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By David B. George

In spite of the many well-known problems inherent in Pierce-Smith converting, it remains the dominant copper converting process. Continuous copper converting and direct concentrate to blister smelting have been commercially available for over 25 years and now produce approximately 15% of copper smelter production. The two fully commercialized continuous converting processes, Mitsubishi MI Process and Kennecott-Outokumpu Flash Converting, and several emerging converting processes are reviewed with view of their potential, limitations, and environmental performance. Some myths regarding these technologies and Peirce-Smith converting are also challenged.

Jan 1, 2002

By Ana P. Paiva, Marc F. Comella, Sandra S. Reis, Joao N. Reis, M. Soledade Santos

"In this work, the influence of the malonamide structure, acidity of the aqueous phase and diluent on the equilibrium interfacial tension (IT) of N,N'-dimethyl-N,N'-diphenylmalonamide (DMDPHMA) and N,N'-dimethyl-N,N'-dicyclohexylmalonamide (DMDCHMA) in 1,2- dichloroethane (1,2-DCE), and DMDCHMA in toluene, with aqueous HCl, were investigated. IT isotherms were determined using the Du N ouy ring method. Densities of the organic phases were determined, and used to screen solute-diluent interactions. Formation of third phases was never observed; furthermore, ITs increase with the phase separation period, constant values being obtained for separation periods larger than 1000 seconds. Each malonamide interfacial efficiency at the oil/water interface is interpreted in terms of malonamide basicity, diluent polarity and malonamide - hydrochloric acid- diluent interfacial interactions.IntroductionFor several years now, N,N'-tetrasubstituted malonamide derivatives have been extensively investigated as liquid-liquid extraction agents since they were first proposed as the organic components of the DIAMEX process, with the aim of advantageously replacing tributylphosphate in PUREX [1]. Therefore, a significant part of research studies with malonamides appearing in the literature deal with the extraction of major and minor actinides in real or simulated spent nuclear fuels in nitric acid solutions [2]. Under typical experimental process conditions, the tendency shown by some N,N'-tetrasubstituted malonamide derivatives to aggregate in the organic phase, leading in a few cases to the formation of undesirable third phases, has been remarked and consequently thoroughly investigated [3, 4]. The increasing use of chloride streams as hydrometallurgical aqueous feeds is becoming a reality, and this fact is obviously deeply founded on an extensive research carried out to recover value-adding metals from these media. Following this trend, a number of N,N'-tetrasubstituted malonamides have already been screened for the recovery of iron(III) [5, 6] and platinum-group metals [7] from hydrochloric acid solutions. The results obtained are quite promising either in terms of total metal ion recoveries or selectivity patterns achieved. The formation of a third phase when iron(III) was extracted by the tested N,N'-tetrasubstituted malonamide derivatives has never been observed under the adopted experimental conditions, and the extraction data collected would need to be reinterpreted accordingly if any aggregation phenomena involving the considered extraction systems were to take place."

Jan 1, 2011

By Keuncheol Choi, Yonghack Lee

"The new lead smelter based on the QSL technology was started operation from May 1992 at Onsan Refinery of Korea Zinc Co., Ltd. The smelter is designed to treat not only various types of lead concentrate but also secondary materials coming from the zinc plant without special pretreatment.Shortly after the start-up of the operation, it has demonstrated that the smelter have a capability to treat wide range of raw materials. Continuous modifications and improvements of the plant are still under way to increase the feed rate and also the ratio of secondary materials to the feed.In this paper, the operating experience and results of QSL smelter, especially the injection of gases and coal to the melt, will be presented with major operation parameters and data.INTRODUCTIONThe QSL lead smelter based on new injection technology was commissioned at the Korea Zinc's Onsan plant from May of 1992. After starting the operation, the QSL lead smelter faced various kinds of mechanical and metallurgical troubles. However, these were gradually worked out by the continuous improvements and efforts.At present, the QSL lead smelter is operated stably at the total feed rate of 57 tonnes per hour with an increased amount of secondary materials."

Jan 1, 1996

By Andres Vikdahl

The Rönnsktär smelter has recently undergone a series of technical and operational changes. This changes are caused by our own will to remain and gain in competivety and to adapt to the ever changing surroundings. To be able to remain competitive in surrounding with high wage costs, high inflation and high environmental standards thorough cost management is needed. The Swedish economic policy in the beginning of the 80'ies consisted amongst other things of two devaluations. The exchange rate of the Swedish Krona was reduced with approximatively 25 %. This boosted the profits of our export industry, some even believed we entered the land of milk and honey ... And working in this promised land where everything turns into profit it is very difficult to be careful and restrictive with your spendings. Apart from some healthy and fruitful investments we allowed ourselves yearly steady increases in salary for ever reduced number of worked hours and we of course employed more people. Inflation rates went up and so did property prices. In 1986 finally reality catched up on us. Reality in the form of too high costs started to hit Swedish export industry 5-6 years after the big devaluations. Furthermore the high inflation rate also hit the domestic industry a couple of years later. Together with other important factors Sweden faced a severe home-made recession in the beginning of the 90'ies. With this background we now report and analyse our smelter's performance and operating results, shown in fig 1 The main constrictions on smelting and refining at Rönnsktär are today: * Income restrictions by governmental production level Limit * Throughput resmctions by governmental emission limit * High capital costs in the aftermath of Swedish high inflation in the recent decade * Low work force turnover Below we will illustrate how we tackled with these issues along the following lines: * People * Quality * Technology

Jan 1, 1993

By B. A. Paponetti

The following report discusses the bioleaching of chalcopyrite of italian origin catalyzed by Thiobacillus ferrooxidans. The developments vcr.ius time of the main .biochemical and chemical reactions involved in the production of soiuble and insoluble species were investigated focusing on the times at which they begin and bow long they last. The precipitates were characterized both in quantity and in quality relating the rate of the process to the precipitates fonnatiom. A material. balance has been made to verify the proposed mechanism.

Jan 1, 1991

By S. E. James

EAF dust has been listed as a "hazardous waste" due to the presence of lead and cadmium, and at times chromium. The 550,00 tpy production of . .EA]' dust, estimated for the United States alone, contains more than 10,000 tpy of lead and about 250 tpy of cadmium in addition to nearly 1'00,000 tpy zinc. Even though the listing of .EAF dust as a hazardous material stimulated extractive metallurgical work worldwide, process development efforts have focused only on the recycle of the potentially-valuable zinc units. However, the recycle of the lead and cadmium, while not lucrative, is the more critical effort. Horsehead Resource Development Company, Inc. (HRD), in conjunction with its sister company, Zinc Corporation of America (ZCA), has taken a unique approach to total recycle of the toxic heavy metals found in the EAF dust. Impure oxide, produced by either a Waelz kiln or FLAME REACTOR Process and containing the lead and cadmium, is calcined in a rotary kiln at Palmerton, Pennsylvania, to produce a refined zinc-rich intermediate for ZCA's electrothermic zinc plant at Monaca, Pennsylvania. During the calcining operation, lead and cadmium are concentrated in a fume product and shipped to ZCA's electrolytic plant at Bartlesville, Oklahoma. At Bartlesville, a new hydrometallurgical circuit has been constructed and the existing cadmium plant expanded. The combined facilities permit the total recovery of cadmium to refined metal and the lead to .a silver-rich intermediate, which is sold to lead smelters. In this paper the Waelzing, calcining and new leaching facilities will be described.

Jan 1, 1990

By N. Voennann

Stillwater Mining Company operates an electric furnace at its smelter in Columbus, Montana to treat a Ni-Cu-platinum group metal concentrate along with secondary PGM bearing materials. Hatch Associates has designed several improvements to this furnace, which was originally built by others. Implementation of these relatively low cost improvements has resulted in substantial increases in furnace availability and capacity, along with reduced unit costs. ? The improvements included: ? Installation of water-cooled copper cooling elements to stabilize refractory wear and increase furnace life.- ? Improved furnace 'bindings, to enhance the furnace's structural integrity by improving the contact between the refractory and cooling elements, and by promoting tight brick joints resistant to matte or slag leaks. ? Adjustment of the electrode regulator to allow higher furnace power levels. ? Installation of an automated air-slide (aeration conveyor) feed system to evenly distribute the furnace feed in an insulating layer on the bath surface. This "black-top" practice reduces unit energy costs and makes available additional smelting capacity.- ? Electrode seals to reduce ingress of air that absorbs heat before exiting the furnace in the off-gas stream. The saved energy can be used to smelt additional concentrate. This paper describes the above furnace modifications, and the benefits derived from their implementation.

Jan 1, 1998

The generation of acid mine water is? due to the oxidation and weathering of sulfide bearing tailings and overburdens. Ferrite precipitation prooess has been applied to treat acid mine water. The conventional ferrite preC1pitatlon requires air oxidation at high temperature, or long aging time or addition of magnetite powder ,as promoter. In this investigation, a modified ferrite, precipitation process is developed by which magnetic ferrite can be produced at an ambient temperature. Acid mine waters from Berkeley Pit (Montana, U. S. A.) and from Noranda Tailings (Quebec, Canada) were used. The co precipitation of heavy metals from these two acid mine waters is studied as a function of FeIM molar ratio, oxidation time and settling rate under applied magnetic field. The investigation indicates that the modified ferrite co precipitation can remove substantially all of the, dissolved metal ions from acid mine water. The ferrite product obtained after precipitation' is characterized by XRD, SEM, BET and saturation magnetization. The results show that spinel ferrite, precipitation can be achieved at room temperature and the saturation magnetization of ferrite product from,acid mine water is comparable to that of pure ferrites.

Jan 1, 1995

By Xie Zhang, Jiang Diao, Xin Qiu, Lu Jiang, Bing Xie, Hong-Yi Li

"Duplex converter process, in which the first converter is used for removing phosphorus from hot metal (De-P), is an important way to produce low P-content and ultra-low P-content steels. In order to improve phosphorization removal and formation of slag with high basicity at relatively low temperature during dephosphorization converter process, effects of temperature, silicon content in hot metal and varied compositions of the De-P converter slag on phosphorus distribution between the slag and hot metal were investigated with thermodynamic calculations and by laboratory scale experiments in present work. Results showed that phosphorus distribution ratio between slag and metal was varied in 10.6~26.6 when basicity of the slag was in the range of 1.5~2.1 at 1370, and the distribution ratio was increased with increasing basicity and Fe10 content in the slag.IntroductionIt is known that phosphorus exists in steel in the form of solid solution, which can significantly improve strength and hardness of steel at room temperature. However, the plasticity and toughness of steel, especially the low temperature plasticity is sharply reduced and leads to high ductile-brittle transition temperature. This phenomenon is commonly known as cold brittleness of steel [1~3]. Hence, phosphorus should be removed as much as possible in the steelmaking process, because it is generally harmful to the iron and steel products."

Jan 1, 2013

By G. G. Richards

"The slag fuming process has operated for close to 70 years to recover zinc from lead blast furnace slag. The process is normally carried out through the batch treatment of slag by submerged injection of coal and air. Within the bath the coal acts as both a reductant, to reduce Zno to zinc vapour, and a fuel, to maintain bath temperature during the endothermic reduction process. The partition of coal between the slag, combustion and bypass is dependent on factors such as bath depth and injection pressure. The option of continuous fuming has been pursued at the D. Blagoev smelter in Bulgaria using heavy fuel oil as reductant/fuel. There has, however, been little attempt at commercial continuous fuming with coal. This paper presents an analysis of a coal-based continuous slag fuming furnace. The data on the Plovdiv fumer is used as a reference point. Critical design criteria for continuous fuming include the slag feed rate, degree of coal combustion and furnace size. Mathematical modelling analysis suggests that continuous fuming with coal can achieve respectable zinc/coal ratios.IntroductionThe slag fuming process was developed in the early part of this century to recover zinc from non-ferrous smelting slags [1-3]. The majority of installed furnaces were put in place to fume zinc from lead blast furnace slag on a batch basis. In most cases coal is used to effect reduction of zinc oxide, but one furnace uses natural gas [4] and, in a curious twist, a continuous fumer was developed based on fuel oil [5].Given the general nature of blast furnace lead smelting, it is not surprising that slag fuming has remained a batch process, in spite of the advantages that could be gained by moving to continuous fuming. Blast furnaces are usually operated as relatively independent units, and tapping has traditionally been done into ladles. The presence of a crane aisle makes direct coupling of the blast furnace to a slag fumer difficult, especially in a retrofit situation. Furthermore, steady-state blast furnace operation is not easy to achieve. The size of these furnaces and the nature of their feed make it difficult to guarantee constant operation."

Jan 1, 1996

By Batric Pesic

Solvent extraction of nickel and cobalt from the real leach solutions was studied by using a novel extraction system. The extraction system was a mixture of 2,6-bis-[5-n-nonylpyrazol-3¬y]] pyridine (BNPP) and dinonylnaphthalene sulfonic acid (DNSSA). The BNPP represents a novel molecule, which was designed and synthesized in our laboratory. Real solutions for the study were prepared by leaching of two different cobalt-nickel bearing concentrates, cobaltite [CoAsS] concentrate from Blackbird Mine, Idaho, and siegenite [(Ni,Co)3S4] concentrate from Missouri Lead-Belt. The major strength of the system was the selectivity of extraction toward nickel and cobalt from iron containing solutions. Other metals such as Mn, Mg, Ca, Al and As were not extracted. Due to the irreversibility of copper extraction, its removal from solution was required prior to the extraction of nickel and cobalt. Zinc was not as strongly extracted (i.e. its stripping was readily achieved) as was copper . Flowsheets for the recovery of nickel and cobalt were also developed.

Jan 1, 1997

By Lauri E. K. Holappa

Ferrochrome, as the central constituent in stainless steels is one of the most rapidly growing primary metallic products. In this contribution results of a comprehensive study on the reduction process of chromite ore to FeCr are presented including thermodynamic examination, experimental work on kinetics and mechanisms in solid state, and smelting reduction conditions as well as kinetic modelling of solid state reduction.

Jan 1, 1999

By H. Hahn, B. H. Kear, K. Kan, S. C. Danforth, G. Skandan, W. Chang

"A new chemical synthetic process for the production of non-agglomeratednano structured ceramic (n-ceramic) powders, starting from metalorganic precursors, is described. The process combines rapid thermal decomposition of a precursor/carrier gas stream in a hot tubular reactor with rapid condensation of the product particle species on a cold substrate. Critical to the success of this Chemical Vapor Condensation (CVC) process are (1) a low concentration of precursor compound in the carrier gas, (2) rapid expansion of the gas stream through an uniformly heated tubular reactor under a reduced inert gas pressure of 1-35 mbar, and (3) rapid quenching of the gas phase nucleated clusters or nanoparticles as they exit from the reactor tube. A wide variety of metal organic precursors is available commercially, all of which can be utilized in the CVC process to produce n-ceramic powders, including single phase, multiphase and multicomponent systems.The CVC process has been used to synthesize non-agglomerated n-SiCxNy and n-ZrOxCy powders, with controlled particle size in the range 2-20 nm. Heat treatment of the assynthesized n-powders in various high purity gas streams causes compositional and structural modifications, including particle purification and crystallization, as well as transformation to a whisker-like morphology. Thus, as-synthesized amorphous n-SiCxNy particles transform to (1) cubic n-SiC particles, when heated in flowing argon at temperatures> 1350 °C, (2) hexagonal n-Si3N4 whiskers, when heated in flowing NH3IH2 at 1400 °C, and (3) cubic nSiC whiskers, when heated in flowing H2 at 1400 °C.Non-agglomerated n-ceramic powders form uniformly dense powder compacts by cold pressing, which can be sintered to theoretical density at temperatures as low as 0.5 Tm' For example, full densification ofn-Zr02 powder compacts under free sintering conditions can be achieved at 1125 °C."

Jan 1, 1994

By Toshitaka Ota, Hisao Suzuki, Minoru Takahashi

"Perovskite-type lead zinc niobate (PZN) exhibits excellent electrical properties such as high dielectric constant, high electrostrictive coefficient and superior piezoelectricity. Therefore, PZN ceramics are very promising for high performance electronic devices. However, perovskite phase PZN is not stable under the ambient atmosphere. Accordingly, it is very difficult to prepare single-phase perovskite PZN ceramics. In this study, A-site cation of lead was partially substituted for barium to stabilize the perovskite phase of the PZN (Ba-doped PZN) powder. In addition, molecular design of an alkoxide precursor was controlled for a low-temperature processing. As a result, molecular design to suppress the lead-volatilization during calcination was preferred for a low-temperature processing. Processing temperature for a single-phase perovskite was depended on the amount of barium dopant. Doping of20 mole% of barium resulted in the single phase perovskite at 900 °C. The temperature for the single phase perovskite of Ba-doped PZN powder, which depended upon the amount of Ba-doping, was lower than that of the powder prepared by the atmosphere controlled conventional powder processing at least by 150 °C.IntroductionFerroelectric thin films and powders with perovskite structure are of renewed interest for micro-electronic applications, including ferroelectric random access memory (FRAM), dynamic random access memory (DRAM), and thin-layer capacitors integrated onto a silicon wafer [1-3]. In addition, recent advancement in micro-machine requires a high performance micro-actuator [4]. A perovskite type relaxor of Pb(Zn113 Nb213)03 is one of the promising materials for a high performance capacitor and microactuator because of their high permittivity and electrostrictive coefficient [5]. Therefore, this paper focuses on the low temperature processing of Ba-doped PZN powders.Chemical solution deposition (CSD) from molecular-designed alkoxide precursor solution is one of the most promising techniques for processing high-performance powders and thin films because it offers precise control of compositions on a molecular scale as well as a low processing temperature [6]. However, chemical solution deposition of perovskite type PZN powders and ceramics are very difficult because of the formation of stable pyrochlore phases. Therefore in the past, PZN powders and single crystal have been prepared by the hydrothermal method or flux method as well as the partial substitution method of a A-site cation [7-10]. In this study, a suitable molecular design for a preparation of perovskite type Ba-doped PZN powders with a chemical solution deposition process is investigated as well as the effect of A-site cation substitution. Chemical solution deposition from molecular-designed alkoxide precursor solution is expected to decrease the amount of a A-site substitution and/or a crystallization temperature for a single phase perovskite. This paper describes ""the relation between molecular-design and processing temperatures for a single-phase perovskite of Ba-doped PZN powders in comparison with the conventional oxides mixing method."

Jan 1, 2000

By ZHANG Ting

In view of the high consumption and contamination of traditional vanadium extraction technology, a new process of leaching the converter vanadium slag without roasting with titanium dioxide waste was proposed. Extraction mechanism of P204 in the leaching solution had been researched and single factor experiments show that after a prereduction of Fe, and under conditions: ambient temperature，leaching solution original pH=2.5, phase ratio (A/O)=1:3, shaking time 8min, the extraction rate of V is more than 98.62% meanwhile the separation rate between V and Fe is up to 135.3 in the 20%P204-10%TBP-Sulfonated kerosene extraction system.

Jan 1, 2015

By Florian Kongoli

The optimal operation of the blast furnace depends considerably on the properties of the sinter fed into the furnace. As a result, the optimization of the sintering processes has a direct effect on the overall effectiveness of the iron making processes. In order to produce a good sinter special care needs to be taken in order to assure it has a good permeability and reducibility and it is able to retain these properties for a certain time. If the sinter starts to melt down early in the upper part of the blast furnace, where its solid state reduction is essential, permeability decreases, the gas channels get blocked, reductibility diminishes and serious problems may also follow. Among the factors that influences the above mentioned sinter properties are the oxygen potential and fluxing components. Nevertheless, their effect on the phase relations during sintering and sinter reduction conditions has not yet entirely clarified and confusion exists in literature. This quantification becomes even more important today where many new minor components such as Al2O3 and MgO enter the sinter through raw materials. This work quantifies the effect of oxygen potential and fluxing components such as alumina and magnesia on the liquidus and phase relations of the sinter primary melts in the iron rich portion of CaO-FeO-Fe2O3-SiO2 system at sintering conditions. This is carried out by the means of new type of industrial diagrams in the form of Fe/CaO vs. SiO2 that can directly help the optimization of the sintering processes.

Jan 1, 2006

By William J. Mallio

Substantial differences between in situ and conventional technology require that in situ ore grade be established for deposit as distinct from the total contained metal value. Establishing an in situ ore grade involves determining the fraction' of the contained metal that can be leached by the fluid. This depends on the proportion of the ore minerals that occur on fluid flow paths as defined by the permeability distribution. Mechanisms involved in the in situ mining of sulfides are: oxidation of the sulfur, solution of the metals, complexing of the released metals, and a transport to a recovery point. Metal ions may be delayed or lost due to inefficiencies in these pro-cess steps or by reactions of the metal ions in solution with the rock. These reactions can involve precipitation of new phases, exchange of the metals of the interest with Ca or Na in clays or zeolites, retention of metals in oxidized mineral grains, or secondary enrichment of other sulfides along the paths of the solution flow. The efficiency of solution of metals and potential loss or delay mechanisms are controlled by local equilibria (the Eh, pH conditions) present in different parts of the ore zone. Permeability distribution in the rock mass and the coincidence of ore minerais with flow channels must be determined before a deposit can be judged suitable for in situ mining. Laboratory studies indicate that the natural permeability system is dependent on the degree of cementation of veins by late generation hydrothermal activities. The major conclusions of the study are:, 1. Deposit selection is critical; suitable deposit types include deep lying sedimentary deposits, selected zones of porphyry systems and vein controlled hydrothermal deposits; 2. Adequate laboratory and geochemical analyses should be undertaken through quantitative petrographic study and permeability mapping; and 3. Economic incentives for in situ mining must consider limitations of recovery caused by inefficiencies in dissolution and transport associated with particular deposits.

Jan 1, 1981

By M. J. Adam

As part of its research programs, the Bureau of Mines is investigating the partitioning of complex sulfide minerals to simpler sulfide phases by sulfidation reactions. Partitioning in this manner can afford opportunity to improve selective extraction of mineral constituents of value. This report describes research involving the sulfidation partitioning of the mineral pentlandite, which is an important source of Ni in primary production. For the laboratory studies, the pentlandite was synthesized in nominally equiatomic proportions of Ni and Fe. Elemental Ni, Fe, and S powders were blended, compacted, and sealed under reduced He pressure in vitreous silica tubes. The tubes were heated under controlled conditions at SOD? C for 24 h. The product was verified by X-ray diffraction and chemical analysis to consist essentially of (Ni,Fe)9S8. Small samples of the (Ni,Fe) S were encapsulated with sulfur in silica tubes at reduced He pressures and heated for 1 to 24 h at specific temperatures between 400? and 600? C, both below and above the boiling point of sulfur (_445° Cl. Reaction rate increased with temperature. Within this temperature range, partitioning to individual Ni and Fe disu1fides proceeded to essential completion according to the reaction

Jan 1, 1988

By Vinod K. Sikka, René Cooper

"Cohoes, New York 12047 Intermetallics are an attractive class of advanced materials. The aluminide intermetallics offer advantages including: (1) lower density, (2) oxidation resistance, (3) carburization resistance, and (4) interesting mechanical properties because of their ordered crystal structure. Even though the attractive properties of the aluminides and other intermetallics have been known for nearly four decades, their practical applications have not been developed for two reasons: (1) the poor ductility (in some cases, both ambient and high temperatures) and (2) the lack of processability into meaningful components. Recent advances such as ductilization of Ni3Al by small additions of boron and the knowledge that environmental effects are the major cause of poor ductility in Fe3Al and FeAl systems have brought the intelmetallics into the forefront of research and their commercial applications. This paper has described a method for melting Ni3AI-based alloys that successfully utilize the exotherrn for the formation of NiAl from the elemental materials. The reaction-synthesis method has also been utilized for the production of NiAI and NiAI-based alloy powders from the elemental powders. The reaction-synthesized powders of NiAI and NiAI-based alloys were consolidated by hot extrusion and evaluated for tensile properties over a temperature range from room temperature to 1050ºC. The powder-processing conditions have been found to have more influence on the ductile-to-brittle transition temperature of NiAI than the powder-production method.IntroductionIntermetallics are an attractive class of advanced materials [1-11]. The alum in ide interrnetallics offer advantages including: (1) lower density, (2) oxidation resistance, (3) carburization resistance, and (4) interesting mechanical properties because of their ordered crystal structure. Even though the attractive properties of the aluminides and other interrnetallics have been known for nearly four decades, their practical applications have not been developed for two reasons: (I) the poor ductility (in some cases, both ambient and high temperatures) and (2) the lack of processability into meaningful components. Recent advances such as ductilization of Ni3Al by small additions of boron and the knowledge that environmental effects are the major cause of poor ductility in Fe3Al and FeAl systems have brought the intermetallics into the forefront of research and their commercial applications. The paper will briefly review the processing techniques being pursued for the commercial applications of Ni3Al-based intermetallics. The major emphasis of the paper will deal with synthesis of Ni3Al and NiAI intelmetallics."

Jan 1, 1994

By Hu Long

In this, the first systematic study of the oxidation of orpiment (As2S3) in sulfuric acid solution under oxygen pressure at temperatures above 170°C, the effects of retention time, temperature, particle size, oxygen partial pressure, the concentration of sulfuric acid and pulp density were evaluated. The effects of cupric and ferric ions on the oxidation rate of As(III) to As(V) were also examined. The products of oxidation are As(III), As(V), SO42- and elemental sulfur. At temperatures ranging from 170 to 230°C, most of the arsenic was found to be in the trivalent state, and oxidation to As(V) with oxygen was very slow. This was confirmed by attempting to oxidize a synthetic arsenious solution. However, the rate of oxidation of As(III) to As(V) is rapid in the presence of ferric ion. Elemental sulfur was found at all temperatures investigated, which can be further oxidized to sulfate at high temperature.

Jan 1, 1999