuously for 87 days. The cobalt extraction ranged from 75% to 86% during 6- and 8-day retention times respectively, whereas the copper extraction was limited to about 9%

Jan 1, 2003

By Xu Weihong

After being pre-treated, composite electro-deposits of semi-bright nickel/nano-SiO2 with bright nickel or with amorphous Ni-P alloy, and Composite electro-deposits of Zinc were prepared on Nd-Fe-B magnetic material. The effect of cathodic current density, nano-SiO2 concentration, stirring strength and surfactants on the corrosion resistance of electro-deposits were studied. In addition surface appearance and structure of the composite coatings were analyzed by SEM. The present investigation shows that the corrosion resistance of composite electro-deposits of semi-bright nickel/nano-SiO2 with amorphous Ni-P alloy was the best, the solution system of semi-bright nickel/nano-SiO2 with bright nickel was stable and its electro-deposits also had an excellent corrosion resistance, composite electro-deposits of Zinc not only had good corrosion resistance, but also low cost, thus making it an excellent electro-deposit for medium or low-class Nd-Fe-B magnetic material.

Jan 1, 2006

By Eoghan T. M Doyle

Oxide mixtures of nickel (NiO), cobalt (COO) and chromium (Cr203) were prepared with graphite in stoichiometric amounts and the powder mixtures were compacted to produce cylindrical pellets. The composition of chromium oxide in these mixtures were varied. Pressed pellets were reduced in a flowing stream of argon-4% hydrogen gas (500 ml/min). Both slow and rapid heating methods were adopted to raise the temperature of a pellet during reduction of oxides to form superalloy powder. The reduction temperature was varied between. 1523 and 1623K. The effect of heating rate and niobium oxide addition on the microstructure of the superalloy produced was studied by using ordinary light and scanning electron microscopes. New phases formed as a result of reduction were identified by X-ray powder diffraction technique. The mechanism of reduction of oxides together with the microstructure of NiCrCo alloy are discussed. The thermodynamics of formation of ternary alloy phase is elucidated on the basis of binary phase equilibria and Gibbs free energy of mixing data for the constituent alloy compositions.

Jan 1, 1992

By Robert W. Bartlett

"Bioheap pretreatment of sulfidic refractory gold ore prior to cyanide leaching is a promising new technology, especially for low-grade ores that cannot afford to be oxidized by pressure leaching or roasting. When an ore contains both refractory and non-refractory (oxidized) gold, an economic decision must be made whether, or not, to pretreat before cyanide leaching. This choice is more complex than the familiar ore/waste cut-off grade decision. Pretreatment usually increases recovery but delays receiving revenue. Based on choosing the processing route that maximizes the present value of the ore, an equation is developed that computes a ""critical cyanide leachable gold grade"" for determining whether pretreating will be profitable. If the ore's actual cyanide leachable grade, without pretreatment, is above this ""critical grade,"" it will not pay to pretreat. The waste/ore cut-off grade, pretreatment yield (leachable grade after pretreatment), total gold grade, pretreatment operating cost and the project's financial discount rate are parameters in the equation. Results of example calculations are provided. This equation can be used for mine development planning and, when bioheap pretreatment is an available option, for daily operating decisions on individual ore blocks.IntroductionOres that are refractory because of sulfide mineral encapsulation of microscopic gold are becoming important. These ores must be pretreated to oxidize the sulfides to liberate the gold prior to cyanide leaching. The conventional pretreatment process technologies are pressure leaching with oxygen and two-stage fluid bed roasting. However, low-grade refractory ores cannot afford the high operating costs of these processes. And, small mines with limited reserves cannot justify the high capital costs of these processes."

Jan 1, 1997

By Yousef Mohassab, Feng Chen, Hong Yong Sohn, Mohamed Elzohiery

The determination of reduction degree in a DR process is sensitive to the total iron in the ore and DRI. An accurate and high throughput analysis method for total iron has been developed. Titration of the solution after tin(II) chloride reduction of ferric ion is a widely used method for iron analysis. However, it is a multistep method that requires many chemical reagents and much time. In this work, an ICP-OES analysis method with higher or equivalent accuracy compared with the titrimetric method was developed. This method has much higher throughput and demands fewer chemical reagents compared with the titrimetric method. In this paper, a comparison of the two methods is presented.

Jan 1, 2016

By Igor Rojkovic

The most important uranium mineralization in the Western Carpathians occurs in the Permian rocks. Low grade stratiform uranium mineralization was formed during the Permian due to adsorbtion and reduction by organic matter, titanium oxides, iron hydroxides, pyrite and clay minerals. During the Alpine orogeny uranium (± molybdenum and copper) remobilized stratabound ores were formed. Dominant ore minerals are uraninite, U-Ti oxides, molybdenite, pyrite and chalcopyrite Two generations of ore minerals are reflected by their textures and chemical composition.

Jan 1, 1995

By K. A. Elbarawy

Processing of Egyptian barite ore with a composition of 85.5% BaSO4; 2.75%SiO2;1.56%Fe2O3 and 5.1% Al2O3 was performed with the aim to prepare pure barium salts. The process took place through pelletization-solid state reduction and leaching steps. Each of these steps was optimized. Pure barium sulphate (99% < 0.82µm) and carbonate (99%<0.75µm )were the final products. This article deals with the reduction process that occur whn coal was added to the ore during pelletization in the ratio of 5:1 stoichiometry. Optimum reduction of pellets of 8-12mm in diameter was achieved after 60 minutes at 1050oC and under a rate of 5 lmin-1 of nitrogen atmosphere, where 87.79% of the ore was reduced. The kinetic studies showed that the reduction process could be modeled according to the core mechanism of diffusion control in which the effective diffusivity is based on the surface area of unreacted ore. The activation energy calculated was 92.7 kJmol-1.

Jan 1, 2006

By M. K. Yelloji Roa

Effect of conditioning with Thiobacillus ferrooxidans on the floatability of sphaierite and galena has been determined in this work. The flotation behavior of the conditioned minerals clearly shows that such bacterial conditioning does produce marked modification of their surfaces. The variables affecting the surface modification and thereby the flotation response of the minerals were found to be cell concentration used for bacterial conditioning, the period of biotreatment and the pulp density. Importantly, while the enhancement in flotation obtained due to sulphuric acid treatment was retarded by biotreatment in the case of galena at all cell concentrations due to electrochemical effects, such decrease occurred in the case of sphalerite only at cell concentration sufficiently high for their attachment to the mineral surface. The effect of bacterial conditioning has significant implications to the differential flotation of sphalerite and galena. Mechanisms responsible for the modification of the surface properties of these sulphides due, to bacterial conditioning are discussed.

Jan 1, 1991

By Katsunori Yamaguchi

The zinc, lead and alumina contents in copper smelting slag are increasing with the increase in waste recycling. The recovery of base metals such as lead and zinc from copper converter slag is important from both an economical and environmental perspective. As a fundamental study of the metal recovery by reduction process, activity coefficients of ZnO and PbO in the CaO-SiO2-FeOx-5mass%AlO1.5 slag under iron saturation at 1573K are derived from the data of slag-metal equilibrium experiments. On the basis of the obtained data, the activity coefficients of ZnO and PbO in the CaO-SiO2-FeOx-5mass%AlO1.5 slag were compared with those of the CaO-SiO2-FeOx ternary system. Addition of alumina increases activities coefficient of ZnO and PbO in SiO2 rich side of the slag, and decreases them in CaO rich side.

Jan 1, 2006

By E. Ilgar

"Deposition studies were conducted in acid copper electrolyte to determine the influence of chloride ions on cathode morphology. A statistically designed screening test was carried out in the absence and presence of 20 ppm CI- using a three factor, two level factorial design, in an electrolyte containing 36 gl'! Cu2+ and 150 gl-! H2S04, The independent variables evaluated were agitation; current density and temperature and their influence on surface roughness was determined. The copper deposited at current densities where activation was the primary control mechanism appeared similar in morphology whether stirring was used or not. The addition of 20 ppm CI- to the electrolyte gave rougher deposits under the same conditions. In the mixed control regions, considerably rougher, dendritic deposits were obtained when CI- was present. Agitation was effective in reducing the copper surface roughness both in the apparent activation and mixed control regions in the presence ofCI-. The results of this study showed that 20 ppm Cl- polarized the copper deposition at low overpotentials but caused depolarization at higher overpotentials.IntroductionChloride ion is inherently present in copper electrolyte, either as an additive or from other sources such as make up water. The behavior of the chloride ion is well documented in electrorefining operations, but its role in copper winning is less obvious. However in both cases there is evidence that cathode growth and solution chemistry are strongly influenced by its presence. The mechanism and electrochemical action of the Cl"" have been shown to be very complex, therefore a better understanding of its influence on electrocrystallization is essential for improved cathode deposit growth control. It was proposed that Cl"" polarizes the copper deposition reaction at low concentrations due to CuCI formation but depolarization occurs at higher concentrations due to the formation of a soluble CuCI2"" complex [1,2]. Franklin [3] reviewed the mechanism of additives in the electrodeposition process and proposed that the Cl"" complexed with copper, adsorbed on the cathode as an induced anion leading to an increase in the reduction rate. At cathodic overpotentials less than 100 mY, lppm NaCl had a polarizing effect, i.e. an increase in impedance of the charge transfer step. At higher Cl"" concentrations up to 100 ppm, depolarization occurred as evidenced by a decrease in impedance, which was attributed to soluble cuprous complexes [4]."

Jan 1, 1997

By Masayasu Kawahara

"The extraction and separation of nickel, cobalt and copper were investigated with a solvent impregnated resin which was produced from UX84-I and XAD-4. The extraction behavior of metals with the solvent impregnated resin is similar to that with solvent extraction. The extraction ability of solvent impregnated resin improves when using finer particle resin and with a higher concentration of extraction solvent.IntroductionSolvent extraction is well known-as a method for separation of metallic elements in solution. However there are problems with intermediate phase and solvent loss. Ion exchange resin is also used in hydrometallurgy, but it is not fit for separating a large quantity of metals. Amberlite XAD-4 resin is known as a absorption agent of organic matter in water. It is expected that the resin which has the ability of extracting metals can be made by absorbing organic extractant on XAD-4 resin In this study, solvent impregnated resin (SIR) was produced from LIX84-I and XAD-4, and extraction and separation of nickel, cobalt and copper were conducted using SIR. The extraction properties of SIR were investigated, and a comparison between ordinary solvent extraction and SIR was made.Experimental ProcedureAmberlite XAD-4 was used as absorption resin for the organic extractant in this study. The physical properties of XAD-4 are shown in Table I. Amber lite XAD-4 has a large surface area and shows good ability to absorb organic matter in water, but the: resin does not have the ability of exchanging metallic ion."

Jan 1, 2000

By Kenji Morinaga, Shigeru Fujino

"Preparation and vacuum ultraviolet (VUV) transmission spectra of aluminum fluoroberyllate glasses, MgF2-CaF2-SrF2-A1Fr BeF2 (MCSA-Be) and MgF2-CaF2-SrF2-AlFrYFrBeF2 (MCSAY-Be), were studied. The influence of YF3 and BeF2 on the thermal stabilization against crystallization and VUV transmittance was investigated. With increasing the BeF2 content, the crystallization tendency decreased and the absorption edge shifted to shorter wavelength in the MCSA-Be and MCSAY-Be glasses. The MCSA-20Be glass composition exhibited the shortest wavelength UV absorption edge (-147 nm) and the highest transmittance at 157 nm (60% for 2 mm sample thickness). The transmission values at 157 nm and the slope (steepness) of the absorption edge were found to be significantly influenced by the trace amount of Fe2+ derived from the BeF2 raw materials.IntroductionPure beryllium fluoride is known to be an only fluoride that forms one component glass on cooling from the molten state and is structurally similar to silica with [SiO4]4- tetrahedra. Molten BeF2 is highly viscous with a viscosity of about 106 poise near its liquidus temperature at 550""C[l]. The addition of modifying fluorides such as LiF, NaF or KF to BeF2 substantially decreases the viscosity[2]. Glass forming region of binary fluoroberyllate glasses has been mainly reported by several authors [3]. LiFBeF2 binary system is structually analogy for Mg0-Si02 system from their phase diagram and ratio of ionic radius for each cation and anion, respectively. LiF-BeF2 binary glasses seems to be promising candidates for the extreme deep vacuum ultraviolet (VUV) transmitting optical materials owing to their larger band gap. However, it is chemically unstable, and so, have no practical application for lens systems in micro lithography equipments and substrate materials for F2 (157nm) excimer laser[4]. There are also few reports on the VUV transparency of multicomponent aluminium fluoroberyllate glasses from the view point of their compositional dependencies. The purpose of this paper is to prepare deep VUV transmitting optical materials and determine the optimum glass compositions for aluminium fluoroberyllate glasses investigating their thermal stabilization against crystallization."

Jan 1, 2000

By Christian Ludwig, Virginie Silberstein, Rizlan Bernier-Latmani, Simona Regenspurg

"Residues from waste incineration (bottom ashes) form large amounts of heavy metal-rich waste. Theoretically, heating and the addition of chloride to the ashes could remove these metals by formation of volatile metal chlorides. The remaining heavy metal-poor ashes could be used, for example, as cement additives. In the proposed process of our study we used bypass dust from the cement industry as chloride additives to the bottom ashes. We aim to determine experimentally the optimal conditions to remove heavy metals from ashes and to simulate this process by thermo- chemical modeling. In our experiment we investigate heavy metal flows by heating of differently composed mixtures of bottoms ash and bypass dust in dependence of different furnace temperatures (500-1200 °C). Furthermore, we investigate the reactivity (leaching characteristic) of the resulting product in order to predict if secondary residues can be landfilled in agreement to Swiss regulations for inert materials.IntroductionThe incineration of garbage is generally considered as the most environmentally friendly method for the reduction of municipal solid waste. This is because, compared to traditional storage of waste on landfills, incineration produces less greenhouse gases and destroys toxic organic compounds. The released exothermic energy can be recuperated and the residues from the combustion chamber (bottom ash) are strongly reduced in volume. However, they still form about 600 kt of waste per year in Switzerland, which needs to be landfilled. However, these residues could be potentially used as construction materials after mechanically recovering ferrous and non-ferrous metals. However, the resulting ashes (discharged dry or wet) still contain increased amount of heavy metals (exceeding state regulation) requiring them to be finally deposed on a hazardous waste site. A thermal treatment of these ashes could enable both, to separate and recuperate the remaining heavy metals and an inorganic heavy-metal poor material. The evaporation of metals depends on temperature and can be lowered by addition of chlorides, which would lower the boiling point of most metals by formation of metal chlorides (table 1). 745"

Jan 1, 2008

By Guozhu Ye

"One of the most essential problems associated with the treatment of EAF dust is its high content of halogens. For most thermal processes for zinc recovery, such as the plasma processes with a zinc condenser, the halides in the gas stream will form a dross phase that results in a low zinc yield. For those with zinc oxide as main product, such as Waelz oxides, the high halogen content in the product implies a great degradation of the product quality and the product can only be sold at a low price. Further processing of zinc oxide with high halogen content either by pyrometallurgical or hydrometallurgical processes will also result in process problems.This paper will review the pre- and post-treatment alternatives for halogen removal based on the comprehensive characterization work that has been carried out at MEFOS and the preliminary experimental results.The experimental results show that chlorine and fluorine content could be reduced to 450 ppm and 50 ppm respectively by selective sulfation, and to about 200 ppm by soda leaching. Selective sulfation of zinc oxide in the EAF dust will also be discussed."

Jan 1, 2000

By Lincoln McCrabb

Correct measurement and interpretation of viscosity data is critical for design of any thickening and pumping process that involves a non Newtonian slurry. The nickel laterite pressure acid leach (PAL) process relies on producing a slurry of maximum achievable solids concentration. Small variations of 1-2% solids concentration can alter economics significantly. For the Ravensthorpe Nickel Project, a rheology protocol has been developed which optimizes the solids concentration across a range of ore types. The vane yield stress technique has been utilized to accurately quantify the flow of thickened slurry in the lower shear range. A yield stress of 100Pa has been used as a benchmark to determine the optimum solids concentration achievable utilizing deep cone thickening. Statistical analysis of the data shows critical rheology distinctions between ore type, particle size, lithology and geochemistry. Linear and power law models have been applied to rheology flow curves to reconcile the material transport properties with the anticipated thickener underflow solids concentration. Keywords: Vane Yield Stress, Thickening, Rheograms

Jan 1, 2004

By Ronald Klepper

In hydrometallurgy, pure gases like oxygen and hydrogen are used for oxidation and reduction. The gases are expensive and therefore should be used efficiently. Non reacted gas can be recycled into the liquid. Historically vortex gassing has been used; Le. a mixing impeller close to the liquid surface entrains gas from the headspace into the liquid through a gas vortex. Novel and more efficient methods are surface gassing with up pumping impellers and self- inducing gassing impellers. These alternative impeller systems are well established and common in the chemical industry, but have not been used until recently in hydrometallurgy. Gassing impellers act as internal compressors and increase the interfacial surface for a much higher mass transfer compared to alternate methods mentioned. In the paper results from lab and pilot tests and data from operated plants will be presented. The reactions with gases normally take place under moderate to high pressure, therefore a safe enclosure with mechanical seals and the safety "philosophy" is important. Experienced life and replacement cycles will be reported.

Jan 1, 2000

By K. S. Kawatra

In recent years, there have been several efforts to develop binder mixtures for iron ore pelletization. Some efforts have been fruitful, while others have encountered failure. For example, adding corn starch to bentonite is effective, while adding fly ash to bentonite is not. When binders are made with fly ash, a pozzolanic reaction occurs, but no such reaction occurs when bentonite and corn starch are used together. The authors analyzed which binders can be mixed, and which binders will succeed. The authors confirmed this analysis with several laboratory and plant studies. This paper presents this critical analysis, along with various combinations of binders for making Iron Ore Pellets.

By Tim J. A. Smith

Fundicion Refimet S.A. has operated a custom copper smelter at La Negra, near Antofagasta in northern Chile since 1993. From an initial operation based on Reverb smelting and Peirce-Smith, converting, the plant was expanded from 90 000 t/y to 160 000 t/y copper production in early 1997, by conversion to oxy-fuel smelting and use of concentrate injection on Converters. As part of this expansion a novel reverb gas cooling and cleaning system was developed and designed by Kilborn SNC-Lavalin Europe, the London, UK-based mining and metals; Office of Canada&apos;s SNC-Lavalin group. The reverb gas cooler needed to satisfy several very specific requirements including low cost, flexibility, robustness and simplicity of operation. Of particular importance was the requirement to cool and clean the ,oxy-fuel reverb gases and render them suitable for subsequent treatment in a conventional sulphuric acid plant. It was also important to avoid accretion or dust handling problems. This paper describes the key design features and subsequent successful installation, commissioning and operation of the unit.

Jan 1, 1998

By Satoshi Yamashita, Noboru Masuko

"Newly prepared bipolar membrane is promising to become a key material of an electrolyser for a production process of strong reducing solvent. This research is basic research for using bipolar membranes as electrolysers of reducing agents, Cr(II), TI(III) and V (II) on the laboratory scale. In this report, a bipolar membrane was tried with an electrolyser, reducing chromic chloride to chromous chloride. An analysis of mass balance demonstrates advantages of it over the former electrolyser equipped with an anion and/or. cation exchange membrane. The effects of current density and concentration of Cr(lll) on the reduction rate of Cr(II) and the current efficiency were examined No deterioration of the bipolar membrane resulted from the electrolytic reduction of Cr(III). IntroductionRecently, bipolar membrane that was the development subject for a long time in the industry of ion exchange membranes has met the stage of the practical application at last [l]. The expectation of the application to the hydrometallurgy field increases. We took up the manufacturing of the strong reducibility solvent as part of the application of bipolar membrane to hydrometallurgy technology. This laboratory has much experience in the electrolytic reduction of Cr (II) aqueous .solution such as chromous sulfateusing bipolar membrane were compared in theory to chromous chloride aqueous solution manufacturing of the strong reducibility solvent. The advantage of applying bipolar membrane by substituting ion exchange membrane is described, and the experimental result is reported."

Jan 1, 2000