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By S. Yuan

Oxygen ion conducting yttria-stabilized zirconia (YSZ) tube was used to remove oxygen from molten Cu at 1373K. Outer surface of the tube was in contact with the melt and the inner surface containing a thin layer of porous Ni-ZrO2 cermet electrode was in contact with a reducing gas. The migration of oxygen species (O2-) from the Cu melt through the YSZ tube is accompanied by an equal and opposite flux of electrons maintaining electroneutrality. Without applying an external EMF, the fluxes are maximized by short circuiting the melt with the cermet electrode. For efficient oxygen removal, the YSZ tube must be thin, contact resistances should be negligible, and the electrodes must be porous and cover the entire electrolyte surface for charge transfer. This refining process is environmentally sound, can use reducing gases such as H2, CH4 and CO without running the risk of increasing H or C content of the melt.

Jan 1, 1993

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 Mark Tsirlin

Kinetics of the initial oxidation stages of diffusive silicide coatings on 8 molybdenum and niobium at 1100 - 1700 and under the pressure of 400 and 1330 Pa has been studied using methods of gravimetry and gas phase analysis of oxygen, as well as by SEK, XRD and EDMA methods. The first oxidation stage described by asymptotic equation in case of NbSi coating changed over to the stage described by parabolic equation. The asymptotic law was shown to depend on non - stationary conditions on the oxide layer boundaries. Interconnection between silicides and quartz structures, on the one hand, and peculiarities of oxidation kinetics, on the other, is [discussed. The possibility of estimation oxygen atom jump frequency in quartz and fractions of oxygen reacting with metal and with silicon proceeding from the analysis of the kinetic data was ascertained. Conditions of oxidation kine- tics transfer from asymptotic (or parabolic) stage to a non - protective "linear" stage, associated with volatile ~roduct formation, are also discussed.

Jan 1, 1995

By Hideya Sato

Refractory wear caused by melts is one of the major determining factors for the interval of shut-down repair of the metallurgical furnaces in general. Calcium ferrite slag employed by M it subishi Continuous Copper Converter, shows hi& fluidity and corrosive characteristics against most of the refractories. In order to improve the corrosion resistance of the refractories, the mechanism of MgO-based refractory wear by the calcium ferrite slag was intensively studied. The dissolution behavior of the refractory into the molten slag and the penetration of the molten slag into the refractory were observed by crucible tests and newly developed oscillating furnace tests. It was found that the wear of MgO-based refractories by the calcium ferrite slag is mainly dominated by the internal structural failure caused by the penetration of CaO-Cu20 rich slag which is formed as a result of the preferential absorption of FeO, from original slag by the spinel of the refractory.

Jan 1, 1999

By Takahiko Okura

Most non-ferrous raw materials are associated with sulphur. To extract the metals, the sulphur is recovered typically as sulphuric acid or liquid SOz, On the other hand, natural gas may contain over 20% of hydrogen sulphide (HzS) and a huge quantity of elemental sulphur is produced through oil and gas refining processes in the world. A large fraction of the sulphur mined from natural sources is eventually returned to the earth as fertilizers, by-products of desulphurisation and neutralisation processes, or as fugitives to the atmosphere. However, the supply and demand for sulphur are in imbalance. Such situation urges to develop a new smelting process without sulphuric acid production. This paper briefly reviews the global sulphur balance and the technologies for recovering elemental sulphur. The core of this paper is a proposal to convert SO2 gas to elemental sulphur by using organic materials. Some results of thermodynamic calculations and experiments are presented.

Jan 1, 2003

By Takahiko Okura

Most non-ferrous raw materials are associated with sulphur. To extract the metals, the sulphur is recovered typically as Sulphuric acid or liquid S02. On the other hand, natural gas may contain over 20% of hydrogen sulphide (H2S) and a huge quantity of elemental sulphur is produced through oil and gas refining processes in the world. A large fraction of the sulphur mined from natural sources is eventually returned to the earth as fertilizers, by-products of desulphurisation and neutralisation processes, or as fugitives to the atmosphere. However, the supply and demand for sulphur are in imbalance. Such situation urges to develop a new smelting process without sulphuric acid production. This paper briefly reviews the global sulphur balance and the technologies for recovering elemental sulphur. The core of this paper is a proposal to convert S02 gas to elemental sulphur by using organic materials. Some results of thermodynamic calculations and experiments are presented.

Jan 1, 2003

By P. Blazy

A hydrometallurgical procedure for the recovery of metal from ore, particularly of copper from sulphide materials is described. In the course of this procedure, the raw material is first of all submitted to the action of an appropriate reducing system and then treated with a ferric salt solution which brings about the selective solubilisation of the elements to be recovered with respect to those constituting the pyritic phase. This procedure is investigated using two ore samples proceeding from massive sulphide deposits, presenting different chemical and mine- ralogical characteristics. The results of this investigation are compared with those obtained by a classical process employing a ferric salt solution. It appears that one solubilisation of copper takes place under particularly advantageous conditions when our procedure is used. The principal parameters affecting leaching of zinc, lead and copper are examined. The selectivity of this treatment is evaluated by following the change during the treatment in the pyritic phase.

Jan 1, 1976

By Akio Ohta

The Hyuga smelter has been producing ferronickel by a rotary kiln-electric furnace process in Miyazaki, Japan. Several approaches to improve our operation have decreased the electrical energy consumption. A new process was developed to decrease the cost of energy even further. Oil and technical oxygen are injected through lances to heat up the calcined ores (calcine) instead of the electric power. Main problems during the development of the process were the short life of the water-cooled lances, the check on security of the safety system and the eruption of combustion gases through the calcine bed. These problems have now been overcome successfully, and stable operation can be maintained. The addition of 1 Litre of heavy oil per tonne of ore can save the electrical energy requirement by 8.6 kwh per tonne of ore. The new process has resulted in a reduction of the electrical energy consumption by more than 10 percent

Jan 1, 1992

By I. M. Ritchie

Cyanide owes its great success as a lixivant for gold to the great strength of the Au-CN bond. A replacement for cyanide must similarly be a strong complexant for gold (I) or gold (III). The various alternatives are briefly considered and it is concluded that only thiosulfate has a reasonable chance of replacing cyanide as a relatively non-toxic lixivant at the present time. However, there are considerable technical problems to be overcome before thiosulfate can be considered to be a realistic alternative to cyanide. Firstly, the leaching of gold using aerated ammoniacal thiosulfate with copper as a catalyst is a complex process which needs to be understood and controlled carefully in order to achieve maximum recoveries with minimum reagent losses. Secondly, there needs to be an option similar to the CIP process for recovering and concentrating the dissolved gold thiosulfate complex from pulps produced in the processing of low grade gold ores. The prospects for overcoming these technical' challenges are evaluated and discussed.

Jan 1, 1998

By G. Gao

Flyash from municipal solid waste (MSW) incinerators is frequently classified as a characteristic hazardous waste due to its lead and cadmium content. Extensive investigation has therefore been carried out to detoxity the flyash by leaching and to recover lead, cadmium and zinc. Detoxification can be accomplished by leaching in HCI/NaCI solutions. Optimization of leaching conditions for effective detoxification and subsequent metal recovery can be achieved by controlling the acidity of the lixiviant and flyash to lixivaint ratio. Lead and cadmium In the leaching solution is recovered by cementation with zinc dust. Leaching and cementation experiments have shown that zinc concentrations suitable for electrowinning, > 15 g/liter, can be achieved. Experiments have also been performed to determine the effects of pH, particle size of the zinc dust used, quantity of zinc added and dissolved impurities on the cementation kinetics. After recovery of lead and cadmium, electrowinning or electrowinning coupled with solvent extraction can be used to recover zinc. A process flowsheet is presented.

Jan 1, 1991

By Lin Yang, Yuanbo Zhang, Zhuoxuan Li, Guanghui Li, Jinghua Zeng, Tao Jiang

A technique has been proposed for recovering iron from hematite-rich diasporic-type bauxite ore in this study. Direct reduction roasting followed by low intensity wet magnetic separation process was carried out. The parameters including reduction temperature and time, sodium salts, grinding conditions and magnetic field intensity for separation of iron were determined. The optimum process parameters as follows: roasting temperature of 1050 oC, time of 60 min, sodium salts involving sodium sulfate, borax, sodium carbonate with dosages of 10 wt%, 2 wt%, 35 wt% respectively, and magnetic field intensity of 1000 Gs with fineness of pulp reached 92.75% passing -0.074mm. Under the optimal conditions, an iron concentrate containing 88.17% total iron grade and iron recovery of 92.51% was obtained, 4.55% total iron grade in tailings. This novel technique provide a potential route for utilizing hematiterich diasporic bauxite ore, recovering iron resource firstly, and extracting alumina from magnetic separation tailings further.

Jan 1, 2015

A comprehensive numerical capability for the analysis of Thermal Spray (TS) systems consisting of a three-dimensional compressible, turbulent flow Navier-Stokes model and a multi-phase particle flow model in Lagrangian formulation, was developed. This capability is validated for a set of flow conditions typical for TS. The developed methodology is used for analysis of the JP-5000 TS gun gas and coating powder flow conditions. Modeling and analysis of particle/turbulent eddies interaction is performed. Details of gas flow field, particle temperature, and particle velocity histories, and particle temperature, velocity profiles in the system are presented. For the validation of numerical analysis, the computed results are compared with available experimental measurements. The flow phenomena for different flow parameters are analyzed and explained as the results of gas dynamics and heat and momentum transfer between the gas and particle phases. This methodology can be used for process control and reliability improvement, and has the potential to significantly improve TS gun performance through control of its parameters.

Jan 1, 1996

By Zhi-biao Yin

Copper smelter flue dusts often cannot be directly recycled to the smelting process and accumulate as hazardous wastes requiring environmentally acceptable disposal. Because of the limited amount of flue dust, a separate copper extraction process must be simple and require-a small plant investment. A flue dust process has been developed, consisting of the following steps: (1) roasting a pelletized mixture of hydrated lime and flue dust to fix arsenic and sulfur as insoluble calcium salts, (2) heap leaching the roasted pellets with a buffered ammonia/ammonium salt solution to extract copper as an ammine complex in a lined cell that is the final repository of the leached pellets, and (3) boiling ammonia from the lixiviant to precipitate copper. Condensed ammonia and the filtered solution are returned to leaching. Heap leaching in the final repository cell lowers the capital investment significantly compared with competing extraction processes. Chemistry with respect to arsenic, sulfur and copper is discussed.

Jan 1, 1992

By M. Z. Mubarok

Effect of single addition of a lignin-based biopolymer additive, DP 2782, at various dosages as well as in combination with thiourea on cathode polarization during copper deposition was investigated by performing potentiodynamic and galvanostatic measurements using a potentiostat. The result of electrochemical measurements was compared with the behaviour of cathode deposition with glue and thiourea additives. Surface micro-appearance of the copper deposit after 1 h galvanostatic scan under current density of 330 A/m2 and various additive type and dosage was evaluated by scanning electron microscopy (SEM) examination. It was found that the addition of 2.5 mg/l biopolymer gave sufficiently polarizing effect of copper deposition. SEM examination of the cathode surface after galvanostatic scan revealed that the combination of the biopolymer with thiourea (2.5 and 3.5 mg/l) resulted in a compact deposit which is comparable with that resulted from the test with glue and thiourea.

By F. Patisson

During exothermic gas-solid reactions, heat generation makes temperature rise and modifies the rate of the various mass transfer processes, namely the chemical reaction itself, the pore diffusion and the external transfer. We have investigated this thermal effect during the oxidation of zinc sulfide porous pellets in a thermo balance furnace, between 550 and 900°C-and under O2-N2 atmosphere. The results have been' analyzed by using, firstly, the law of additive reaction times derived from the isothermal Grainy Pellet Model, and, secondly, a new numerical model taking into account non-isothermal conditions. Both the models can satisfactorily simulate conversion versus time, but the numerical model also depicts the temperature evolution within the pellet. Finally it is shown that owing to the heat generation the zinc sulfide oxidation takes place under diffusion control (3/4 internal, 114 external) in all the cases studied. During the course of reaction, the. pellet undergoes strong temperature variations, with thermal gradients confined to a shell oxide layer.

Jan 1, 1996

By Felipe Daroch, Maria C. Ruiz, Rafael Padilla

Copper concentrates with high arsenic contents must be pretreated before conventional smelting to prevent environmental pollution with arsenic compounds. In this work, experimental results concerning the selective removal of arsenic and antimony from copper concentrates are presented. The process consists of an alkaline digestion using concentrated NaHS-NaOH solutions to transform the arsenic and antimony sulfides into soluble compounds. A water leaching follows the digestion to dissolve the arsenic and antimony, leaving clean copper sulfide solid residues. The laboratory scale tests were carried out using a copper–arsenic concentrate with 15.05% As and 1.42% Sb. The results showed that the most important digestion variables were temperature and concentrations of NaHS and NaOH. Over 97% of arsenic and 92% of antimony could be removed in 10 min of digestion using 8.9 M NaOH and 100% excess of NaHS at 80 °C. The subsequent water leaching was performed at 80°C for 20 min.

Jan 1, 2015

By Derek J. Fray

Electric arc furnace dusts, especially those containing zinc ferrite, are notoriously difficult to process to give valuable products and non-toxic residues. The ideal process would remove and recover the toxic non-ferrous metals as pure metals, of commercial value, and non-toxic residue which can be used as a raw material in the steel industry. From an examination of the thermodynamics of the oxides and chlorides of the various elements in the dust, it is apparent that the chlorides of the toxic non-ferrous elements are more stable than the oxides while the reverse applies to the ferrous elements. This offers the opportunity for a complete separation of the zinc, lead and cadmium from the iron oxide. Results are presented for the chlorination of electric arc furnace dusts under oxidising conditions and the subsequent treatment of the chlorides to recover the pure metals and chlorine which can be recycled back to the reactor.

Jan 1, 1994

By Rolf R. von Oppenfeld

Onsite hazardous waste processors often find obtaining a Treatment Storage and Disposal (TSD) permit one of their first major challenges. Some processors may spend the time and money required by the permitting process, only to find out later that a permit was not necessary. This paper will present and analyze four strategies that processors may use to avoid obtaining a TSD permit. Some facilities will be able to remove their waste streams from RCRA's oversight by ensuring the material is not "hazardous" waste. Parties that treat waste while it is in process may be able to avoid generating "waste" altogether. Certain treatment facilities have been specifically exempted by EPA. Finally, treatment of waste while it is in generator storage tanks may be allowed without a RCRA TSD permit. Hazardous waste point of generation, an important determination relating to these strategies, will also be discussed. Generators and processors will find this paper useful when evaluating their permit exemption potential

Jan 1, 1996

By Nagy El-Kaddah

One of the emerging technologies for the production of ultra-clean metals is electromagnetic filtration. The theory and the mechanism of electromagnetic separation of inclusions from molten metal are briefly reviewed along with basic electromagnetic separation systems. This paper focuses on inclusion removal in the induced current separators, with specific reference to a new separator developed at the University of Alabama. A simple analytical model is presented for the analysis of particle separation in such a system. The role of the applied magnetic field on inclusion removal will be discussed. It is shown that particle velocity increases exponentially with increasing magnetic field strength. At moderate field strengths, the velocity of 50 to 100µ inclusions are an order of magnitude larger than those achieved by buoyancy. The separator developed at the University of Alabama is described together with experimental results of laboratory and large scale experiments on purification of molten aluminum. These results demonstrate ?the capability of the system for producing super-clean metals.

Jan 1, 1996

By Bart Blanpain, Tom Peter Jones, Muxing Guo, Liugang Chen, Huayue Shi

Fayalite based slag is formed during the smelting process of secondary copper resources. It was found that with the presence of high ZnO, the slag became viscous, causing a slag tapping problem. In the present paper, the phase relations of the slag system ZnO-“FeO”-SiO2-Al2O3- CaO (ZnO = 0-12 wt%, Al2O3% = 0-15 wt%, CaO = 0-1.5 wt%, with iron saturation) at 1150 °C is studied by using quenching technique followed by phase identification and compositional analysis of equilibrated samples. The dependence of FeO and Al2O3 solubility in the liquid slag on the chemical composition of slag is characterized. Based on the experimental data, the solid fraction of the slag, which may considerably, influences the slag viscosity, at the tapping temperature can be reasonably estimated and, therefore an appropriate modification of the slag composition can be made.

Jan 1, 2016