Search Documents

By T. T. Chen

Raw anode slimes consisting primarily of PbSO4, AgCuSe, Cu3Se2, Cu2-x Se, Cu2O, CuSO4.5H2O, Sn arsenate and Sb-Bi-As oxide are batch-leached with electrolyte-O2 to dissolve Cu. During this process, Cu2O and CuSO4.5H2O are solubilized and the Cu in the selenides is leached with the formation of Ag2Se and Se. A small amount of Cu remains in the Ag2Se, Sn arsenate and Sb-Bi-As oxide. The decopperized slimes are repulped in Na2CO3 solution to convert most of the PbSO4 to NaPb2(CO3)2(OH). The Sn arsenate and Sb-Bi-As oxide partly react, but the Ag2Se is not significantly affected by the Na2CO3 solution. The NaPb2(CO3)2(OH) intermediate phase is dissolved in acetic acid to leave a final product consisting of Ag2Se, Se, Sn arsenate and Sb-Bi-As oxide, together with small amounts of PbSO4, NaPb2(CO3)2(OH) and various gangue constituents.

Jan 1, 1993

Although anion exchange resins are widely used for gold recovery in Russia and the former CIS, accounting for almost 50 percent of gold recovery in that part of the world, the technology has not been adopted in the West, apart from one small operation in South Africa. This situation is likely to change as the gold industry heads into the twenty first century. With gold prices having declined steadily through the 1990's, mining companies are under great pressure to reduce costs and improve gold recovery. Most studies on the use of resins for gold recovery from cyanide solution or pulp have shown that this technology has the ability to achieve both these goals. Resins can also be used to recover and recycle free and complexed cyanide in gold plant tailings, which has the potential to significantly lower operating costs, and latest developments in this area of technology are discussed. Finally, recent studies on thiosulphate leaching of gold have'shown that this process is very well suited to the treatment of carbonaceous, preg-robbing ores from the Carlin trend (Nevada, USA), and elsewhere in the world, because the gold thiosulphate complex does not load on to carbon. Whilst this obviously benefits the leaching process, it means CIP and CIL are ineffective in this situation, and the use of ion-exchange resins for gold recovery from thiosulphate leach solution are discussed.

Jan 1, 1998

By M. Waladan

The top submerged lancing Sirosmelt system has been developed through laborator.y scale testwork and pilot plant trials for recovery of zinc from ISF slag. The effects of the process variables of gas injection rate, method of coal feeding, and temperature on zinc fuming rates were studied in the laboratory. It was found that the rate of zinc elimination was dependent on all of these variabl.es. The rate of zinc removal from slag was independent of zinc content of slag down to approximately 1.5% Zn, below which the rate was proportional to zinc content in slag. Pilot plant trials were carried out to evaluate a proposed process and results followed predictions from the laboratory scale tests. A comparison of the proposed process with conventional slag fuming operations is made and it is shown that the process has a number of advantages which have a significant impact on the economics of zinc slag fuming.

Jan 1, 1990

By Kevin L. Gering

A detection method and apparatus have been developed to perform real-time measurement of aqueous free cyanide, C-. A laboratory prototype can measure cyanide ranging from 5 micrograms ,per liter to 100 milligrams per ?liter for analysis times as short as 2 minutes per measurement. Sample size per measurement is typically only a few mI, thus? minimizing the waste volume produced from spent samples. The basis for this detection device is a quantifiable, stable affinity between the electrode material and free cyanide in the sample; The electrode exhibits piezoelectric behavior, allowing it to be used as a microbalance. This technology 'has experienced two generations of laboratory prototypes, and has been thoroughly tested to determine the operational sensitivity toward process variables such as pH, competing reactions, etc. The speed and ,accuracy of this method make it superior to conventional wet chemistry methods used for quantifying cyanide levels in water. A device based on this technology could be useful in areas involving process monitoring and environmental compliance, .particularly in the cyanide-based leach mining industry. Interest for this detector has been shown by the gold mining industry and others. Patent application is in progress.

Jan 1, 1998

By Graham Cooke, Abhishek Lahiri, Animesh Jha, E. Jeya Kumari

"CO2 reduction by alternative energy devices such as wind-power, electric vehicles utilize rare-earth elements (REE) in several forms; such as in piezo-electric devices, batteries and magnetic materials. In 2010, the 95% of Rare Earth supply is controlled by China, compared to USA being dominant supplier in the 1980s. The dependence upon a single source of lanthanides has prompted the utilization of lower grades of titaniferous mineral concentrates, which often have rich seams of REE. We propose a new methodology, which utilizes the low-grade minerals for the extraction of synthetic rutile and also significant quantities of REE. We demonstrate the alkali roasting of lower grades of mineral concentrates and subsequent leaching in an aqueous medium for preferential flocculation of REE during the extraction of synthetic rutile. Changes in mineral structure during alkali roasting and leaching determine flocculation of REE and permit their separation at the front end of unit process.The physical chemistry and crystal structure of minerals in equilibrium with alkali and aqueous medium play an important role, which we explain by demonstrating the changes in the crystal structure. The quantification of separation of RE oxide via chemical analysis suggests that it may be possible to separate rare-earth oxides between 50 and 80% of the initial concentration in the non-magnetic fractions of ilmenite, for example. The microstructural and X-ray diffraction analysis points out that the presence of alumina and roasting with potassium based alkali enhances the separation and flocculation of rare-earth elements at the front end of the process after roasting. The process allows the recovery of CO2 generated by recycling into the process for the regeneration of alkali."

Jan 1, 2011

By J. W. Matousek

Cobalt behavior in pyrometallurgical processes is traditionally analyzed using slaglmatte distribution coefficients as functions of matte grades or matte iron contents. L(s/m) = (%Co) I [%Co] = f [%CuNi] or f [%Fe] The method is inconvenient to use in predictive mass balance work because of the interdependence of assays and mass quantities. An alternative procedure is proposed based on cobaltliron ratios for slags and mattes: Js = (%Co) / (%Fe), Jm = [%Co] / [%Fe], and J, = b + m [Jm]

Jan 1, 1993

By T. C. -M. Cheng

Iron removal and disposal in zinc plants has imposed a major environmental challenge to the industry. Among the existing options of precipitating iron as jarosite, goethite, and hematite, the Hematite Process seems to be the best candidate for the future development of a waste-free technology, because of its potential of producing saleable iron oxide residues for feed in iron-steel making industry. Unfortunately, under the current practice of the Hematite Process, it is not possible to produce iron residues clean enough to meet the specifications of the said industry. In this paper, the practice of industrial hematite precipitation and the relevant technical literature are reviewed with the objective to identify the critical processing parameters which are responsible for the contamination of hematite, particularly with sulfur and zinc. The analysis is conducted from a crystallization theory standpoint with emphasis given to the role of supersaturation with respect to the cleanliness of hematite precipitates.

Jan 1, 1997

By Yang Xianwan, Zhu Xiaoyun, Guo Zhongcheng, Zheng Yanping, Zhai Dacheng

"Corrosion resistance of RE-Ni-W-P-SiC composite coating and 3 l6L stainless steel in corrosion media of H2SO4, HCl, H3PO4 and FeC13 solutions at different concentrations by means of immersion methods and anodic polarization curves obtained by DHZ-1 electrochemical synthetic tester and HDV-7 transistor constant potentiometer. Immersion experiment results show that corrosion rate of RE-Ni-W-P-SiC composite coating as-deposited in HCl solutions increases with the rise of HCl concentrations, on the contrary, the corrosion rate of the composite coating after heat treatment decreases with increasing the HCl concentrations the corrosion rates of the coatings as-deposited and after heat treatment in H2SO4 and H3PO4 solutions respectively decrease with the rise.of H2SO4 and H3PO4 concentrations the corrosion rate of the deposit as-deposited in FeC13 solutions decreases with increasing FeC13 concentrations, while the rate of the composite coating after heat treatment increases .with the rise of FeC13 concentrations.In addition, the corrosion rate of 3 l 6L stainless steel in the corrosion media of H2SO4, HCl, H3PO4 and FeC13 solutions at different concentrations increases with rising of concentrations. Furthermore, the corrosion rate of 316L stainless steel in the corrosion media of H2SO4, HCl, H3PO4 and FeC13 solutions respectively is much greater than that of the RE-Ni-W-P-SiC composite coating as-deposited and after heat treatment in the same corrosion media.1. IntroductionAll the materials and their products, when processed, stored and used, it is inevitable that the corrosion, wear, fatigue and crack occur owing to the actions of surroundings. Those early failure and abrasion, through all kinds of departments and profession that corrosion consumes one percent of tens of the steel products of the whole world; and two or four percent of the GDP is lost because of the corrosion."

Jan 1, 2000

By Jayagopal Ucbil, M. Krishna, V. T. Vijayalakshmi

"The pitting susceptibility of aluminium metal matrix composites reinforced with garnet particles has been examined using static weight loss method by exposing the metal matrix composites (MMC) specimens to the action of IN HCI acid at laboratory temperature for different time intervals. It was found that the corrosion rate decreased with increase in weight percentage of reinforcement while the corrosion rate was a function of the matrix alloy but not of the reinforcement material. Further, it was found that the rate of corrosion was dependent on the interface region formed between the reinforcement and the matrix. A comparison of the base matrix with the corresponding composite when subjected to heat treatment for varying periods of 4, 8, and 12 hours respectively was made. The comparison revealed that corrosion resistance of the composite increased with the duration of heat treatment and this has established a considerable improvement in corrosion resistance of the composite when compared with the base matrix.IntroductionMetal matrix composites (MMCs) offer designers many added benefits, as they are particularly suited for applications requiring good strength at high temperature, good structural rigidity, dimensional stability, and light weight [1-5]. The trend is towards safe usage of the MMC parts in the automobile engine, which work particularly at high temperature and pressure environments [6-7]. Particles reinforced MMCs have been most popular over the last two decades. Among the MMCs, the most popular families are represented by aluminium reinforced with ceramic particles. Although the incorporation of the second phase into a matrix material can enhance the physical and mechanical properties of the base metal, it could also significantly change the corrosion behavior."

Jan 1, 2000

By D. Neuschiltz, M. Witthaut, R. Cremer

"Metastable (Ti,Al)N coatings with fee structure have been shown to exhibit superior performance as compared to TiN under conditions of wear at elevated temperatures due to their better oxidation resistance and hardness. The oxidation resistance of these coatings increases significantly with increasing Al-content. However, the deposition of (Ti,Al)N films with Ti/ Al ratios below about 30/70 leads to a hexagonal structure which is not suitable for tribological coatings. Only little is known about the location of the cubic to hexagonal phase transition and hence about the optimum composition of (Ti,Al)N hard coatings.To determine the position of this transition, Tii-xAlxN films with different Ti/Al ratios were deposited on high speed steel at substrate temperatures between 100 and 700 °C by means of reactive MSIP. The composition of the films was determined by electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS), the crystallographic structure by thin film X-ray diffraction (XRD).It could be shown that in case of deposition temperatures of 300-700 °C a two-phase region exists in the metastable TiN-AlN phase diagram, which expands with increasing temperature, wheras at 100 °C substrate temperature no two-phase region was observed. But in opposition to the phase diagram known from literature, which is based on thermodynamic estimations, the detected two-phase region is narrow for typical PVD temperatures, thus allowing the deposition of cubic single-phase Al-rich (Ti,Al)N hardcoatings for tribological applications. Based on these results, a new Ti1-xAlxN film with x = 0.62 has been developed, which showed an increase of oxidation resistance by a factor of 4."

Jan 1, 1998

By Mark Tjerkstra

In ,1993, the WMC Resources Ltd.-owned Kalgoorlie Nickel Smelter, underwent a capacity upgrade. This capacity increase was offset by .air quality control restrictions limiting the smelter's availability to 80%. As the direct. result of this limitation, WMC Resources Ltd commissioned a double absorption contact ,acid ,plant for the desulphurisation of furnace waste gas in August 1996. The history and the impact of the acid plant on S02 emissions and air quality is reviewed. General descriptions of the other aspects of the Kalgoorlie Nickel Smelter's Environmental Project are also included in the paper. Information on 'the design features? and operating practices that relate to or contrast with practices at operations visited by KNS personnel prior to acid plant commissioning provide the paper's focus. Smelter operation has changed markedly from unstable operation prior to 1997 to continuous" operation with little down time due to mechanical or process failures resulting in increased smelter availability to more than 90%

Jan 1, 1998

By David G. Dixon

A mathematical model is derived in dimensionless form which simulates the effluent concentration response of reagents from spent heaps under both fresh and recycled water rinsing. The model is based on dispersion from isochoric pathways distributed in length and cross-section, oriented normal to convection channels in ideal plug flow. The effects of heap height, rinsate flow, and initial reagent concentration are examined. It is shown that the rinsing cycle undergoes a distinct shift between fast and slow rinsing at a certain time depending on the amount of stagnant solution in the heap, and the distribution of dispersion pathways. Results of preliminary column rinsing tests on both agglomerated and unagglomerated ores are presented which partially validate the model.

Jan 1, 1994

By P. F. Stratton, M Huggahalli, N Saxena

"Several studies have been carried out to determine how the optimum atmosphere conditions in the heat treatment of metals can be established for a given product by using different gas injectors and varying atmosphere flow rate and composition. The most common approach taken to gain insight into furnace atmospheres has been to use commercial computational fluid dynamics codes and examples of their use are shown. However, the complexity of these codes, the difficulty in establishing boundary conditions, their cost and computational demands limit their usability in solving day-to-day production problems.A simplified, web-based model of a furnace atmosphere is described where the conservation equations are solved to determine the composition profiles of the atmosphere in the furnace. Although the model is restricted in scope to certain types of furnace, it is shown to give better results than CFD when boundary conditions are uncertain. The application of the model to the understanding of existing furnace conditions and to determining ways of optimising the use of gases are discussed. IntroductionThe important role of protective atmospheres during heat treatment of metals, furnace brazing of assemblies and soldering of printed circuit boards is well established. The atmosphere in the furnace prevents air ingress and oxidation of the parts, helps flush away any flux or binder from braze and solder pastes and provides an important mode of heat transfer [1]. In a batch furnace having typically one or two gas injectors, the gas utilisation and process can be optimised by minimising air leaks and mantaining atmosphere homogeneity with fans or other atmosphere circulation techniques. In a continuous furnace, however, atmosphere optimisation is more difficult as furnace inlets and exits can also let in air. The atmosphere requirements of different stages of heat treatment, brazing or soldering vary [2]. Achieving these atmospheres in different sections of the open-ended furnace is a relatively complex task. Methods such as atmosphere zoning and the use of physical curtains and gas injectors have evolved with time, though it is hard to predict how effective these techniques will be for a given furnace and process. Experts in the field tend to rely on experience and rules-of-thumb rather than scientific method to achieve the required results."

Jan 1, 2001

By Ray Y. Lin, Randall A. Blue

"Joining of silicon carbide with infrared using a mixture of Si-30wt.%C as the brazing material has been investigated. Joining was performed at a temperature of 1500 °C in a flowing argon atmosphere for processing times ranging from 5 to 60 seconds. The joining filler materials include thin film silicon obtained by thinning down silicon wafers to about 70 /!m and graphite powder of a 15 /!m average particle size. Joint strengths were determined with a specially designed shear-in-compression jig for testing shear strengths of brittle materials. Cross section examinations of the joined specimens with optical microscopy, scanning electron microscopy and transmission electron microscopy have shown that all joints are essentially void free with excellent wetting between the base SiC and the brazing material. Silicon carbide in the B form has been identified as the reaction product in the joining zone with a transmission electron microscope (TEM) and selected area diffiaction (SAD) analysis. At 1500 °C with a joining time of 60 seconds, the joint has consisted of primarily SiC. With such a high SiC content in the joint, the joint strength is comparable to those by other joining techniques, such as diffusion bonding, as reported in the literature. A kinetic model for the formation of SiC from liquid silicon and carbon is proposed to explain the observed joint microstructural evolution.IntroductionSilicon carbide is of great interest for high temperature structural applications because of its excellent high temperature strength, wear resistance and anticorrosive characteristics [1]. Even though the interest in SiC is high, the use of the material has been limited by the high cost and difficulties involved in forming components of complicated shapes [2]. It is these limitations that necessitate the development of effective joining techniques that are cost effective and able to provide strong joints."

Jan 1, 1996

By M. A. Neri

A lead-free solder alloy Sn-57.5Bi-0.5Ag has been developed by mechanical alloying and foundry processes, and has great potential as a lead-free solder system, to low temperature applications. The mechanical alloying powders show a microstructure different to the microstructure obtained by the foundry process for the same alloy. Its melting point of 142°C is slightly higher than that of eutectic tin- bismuth solder. Examination of the microstructure revealed that eutectic microstructure is refined by the mechanical alloying process Ag additions. The lamellar structure of tin-bismuth gradually disappeared with the process of mechanical alloying, while intermetallic compounds AgaSn phase was formed. The Cu-Sn intermetallic compound layer formed at solder-copper interface is the Cu6Sn5 phase. Keywords: Lead-free solder, Microstructure. Mechanical alloying

Jan 1, 2003

By Garth James

Bacterial consortia capable of degrading cyanide and metal-cyanide complexes were obtained from gold mine process waters using enrichment cultures. The cultures contained either cyanide, tetracyanonickelate, or ferrocyanide as a sole nitrogen source. Several bacteria were isolated from the consortia, but none of these organisms were capable of degrading cyanide or cyanide-metal complexes at rates equivalent to those of the intact consortia. The consortium from the cyanide enrichment was capable of completely degrading cyanide from an initial concentration of over 100 ppm in less than one day, when cultured using a fed-batch method. Tetracyanonickelate and ferrocyanide were degraded more slowly. Overall, these results demonstrate that bacteria capable of degrading cyanide and cyanide-metal complexes can be isolated from mine process solutions and are capable of significantly reducing cyanide concentrations under appropriate conditions.

Jan 1, 1998

By Mariane Costalonga de Aguiar, Carlos Mauricio Fontes Vieira, Sergio Neves Monteiro

"This work evaluates the effect of incorporation of an ornamental rock waste into an industrial clayey body used for roofing tiles fabrication. Formulations with 0, 10, 20 and 30 wt.% of waste were prepared by replacing the sand in the industrial clayey body. The plasticity of the formulations was determined by the Atterberg limits. Specimens were fabricated by 18 MPa press-molding and then fired from 850, 950 and 1050°C. The specimens were tested to determine the water absorption, linear shrinkage and three points bending flexural strength. The results indicated that the waste improves the extrusion performance of the clayey body by decreasing its plasticity. The use of the waste was beneficial to the water absorption and mechanical strength of the fired clayey ceramic at 1050°C.IntroductionOrnamental rock is a natural resource available in the municipal area of Santo Antonio de Padua and located 150 km from the city of Campos dos Goytacazes, northe of state of Rio de Janeiro, Brazil. Intense industrial activity related to ornamental stones, especially gneisses, is traditionally occurring in the region. After mining, the flagstone is submitted to sawing to obtain blocks and then, after a manual operation, the final products are small flagstones [1,2]. During the sawing operation, a sludge composed of water and fine particles of rock is generated. A monthly production of 1000 tons of ornamental rock waste is estimated to be produced at Santo Antonio de Padua. The final disposal of this waste has brought serious environmental problems. Since most industries do not have an adequate sludge treatment, the waste is contaminating the soil and underground waters as well as obstructing rivers and lakes.Ceramic bodies industrially fabricated in the municipal area of Campos dos Goytacazes, 280 km from the city of Rio de Janeiro, are still empirically elaborated using a mixture of local clays. These clays are predominantly kaolinitic mineral, associated with high plasticity. Due to the excessive plasticity of the ceramic bodies, it is common to have dimensional defects in the final products after the drying and firing processes. Moreover, the kaolinitic structure and the presence of aluminum hydroxide confer a refractory behavior to the local clays. This impairs sintering during the firing operation. In the case of clay ceramics for civil construction, this results in greater porosity associated with elevated values of water absorption [3,4]. To avoid this problem, it is necessary to reformulate the ceramic body composition. The addition of both non-plastic materials to reduce plasticity and fluxes to condition the refractoriness is a possible alternative."

Jan 1, 2011

Primary sulphidic gold ores in the Archean provinces of Western Australia can be broadly sub-divided into pyritic, pyrite-telluride, arsenical and antimonial types. Pyritic ores contain only native gold, and are essentially not refractory. Arsenical ores almost always carry some invisible gold, and may vary from mildly to highly refractory. Pyrite-telluride ores contain gold-bearing tellurides, and are refractory to varying degrees. Antimonial ores usually contain aurostibite, and may be very difficult to process. A classification scheme for metallurgical processing, based on mineralogy, is proposed for the ores, and implications for processing are discussed.

Jan 1, 1995

By F. Ajersch, P: Tsantrizos, K: Shanker

"TiN films have been deposited on various substrates by a novel reactive plasma technology. In this process, a nitrogen source (NH3 or N2) and TiCl4 are reacted in the jet of a plasma torch, and are deposited onto a substrate forming TiN films at a high growth rate ( > 2µm/min). It was found that the process parameters strongly affect the microstructure, thickness, density, and growth rate of the TiN films. These parameters include source of nitrogen (NH3 or N2, N/Ti ratio, temperature of substrate, and spray distance. In general, it was found that thick and dense coatings were deposited when the N:Ti ratio was kept low, and the substrate temperature was high. Also, for the series of conditions investigated, NH3 was found to give much better results than N2•. The limitations and advantages of this technique are also discussed in this paper.IntroductionTiN is an extremely hard material and is used in many wear applications, particularly as a protective coating on cutting tools to extend their Iife(1.2). Owing to its excellent chemical stability, TiN is also frequently used as a diffusion barrier in the electronics industry for sub-micron Al/TiN/Si ohmic contact systems (3) or as a coating on high-temperature resistant alloys in gas turbine applications (4), based on its good resistance to oxidation. Other applications include decorative coatings in the jewelry industry, and specialized applications such as solar energy absorbers and transparent heat mirrors(5).TiN films can be deposited/formed using various techniques. The main techniques of deposition are CVD (Chemical Vapour Deposition) and PVD (Physical Vapour Deposition). Each of these techniques can have many variations in equipment characteristics, reactants as well as a range of process parameters (pressure and temperature). In the CVD process, TiN is generally deposited onto a heated substrate where a chemical reaction takes place. The reaction can be one of reduction(6) (e.g.: TiCI4 + 0.5N2 + 2H2 --> TiN + 4HCI), of thermal decomposition(7) (e.g. decomposition of titanium dialkylamide), or of displacement (e.g. TiCI4 + NH3 --> TiN + 3HCI + 0.5CI2)' The displacement and reduction reactions are the most common."

Jan 1, 1994

By Dhanesh Chandra

Metal carbonyls are of great importance in chemical vapor deposition (CVD), composite materials fabrication, and other near-net shape technologies. Carbonyl CVD application applies to deposition of high-purity metallic/alloy coatings. Vapor pressures of solid Os3(CO)12,Rh6(CO)16, Ru3(CO)12, Ir4(CO)12, Re2(CO)10, Co2(CO)8, Cr(CO)12,, and W(CO)6carbonyls have been measured using gravimetric-torsion effusion system. The vapor pressure data is used for many low and high temperature CVD applications. Interesting decomposition/disproportionation vaporization behavior has been notedfor Rh6(CO)16, Ru3(CO)12 and Co2(CO)8. The vaporization studies of Rh6(CO)16 showed virtually complete decomposition to Rh metal and the measured molecular weight of the effusing gas from the solid Rh6(CO)16 was 27.75 g/mol, close to that of carbon monoxide as compared to 1065.56 g/mol for the value of solid Rh6(CO)16. Electron microscopic characterization, X-ray line broadening results for Rh carbonyl has been performed on the vaporization product. However, Ru3(CO)12, Co2(CO)8 showed very complex behavior. The molecular weights of the vaporizing species have been estimated and the numbers of vaporizing species are proposed. For example, there was partial decomposition of Ru3(CO)12to(approx. 52%) metallic Ru and CO gas during vaporization, as suggested by the difference in the molecular weight of the vaporizing species of 107.58 g/mol compared to the actual value of 639.33 g/mol. The dimer Co2(CO)8 partially disproportionates to tetramer Co4(CO)12, monomer Co(CO)4, and CO gas. Whereas, the Os3(CO)12, Cr(CO)12,, and W(CO)6have shown virtually no disproportionation. The total vapor pressures of all the above-motioned carbonyls, partial pressures of various species, average molecular weights of the effusing gases, equilibrium constants for the vaporization reactions, their enthalpies, entropies, and Gibbs energies will be presented.

Jan 1, 2006