Search Documents

By David G. Dixon

A general, unsteady-state model for leaching of one or more solid reactant species from a non- reactive, porous, spherical pellet is derived in dimensionless form for the interpretation of leaching data, and for use in the design of coarse-ore leaching processes. The effects of diffusion rate, chemical reaction rate, variable reaction order, and competition between multiple solid reactants are examined using the concept of the effectiveness factor. It is shown that the model is capable of simulating both "reaction-zone" and "heterogeneous" kinetics, depending on the choice of three dimensionless parameters. Results of batch leaching tests of artificial ore pellets are presented, and their relationship to the model is discussed.

Jan 1, 1993

By Keizo Uematsu, Satoshi Tanaka, Nozomu Uchida, Anze Shui, Joaquin Lira, Cyril Lavelle, Midori Saito, Thierry Poirier

"Dispersed and flocculated alumina (non-spherical particles) slurries were prepared by pH controlling with HCL Spray-drying of these resulted in dimpled granules with a smooth surface and high density, and spherical granules with rough surface and low-density, respectively. Detailed characterization on granules and their compacts includes: SEM observation, density measuring (mercury porosimetry and Archimedes's Principle) and liquid immersion optical microscopy. Compaction of these granules originated a larger particles rearrangement in the samples made with the spherical granules than with the dimpled granules. This was verified through the orientation of alumina particles, which was pronounced in the compact made with the former granules.IntroductionOn immersing a ceramic powder in water, the surface usually acquires a charge by interaction with ionic species in solution. The charge is affected by pH and the electrolyte concentration of the water. 1 The dispersion in a slurry is achieved through the interaction of charges on the particle surface with the media. In the ceramic processing, especially in the process of casting, the dispersion of slurry has been one of the most important topics studied for many years. Recently the attention is paid on its role in the pressing. The granule characteristics are governed by the dispersion state of slurry. Takahashi et al2 , Tsubaki et al3 and Walker et al4 showed that the granules from dispersed slurry were dimpled and of high density, while granules from flocculated slurry were spherical and of low density. This variation in the granules characteristics should have a marked effect on the structure of compact.This paper presents the influence of the dispersion state of alumina slurry on the granules characteristics and also on the internal structure of compacts. Different dispersion states were elaborated by adjusting pH of the slurry. In this method, the particles are dispersed or flocculated only by the effect of surface charging, and thus some secondary effect such as the steric hindrance from an electrolyte dispersant is avoided. The characteristics of granules and compacts are examined with SEM, density measurements by mercury porosimetry and by Archimedes's Principle and liquid immersion optical microscopy. This novel microscopy provides various important information on packing structure of particles, such as their orientation. 5"

Jan 1, 2000

By E. Salinas-Rodriguez, J. Hernández-Ávila, E. O. Ávila-Dávila, A. Romero-Serrano, M. Perez-Labra, G. Juárez-López

"Single phase rubidium jarosite was synthesized by precipitation from aqueous solution. X-ray diffraction and SEM-EDS analyses showed that the synthetic rubidium jarosite formed in subspherical particles with an average particle size of about 35 µm. The chemical analysis showed an approximate composition of Rbo9432Fe3(SO4)2 1245(OH)6. The decomposition behaviour of the jarosite in terms of solution pH was thermodynamically modeled using FACTSage by constructing the potential-pH diagram at 298.15 K. The E-pH diagram showed that the decomposition of jarosite leads to goethite (FeOOH) together with Rb+ and SO42- ions. The experimental decomposition of the Rb-jarosite was carried out in alkaline solutions with five different Ca(OH)2 concentrations. The decomposition process showed an ""induction period"" followed y a progressive conversion period where the Rb+ and SO42- ions formed in the aqueous solution. In contrast, calcium was incorporated in the solid residue and iron was transformed into amorphous ferrihydrite. The kinetic analysis showed that this process can be represented by the unreacted-core chemically controlled model. The reaction order with respect to Ca(OH)2 is 0.4342 and the calculated activation energy is 98.70 kJ mol-1. IntroductionJarosite type compounds are hydrous sulfate minerals containing alkalis and ferric ions, MFe3(SO4)2(OH)6, where M can be H3O+· Na+, K+, Rb+, Ag+, NH4 +, Tl+, ½ Pb2+ or ½ Hg2+. Jarosite-type compounds were formed by the natural ""in situ"" oxidation of pyritic ores leading to the replacement of the original iron sulfides and iron oxides (Dutrizac and Kaiman) [1]. The great interest in jarosites is due to its ability to eliminate or diminish the iron concentration of the acid leach solutions produced in the hydrometallurgical zinc process, with relatively low losses of divalent metals such as Zn2+, Cd2+, Cu2+ or Co . However, the losses of the metal values demand a careful study of the conditions under which the jarosite compounds are formed together with their chemical properties."

Jan 1, 2012

By Colin Dessemond

Since 1950, the traditional process has been dominating the production of lithium compounds from spodumene ores to sustain the lithium market because of its economic viability and the markets need for technical grade (99.5% purity) product. This traditional process includes thermal conversion, acid roasting and lithium leaching. However, this process has not been challenged and very few studies have tried to explain its limitation (95% lithium yield) or optimize the thermal treatment. Here, α to β spodumene conversion and lithium extraction were performed in a rotary kiln on a 2 mm to 2 cm spodumene concentrate instead of a micrometric one using a 1050 °C, 30 min conversion treatment and 250 °C, 30 min, 30% H2SO4 excess leaching treatment. X-Ray Diffraction analyses were performed on the converted material to determine the conversion rate by Rietveld analysis. It was observed after thermal treatment that the α-spodumene particles fractured and divided while the impurities remained compact. A sifting was performed after thermal treatment and it was determined that 65% of the initial mass became finer than 180 μm. X-Ray diffraction analyses and lithium content measurement were performed on both fractions and it was determined that the finer fraction had a very high lithium content of 3.24 wt%. Lithium extractions were performed on both fractions separately. While the coarser fraction’s lithium yield was only 61% the finer fraction’s lithium yield went up to 99% without any additional treatment. These observations may open more economical ways for the traditional process by potentially bypassing two third of costly steps such as grinding.

By Ko-ichiro Ohno

It is recently recognized that the iron reduction and melting as well as the slag separation of a composite of granular iron ore and coal are completed in a very short period of about 10 minutes when the composite is rapidly heated up to approximately 1673K. These phenomena are expected to be applied to a new iron-making process. The mechanism of iron ore reduction and iron-slag separation during rapid heating has not yet been revealed and the fundamental research has just started. Carburization of the reduced iron is regarded as one of the most important steps in this process. In the present work, the composite was prepared from four kinds of coal or graphite as a carbon source and electrolytic iron powder as a completely reduced iron ore. The temperature at which the liquid formation and iron carburization occurred was monitored. Direct observation of smelting reduction behavior was made by a confocal laser-scanning microscope combined with the infrared image-heating furnace to clarify the effect of molten ash on iron carburization. It was found that the meltdown temperature of composite became lower as the melting temperature of coal ash decreased. From the observed result, it was presumed that the liquid slag would act as an important media for the carbon transfer from coal to iron. The carburization mechanism during the smelting reduction was estimated as follows. When slag containing iron oxide melted down and contacted carbon, iron oxide in the slag was reduced and the formation of the metallic iron particle as well as the its carburization occurred simultaneously at the slag-carbon interface. Carburized iron particle was carried from slag-carbon to slag-iron interfaces due to the slag convection flow caused by the difference of the interfacial tension between the carbon-slag and iron-slag interfaces. Carburization of reduced iron could proceed with a repeat of the above-mentioned process.

Jan 1, 2003

By Yuzo Hiroshige, Masayuki Kyoi, Tomonori Saeki, Masahide Okamoto, Toru H. Okabe, Yu Miyamoto, Tomohiko Akahori, Takeshi Nemoto

We report Hitachi's approach to establish the recycling process for rare-earth metals in magnet. We have developed a process to disassemble the used electric products to collect the magnets, a process to remove the surface plating film of the magnet, and processes to separate rare-earth metals from the magnet. All processes are operated without chemical solutions in order to minimize the environmental impact due to the waste water emission. For the disassemble process, we have developed an equipment to generate continuous shock on the electric products to loosen screws. A sand blast technique is applied for the plating removal process. Rare earth metals in the magnets are extracted by immersion of the magnets in molten magnesium. The extracted rare-earth metals are separated from Mg by evaporation of Mg. The overall yield of recovery is 86.8 %. The purity of the final rare-earth metal is 98.8 %.

Jan 1, 2014

By Carlos M. Fontes Vieira, Ruben J. Sanchez Rodriguez, Carlos E. Gomes Ribeiro

"In this study we attempted to model a response surface for the apparent dry density of ternary blends of calcitic marble particles. The crushed marble was divided into three granulometric ranges. Simplex network methodology was used to determine the mathematical relation between granulometric ranges and apparent dry density (ADD) of particle mixtures. A highly significant regression was obtained and the simplex network methodology proved to be able to predict high packing particle compositions.IntroductionProblems with packing and expected porosity of particles are common and widely recognized to be important in terms of both fundamental physics and engineering applications. For example, densification of a powder mass is important in the shaping of solids in ceramics, powder metallurgy or composite synthesis; chemical processes such as solid-liquid separation (sedimentation, thickening and filtration), raw material handling (stockpiling, blending, drying, storage and transportation) and pyrometallurgical processes (agglomeration, coke making, ore sintering, blast furnace iron making and new iron making processes) [1,2].Many factors can affect particle packing, but in practice, there are three main factors: (dimensionless) particle size distribution, particle shape and absolute particle size [2].Geometrical and practical methods were developed to predict properties in mixtures. Zou, Gan and Yu [2] present a paper treating a prediction of the porosity of multi-component mixtures of cohesive (fine) and non-cohesive (coarse) particles. Bahiense et al. [3,4] used a simplex network to determine a mathematical model for obtain the optimal compositions between aggregates to a greater packing of a ternary particles mixture. Despite these techniques for predicting particle packing, some studies in particulate composites production don't present clear criteria for choice of particle distribution [5,6]. As the best particle packaging depends on the size, distribution and shape of these particles, individual models can be constructed for specific combinations of these factors."

Jan 1, 2014

By Rafael Colás

Computer visualization can be employed in industry as an aid to the understanding of the complex interactions between variables encountered in production. The examples of ingot casting of rimming steel and that of hot rolling of low carbon steel strip are presented. Both processes are mathematically modeled, and their results are presented in a graphical way. Such models have been proven to be an asset in quality improvements and increase of productivity as the personnel involved get a better understanding of their job.

Jan 1, 1993

By Liang Li

Thermodynamic analysis and experiments were conducted in order to verify the feasibility of preparing crude titanium tetrachloride (TiCl4) via the carbochlorination of low-grade titanium slag in molten salt. Titanium slag, assaying 74.6 wt% TiO2 with high calcium and magnesium oxide impurities, was treated by an optimized carbochlorination process in NaCl molten salt. These impurities in the titanium slag were chloridized simultaneously, and chlorination products FeCl2, MnCl2, MgCl2, CaCl2 and CrCl3 were collected in the furnace slag. XRD and SEM/ EDS analysis of residue shown that SiO2 and Al2O3 in titanium slag were difficult to chlorinate completely. Theoretical calculations and industrial-scale experimental studies reveal the content of TiCl4 in the products was more than 98.8 wt% and thus proved the feasibility of utilizing low-grade titanium slag for TiCl4 preparation by molten salt chlorination technology.

By Arthur G. Hunt

Smelting using the direct-to-blister process commenced at Olympic Dam on 31 July 1988. The unique nature of the Olympic Dam ore body led to the selection of the direct to blister smelting process. Significant improvement in the design of the furnace and the understanding of the fundamentals of the process and its operation has occurred in the 10 years of operation. The paper will discuss the operation of the #1 Smelter and the design, preparation for start up and early operating experience of the #2 Smelter.

Jan 1, 1999

By M. Arenas

A corrosion study of a bonded NdFeB permanent magnet materials alloyed with titanium carbide additions has been undertaken. The materials were produced by rapid solidification by melt spinning. Commercial epoxy was used as a bonding medium. The corrosion results were compared with those of a near stoichometric unalloyed NdFeB. Anodic polarization and potentiostatic techniques in 0.9 M Na2SO4 solutions were used to characterize corrosion behavior. It was found that the addition of 6 a10 Tic resulted in superior corrosion resistance, as indicated by lower corrosion currents and less iron dissolution at fixed potential.

Jan 1, 1997

By K:-I. Rhee

The recovery of tellurium from Te-cement obtained during the processing of copper anode slimes was carried out by a series of hydrometallurgical processes, i.e. leaching Te-cement in NaOH solution, precipitation of impurites with the addition of Na2S followed by direct electrowinning of tellurium in NaOH solution. The optimum conditions for each process were determined and discussed in terms of various parameters associated with each step to maximize the recovery and purity of tellurium. The final purity of tellurium from electrowinning in alkaline solution was found to be more than 99.9 %.

Jan 1, 1997

By O. Forsén

In the first part of this paper is studied the behaviour of small amounts of impurity elements? in the solidification of copper anodes. In the second part the dissolution of these impure anodes in sulphate based electrolysis is discussed. The first part is introduced with practical examples, the .model of solidification of impurities during the solidification of anode copper. According to this model the solidification structures of anode copper are strongly influenced by both thermodynamic and kinetic factors. Thermodynamics determine the microstructure of anode copper, but kinetics can alter the composition of melt to such that there is formed unequilibrium structures during the solidification, especially when the residual melt is solidified. The electrolysis experiments have clarified the behaviour of impuririties in the electrochemical dissolution in sulphate. Based copper electrolysis. In this study it is widely investigated to what extent any impurity elements or oxides will dissolve. In copper electrorefining. With the aid of the electrochemtcal experiments it was possible to fulfil quantitatively the qualitative results accomplished by microstructure studies.

Jan 1, 1985

By M. E. Myers

An experimental program is being carried out to determine the thermodynamic characteristics of zinc solubilization in high-temperature iron and iron-carbon alloys. Two versions of an isopiestic technique are being used, with zinc at a lower temperature being equilibrated with pure iron foils or molten iron-carbon alloys at a higher one. The lower temperature sets the partial pressure of zinc vapor, and thus the activity relative to a given reference state. Initial results show Henrian behavior for dilute zinc solutions in austenite and a molten 4.6% C alloy, with unit-pressure solubilities in pure Fe that closely match the predictions of Wriedt.

Jan 1, 1992

By Akira Yazawa

The continuous converting has attractive advantages, but further experimental studies on the slag are required, when the process is considered thermodynamically. The summarized experimental results, obtained with iron silicate slag and with ferrite slag and results relating to actual operation are described and discussed in this paper. At first, equilibrium relations at controlled oxygen potentials among three melts of silica-saturated iron silicate slag, white metal and copper are investigated. The results obtained for slag agreed with the thermo-dynamical predictions. Namely, to suppress a magnetite separation, the system should be at high temperature; in the case of the S02 gas of 10 kPa, for example, magnetite did not separate from the slag at 1300°C, but at 1250 and 1200°C the slag was saturated with magnetite even at lower SO2 pressure. Copper losses caused by dissolution of its oxide increased with increasing 5O2 pressure, and were slightly lower than those reported in previous papers without the matte phase. When the continuous converting slag does not contain any appreciable amount of silica - in contrast to the conventional smelting slag ferrite slag would form, but there was no published fundamental work on-ferrite slags. Hence, the melting behavior and activities of the system CaO-Cu2O-Fe2O3 have been investigated. The liquidus diagram in nitrogen atmosphere was, constructed using both thermal analysis and quenching method. The low liquidus temperature region without magnetite separation was found in the part of low content of Cu2O in the section Cu2O-CaO-Fe2O3 and Cu2O?Fe2O3¬CaO?Fe2O3. The activity of Cu2O in the system was also measured. Slags, composed-of CaO, Cu2O and Fe2O3, in platinum crucibles were equilibrated at 1250°C and controlled oxygen pressures. After quenching, the-composition of slag and platinum crucible were determined qualitatively. On the thermo-dynamic analysis of the results, iso-activity lines were drawn, and it was shown that the slag in the converting furnace of the Mitsubishi process exists in an adequate region of the composition triangle.

Jan 1, 1976

By Leonard J. Friedman

The recovery of sulfur dioxide from metallurgical gases for the production of sulfuric acid has been an effective means of reducing sulfur dioxide emissions from non-ferrous smelters. Sulfuric acid has been produced from gas originating from fluid bed roasters, electric furnaces, reverberatory furnaces, flash smelting furnaces, Pierce Smith and flash converters, sinter machines, etc. The gas from each of these sources has a unique set of variables that affect the design and operation of the sulfuric acid plant. In addition, the sulfuric acid plant itself has been evolving, with new equipment designs and materials. This paper will review each of the unit operations in the gas cleaning and contact sections of the metallurgical sulfuric acid plant, discussing various equipment designs, materials and the handling of gas stream variables and impurities. The paper updates to 2006 previous works on metallurgical sulfuric acid plants by the authors.

Jan 1, 2006

By Zongliang Zhang

Electrowinning is a significant step in metal extraction processes. Because the nature of electrowinning is to reduce metal from its oxidized state, substantial energy consumption accompanies it. Electrowinning processes of different metals have much in common—the deposition of the metal on the cathode and the counter-reaction on the anode. An advanced model was developed that can be applied to a variety of metal electrowinning processes. A model for specific metals can be readily obtained by modifying parameters such as potential, kinetics, and side reactions in the model. The model incorporates mass transfer, gas-liquid flow, electrochemistry, and deposition, making it a comprehensive electrowinning model. The model is applied to copper, nickel, and zinc and verified with the experimental results. In addition, the parameter settings and results of different metals were compared, showing that this model has great versatility and accuracy, thereby making it an efficient and effective research tool.

By B. M. Fisher

A process for making electrolytic copper of high quality from copper flotation concentrates is described. The concentrates are first slurried and then subjected to a high-temperature, high-pressure, oxidation-leaching operation under controlled conditions. The resulting slurry from the oxidation-leaching operation is cooled or flashed to atmospheric pressure and then subjected to a solids-liquid separation. The separated liquor, containing the recovered copper values, is cooled and then fed to an electrolytic deposition operation where metallic copper cathodes of high purity are produced. The spent electrolyte is then subjected to a sulfide treatment to precipitate the residual amounts of copper not deposited in the electrolytic cells. The precipitated copper sulfide is recovered and recycled in the form of a slurry to the initial stages of the process.

Jan 1, 1976

By F. Mucciardi

While flash smelting and converting are capturing a greater share of the market, injection through circular injectors will remain with us for the foreseeable future. The use of top lances for injection is a key feature in several processes (e.g. Mitsubishi, Ausmelt). Tuyeres, on the other hand, are incorporated into a number of processes (e.g. Noranda, Peirce-Smith). To date no lances or tuyeres are cooled by an external source. The reagent provides the bulk of the cooling. With limited cooling, it is normal to have substantial wear on the nozzles - especially in the case of lances. To overcome the issue of wear, a new patented injector (lance or tuyere) has been developed by Noranda and McGill University. This novel unit is based on heat pipe technology. It can operate for an extended period of time without wearing. Enhanced lance/tuyere life is achieved by operating the injector at a low enough temperature that promotes the formation of a thin frozen layer on the outer body of the unit. The vaporizing and condensing substance within the unit acts to cool' the high heat flux portions and dissipate the heat to areas of low heat flux outside the vessel. A fairly large number of tests have been conducted with a prototype unit. The tests have shown that the heat pipe lance is a viable unit. In this paper is detailed a test which illustrates how the lance functions when pure oxygen is injected into copper matte. In addition, the findings from a basic study of a heat pipe in high heat flux environments are also presented.

Jan 1, 1999

By Björn Saxen

Outotec atmospheric Direct Leaching has so far been implemented for zinc production capacities of around 100,000 t/a. Lately, there has been growing interest for small scale direct leaching plants, producing circa 30,000 t/a of Zn. Such small leaching plants can provide extra front-end capacity in existing roaster-based plants and enable treatment of feed materials not suitable for roasting. In small scale plants the proven OKTOP® 9000 Direct Leaching reactors are not readily applicable, due the large size. For smaller installations a modular approach is proposed providing multiple advantages, such as reducing the construction time and amount of the site work required causing less disturbance to regular plant operation with reduced cost. In this paper, we present advantages that can be achieved by using modular OKTOP®C reactors and discuss also process design when connecting a small scale direct leaching process to an existing zinc plant. Also benefits of direct leaching expansion are presented.