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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 Patricio Barrios

The Rio Tinto Metal (RTMetal) copper smelter, located 5 Km from Huelva, Spain, began operations in 1970. Since then a series of expansions and modifications have allowed a progressive increase in copper production. Environmental considerations having become increasingly important, environmental protection has come to represent an important aspect of the investments in production. As a result, modifications have been carried out in the two existing acid plants: -Modification of the RTM I gas cleaning section to closed circuit. -Substitution of cascade filters and acid lines. -Modification of the RTM I plant to double absorption. The Expansion and Environmental Improvement Project, completed end 1995, will allow 270,000 t Cu and 800,000 t H2SO4 to be produced yearly, at the same time achieving a decrease in specific and overall emissions. RTMetal's goal is to be an efficient smelter, with the avowed intention of respecting the environment and adopting the best available technologies.

Jan 1, 1996

By Rudolf Keller

"EMEC Consultants is developing a process to extract oxygen, aluminum and silicon from lunar anorthositic soil. The process will provide oxygen in space for propulsion, aluminum as a structural material, and possibly silicon for the construction of solar cells.The evolution of the process concept in the course of our present NASA-sponsored SBIR effort is discussed. A molten salt electrolysis producing aluminum and oxygen is the central step; inert anode technology is to be employed. Silicon will be produced by reducing the anorthite, CaAI2Si20S' with aluminum. In a steady-state operation, all components of the ore added have to be removed from the process, and the removal of calcium is a major topic of our experimental studies.Utilization of Lunar ResourcesUtilization of lunar resources may play an essential role in the exploration of the solar system and the conquest of space. High costs are involved in overcoming Earth's gravity to supply missions in space. Even at a low projected cost of $ 300 for transporting a pound of payload into Earth orbit -- today's costs are many times higher -- it appears attractive to use resources in space to produce needed materials. Processing of lunar resources on the lunar surface is an obvious possibility.Oxygen is a product of major interest. It is required for support of human life in space. Even greater quantities may be needed for propulsion, to conduct further missions into space. To satisfy this demand for oxygen through lunar processing requires a quite different solution than to supply oxygen on Earth, where oxygen gas is abundant and easy to extract from air or water. On the lunar surface, solid oxide materials have to be used. Hydrogen reduction of ilmenite and subsequent electrolysis of the resulting water is being studied [1]. Other suggestions include fluorination of lunar soil [2], reduction with lithium and electrolytic decomposition of the resulting lithium oxide [3], and aqueous HF leaching [4]."

Jan 1, 1988

By Aïda Espinola

Decontamination of synthetic solutions containing cadmium ions using coconut fibers in natura was investigated in laboratory scale. Cadmium ions, a serious pollutant of water ways, where it is detrimental to the environment, may be absorbed by fish and mollusk used as food, which will, eventually, poison humans; these ions are usually present in minero-metallurgical and electroplating industrial effluents. Usually employed for the aqueous effluents treatment are chemical precipitation, adsorption and electrolytic processes. Precipitation is not effective for cadmium removal, because of the high KpS of the cadmium hydroxide, which requires high pH; only sulfide would be efficient in cases of very small amounts. Some vegetal refuses have shown to be practical for absorption processes of several metallic ions. We have applied coconut (Cocos nucifera) shells, which are extremely abundant over most of the extensive Brazilian coast, in the removal of cadmium: it has been verified, in our laboratory, that the surface of the fiber of this coconut is rich in chemical compounds which are active scavengers for Cd2+. For the optimization of the process, hydrosoluble components existing on the surface of the fiber, which may be deleterious, were previously washed out by water, and variables, such as the pH and the proportion of mass of fiber to volume of solution, were adjusted. As much as 99% of the initial contaminant metallic ion has been eliminated, resulting a solution to be discarded which contains ca. 0.1 ppm; this attends to the maximum impurity legally admitted by the environmental control agency of Rio de Janeiro, FEEMA, for cadmium ions in aqueous effluents to be disposed in rivers and in the Guanabara Bay area.

Jan 1, 1998

By D. A. Robbins

The Resource Conservation and Recovery Act. of 1976 (RCRA) requires testing of waste materials as part of the determination of whether these materials are classified and managed as hazardous wastes. The adoption of one standard testing procedure and its application to all types of waste materials has stirred much controversy. In the center of this controversy is the appropriateness of this testing procedure in characterizing non-ferrous metal intermediates and slags. The authors have evaluated the relative availability of metals in several types of copper and lead slags as defined by various testing protocols. Also discussed is the relationship between the chemical character of the slag and the availability of metals to leaching and certain metallurgical practices that can influence metals availability.

Jan 1, 1983

By L. J. Lutz

The U.S. Bureau of Mines has developed an electrorefining process to recover Ni, Co, Cr, and other metals from mixed and contaminated superalloy scrap. The superalloy scrap is cleaned then directly electrodeposited as a Ni -Co deposit. The process recovers approximately 90 pct of the Ni-Co available from the scrap as a 99t pct pure Ni-Co alloy. During electrorefining the electrolyte undergoes a purification process which results in Cr and other refractory metals reporting to the purification residue. Operating data is given for a 3-L compartmented electrolytic cell. Techniques for the removal of Fe, Cr, and trace impurities from the recycled electrolyte are outlined. The economics of a facility producing 15 mt/d of a Ni-Co alloy are also discussed.

Jan 1, 1993

By G. B. Harris

Much has been written over the past decade concerning the disposal of arsenic from metallurgical processes. In Canada, there are proposed regulations which would classify arsenic in the Primary Group of twenty one persistent, toxic pollutants to be banned or phased out. Since many nickel and cobalt ores, not to mention those of copper, gold and uranium, contain significant amounts of arsenic, it is pertinent to assess the current state-of-the-art of its disposal. The literature is reviewed, and it is demonstrated that from a purely chemical point of view, the family of ferric arsenates largely immobilize arsenic. There is clear evidence from laboratory studies that both crystalline ferric arsenate (scorodite) and amorphous ferric arsenates in which the molar Fe/As ratio is at least three (Fe/As = 3) have very low arsenic solubility; plant data are given to support this. The debate over the long term stability of these compounds continues however; the evidence presented for long term stability and for compound breakdown is critically reviewed in the light? of the recent structural studies, and the role of base metals in these compounds evaluated. Finally, conclusions are drawn as to the viability of a purely chemical process for the long term disposal of arsenic from metallurgical processes.

Jan 1, 1993

By W. Riekehof

The paper explains required practice and equipment for capturing airborne fumes and particulates in hot-dip zinc galvanizing plants. An economic and technical comparison of enclosure and tank rim suction options is presented. The paper also compares the performance of various filter media in filtering fumes, to determine the effect of changes in flux as well as changes in filter finishlcoating methods. This includes a recommendation for how to achieve the best result with respect to pressure loss and cleaning behavior of the filter.

Jan 1, 1992

By David G. Dixon

Although the kinetics of leaching processes are of paramount importance in the design and analysis of nearly all hydrometallurgical flowsheets, these concepts remain poorly understood and, as a result, are only rarely applied to mass and heat balance models. In this second of two papers, we demonstrate how simple yet powerful models of leaching kinetics and other rate processes may be added to mass and heat balance models, and apply these concepts using a spreadsheet model of a simplified pyrite autoclaving flowsheet. In particular, we focus on the interpretation and scale-up of batch leaching data, and on simple means for modeling other phenomena commonly associated with leaching, such as reagent depletion, gas-liquid mixing, and the precipitation of oxides and basic salts.

Jan 1, 2002

By E. M. Weenink

One of the new direct smelting technologies for the production of lead from sulfide concentrates that has reached the commercial stage is the Outokumpu lead flash/electric furnace ?smelting process. Using data from pilot plant test work, energy and mass balances for a commercial plant were initially calculated by hand. To optimize process conditions, a large number of such balances had to be generated and a computer program using Lotus 123 was developed which provided an excellent opportunity for computer simulation. Operating parameters can be calculated by iteration using input values for feed composition, feed rate, smelting temperature, and lead content of the slag'" The output is presented by means of various views of the appropriate process steps, or in 68 different graphs.

Jan 1, 1990

By Keizo Uematsu, Satoshi Tanaka, Nozomu Uchida, Ronne Hendrajaya

"The influence of microstructural defects on strength in Si3N4 is reviewed. The presence of cracks, pores and inclusions greatly affects the strength of Si3N4. The micron order crack size and distribution were quantified by micrographic technique. The observed defect size was range from 4 µm to 28 µm.The density of defect increases as the defect size decreases. The correlation between defects size and density was better represented on the logarithmic graph. The correlation was linier. IntroductionFracture in ceramics materials occurs from. In order to understand the relationship between strength and defects, it is necessary to examine the fracture process quantitatively.1In this study, the micrographic technique is used to determine the defects size and distribution in Si3N4. The observed data will be used to predict the material strength by using fracture mechanics rnodel.2Experimental ProcedureThe sintered Si3N4 specimens ( SNl, Japan Fine Ceramics Center) were sliced into 1mm thick . The both sides of specimen surface were polished into by using diamond slurries with particle size down to 2µm. The final thickness was 0.045 mm. The optical microscope (NIKON OPTIPHOT02-POL) was used to observed the internal defects with transmission mode. The reflection mode was used to determine the surface defects, so that the internal defect could be distinguished from surface defect. The measurement and counting was taken on the micrograph and the longest part of the defect was measured as the defect size. The size density distribution of internal defect is taken."

Jan 1, 2000

By Veneta Groudeva

A pyritic ore containing zinc, lead and copper as? the relevant primary sulfide minerals, .as well as gold and silver finely disseminated in the sulfide matrix, was? leached in percolation columns. Each column contained 30 kg of ore crushed to minus 10 mm. Firstly, zinc and copper were efficiently leached by means of chemolithothrophic bacteria? in acidic sulfate bearing medium. Zinc was leached more rapidly than copper but the final extractions of these metals were similar (about 75% in 300 days). A part of the galena was oxidized to the. insoluble lead sulfate during the leaching. The pyr:ite was, however, relatively slightly attacked. The ore was then leached by means of FeC11 - HCl solutions both in the presence and in the absence of bacteria to solubilize the lead. The chemolithotrophic bacteria grew in media containing both chloride and sulfat~ ions and maintained a high ferric to ferrous ion ratio in the percoiating solutions. The chemical leaching was, however, more efficient since ft was possible to carry it out at higher chloride ion concentrations. About 10% of the lead was leached in this way in 90 days. Finally, the ore was leached by thiourea in the presence of a gold-oxidant (oxone) to extract the gold and silver. Over 60% of the gold and over 55% of the silver were extracted from the ore in 150 days, while. the extractions of these precious metals from an untreated ore sample were lower than 25%.

Jan 1, 1991

By Rune Gammelsmter

Turbulent chemically reacting flows are generally very complex, involving interactions of chemical, thermodynamic, and fluid mechanical processes. A combustion model based oh algebraic moment closure has been developed. The model is applicable for reaction rates where the chemical kinetics can vary from slow to fast. The effects of turbulence is taken into account by means of modifications to the well known k-e modelling procedure. The model is applied to an industrial combustion process. Calculation of furnace off-gas combustion from an aluminum reduction cell has been performed. The theoretical results agree well with experimental values.

Jan 1, 1992

By O. Forsén

A new cell construction was designed for the study of the electrochemical behaviour of additives in conditions that simulate real copper, electrorefining. The behaviour of gelatine and thiourea was studied by applying different electrochemical methods, i.e. polarization resistance and voltametric measurements. In this study, individual galvanostatic electrolysis experiments were carried out for 120 hours. The organic additives were introduced to the electrolyte at certain intervals and their concentration was varied in the range &om zero to four ppm. An optical microscope was applied for the examination of copper cathode deposit microstructures. The results show that gelatine has a polarizing effect on the deposition potential of copper whereas even small amounts of thiourea depolarize the electrodeposition of copper. The maximum inhibitor efficiency of gelatine was obtained at a gelatine concentration of slightly lower than two ppm. When both gelatine and thiourea were present in the electrolyte, the depolarizing effect of thiourea exceeded completely the polarizing effect of gelatine. If chloride ions were added to gelatine and thiourea containing electrolyte, the electrochemical behaviour of the system was altered drastically. Chloride ions resulted in the prevailing of polarization effect caused by gelatine while the depolarizing effect of thiourea disappeared in this system. The polarizing effect of gelatine increased until chloride ion concentration of 30 ppm was reached. Also, the above electrochemical phenomena could be detected in the optical examination of copper deposit microstructure.

Jan 1, 1995

By C. R. Bennett

The first phase in the design, development and implementation of a comprehensive computational model of a copper stockpile leach process is presented. The model accounts for transport phenomena through the stockpile, reaction kinetics for the important mineral species, oxygen and bacterial effects on the leach reactions, plus heat, energy and acid balances for the overall leach process. The paper describes the formulation of the leach process model and its implementation in PHYSICA+, a computational fluid dynamic (CFD) software environment. The model draws on a number of phenomena to represent the competing physical and chemical features active in the process model. The phenomena are essentially represented by a three-phase (solid-liquid-gas) multi-component transport system; novel algorithms and procedures are required to solve the model equations, including a methodology for dealing with multiple chemical species with different reaction rates in ore represented by multiple particle size fractions. Some initial validation results and application simulations are shown to illustrate the potential of the model.

Jan 1, 2003

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 Yunhua Gan, Xiaowen Chen, Yang Tong

Experimental studies of electro-spraying were carried out using ethanol as fuel in a microcombustor under combined electric field. And the effects of different electro-spraying modes on the combustion efficiency were analyzed. Results showed that when ring electrode potential was invariant, there were four different electro-spraying modes with the variations of nozzle potentials, which were varying with the flow of ethanol. The cone-jet mode was the stablest one during the whole experimental process. The atomized ethanol was ignited and combusted stably near the steel mesh, the combustion efficiency increased firstly and then decreased along with the increasing of the equivalent ratios, reached the maximum values when the equivalent ratio equal to 1.0. And the maximum values were the highest at the cone-jet mode, and the lowest at the pulsed-jet mode.

Jan 1, 2016

By S. C. Grund

In secondary copper smelting as it is performed at Hüttenwerke Kayser plant in Lünen, tin-and lead-containing flue dusts are produced as intermediate products. These flue dusts are further processed in a hearth furnace. Followed by certain refining operations a saleable tin-lead-alloy is produced. Even though the hearth furnace technology has been in use for this purpose for a long time still its performance undergoes changes in search for optimum processing conditions regarding to the increasing complexity of the raw materials and tightening economical and ecological boundaries. The use of modern statistical tools for the calculation of accurate mass balances is demonstrated for the tin-lead hearth furnace. These reliable mass balances are the basis for any further modelling of the process with the aim of optimization. Incorporating metallurgical knowledge and experience as well as different mathematical modelling techniques, further studies are planned in which the recoveries of valuable and minor elements and their dependency from various process parameters are examined. The aim of this modelling is to optimize the recoveries of the valuable elements, to minimize the energy consumption and the processing costs and thus to keep the process competitive in a harsher economical and ecological surrounding. The modelling principles are transferable to other metallurgical operations and are especially suited for ill-defined pyrometallurgical processes.

Jan 1, 1999

By R. G. Robins

Metal separations based on the selective precipitation of phosphates have a potential application in many hydrometallurgical processes. This paper reviews the literature on the solubility of a number of both divalent and trivalent metal phosphates and presents the result of some additional experimental measurements. The systems examined have been modelled to obtain free energy of formation data for the various species. Computer generated solubility diagrams which are described can be useful in predicting a variety of metal separations.

Jan 1, 1991

By ZhiLong ZHAO, Lin Lin, Zhancheng Guo, Jingtao GAO, Huiqing Tang

Grain sticking often occurs in the fluidized bed reduction of f ine iron ore, which is closely related to the precipitation morphology of metallic iron on the surface of ore particles. In this work, simulating the gas-solid reduction process of iron ore, in situ observations were carried out to investigate effects of doping mineral oxides on the precipitation morphology evolution of metallic iron during reduction of iron oxides with CO. Results indicate that the precipitation morphology of metallic iron is related to the quantity of doped mineral oxides. The minimum mole fraction of doped oxide ( xyOA N ) that can inhibit the growth of iron whiskers is related to its cation radius ( Ax r ), extranuclear electronic layers ( Ax n ) and valence electrons ( Ax q ). Their relation can be expressed as:

Jan 1, 2016