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By I. J. Moon

The reduction behavior of hematite by H2 and H2-CO gas mixtures was investigated to elucidate the reduction mechanism at 800-950 °C. The hematite compacts were made by Cold Isostatic Pressing to produce compacts of uniform shape and size. The compacts were sintered at 1000° C for 30min, and showed a contraction of 29%. Mercury pressure porosimeter was used for measuring the total porosity, pore size distribution and pore surface area of the compacts. Reduction was measured by means of weight-loss technique using Cahn Balance (Model : TG-171, capacity log, accuracy f 10pg). Microscopic examination and X-ray analysis were used to correlate the structure of reduced compacts with the mechanisms of reduction. Neither chemical reaction control nor diffusion control is adequate in describing the complete course of reduction of the hematite compact. The reduction of hematite compacts was initially controlled by the chemical reaction at oxidelmetal interface. The reaction goes through a transition phase .where it is undergoing a mixed control, followed by the diffusion control towards the end of the reduction. The values of apparent activation energies for chemical reaction control were 3.48-8.43 kcal/mol depending on the gas compositions.

Jan 1, 1997

By A. S. Block-Bolten

Two innovations in nickel-arsenic separation have been studied on a laboratory scale. The first requires only a nitric acid atmospheric leach without preliminary roasting and leads to favorable final conditions for precipitation of arsenic as highly stable FeAsO4, The second is an NaOH-H2O2 pressure leach which is an alternative to the known NaOH-O2 pressure leach. Either method offers the possibility of rapid and efficient separation of nickel from arsenic and is applicable, for example to the high grade niccolite deposits in the Great Slave Lake area of northern Canada.

Jan 1, 1982

By Dong Joon Min, Joo Hyun Park, Mi Sun Choi, Jae Hong Shin

Sublimation of ZrCl4 is important for the production of nuclear grade metallic Zr in Kroll’s process. The sublimation kinetics of ZrCl4 was investigated by TGA under both isothermal and non-isothermal conditions. The sublimation rate of ZrCl4 increased with increasing temperature under isothermal conditions. ZrCl4 sublimation was confirmed to be a zero-order process under isothermal conditions, whereas it was first-order kinetics under non-isothermal conditions. The activation energy of ZrCl4 sublimation under isothermal conditions was 21.7 kJ/mol. The activation energy for non-isothermal sublimation was 101.4 kJ/mol and 108.1 kJ/mol with the Kissinger method and Flynn- Wall-Ozawa method, respectively. These non-isothermal activation energies were very close to the heat of sublimation (103.3 kJ/mol). Sublimation occurs by two elementary steps: surface reaction and desorption. Therefore, the overall activation energy of ZrCl4 sublimation is 104.8(±3.4) kJ/mol. The activation energy of the surface reaction and desorption steps are proposed to be 83.1 kJ/mol and 21.7 kJ/mol, respectively.

Jan 1, 2014

By Chuan-fu Zhang

Li(Nil/3Col/3- xMnl/3)MxO2(M=Ti, Mg) cathode materials were prepared from LiOH?H2O and oxalate precursor. The physical and electrochemical properties were studied by XRD, SEM, cyclic volt-ampere (CV), AC impedance and constant current charge-discharge. The results show that crystal volume of Ti4+ or Mg2+ doped sample is increasing and the electrochemical reaction resistant Rct is decreased at high rate, improving the cyclic performance and rate capability. The effect of Ti4+ doped is better than Mg2+. The sample is well crystallized and simple pure phase with a-NaFeO2 layered structure when doping quantity x=0.025. The second specific discharge capacity of Li(Nil/3Col/3- 0.025Mnl/3)Ti0.025O2 is 143.2mAh/g at 1C,128.0mAh/g at 2C in the voltage of 2.75-4.3V,and still has 140.7mAh/g and 121.7mAh/g after 20 cycles, respectively, keeping 98.25%, 95.07% capacity.

Jan 1, 2009

By Jingwei Lou, Bing Li, Suzhen Li, Miao Shen, Jianguo Yu

"As a main impurity in primary lithium metal, magnesium is difficult to remove because of the very close relative volatility of the two metals. Electrochemical refining provides a possibility to completely remove Mg in the LiCl-KCl melt prior to Li reduction. MgCl2 reduction processes in LiCl-KCl- MgCl2 melt were investigated by cyclic voltammetry (CV), square wave voltammetry (SWV), chronoamperometry and chronopotentiometry. Then potentiostatic electrolysis was carried out and Mg (II) ion was reduced onto a liquid lead cathode from the LiCl-KCl-MgCl2 melt at the Mg deposition potential. The results show that Mg ( II ) is reduced in one step with two-electron transfer. The reduction potential of Mg ( II ) was well defined. The reduction of Mg( II) results in Li ( I ) underpotential deposition at 0.2V more negative potential than that of Mg( II) reduction. Therefore, in order to prevent Li ( I ) from codeposition with Mg, accurately controlling Mg ( II) reduction potential during the potentiostatic electrolysis was necessary. Ninety three to 99 % removal rate of MgCl2 was achieved after 8-12 h electrolysis when liquid lead was used as cathode.IntroductionMetallic Li has been widely used in batteries, light weight alloys and in fusion reactors because of its excellent properties. Currently, the only way in industry to produce metallic Li is by electrowinning from molten LiCl-KCl at about 450 °C [l-5]. LiCl-KCl is the only electrolyte used, because they presents a lower eutectic temperature and KCl shows a slightly higher theoretical decomposition voltage than LiCl, as shown in Table l .The produced metallic Li generally contains 1-2 wt% impurities including Na, K, Al, Ca, Mg, Si, etc. [6l, which are derived from the corresponding metal chloride compounds or metal oxide compounds existing in the LiCl and/or KCl raw materials. These impurities have to be removed by subsequent vacuum distillation at high temperatures to meet the requirements for metal Li purity in the final products. Separation of Mg from Li by vacuum distillation is difficult because their relative volatilities are very close, as shown in Table 2."

Jan 1, 2011

By H. Deveci

Bioleaching/biooxidation is essentially a dissolution process with the involvement of acidophilic bacteria acting as the "catalyst" to accelerate the dissolution of metals from sulfide minerals. The contribution of bacteria to the metal dissolution is closely controlled by the growth of bacteria, which is itself affected by the physico-chemical conditions within the bioleaching environment. There are a number of operating parameters controlling bioleaching processes, which are required to be maintained within a certain range in the leaching environment whereby the activity of bacteria with the resultant oxidation of sulfide minerals can be optimized. In this regard temperature, acidity, oxidizing conditions, availability of nutrients, oxygen and carbon dioxide, surface area and presence of toxic ions are of prime importance for control and optimization of bioleaching of sulfide ores/concentrates. Bioleaching processes are temperature and pH dependent with optimum metal dissolution occurring in a particular range where the bacterial strain is most active e.g. mesophiles at 35-40°C and pH 1.6-2.0. Provision of nutrient salts is required to maintain the optimnm growth and hence metal dissolution with the quantity of nutrients apparently being dependent on the availability of substrate i.e. head grade/pulp density of an ore/concentrate. Oxygen transfer is one of the most critical factors since the oxygen levels below 1-2 mgll may adversely affect the oxidizing activity of bacteria. Bioleaching rate tends to improve with increasing the surface area at low pulp densities but, in practice. the pulp density is limited to -20010 w/v. Increasing concentrations of ions such as cr may also adversely affect the oxidative activity of bacteria. Keywords: Bioleaching, Biooxidation, Acidophilic bacteria

Jan 1, 2003

By L. I. Rosato

A novel hydrometallurgical process for the recovery of silver and gold from neutral leach residue that is based upon leaching with thiourea, is described. Laboratory and pilot plant studies have shown that 80-90% of the silver and 60-70% of the gold can be recovered by:? ( i) leaching zinc calcine with 'Spent electrolyte at pH 2.0-3.0 to generate a precious metal-bearing zinc ferrite residue, (ii) leaching of the thickened zinc ferrite with 3-5 g/L thiourea in a six stage carbon-in-pulp circuit, (iii) elution of silver and gold from the loaded carbon with a thiourea- butanol solution, (iv) thermal regeneration of the stripped carbon and (v) recovery of the precious metals from the pregnant eluate by cementation with zinc dust. The reasons for adopting the thiourea CIP leach and the preferred operating parameters for each process step are presented. The requirements for the destruction of any thiourea transferred to the zinc circuit are outlined, and the results of an integrated one tonne/day pilot plant operation at Canadian Electrolytic Zinc are given.

Jan 1, 1990

By G. Coryell, S. Blaskovich

"A computer model has been developed to simulate the flash furnace and converter operations at the ASARCO Hayden Copper Smelter. The focus of the modeling was to optimize the converter operation to eliminate high matte level episodes in the flash furnace. These episodes (reducing feed to the furnace) resulted from the lack of converter operation scheduling. The model provided ""what if?"" scheduling scenarios that led to increased efficiency of the converter and flash furnace operations.This paper discusses alternatives studied to optimize the converter operation and the development of the computer modeling program, including implementation of the project. The discussion details the results of the project including the conversion from batch to a real time converter scheduling process. IntroductionASARCO's Hayden Smelter consists of a fluid bed drying system, an Inco oxygen flash smelting furnace, Peirce Smith converters, two anode furnaces and two casting wheels, gas cleaning plant, 2800 stpd sulfuric acid plant, 650 stpd oxygen plant and 200 gpm water treatment plant. The process flow sheet of the plant is shown in Figure 1.Over the past several years, the Hayden smelter has been involved in productivity improvement and cost reduction programs. This has been necessary to become a low cost copper producer in today's market. Part of the productivity improvement program was the use of process control to streamline the flash furnace and converter operations. Process control, through the use of computers and electronic controllers, has played an increasingly important role in optimizing processes in the Hayden Plant since the startup of the Inco flash furnace in 1983."

Jan 1, 1989

By Luis M. Chia

The direct dissolution of zinc in an organic solution of di-(2-ethylhexyl) phosphoric acid (D2EHPA) and kerosene was studied. The objective was to gain a better understanding of the fundamentals involved in the anodic step of the galvanic stripping process. Results showed that metallic zinc does dissolve spontaneously at ambient temperature by an electrochemical mechanism and the presence of additional oxygen activated the process. When oxygen was removed by prior nitrogen sparging, dissolution did not occur indicating a depolarizing cathodic reaction is necessary. The concentration of water in the organic also affected the rate of dissolution. A factorially designed experiment was made using four variables at two levels selected by evaluating results from previous screening tests. D2EHPA concentration, surface area and agitation were all found to be significant for the values chosen. Temperature was less significant and it was found that zinc dissolution is probably a diffusion or mixed controlled process, as indicated by the calculated activation energy of 6 kcal/mole.

Jan 1, 1995

By M. K. Mohan

Lead recovery from process solutions contributes not only to the conservation of resources but also clean environment. Zeolites are natural aluminosilicates, which finds applications as catalysts and in wastewater treatment. In the present investigation, studies were taken up on the processing of Pb from process solutions by zeolites. Effects of pH of the solution, time and type of zeolite viz. chabazite, mordenite, erionite and clinoptilolite on the removal of Pb from solutions was investigated. Rate of sorption was found to depend on the pH of the solution and about 99 pct. recovery was observed at pH 6. Optimal conditions were established for the maximum recovery of lead from process solutions. Possible sorption mechanisms were proposed. The calculated adsorption constants calculated from Langmuir and Freundlich equations showed that the adsorption of lead on chabazite was strong.

Jan 1, 1999

By K. Narayana Swamy

Experimental results of 3-phase mixing in a physical model of a CCRL for metals refining, at high levels of bottom gas injection (up to a superfIcial gas velocity (Us) of 12.5 cm/min), are presented. A thermal tracer technique was used to elucidate both longitudinal mixing and interphase heat transfer. The results indicate that even under conditions of significant bottom gas injection, it should be possible to maintain acceptably low longitudinal mixing (D. < 20 cm2/s and D/uL < 0.1) in the CCRL. Interphase mass-transfer coefficients of the order of 0.02 cm/s and higher, are predicted from the measured interphase heat transfer coefficients using the mass and heat transfer analogy. Adequate performance is likely to be possible for an industrial CCRL, based on extrapolation of these results to full-scale conditions.

Jan 1, 1996

By Ahmad-Bitar¸ Riyad N., Shadia J. Ikhmayies

"CdSi-xTex thin films with O<x<0.3 were prepared on glass substrates by the annealing of CdS:In thin films produced by the spray pyrolysis technique. The annealing was performed in nitrogen atmosphere at 400 --,C in the presence of Te vapor. The compositions of the films were determined by energy dispersive X-ray detection (EDAX) measurements. Scanning electron microscopy (SEM) was used to investigate the morphology of the films. The transmittance of the films was measured at room temperature in the wavelength range 400-1100 nm and used to produce the absorbance of the films. The first derivative of the absorbance was used to estimate the optical bandgap energy Eg by using the minima in the first derivative. The relation between the bandgap energy and the fraction x was found to fit with a parabola and bandgaps in the range 2.196: =Eg: =2.480 e V were obtained. Urbach tailing in the bandgap was also investigated.IntroductionPolycrystalline thin film CdS/CdTe solar cells are promising candidates for low cost and high efficiency photovoltaic applications. The fabrication process of these cells involves the deposition of a p-type CdTe absorber layer on top of an n-type CdS one which acts as a window. The efficiency of the solar cell is affected by the method of preparation of both layers [1, 2].Interdiffusion processes taking place at the CdS/CdTe interface have largely been realized to significantly affect the device performance [3] by changing the bandgap of both CdTe and CdS which modifies the spectral response of the solar cell [ 4]. The formation of a mixed crystal or a graded layer causes a reduction in the lattice mismatch at the CdS/CdTe junction [5] which is about 9% [ 6] and then a reduction in the number of interfacial states and recombination centers, thus enhancing the solar cell performance [7, 8]. A complete understanding of the properties of the intermixed layers CdSxTe1-x that usually constitutes the interfacial region in the CdS/CdTe solar cell is essential. According to our knowledge, a lot of research was devoted to the investigation of the diffusion of S into CdTe [3-5, 9]; but little on the direct investigation of the diffusion of Te into CdS [6]."

Jan 1, 2011

By T. Innmi

The potential of the nickel matte anode was measured during the matte electrolysis in the commercial cell. The slime layer consists of elemental sulfur and was found to greatly influence the potential of anode. The measurements of porosity and permeability of the slime suggest that the voltage drop of the slime layer dominates the potential. Furthermore, the diffusion of the electrolyte through the slime layer is also one of the factors to determine the potential. In addition, the copper content of the nickel matte anode was found to affect the change in the anode potential during the electrolysis. The role of copper on the anodic dissolution of nickel matte is discussed in this work.

Jan 1, 1988

By Vitalij K. Pecharsky

Recent interest in complex aluminohydrides as potential near ambient, ultra-high capacity, solid-state sources of hydrogen (e.g., for fuel cells) calls for an improved understanding of the processes occumng in these hydrogen-containing materials during both the release and the uptake of hydrogen. Lithium aluminohydride (LiAlH4) rapidly releases 5.2 wt. % of hydrogen (i.e., nearly four times more than LaNis-based alloys) during mechanochemical processing at ambient conditions in the presence of transition metal catalysts. Using a variety of solid-state characterization techniques, the mechanochemical transformations in a series of LiAlH4 - metal catalyst systems have been examined and preliminary insights on the mechanism have been obtained. Surprisingly, the well-known hydrogenating-dehydrogenating catalysts, such as Ni and Pt, are practically inactive in the mechanochemical dehydrogenation of LiAlH4.

Jan 1, 2002

By J. R. Sarazin

Density driven convection during solidification has been recognized for some time to result in macrosegregation particularly when lower density alloying elements are rejected into the interdendritic liquid. The resulting segregates are commonly referred to as channels, freckles or A-segregates. Buoyancy driven convection leading to channel formation has been examined in three model systems possessing somewhat different materials parameters. They are the Pb-Sn eutectic system, the transparent aqueous-salt NH C1-H 0 4 2 eutectic system and the transparent organic succinonitrile-ethanol monotectic system. Convection in these systems is controlled by a balance of buoyant and viscous forces, which are strong functions of composition and temperature. Composition, temperature and flow velocity were measured and elimination of channels through heavier ternary additions is discussed.

Jan 1, 1991

By A. W. Bryson, K. C. Lenthall

"With the growth in the use of cobalt in industry, interest in its extraction and recovery has increased. With this increased interest comes the need for a fundamental knowledge of the processes involved in the recovery of cobalt metal. This paper examines the effects of cobalt concentration, catholyte pH, operating temperature and current density on cobalt electrowinning with respect to the current efficiency, cell potential and nature of the cobalt deposit. It is found that the cobalt concentration and catholyte pH affect the current efficiency, while current density and temperature affect the cell potential and thus the specific power consumption. Pitting on the deposit is affected by the catholyte pH and the operating temperature. Furthermore, the effect of feed flow-rate on catholyte pH, and thus current efficiency, is investigated. A model to predict the cell performance, which includes the flux of hydrogen ions through the diaphragm, is proposed.IntroductionCobalt metal is a silvery transitional metal found between nickel and iron on the periodic table. Due to its resistance to corrosion and other properties under high temperatures and its good work-hardening characteristics, it is favoured in alloys used in high temperature applications. These include aerospace, aircraft and high speed tools. Other applications include its use as a colourant in glass and ceramics, a drying agent in paints, a nutrient for livestock, a catalyst in the petroleum industry and, in the medical field, in prosthetics and radiology.The main deposits of cobalt are found in Central Africa, specifically Zaire and Zambia, although deposits also occur in Morocco, Canada and Australia. The cobalt is generally associated with other transitional metals including nickel, iron and copper. It is generally extracted by hydrometallurgical means and recovered from solution by electrowinning or hydrogen reduction. Little data [1-2] exists in literature on the electrowinning of cobalt from aqueous solutions. This paper investigates the effects of various operating conditions on the current efficiency, cell potential and deposit nature under continuous operation."

Jan 1, 1997

By Russell E. Clemons

Coarse-crystalline granite, quartz syenite, syenite, meladiorite, and anorthosite in the Florida Mountains, southeast of Deming, New Mexico, were originally mapped as Precambrian. They were remapped in 1971 and some of them described as Mesozoic intrusives. Several subsequent papers presented Precambrian and Ordovician ages. Zinc, lead, copper, silver, gold, manganese, fluorite, and barite mineralization in the Florida Mountains invite more extensive exploration. Clarification of ages of rocks and periods of alteration and mineralization are necessary for efficient exploration. Field observations combined with petrographic studies strongly suggest that all the coarse plutonic rocks are Precambrian and most were altered extensively by late Tertiary hydrothermal activity.

Jan 1, 1982

By Michele L. Bustamante, Gabrielle Gaustad

In recent years, t h e future supply of tellurium has been called into question due to the anticipated rapidly increasing demand from thin film cadmium telluride photovoltaics. Since tellurium is produced as a byproduct of other extractive processes – principally, the electrolytic refining of primary copper sulfide ore – it is important to explore the dynamics of the parent metal extraction and processing – in this case copper – when attempting to answer this question. This research explores the changing landscape of global copper production; introducing system diagramming and the concept of byproduct intensity (BPI) to illustrate concerning downward trends in tellurium supply potential. Upon closer inspection, it is concluding that, while a likely contributor to these downward trends, the increased use of non- traditional copper production techniques alone are not responsible; other factors include market substitution and incomplete data reporting. Additionally, a review of literature on tellurium recovery processing reveals a promising outlook for future supplies; highlighting potential for improvements in yield, which allow producers to make better use of what is available, even in the face of suppressed BPI.

Jan 1, 2014

By Lanre M. Oshinowo, André Bakker

"An understanding of the parameters that govern the just-suspended impeller speed, Njs, and the distribution of solids, is critical to the efficient operation of hydrometallurgical and other processes involving solid-liquid suspensions. In this paper, the distribution of solids in stirred tanks under a range of solids loadings (0.5 to 50 vol%) was predicted using CFD and validated against experimental data obtained from the literature. The multiphase flow is modeled using the Eulerian Granular Multiphase model. This paper will also review the established design parameter Njs in the context of scale-up and compare it to the quality of solids dispersion as a means of assessing correct scale-up in suspension tank design. The results of this study will describe a straightforward procedure to obtaining comprehensive information about reactor behavior with complex CFD models.The performance of hydrofoil impellers and a 45° pitched-blade turbine at suspending solids under different agitation speeds was studied. Both single and dual impeller operation have been evaluated. The settled solids fraction for speeds below N js, and the cloud height for impeller speeds above Njs were predicted. The CFD predictions are in good agreement with experimental literature data on velocity distribution and cloud height."

Jan 1, 2001

By Mark William Kennedy

Modern metallurgical plants typically have complex flowsheets and operate on a continuous basis. Real time interactions within such processes can be complex and the impacts of streams such as recycles on process efficiency and stability can be highly unexpected prior to actual operation. Current desktop computing power, combined with state-of-the-art flowsheet simulation software like Metsim, allow for thorough analysis of designs to explore the interaction between operating rate, heat and mass balances and in particular the potential negative impact of recycles. Using plant information systems, it is possible to combine real plant data with simple steady state models, using dynamic data exchange links to allow for near real time de-bottlenecking of operations. Accurate analytical results can also be combined with detailed unit operations models to allow for feed-forward model-based-control. This paper will explore some examples of the application of Metsim to real world engineering and plant operational issues.

Jan 1, 2014