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By Yifei Zhang, Jianzhong Li, Wenhao Zhang

Eletrochemical behavior and corrosion properties of a Ti–6Al–4V alloy fabricated by selective laser melting in artificial seawater at temperature ranges from 20 to 40 °C were investigated using electrochemical techniques, including potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and Mott-Schottky measurement, etc. Equivalent circuits were simulated to investigate alloy surface and analytic effects of temperature on interface of alloy and solution. The results showed that corrosion potential increased with temperature rise, and the EIS presented a single capacitive resistance characteristics. When the temperature reached 35 °C or above, passive current increased, while the passivation phenomenon was not obvious and corresponding radiating arc radius reduced, indicating that the resistance decreased, conductivity of surface passivation film improved, and corrosion performance improved. According to the Mott-Schottky curves, alloys exhibited n-type semiconductor characteristics. With increasing temperature, conductivity of passivation film enhanced, and alloy corrosion resistance decreased. At 40 °C, alloy possessed the worst corrosion resistance.

Mar 1, 2018

By R. Nilsson

In the present work, an assessment of the sulphide capacities of a number of binary and ternary slag systems have been carried out in the light of a sulphide capacity model. The model is based on the expression: {CS- exp (-A G °/R T) ? ao2 / fs2-} where AGO is the standard Gibbs energy change for the above reaction, ao2 is the activity of oxygen ions and f, is the activity coefficient of the sulphide ion in the slag. In the present model, the ratio (ao2/fs2) is optimized for the experimental data available in literature. The systems assessed are the binaries MnO-SiO2, CaO-SiO2, Al2O3-CaO, as well as the ternaries CaO-Al2O3-SiO2 and CaO-MnO-SiO2. In the case of all these systems, the experimental data available in literature were complemented by measurements carried out at the Division of Theoretical Metallurgy. The sulphide capacities of some FeO- containing binary, ternary and quaternary slags are also examined. The potentiality of the model to estimate the sulphide capacities of complex slag systems from binary and ternary data is demonstrated.

Jan 1, 1996

By Jing Zhan

The fibrous precursor can be obtained by coordination precipitation process, using oxalate, cobalt chloride and ammonia. The composition and morphology of fibrous precursor were characterized by XRD, IR, DTA/TGA and SEM analysis. The results show that XRD pattern and composition of the precursor with fibrous morphology precipitated at pH=9.0 were different from that of ß-CoC2O4?2H2O precipitated at pH=1.0. The mechanism on the thermal decomposition of fibrous precursor was addressed. The influences of various conditions in pyrolysis, including the temperature, time, atmosphere, and the morphology of the precursor, on the morphology, average size and specific surface area of the Co powders were investigated in detailed. At last, the final product, fibrous cobalt powders with diameter about 0.3~0.5µm in size and 40~60 in aspect ratio, were produced by thermal decomposition at 400~500? in the weak reducing atmosphere. The structure of pores in cobalt powders was capillary tube with open ports and the majority was mesoporous.

Jan 1, 2009

By Shenghui Guo, Ying Lei, Wei Li, Jinhui Peng, Libo Zhang, Yu Li

"Abstract: In this work, low temperature carbothermic reduction of Panzhihua low grade ilmenite after ball milling were investigated. The ball milling of ilmenite and graphite were processed in a ball mill. The milling process can attenuate the particle of ilmenite, and the ilmenite characteristic peak were broadened and weakened. The reduction temperature and behaviors are studied on the thermo gravimetric apparatus; lower temperature and higher reaction rate were obtained for the reduction of ilmenite with graphite after milled. The reduction temperature and times of ilmenite decreased to 1000-1025°C and 40-60min via milled for 4 or 8h; Low down the reduction temperature can eliminate the solution of Mg2+ and FeTi03 in a certain degree; the reduced ilmenite has an obvious loose structure, can favored the subsequent procedure such as leaching.1 IntroductionThere is about 9.66 billion tons of Vanadic Titan-magnetite deposited in Panzhihua, China. In this reserve, there is about 8.73x108 t ofTi02, Accounting for 90.54% of the Chinese reserves, and 35.17% of the international reserves and ranking first in the world. [JJ Titanium mineral deposits major classified into Rock type and Placer type. Rock type is the igneous mineral, which have great content of FeO (Relative to Fe20 3) and gangue. The rock textures are compact and almost are complex ore. Rock type Titanium mineral major are ilmenite and titan magnetite ore, difficult to separate the metal ore and gangue. l.21 Thus, the Ti02 grade of Rock type ilmenite much lower than the Placer type (Table land 11). Panzhihua ilmenite are the typical Rock-type, due to the higher contents of MgO, CaO and Si02 and the complex mineralogy in ilmenite in Panzhihua region, making its direct reduction progressively more difficult. Mechanical activation, usually carried out by energetic milling or ball milling, was reported to significantly decreased the reduction temperature and accelerate the reaction rate of reduction of ilmenite with carbon, silicon and Magnesium. f3·(>J It reported that the process temperature were decreased to 600-1000°C and the annealing time were reduced to 30-120min after milled for 50-400 h. Shorter milling time involved was imported for else procedure such as direct leaching. 171 Hardly any research had referred to the carbothermic reduction reactivity of ilmeite milled for a short time as 1-1 Oh. In the present work, the aim is to investigate the reactivity and reaction temperature of carbothermic reduction of Panzhihua ilmenite. The Phase composition and micro morphology of samples are characterized."

Jan 1, 2011

By I. D. Reznik

On blowing nickel matte in a converter without quartz, first the oxidation of metallic iron and a part of FeS occurs without evolving sulfur dioxide, the formed FeO dissolves in a sulphide smelt and form a homogeneous oxysulphide smelt. On further increasing the FeO content, the oxysulphide separates into 2 layers. Based on the laboratory investigation of FeO-(FeS+Fe°) - (Ni3S2+Ni°) ternary phase diagram we have identified the separation region at 1250°C. The boundaries of the separation region have the form of an arc and the composition of the separated oxysulphide layers is defined by the canodes. In the nickel or copper-nickel matte - silicacalcium oxide slag system at 1250°C three layers, namely sulphide, oxysulphide, and slag may be formed. A high slag basicity due to the presence of CaO can serve to enhance the activity of FeO; a low nickel content in the matte corresponds to a high concentration of FeS therein; FeO from slag and FeS from the matte form a homogeneous FeO-FeS solution, i.e. an oxysulphide layer. The investigation on the "Camebaks" apparatus and by the nuclear gamma-ray resonance spectroscopy method of the phase composition in a slowly cooled oxysulphide layer has shown the presence of four phases: wustite, troilite, ferronickel grains, and calcium oxide-silica inclusions. Knowledge of regularities in the oxysulphides formation makes it possible to use them in pyrometallurgy of nickel and cobalt or preventing their formation.

Jan 1, 1997

By Zemin Ma

A novel chromate [Cr(VI)] reducing bacterium was isolated from chromite ore processing residue disposal site of China and identified as a Leucobacter sp. by 16S rRNA gene sequence homology. The minimum inhibitory concentration of strain CRB1 was 820 mg l-1 of Cr(VI). The reduction of Cr(VI) occurred only under aerobic conditions. With an initial concentration of 2.5×108 cells ml-1, 1800 mg l-1 of Cr(VI) was reduced entirely within 38 h under the optimum conditions, at 30 °C and pH 9.0. Increasing Cr(VI) concentrations prolonged reduction process and higher cell densities meant quicker reduction. A blue precipitate was produced during chromate reduction of strain CRB1, which was binding to the surface of bacterial cells and determined as trivalent chromium with electron paramagnetic resonance (EPR) spectrometry. The conspicuous chromate reduction ability of Leucobacter sp. CRB1 suggested a potential for bioremediation of Cr(VI) containing wastes.

Jan 1, 2008

By Mei-le He, Min Chen, Xiang Shen, Lei Xu, Lei Liu, Nan Wang, Xue-liang Yin

In the current study, Al2O3-MgO-CaO refractories were prepared at 1400-1600 by the addition of MnO micro-powders, and the effect of MnO addition on densification behavior of the refractory was discussed. The results showed that the doped MnO dissolved to MgAl2O4 phase, and promoted the growth of MgAl2O4 grains by the formation of MgAl2O4 solid solution. As a result, the dense microstructure was obtained, with the apparent porosity decreased from 19.2% to 5.4% and the bulk density increased from 2.78g/cm3 to 3.15g/cm3 after firing at 1600 for 2h by the addition of 4% MnO. In addition, a texture microstructure was observed, which is considered to be favorable to improve mechanical properties and the service life of Al2O3-MgO-CaO system refractories.

Jan 1, 2016

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

By S. K. Wu, Ray Y. Lin, Sunil Annaji

Infrared joining of TiAI using aluminum foils as the filler material was investigated at temperatures between 1050 °C and 1350 °C in a flowing argon environment for times varying between 15 and 60 seconds. Using aluminum foils, the attempt was to form the Al3Ti phase in the joint as a result of reaction between Al and TiAI at temperatures above the melting point of Al. It has been found based on X-ray diffraction and TEM analysis that, Al3Ti, indeed is the product of infrared joining of TiAI using Al as the joining alloy. Al3 Ti was detected even in the joint processed at 1050 °C for only 15 seconds. Since the aluminum foil used in this study contains 27 at% Si, the t 2 phase in the Ti-Al-Si ternary system is believed to have also formed at the joint/base TiAI interface. Cross sectional studies on the joined specimens have shown different degrees of reaction depending on the temperature and time of joining. Micro hardness evaluations across the joint show that the hardness near the center of the joint is typically smaller than that near the joint edge next to the base material. However, as the joining temperature and time increase, the increment of the hardness at the center of the joint is faster than that around the periphery of the joint.

Jan 1, 1996

By Bora Derin

The partial pressure ratios of sulfur and oxygen for several copper flash smelting plants were derived using the Reddy-Blander (RB) model and predicted dissolved sulfur contents available in the literature. The sulfide capacities (Cs) of six different flash smelting plants (FeO-CuOo.5- CaO-MgO-FeOu-AlO15-SiO2) slags were calculated. The log (PO2/PS2) versus matte grades of various industrial processes was determined. The PO2/PS2 ratio increased with an increase of copper grade. The calculated partial pressure ratios for the copper flash smelting are in good agreement with those of the experimental data.

Jan 1, 2003

By Craig A. Johnson

Cyanide speciation and behavior have been examined at three active heap leach operations, three heaps undergoing rinsing, and three sites with cyanide contaminated groundwater, all in the southwestern U.S. Data from these studies demonstrate that strong cyanometallic complexes of iron and cobalt can play ?an important role in cyanide behavior throughout the lifetimes of heap leach operations. In active circuits, we find evidence that significant amounts of cyanide combine with iron and cobalt to form strong cyanometallic complexes, and that these species can be adsorbed, probably onto iron hydroxides, or precipitated as insoluble cyanometallic compounds. When spent heaps are rinsed, the release of this cyanide is likely controlled by the slow kinetics of desorption from, or dissolution of, solids that have gone largely uncharacterized. We find evidence that strong cyanometallic complexes can give rise to transient free cyanide in some settings by rapid photo dissociation where heap rinse effluent is exposed to sunlight in open channels or translucent sample bottles. Thus, these species can complicate the ,preparation of spent heaps for decommissioning, even where regulatory standards ?are based on weak acid dissociable cyanide. There is a critical need for information on the form and stability of adsorbed and precipitated cyanide in spent ore heaps, on the concentrations of strong cyanometallic complexes in mineral processing effluents -particularly the complexes of cobalt, and on the natural attenuation of iron and cobalt cyanometallic complexes in both surface and subsurface waters.

Jan 1, 1998

By Fabiola Alvarez, Ana E. Bote, Daniel Pasquevich

"The oxidation of aluminum and its alloys was extensively studied for improving the corrosion resistance in structural materials having high specific strengths. But this reaction involves the formation of a very thin barrier layer on the metallic pieces. Furthermore, the ·recent development of the directed melt oxidation process for producing metal-ceramic; composites has renewed the interest in the study of interaction between gases and metals. Oxidation experiments in the presence of different chlorine partial pressures and at different temperatures were performed in ·a thermogravimetric balance, and microstructures were analyzed by electronic microscopy and X-ray diffraction. The oxy-chlorination kinetics was determined and the oxide formed W(IS amorphous at temperatures below 600 °C and crystalline .at higher temperatures. The appropriate experimental conditions for the fastest completed oxidation was further determined.IntroductionThe use of fine powders for the manufacture of ceramic components has significant advantages. They include excellent sinterability; low sintering temperature and better microstructure leading to improved mechanical properties. The conventional method of producing fine oxide powders involves controlled precipitation and pirolysis of suitable salts. The main limitation of the high temperature decomposition route is the evolution of environmentally unacceptable and corrosive gases. Controlled precipitation of hydroxides from solutions of salts, followed by thermal treatment involves large volumes of solutions and the calcination step that can induce grain growth (1).Direct oxidation of aluminum metal for producing alumina powder requires high temperatures for the direct oxidation of molten Al alloys by a vapor phase oxidant process (2, 3) or high technological process like thermal plasma reactor ( 4).Oxidation of high purity aluminum (5, 6) below the melting temperature· is initially characterized by a nearly linear reaction rate, followed by a rate which decreases rapidly with further weight gain. However, the oxidation rate of an aluminummagnesium alloy is much faster and it does not conform to any common oxidation law, but it is nearly parabolic at temperatures between 200 and 400 °C, an nearly linear· above 400 °C."

Jan 1, 2000

By Carlos A. Nunes

V-AI alloys have been used commercially to produce pure vanadium by Electron Beam Melting (EBM), as well as to obtain Ti-based alloys (ex. Ti-6AI-4V). The aluminothermic reduction of vanadium pentoxide (V205) is the primary method to obtain these alloys. Concerning the obtention of pure vanadium, earlier studies have indicated alloys presenting Al content between 10 and 15wt% as the most suitable alloys for direct EBM. In the present work we investigated the aluminothermic reduction of V205 in order to define process parameters for the obtention of V-AI alloys with composition in the previously mentioned range. It was studied basically the effect of excess AI, CaO addition and reaction atmosphere (air, argon) on the alloy composition (AI, 0, N). In addition, microstructural analysis of selected alloys by SEM (BSE images) and EPMA (WDX) were also performed.

Jan 1, 1996

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 Zhang Yongzhu

Developments on bioleaching of low grade ores and refractory gold ores by T. Ferrooxidans in China are summarized. Effect of the ions on bacterial growth, bioelectrochemical reaction mechanism of sulfide minerals and bacterial reaction mechanism are also discussed.

Jan 1, 1992

By Niko Hellstén

To capture efficiently the valuable trace metals from nickel slag using electric furnace, it is important to study their distributions between the slag and metallic phases in the furnace. It is impossible to calculate accurately these distributions without experimental measurements. Therefore, in this work, selected trace metal distributions and phase equilibria between K2O containing iron-silicate slags and a metallic Ni-Fe-Cu alloy in nickel slag cleaning furnace conditions were studied. The experimental method developed and applied during the work, involved a modified quenching technique that included equilibration of the samples in semi-sealed quartz ampoules in an inert atmosphere and metallic Fe saturation. The use of the semi-sealed quartz ampoule prevents the escape of volatile elements from the sample during equilibration. Chemical compositions of the phases and the trace elements were analysed by EPMA. From the measured compositions, the trace metal distribution coefficients between the molten Ni-Fe-Cu alloy and slag were calculated.

By Jianjun Wang, Jiaqing Peng, Lingen Luo, Zhenbang li, Yinghe Lin

Copper removal from ferronickel by FeS has been exploring studied. It is found that the decopperizing agent FeS makes the copper removal in ferronickel effectively. The effects of FeS addition amount, carbon content in ferronickel and experimental temperature were investigated. The results showed that the removal rate of copper in ferronickel increased with the amount of FeS increasing. When the dosage of FeS is 20% (mass percentage)，the removal rate of copper can reach higher than 11%. The rate of copper removal rises with the amount of carbon content increasing in ferronickel. When the amount of carbon content is 1.86%, the removal ratio of copper is 41.3%. Higher experimental temperature promotes the copper removal reaction in certain extent. The flux is acidity and weak oxidative can also promote the reaction of copper removal.

Jan 1, 2015

By Chuandong Wei, Mao Chen, Baojun Zhao, Zhixiang Cui

The first bottom blown copper smelting furnace (BBF) has been successfully operated for 10 years at Dongying Fangyuan Nonferrous Metals. In addition to many advantages of the BBF reported previously, stable operation with spinel-containing slags enabled the BBF refractories to achieve three-year campaign life. Understanding of the degradation mechanisms of the magnesia-chromite refractory will be able to further prolong the service life of the refractories and develop new refractories. In the present study, the post-mortem refractories were collected from different locations of the BBF during the annual maintenance. It is the first systematic study for the used refractories of a BBF. The phases present in the refractories and their compositions have been determined by Electron Probe X-Ray Microanalysis. The degradation mechanisms of the refractories are discussed based on the analyses. The results will be used to optimize the operation and select proper refractories in the furnaces.

Mar 1, 2018

By Raymond E. Healy

Circuit samples from the HBMS concentrator were assayed for l5elements, and image analysis was done to determine the modal quantities, grain size distributions and liberations of the minerals. Material balancing was done on these data to determine distributions of the minerals in each concentrator stream. The ore was mined during the waning phase of mining and is diluted with backfilled copper smelter slag. The mill feed grades 1.0 wt% Cu and 1.8 wt% Zn. The slag silicate phases contain approximately 1.5 wt% Cu and 6.5 wt% Zn; therefore the Cu and Zn head grades due to chalcopyrite and sphalerite, are only 0.9 wt% Cu and 1.2 wt% Zn, respectively. The recovery of Cu in the Cu-concentrate (Cu-conc.) is only 77.5 %, whereas that of chalcopyrite is 89.2 %. Similarly, the recovery of Zn in the Zn-concentrate (Zn-conc.) is only 40.2 %, whereas that of sphalerite is 71.0 %. The slag accounts for approximately 60 % of the Cu, and 85 % of the Zn in the tailings. The main loss of chalcopyrite is as unliberated grains to the tailings, and the main loss of sphalerite is as free grains to the Cu-concentrate and as unliberated grains to the Cu-concentrate and tailings. Approximately 85 % of the chalcopyrite and sphalerite lost to the tailings. accounting for 8 % and 10 % of the respective minerals in the concentrator feed, occur as middling and sub-middling grains. Extremely fine regrinding would be required to liberate these minerals.

Jan 1, 1989

By Yuchun Wang

In principle, supported liquid membranes could be an exceedingly elegant separation process. However they tend to fail by displacement and emulsification of the organic solution in the pores, which allows mixing of the feed and strip solutions. We have stabilized supported liquid membranes comprising moctylamine in nylon and PVDF supports by covering the pores with semi-permeable polyamide films, using an in-situ polymerization technique. Scanning electron microscopy demonstrates that the polyamide films are sensitive to production conditions and the nature of the support. The transport properties of stabilized supported liquid membranes for Cr(VI) are compared with those of unstabilized membranes.

Jan 1, 1998