Search Documents

By Aichun Dou

Au-Sb alloy sample in which the total amount of Cu and Ni is below 25% (wt. %). In practice, Cu and Ni were difficult to be dissolved in sulphuric acid solution by oxidative leaching under the atmospheric pressure conditions, because of the lower concentration of Cu and Ni in the sample. In this paper, pressure oxidation leaching in sulphuric acid system (POLS) followed by hydrochloric acid leaching (HAL) was employed to remove impurities in the Au-Sb alloy. The effects of variables in POLS on leaching ratios of different metals were investigated in detail. Under the optimal conditions: the concentration of H2SO4 is 1.5 mol/L, liquid-solid ratio is 7:1, the amount of oxidizer is 1.2 times of the theoretical amount, leaching time is 4h and leaching temperature is 427K, the leaching ratios of copper and nickel reached up to 99%, antimony, lead and silver were not dissolved in dilute sulphuric acid solution. The residue from POLS was then treated with hydrochloric acid solution in fixed conditions, the leaching ratio of antimony reached over 92%, the grade of gold in the ultima residue was enriched up to 66%.

Jan 1, 2016

By Ying Qin, Shujing Zhu

The characterization of adsorption of natural and composite bentonite in lead aqueous solution has been studied. The results showed that adsorption of both natural and composite bentonites strongly depended on the pH values of the solution. At lower pH values, the mechanisms that govern the adsorption of bentonites were dissolution of crystal structure and competition between the metal ions and the H+. To composite bentonite, the lead ion removal capacity was close to 250 mg/g. At higher pH values, formation of lead hydroxyl species might lead to either participation to the adsorption or precipitation onto the bentonites. Hence, a rapid increase in the equilibrium removal capacity of lead was obtained when pH > 7.0. An increase in the initial lead ion concentration led to the increase in the equilibrium adsorption capacity increased to a certain degree; and then, a plateau was obtained at higher concentrations. As a result, the adsorption performance of composite bentonite was better than the natural bentonite in both physical and chemical changes. The data fitted well with both Langmuir and Freundlich isotherms.

Mar 1, 2017

By Bryce Clark

An outline of the current world's known sources and resources of cobalt, looking at both land and possible undersea deposits, is given as a prelude to an examination of current and historical actual world production on geographic/company basis. These production figures will be compared to apparent consumption by segments, both geopraghically and end-use based. Consumption of cobalt has been regarded as price sensitive and a historical look at prices against all other figures will be considered. Included in this scenario will be a brief overview of cobalt's uses and a comment on future trends. Tables will include: Resources, Production, Consumption, Prices, Markets.

Jan 1, 1993

By Karin Soldenhoff

Recovery of uranium in conventional ion exchange circuits, using strong base or weak base resins containing quaternary or tertiary amine functional groups, is based on an anion exchange mechanism. In saline liquors, chloride competes with uranium for the active resin sites and reduces resin loading. This results in significant negative impacts on the IX process in terms of plant throughput and operating costs. In this paper we present the results of a study on the recovery of uranium from an acidic in situ leach liquor containing approximately 9 g/L chloride. A range of resins was tested, and a high capacity strong base resin was identified with significantly enhanced loading compared to conventional resins. Other process-relevant criteria such as loading kinetics and elution efficacy are also discussed. The process developed was successfully tested during a recent ion exchange pilot plant operated in conjunction with a field-leach trial.

By Bin Xu, Qian Li, Ya-xuan Wang, Yong-bin Yang, Xi Zhang, Tao Jiang

The effects of common associated sulfide minerals including pyrite, arsenopyrite, galena and sphalerite on thiosulfate leaching of gold were studied in this work. Sulfide minerals had significant effects on gold leaching because that the dissolved products of sulfide minerals precipitated on gold surface to form coating layer. The degree of sulfide minerals impact on gold dissolution decreased in the order of pyrite ≈ galena > arsenopyrite > sphalerite, while the degree of effects on thiosulfate consumption decreased in the order of pyrite > arsenopyrite > sphalerite > galena. The additive CMC (Carboxymethyl cellulose) could not only reduce thiosulfate consumption but also increase gold dissolution. The mechanism of this might be that CMC could restrict the decomposition of thiosulfate by cupric ions and the precipitates on gold surface.

Jan 1, 2015

By D. Gu, R. G. Anthony, C. V. Philip, M. E. Huckman

"In this paper, we review the equations needed to construct an ion exchange column model. These models contain three major components: 1) a differential material balance around the column, 2) a differential material balance around an ion exchange particle, and 3) a constitutive equation for diffusive flux. We then examine the ability of a fairly simple mathematical model to predict ion exchange column experimental data. This model contains the traditional absorption theory equations and is used to predict the behavior of a column filled with a hydrous crystalline silico-titanate and which is removing trace amounts of Cs+ from a high pH, complex electrolyte solution. Finally, we propose replacing Fick's law with the Nemst-Planck equation as the constitutive equation for diffusive flux. We use a NemstPlanck type model to predict batch experimental data, then evaluate it by comparing it's ability to predict experimental data to that of a more traditional Fick's law type model. The data from this comparison suggests that the Nemst-Planck type model yields better results.IntroductionMillions of gallons of strongly basic, radioactive waste are currently stored in underground storage tanks at Hanford and Savannah River and several locations within the United States. Due to the limited life expectancy of the tanks, there is a pressing need to remediate these wastes. This need has prompted the recent development of new ion-exchange materials for removing radioactive elements from aqueous solutions. A novel material called TAM-5 has been developed jointly by Texas A&M University and Sandia National Laboratories. TAM- 5, a crystalline silico-titanate, is highly selective for Cs + in the complex electrolytic solutions typical of these wastes. It is stable in very basic solutions and in radioactive environments [1, 2 ,3]. In laboratory testing to determine the selectivity of various materials, TAM-5 was superior to other candidate ion exchangers [4, 5]. The selectivities were determined by measuring a distribution coefficient, Kd, which is defined as the concentration, gig or mmols/g of Cs in the solid phase divided by the concentration, mg/L or mmols/mL, of Cs in the liquid phase. The units of Kd are ml/g or L/kg. Table 1 shows Kd values for TAM-5 compared to 9 other candidate materials in a typical waste solution [6]."

Jan 1, 1996

By Hongfa Hu, Stavros A. Argyropoulos

"This paper describes a mathematical model which simulates numerically reaction driven fluid flow phenomena. The driving force of this reaction is an exothermic heat of mixing. In addition, the model predicts the heat and mass transfer phenomena where both heat source and heat sink co-exist in close proximity. The heat source is generated by an exothermic reaction. The heat sink is formed by a moving boundary such as the melting of a solid. This type of phenomena occur quite often in various metal processing operations in which exothermic additions are immersed in liquid metals. The model is based on the SIMPLER algorithm and uses an enthalpy method to predict the fluid flow, temperature, and concentration fields. The results indicate that the exothermic mixing reaction was responsible for an abrupt rise in temperature around the moving boundary. The intensity of this reaction was also found to be responsible for the enhanced convection of fluid and the acceleration of the moving boundary. The modelling results were also verified by experimental work which included velocity and temperature measurements in a low temperature physical model. IntroductionAlloying additions are used extensively in the treatment of liquid metals during metallurgical processes. The alloying additions introduced into liquid metals can be classified into various classes, each of which follows its own route[l]. As a major group, the exothermic additions follow two different steps during their assimilation into liquid metals. In the first step, upon immersion, a metal shell solidifies around such additions, and then melts back. At this point, the second step commences. During this second step, due to the mixing of the addition with a liquid metal, an exothermic reaction occurs, which liberates large amounts of heat, resulting in an enhanced convection in the liquid metal surrounding the addition."

Jan 1, 1994

By Theo Lehner

"During my first contact with industrial metallurgy as a summer vacation worker at the Steelplant at Luleå, Sweden, I came during a visit to MEFOS into contact with works of Prof. Worner caried out during the piloting of the Worcra continuous steelmaking process. These tests are still today remarkable as an innovative step in the art of metalmaking. By that they involved the necessary ingredients for the development of our art: seeing, knowing and doing. Industrial injection as applied during slag fuming will be discussed below.Phenomena of injection metallurgyPhenomenon according to Collins dictionary is"" anything that can be perceived as an occurrence or facts by the senses"". To open the senses for the interesting phenomena in pyrometallurgy must be the main task of any educator. The investigations by Engh et al. around the mixing phenomena of the WORCRA process are an early example of combining senses with knowledge. To see what you model must be a crucial part in any development. This can also involve to see and control that one is subject to the same conditions as in published models. Below the need ""to see"" will be illustrated by some recent investigations around slag fuming. In the literature various models for reactions occuring during the fuming of slags are presented. Two recent models hint ·ata) the occurrence and importance of iron for the fuming processb) the occurrence and importance of lead droplets during respectively."

Jan 1, 1996

By H. Kamarudin

The behaviour of cassiterite-sulphosuccinamate flotation system was examined in the light of zeta potentials measured by micro-electrophoresis method. It was observed that sulphosuccinamate substantially affects the zeta potentials of cassiterite, lowering its i.e.p. to pH 2.5 and indicating a specific adsorption and/or chemical interaction. The optimum concentration for flotation, as seen in micro-flotation tests, was found to be associated with the most effective lowering of the zeta potentials, the optimum pH being 3.0. The effect of cations in the pulp was examined for the presence of ferrous, ferric, aluminium and lead ions. The ions ferric and aluminium were observed to create an intense effect of increasing the potentials to positive side, possibly due to adsorption of cation hydroxy complexes, as indicated by their respective species distribution diagrams.

Jan 1, 1994

By Donald R. Sadoway

The viability of treating certain forms of hazardous waste by direct electrolysis in molten oxides is under investigation. Secondary residue or waste mud produced in the course of chromate chemical production is the focus of attention in this study. The goal is to reduce the water soluble hexavalent chromium either to insoluble trivalent chromium or to chromium metal. Electrolysis tests have been conducted in a high temperature cell containing chromate sludge dissolved in an electrolyte composed of Al2O3, SiO2, CaO, and MgO. Oxygen production on a carbon-free anode has been confirmed.

Jan 1, 1992

By Shunli Zhang

Metals recovery from electronic scrap by physical separation may provide an alternative to the current recycling approach, through which halogenated flame retardants can result in hazardous dibenzo-p-dioxins and dibenzo-furans. On the basis of a complete sink-float analysis of personal computer and printed circuit board scrap, and in view of the advantages of dry processes for electronic scrap recycling by mechanical separation, air table separation is prioritized in an attempt to separate metals from plastics and glass involved. In the present paper, theoretical and practical considerations of air table separation have been detailed. It has been shown that air table separation is effective for recovering copper and precious metals from this specific waste stream. With the feed rate of 60 kg per hour, the combined grade and recovery of copper, gold, and silver attainable for the two heavy products produced by the air table used in the present study was shown in the following table:

Jan 1, 1998

By Qiang Yu

This paper reports on a research project supported by NSF, which aims at developing a multi-scale methodology for systematic microstructure prediction in thermo-mechanical processing of metals. This methodology is based on combining mesoscopic microstructure models with macroscopic process formulations and involves the following three main steps: (I) based on the given global processing conditions, the gross deformation patternof the entire workpiece is modeled using a continuum-based algorithm, (2) the resulting parameters are then extracted from the continuum-based simulation, post-processed and passed on to the mesoscopic numerical module, and (3) the microstructural changes are finally modeled at the mesoscopic scale. This approach is expected to overcome the disadvantages of current microstructure prediction practice employing empirical relationships between microstructural features and processing parameters. Keywords: Thermo-mechanical processing, Microstructure, Grain growth; Recrystallization; Mesoscopic models; Finite Element Method

Jan 1, 2003

By Donald R. Sadoway

Molten salt electrolysis is a proven technology for the extraction of metals -- all the world's primary aluminum is produced in this manner. The unique properties of molten salts, also make them excellent media in which to treat a variety of forms of waste. Of special .note in this regard is electrolysis in molten oxides, a .concept put forward by. the author, initially as a ."clean technology" for producing primary metal. However, in the context of waste treatment, electroly-sis in molten oxides is a process offering the prospect of changing the. valence of dissolved heavy metals while making pure oxygen gas as the main by-product .Laboratory tests conducted at a temperature of 1550°C on chromate sludge dissolved in an melt composed of Al2O3 and MgO have confirmed electrochemical production of oxygen on a carbon-free anode.

Jan 1, 1996

By Kumar P. Dharmasena, Haydn N. G. Wadley, Bill W. Choi

"Non-contact eddy current sensing methods have been developed and applied to Cd0.955Zn0.045Te crystal growth to obtain a better understanding of the melt, solid nucleation, and the growth process. The application of this sensor approach relies on a large difference in liquid and solid electrical conductivities near the melting point and requires knowledge of the relationships between the electrical conductivity, melt composition, and temperature. Using a multifrequency encircling eddy current sensor, the electrical conductivities of three different Cd1-xZnxTe (x=0.00, 0.045, and 0.08) alloys were measured as a function of temperature in a laboratory-scale vertical Bridgman furnace. The measured solid and liquid electrical conductivities were then used in electromagnetic finite element models to analyze the multifrequency responses of eddy current sensor designs during the simulated growth of a crystal. These eddy current sensors were fabricated and installed in a vertical Bridgman furnace and used to monitor many Cd0.955Zn0.045 Te growth runs. One sensor was placed in the vicinity of the ampoule tip to detect undercooling/spontaneous nucleation and two other sensors (""absolute"" and ""differential"" designs) placed to monitor the movement/curvature of the liquid-solid interface during crystal growth. The sensor data was used to characterize the initial melt state, detect the onset of nucle-ation, determine the growth velocity, and identify the shape of the interface.IntroductionSingle crystal CdTe and its solid solution Cd1-xZnxTe alloys (0.03<x<0.05) are used as infrared transparent substrates for infrared focal plane array (IRFPA) detectors [1-6] and as solid state y- ray detectors [7-9j. Cd1-xZnxTe substrates are normally ""mined"" from large polycrystalline boules grown by the unseeded directional solidification of Cd1-xZnxTe melts using either a vertical or horizontal Bridgman process [10-14]. The vertical Bridgman method is particularly popular for growing CdTe and its related compounds. In this process, a Cd1-xZnxTe ingot is produced by first melting a charge in the hot zone of the furnace and then vertically translating the furnace (with its associated axial temperature profile) relative to the stationary crucible to cause directional solidification. In spite of many experimental efforts to investigate the relationships between material purity, stoichiometry, the controllable growth parameters (furnace temperature profiles, ampoule geometries/materials, furnace translation rates and starting position) and the resulting material characteristics (grain structure, dislocation densities, IR transmission, macro-segregation etc.), the yield of Cd1-xZnxTe of a quality suitable for large area (e.g. 4 cm x 6 cm) substrates remains low (<10%). Since much of this poor yield is directly associated with the crystal growth process (e.g. melt stoichiometry, solidification velocity, interface shape, temperature gradients, cooling rate, etc.) intensive efforts are under way to improve this technology."

Jan 1, 1997

By M. Okido, H. Yamamoto, T. Sakamoto, R. Ichino, K. Kuroda

"Hydrogen absorption alloy films have been produced by molten salt electrolysis. Lanthanum-Nickel alloy film can be formed on a nickel substrate in KCl-NaCl-LaCb molten salts by electrolysis diffusion process. LaNi5 alloy was formed by mutual diffusion between La ·and Ni after La deposition on Ni substrate. Though several kinds of La-Ni compound existed in deposits, the alloy compounds on Ni substrate changed by electrolysis condition. According to the open-circuit potential measurement in molten salts after La electrodeposition, the formed compounds had a relation to the potential. In the case of the substrate electroplated a cobalt thin film on nickel, LaNi4_5Co0.5 was formed by the electrolysis in the molten salts with lanthanum ions. This ternary alloy film showed better hydrogen absorption behavior in cyclic charge/discharge test in alkaline solution.IntroductionHydrogen storage alloys have attracted attention as the active materials for batteries with the charge/discharge property at ambient temperature. The alloy of nickel and misch metal, mainly consisting of La and Ce, has been commercially 'used as a metal hydride with rechargeable property. In recent years, researches have been developed many kind of new alloys with better hydrogen absorption properties. The hydrogen absorbing alloy ingots are commonly produced by melting method of both metals in furnace, otherwise, prepared by mechanical grinding and metallurgical sintering technique with metal powders. The film is also made by vapor-phase techniques such as sputtering method, ion plating method, etc. ·We have proposed a new method to produce hydrogen absorbing alloy films by molten salts electrolysis technique [1-3]. The hydrogen absorbing film, LaNi5, Mg2Ni and CaNi5, were obtained in this process through controlling the electrolytic condition. The active metals, La, Mg and Ca, are electrodeposited on Ni substrate, diffuse into the substrate and form various kinds of intermetallic compounds. This technique provides a direct process using metal chlorides as resources to produce functional films without using active metals such as La, Ca and Mg."

Jan 1, 2000

By Ki Bui Ma

Momentum wheels with superconducting bearings can integrate both attitude control and energy storage functions, with attendant savings in the total volume and weight of hardware, and power consumption, all of which are in short supply on mini-satellites. We have built and tested a prototype with a wheel of mass 1.9 kg, diameter 3.25 in, and height 3 in, which can store 3.5 J-sec of angular momentum and 5 kJ of energy when it rotates at an angular speed of 15000 RPM. The energy density of 2.5 kJ/kg achieved is comparable with the lower range for lead-acid batteries. To show that the wheel is energy efficient, we have performed spin down tests and measured the input power required to sustain rotational speed. Results indicate that power consumption, even accounting for the needs of cooling system, is significantly smaller than that for state of the art commercial reaction wheels.

Jan 1, 2002

By James A. Voigt

"The efficient separation of metal species from aqueous streams by precipitation techniques requires a fundamental understanding of the various processes that occur during precipitation. These processes include particle nucleation, particle growth by solute deposition, agglomerate formation, and agglomerate break-up. The application of the population balance approach has been used to develop a kinetic model that accounts for these competing kinetic processes. The usefulness of the model is illustrated through its application to the precipitation of yttrium hydroxynitrate, YHN. The kinetic parameters calculated from the model equations and system specific solution chemistry are used to describe several aspects of the effect of pH on the precipitation of the YHN. Implications with respect to the simultaneous precipitation of more than one cation type are also discussed through use of example systems. The effects of solution chemistry, precipitator design, and solvent choice are considered.IntroductionThe application of precipitation technologies to the separation of metals from solution is widely used. Regardless of its application, be it in such diverse areas as the preparation of metal oxide powders for use in commercial products or as a unit operation in the removal of trace metals during wastewater clean up, the fundamental processes involved are the same. These processes include: nucleation from solution, either homogeneous or heterogeneous; growth from solution with chemical reaction either in solution or at the precipitate/solution interface; growth by particle agglomeration; and particle break-up by collisional or shear forces. The effectiveness of the operation and the properties of the precipitate formed, or ""quality"" of the product, are determined by the competing kinetics of the different processes. The kinetics of the processes, in tum, are determined by system-specific solution chemistries and the conditions used to carry out the precipitation operation. For example, generally, when system conditions are such that the supersaturation driving force for precipitation is very high, growth species normally do not have the time to organize themselves with a high degree of crystallographic order and the precipitate is amorphous. In this case nucleation rates are invariably extremely high and the primary mechanism for growth is the agglomeration of nuclei. Conversely, when the supersaturation levels for the same system are reduced, the kinetics of the nucleation and growth processes also are greatly reduced, and a crystalline precipitate can be formed, since the growth species have time to order on particle surfaces."

Jan 1, 1996

By Kotaro Ogura

"The electrolysis process in which CO2 is selectively reduced to C2H4 at a three-phase(gas/solution/metal) interface on a copper-mesh electrode has been developed in a concentrated solution of potassium halide. At open-circuit potential, CO2 is captured on the electrode by being inserted into the double-layer consisting of halide anions specifically adsorbed and potassium cations which are located in the Helmholtz inner and outer layers, respectively. CO2 thus activated is subjected to the electrochemical reduction. In the early stage of reduction, CO2 is converted to formate radicals that are adsorbed on the electrode by taking the place of halide anions. The reductive coupling of these radicals results in the formation of intermediates such as -CH2C(O)- and CH2=CH-, and C2H4 is finally produced. The catalytic activity of the electrode process involving the insertion of CO2 into the double layer is not deteriorated at all during the electrolysis, and the continuous reduction of CO2 to C2H4 is possible with the addition of inorganic acid under the assistance of natural energy.Carbon dioxide is a serious pollutant released from fossil fuel power station, internal combustion and many industrial operations. The easy release of CO2 to the air has caused the global warming, and the technique which intends to curtail CO2 by pushing it back into the ground has been suggested. However, this problem should be greatly mitigated if CO2 can be converted to innocuous substances. Especially, the reuse of CO2 as fuels and chemicals is extremely effective not only for the mitigation of the global warming but also against the depletion of the fossil fuel reserves. Several processes for converting CO2 to valuable compounds have been proposed including hydrogenation over heterogeneous catalyst at high temperature and electrochemical and photochemical reduction. In the conversion and cutback processes of CO2, however, it is of importance that the process is feasible under mild conditions, because the secondary generation of CO2 is feared if high energy is required and supplied with a fossil fuel. In this meaning, the electrochemical reduction of CO2 taking place at room temperature, which is similar to photosynthesis, is promising. From the practical point of view, it is further necessary that the conversion rate is high enough and the product is satisfactorily valuable."

Jan 1, 2008

By Donald R. Sadoway

"Molten salt electrolysis is a proven technology for the extraction of metals -- all· the world's primary aluminum is produced in this manner. The unique properties of molten salts also make them excellent media in which to treat a variety of forms of waste. Of special note in this regard is electrolysis in molten oxides, a concept put forward by the author, initially as a ""clean technology"" for producing primary metal. However, in the context of waste treatment, electrolysis in molten oxides is a process offering the prospect of changing the-valence of dissolved heavy metals while making pure oxygen gas as the main by-product. Laboratory tests conducted at a temperature of 1550°C on chromate sludge dissolved in an melt composed of Al2O3, SiO2; CaO, and MgO have confirmed electrochemical production of oxygen on a carbon-free anode. IntroductionMolten salt electrolysis is the electrolytic decomposition of a compound dissolved in an ionic melt. The prime example of this process can be found in the production of aluminum. The compound, alumina (Al2O3)' derived from the mineral bauxite, is dissolved in an ionic melt comprising a multicomponent solution of cryolite (Na3AlF6)' aluminum fluoride (AlF3)' and calcium fluoride (CaF2,). The products of electrolysis are molten aluminum and carbon dioxide, the latter due to the attendant consumption of the carbon anode. Primary aluminum is produced in a reactor known as the Hall cell.' Alternatively, the compound undergoing electrolytic decomposition can be derived from waste. Processing in molten salts, with their capacity to dissolve materials to very high concentrations compared to those attainable in aqueous solutions, can be rather advantageous. High solubilities lead to high limiting current densities, and this, in tum, results in high productivities: For a primer on molten salt electrolysis and a review of the basic literature in the field of molten salts the reader is directed to an earlier publication of the author (1)."

Jan 1, 1996

By Valery M. Paretsky

The effect of the degree of nickel oxide reduction and the reaction gas composition on the furnace productivity has been estimated by computations and the established relationship is in good agreement with the practical data obtained in the process of electric smelting at the Severonickel smelter. An increase in the reduction degree within a range of =0.65 - 0.9 results in an increase in the furnace productivity by 19% to 37% and in a decrease in the unit electric power requirement by 16% to 27% depending on the reaction gas composition. The agreement between the computed and practical data has confirmed that the decisive factor for the process of treatment of reduced nickel oxide in an electric-arc furnace under the given conditions is the specific heat absorption, which is dependent on the nickel oxide reduction degree and the reaction gas composition.

Jan 1, 2005