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By David R. Jessey

An ore microscopic and geochemical study of the nickel-cobalt occurrence in the Southeast Missouri Mining District has revealed several significant relationships. Siegenite [(Ni,Co)3S4] is the dominant nickel-cobalt sulfide in the ores, however, several other members of the thiospi¬nel group (AB2S4) occur: carrollite (CuCo2S4), nickelean carrollite [(Co,Ni,Cu)3S4], fletcherite [Cu(Ni,Co)2S4] and polydymite (Ni 3S4). In addition, bravoite [(Ni,Fe)S2], vaesite (NiS2), millerite (NiS) and gersdorffite (NiAsS) are present. Thiospinel composition varies dramatically within the district. Paragenetic studies have shown that the stratigraphically lowest thiospinels are the most cobalt-copper-rich. A detailed ore microscopic study of the AMAX Lead Company Buick mine has also shown significant changes in mineralogical association, texture and grain size of the siegenite along the north-south strike of the major ore bodies. Siegenite commonly replaces and veins chalcopyrite and is subsequently replaced by sphalerite. Less commonly, siegenite and chalcopyrite are observed to form linear replacements along sphalerite grain boundaries. The grain size of the siegenite varies markedly, but in a predictable north-south pattern that is consistent with a genetic model formulated from geo-chemical data. The compositional as well as textural trends displayed by the thiospinel mineralization could be exploited to optimize recovery of any or all thiospinels of economic interest.

Jan 1, 1981

By David M. Davidson

Seven intrusive phases have been mapped to date in the 1 b.y. Red Bluff Granite Complex (RBGC) near El Paso, Texas. This batholith is 20 km2 in area and intrudes older supracrustal units as well as a trachyte ignimbrite cap. Two early microgranite sills are spatially separated 6 km from a porphyritic, three-phase "ring complex" by a tin-bearing, biotite granite which cores the RBGC. These units are intruded, in turn, by a riebeckite granite which locally exhibits lineated and pegmatitic textures as well as exceptionally high light REE and Zr values (800 ppm La; 3,000 ppm Zr). The riebeckite granite is exposed in three separate occurrences within the Franklin Mountains. REE values in the RBGC are depleted in HREE and show distinct negative Eu anomalies. Typical La/Yb ratios are 5:1-2:1 with Eu values ranging from 10-80 ppm. The mineral source of the high REE values in the riebeckite granite has not yet been specifically identified, but is believed to be zircon.

Jan 1, 1988

By Charles H. Bucknam

A gold sampling optimization study was carried out in support of open pit gold mining operations for the Newmont Gold Company Bootstrap-Capstone deposits in Northeastern Nevada. Six bulk samples were tested using fire refining techniques at field particle size, to determine coarse particle heterogeneity of the ores, and by gravity .concentration methods at 10 mesh particle size, to observe any particulate gold liberation. An overall sampling model is presented for the deposit based on the pooled test information, to reconcile the results of coarse particle heterogeneity testing and the fine particle 'liberation testing. The sampling model is used to recommend procedures to control the variability of gold grade estimation due to the fundamental error (nugget effect) during sampling, sample preparation and assaying of the ores and other fundamental variances. The technique of simplified quantitative risk analysis (SQRA) is used to provide an economic justification for implementation of. recommended improvements to field sampling practices.

Jan 1, 1999

By Messias dos Santos Machado, Renato B. Godoy, Roberta Lima, Andressa Silva, Francisco Valenzuela-Díaz, Rene R. Oliveira, Esperidiana Moura

This work aims to incorporate the Bof White Clay, from Boa Vista, Paraiba State, Brazil, as natural nanofiller in Ehylene vinyl alcohol copolymer (EVOH) and obtain flexible films. Nanocomposite was obtained using a twin-screw extruder, and film formed using a blow extruder machine. The flexible film nanocomposite was characterized, by tensile tests, XRD, DSC and their properties were evaluated. The results showed a good interaction between the clay and the EVOH resulting in an increase of properties of films nanocomposites as compared to films neat polymer.

Jan 1, 2015

By Cang Daqiang, Li Yu, Liu Xiaoming, Zong Yanbin

"Utilization of high-quality heat in melting slag is a great challenge for iron and steel industry. In the paper, a new method is put forward to concurrently utilize heat and slag by converting the melting slag directly into high valued materials, slag glass-ceramic. A glassceramic with a higher basicity of 0.7 than traditional basicity of 0.45 was prepared from steelmaking slag in order to utilize more hot melting slag. Effects of Alz03 on its crystallization processes were researched by XRF, DTA, XRD and SEM. Results show that Alz03 in glassceramic would have great effected on its property. When the Alz03 content ranges within 12%-15%, glass-ceramics with basicity of0.7 could reach the best performances. The change of dominant phase in glass ceramics from akermanite and wollastonite to akermanite and gehlenite would significantly degrade its mechanical property. An increase of Al2O3 content leads to a rise of the viscosity and crystallization activation energy of the glass, while results in increasing sintering temperature and crystallization temperature of glass, which contributed to its fully crystallization and densification process.IntroductionSteel slag is a by-product under a process of converting iron to steel at above 1600°C, and 0.1-0.15 ton molten steel slag would be discharged for producing per ton of steel in the process. The discharged steel slag at 1600°C has heat of 68 kgce/t. In 2012, China's steel output reached 716 million tons, and produces about 100 million tons of steel slag and 68,000 tee of heat in it [1,2]. But at present, utilization of both slag and its heat at 1600°C is a great challenge for iron and steel industry.Dry granulation of melting steel slag by air and then recovering the heat of the hot air are a traditional technology which have not yet been put into practice for very low heat conductivity of the slag and low efficient of heat exchange among the different processes [3,4]. Therefore, a new method for high efficient utilization of both steel slag and its high temperature sensible heat is put forward [5,6], which is on-line reducing and extracting iron from molten steel slag and then directly preparing glass-ceramic by use of the residual molten slag."

Jan 1, 2014

By Alice Barreto Bevitori, Felipe Perissé Duarte Lopes, Denise Cristina Oliveira Nascimento, Sergio Neves Monteiro, Isabela Leão Amaral da Silva

"The piassava fiber is one of the most rigid natural lignocellulosic fibers, which has since the last decade been investigated as possible reinforcement for polymeric composites. In the present work, the tensile properties of polyester composites reinforced with piassava fibers with thinner diameters were investigated. Composites with volume fractions up to 30% of continuous and aligned piassava fibers were tensile tested at room temperature to evaluate the ultimate strength, elastic modulus and total strain. For each volume fraction, individually separated fibers with the smaller diameters were tested. The results indicated that the tensile properties tend to improve with increasing volume fraction of the thinner piassava fibers. The role played by the fiber/matrix interaction was analyzed by scanning electron microscopy.IntroductionA significant change in the transportation sectors mainly the aerospace and automotive, occurred last century with the introduction of stronger and lighter materials. The most relevant example was the polymer composite reinforced with synthetic fiber. They are nowadays replacing conventional materials such as the aluminum alloys in airplane body owing to superior specific strength. in recent years, however, environmental problems in a global scale are imposing a reversion in the use of synthetic fiber specially the glass fiber. In spite of its higher specific strength, this fiber and its polymer composites can neither be recycled nor incinerated in a thermal plant to generate electricity [1]. Moreover, the fabrication, processing and transportation of a glass fiber composite are associated with C02emission, the major responsible for global warming [2].A possible substitute for glass fiber without the above-mentioned environmental problems, could be a natural fiber. In fact, natural fibers obtained from cellulose-rich plants, also called lignocellulosic fiber, are already being used in several engineering fields, particularly the automobile industry [3-6]. Figure 1 illustrates an automobile and its many components made of lignocellulosic fiber composite [7]."

Jan 1, 2011

By Kenneth McGowan

"The aluminum industry is the 5th largest consumer of energy and the largest consumer of energy on a per-weight basis. Process heating accounts for 25% of the energy consumed to manufacture aluminum. Consequently, the generation of this energy results in the production of a significant amount of CO2 (over 3.75 million metric tons in 2003)1. As a result, the Aluminum Industry Technology Roadmap of 2003 listed the development of improved refractory materials as a goal to reduce energy use and decrease greenhouse gas creation. The result of a R&D effort addressing this desire is the development of patented microporous refractory materials for metal contact applications in all furnace areas including the belly band. It has been demonstrated that this material can reduce energy consumption up to 38% in furnaces and significantly reduce heat loss in launder and trough systems. Furthermore the material developed is non-wetting and remains un-penetrated by metal throughout its lifetime. The material does not contribute to the formation of corundum. As a result, the energy efficiency of an older lining remains intact compared to standard refractory materials which may have an initial high insulating value (such as lightweights and board) or standard dense refractory (even with penetration inhibitors) both of which show a rapid increase in thermal conductivity as the refractory is penetrated with aluminum and formed corundumIntroductionThe aluminum industry is the second largest producer of metal in the United States, behind the iron and steel industry. It is the 5th largest consumer of energy and the largest consumer of energy on a per-weight basis. Process heating is required to melt, hold, purify, alloy, and heat treat the metal and accounts for 25% of the energy consumed to manufacture aluminum. As such, process heating is the second largest energy consuming operation. Smelting, which utilizes an electrolytic reduction process is the largest energy consuming operation1.Most process heating is accomplished through the use of fossil fuels, either directly or indirectly. The choice of fuel is dependent on a plant’s location and fossil fuel availability. Table I shows the processes impacted by refractories and the calculated BTU’s generated by usage of the respective fuels as well as the Metric Tons (MT) of metal passed through each process in 20001."

Jan 1, 2009

By Onuralp Yiicel, Ozlem Okur, Murat Alkan

"In this study, Co-Cr-Mo alloys were produced using a mixture of Co304, Cr203 and Mo03 powders with Al powders by a Self-propagating high temperature synthesis process. SHS is a process of material synthesis that has revealed a number of reactants combinations capable of much higher energy release than conventional explosives. Al203 is added to the mixture to decrease the adiabatic temperature of the system. The thermodynamic simulations and the calculations of adiabatic temperature were examined with FactSage 6.2. In the SHS experiments, different Co304/ Cr203/Mo03 ratios were examined, and their effects on the metal recovery and alloy compositions were carried out. The samples were characterized by using chemical analysis, XRD, XRF and SEM/EDS techniques.IntroductionSelf Propagating High Temperature Synthesis (SHS) has significant advantages compared to the high technology furnace applications, such as very short processing time, simple operation, low energy requirement and low cost [l, 2]. In a SHS process, the ignition starts the combustion and propagates throughout the reactant mixture yielding the desired product. However, the disadvantages of the process such as inhomogeneous or unreacted products due to undesirable reaction rates needs to be overcome by changing some parameters such as ignition temperature, particle size, additive, atmosphere etc. [3, 4]. This work aims to establish a scientific and engineering background in the production of some cast Co-Cr-Mo master alloys via SHS (Self Propagating High Temperature Synthesis) metallurgy which is attractive process technique regarding fast and low-cost production ability of cast alloys."

Jan 1, 2013

By Carlos Mauricio Fontes Vieira, Sergio Neves Monteiro, Thiago Samarão Motta

This work has as its objective to characterize ceramic bodies formulated with ornamental rock waste and two different clays to produce ceramic paver. Specimens were made by uniaxial press-molding at 20 MPa and then fired at 950 and 1050oC respectively. The determined technological properties were: plasticity, dry bulk density, linear shrinkage, water absorption and flexural rupture strength. The results showed that the type of the clay has strong influence on the properties of interest for heavy clay ceramics. The investigated waste must be incorporated in small amounts to avoid increasing in the porosity of the ceramics.

Jan 1, 2015

By Donna Post Guillen

"Cyclopentane, a flammable hydrocarbon, is being considered as a working fluid for waste heat recovery applications using Organic Rankine Cycles with Direct Evaporators. A postulated failure mode consisting of a pinhole leak in a heat exchanger tube raises safety concerns due to autoignition of the working fluid. Experiments were conducted to determine the ignition delay time (IDT) of cyclopentane using an Ignition Quality Test™ (IQT™) device. Two sets of experiments were conducted per ASTM D6890 (with exception to charge pressure and temperature) to determine ignition delay of the fuel at atmospheric pressure for standard air (-20.95% oxygen) and vitiated air (13.3% oxygen) at a temperature of 803 K. Operation of the IQT device at a much lower pressure (1 bar) than normal operation (21.4 bar) with a standard injector led to very rich conditions and wetting of the stainless steel chamber walls. Catalytic effects are postulated to produce the small IDTs observed. Experiments were repeated with a modified injector to prevent wall wetting, resulting in average IDTs that are substantially longer.IntroductionCyclopentane is being considered for use as a working fluid in a Direct Evaporator of an Organic Rankine Cycle (ORC). In this configuration, the heat exchanger is placed directly in the flow of the hot exhaust gas, rather than using a secondary heat transfer loop to isolate the flammable working fluid from the heat source. This configuration offers the advantages of approximately 15% lower cost and improved efficiency over a standard ORC. However, placing a heat exchanger operating with a flammable hydrocarbon in the hot exhaust gas stream presents potential safety risks. If a pinhole leak were to occur in the heat exchanger, working fluid could leak into the hot exhaust stream. Gas turbine exhaust is provided to the Direct Evaporator at a temperature of approximately 803 K, whereas the autoignition temperature of cyclopentane is 634 K (Gallant and Yaws, 1993). Autoignition of the working fluid has been identified as the key risk for this type of system.Autoignition occurs when sufficient self-heating by chemical reactions takes place to accelerate reaction rates to produce full-scale combustion. This is in contrast to forced ignition, in which an external source (e.g., spark) is employed to initiate the combustion process. For combustion to occur, the fuel to oxidizer concentration must be between the lower (lean) and upper (rich) flammable limits. The reaction rate depends on the species concentration of the fuel and oxidant, the local temperature and pressure. Ignition processes are comprised of steps that take a fmite amount of time. This latent period prior to the start of combustion is referred to as ignition delay time (IDT)."

Jan 1, 2012

By Dominik Hofer

A broad spectrum of tantalum containing input materials can be processed for the production of synthetic tantalum concentrate (“SynCon”). The use of these low grade substances offers a secure alternative to mining of coltan in Central Africa. SynCon is produced in a multi-stage pyrometallurgical process, wherefore the melting behaviour of slags presents an important factor especially regarding the energy consumption and its optimisation. The characteristics of a slag comprising mostly Al2O3, CaO, SiO2 and MgO are influenced by the amount of other oxidic constituents which enfolds the main focus of this study. A hot stage microscope serves for the investigation of the slag behaviour in a temperature range from 1000 to 1600 °C under reducing atmosphere (CO/CO2 gas). The experimental results are compared with thermodynamic calculations (FactSage) to get a better understanding of the process.

By Wei Lv, Xuewei Lv, Senwei Xuan, Chenguang Bai, Kai Tang

The contact angle between six iron ores and water were determined by the capillary pressure method with cyclohexane as the perfect wetting liquid. The factors influencing the contact angle were discussed, and a relationship between the content of oxy–hydroxides and the contact angle of iron ores was obtained. The results show that the ore F has the lowest contact angle but the ore D get the biggest, which are 32.09° and 78.16°, respectively. The volume fraction of oxy–hydroxides is linearly dependent on the contact angle. The contact angle decreased with increasing the volume fraction of Fe2O3*H2O.

Mar 1, 2017

By Petrus Christiaan Pistorius, Farzin Fatollahi-Fard

The production of synthetic rutile—a common starting material for most titanium production processes—from iron-rich titanium minerals such as pseudorutile and ilmenite is described. The process for “upgrading” the mineral to synthetic rutile is by carbothermal reduction of the mineral while immersed in a molten salt at high temperature, followed by magnetic separation of the reduced iron. A variety of factors are also investigated, such as particle size of the mineral, the type of mineral, and the molten salt used. The solubility of iron(III) oxide in different molten salts is also experimentally determined.

Jan 1, 2016

By Guan-zhou Qiu, Shui-shi Liu, Yu-feng Guo, Tao Jiang

"The preparation of high-quality synthetic ruitle from electric furnace titanium slag was systematically investigated by activation roasting followed by acid leaching process. The results showed that impurities such as Ca and Mg in titanium slag can be effectively removed and TiO2 grade of the product was markedly improved by the process. High-quality synthetic rutile containing 88.54% TiO2, 0.42% (CaO+MgO) was obtained under the conditions that roasted with 7.5%(wt) H3PO4 at 1000 oC for 2h, followed by two-stage leaching in boiling dilute sulfuric acid for 2h. Mechanism studies showed that anosovite solid solution and silicate minerals were reacted with phosphoric acid in the roasting process. As a result, titanium components in titanium slag turned into rutile (TiO2) and impurities were transformed into acid-soluble phosphate and quartz.IntroductionWith the gradual depletion of natural rutile and the rapid development of titanium industry in China, the natural rutile reserves cannot satisfy the requirement for production of titanium pigment and titanium sponge. Ilmenite is, therefore, becoming main raw material for titanium industry. However, because of its low TiO2 grade, it generally requires preconcentration to titanium-rich material such as titanium slag or synthetic rutile [1-3].Ilmenite resources are extremely rich in Pan-xi area of China, which account for 90.54% of total ilmenite reserves in China [4]. The titanium slag produced by electric smelting of ilmenite concentrate has high contents of Ca and Mg, and is not suitable as a raw material for chloride process and titanium sponge production. Therefore, upgrading titanium slag to prepare raw material suitable for chloride process and titanium sponge production has important significance for the development of China's titanium industry."

Jan 1, 2011

Numerical simulation of the fluid flow and heat transfer has been carried out for a waste-heat boiler in an Outokumpu type copper flash smelter. In this boiler, SO2-containing off-gas flows into the waste-heat boiler radiation section at about 1350°C. A fraction of cooler off-gas from the electrostatic precipitator at about 200°C was recirculated into the radiation section, and a small amount of ambient air was leaked into the boiler from the bottom. The computational results show that the flow is strongly recirculating and distinctly three dimensional in most of the boiler, particularly in the radiation section. The hot off-gas cooled down rapidly after entering the radiation section due to radiation. The predicted flow pattern and temperature distribution were in a good agreement with laboratory models and industrial measurements.

Jan 1, 1995

By R. Parada

A real-time dynamic simulation model has been developed to characterise the flash furnace operation at the Chagres smelter. This model permits the operators to plan the process to meet the Peirce Smith converters' schedules and feed the acid plant with gases that satisfy its best operating efficiency range. Essential control parameters for the furnace (process air enrichment, oxygen coefficient and supplementary heat) are calculated to satisfy process targets such as matte grade, slag silica and matte/slag temperatures. These calculations are carried out with a real-time simulation. Flash furnace control and operational stability permits setting up control strategies that streamline the flow of copper to converters and of sulphur to the acid plant.

Jan 1, 1999

By Glenn C. Miller

Cyanide is the most common lixiviant for extraction of precious metals, and its efficient use in open pit mines has contributed to the increase in world production of gold during the previous two decades. With this expansion of precious metals mining using cyanide, public concerns have developed in response to the inherent public perception of cyanide as a tox-in as well as a series of environmental problems that are directly or indirectly related to cyanide use in open pit mining. Some of these have technical or regulatory solutions, while others will require additional investigation before they can be resolved. The following discussion will summarize some of the public concerns regarding the use of cyanide in precious metals mining. The issue of cyanide use in large scale precious mining is controversial, and recent banning of cyanide use in open pit mines in Montana, or complete banning of cyanide in Hungary has reflected those international concerns. The underlying basis for some of the bans (e.g. Montana) reflect a general concern of the environmental impacts of mining, rather than specific issues related to risk of cyanide use. The human safety record for cyanide use, particularly in the developed countries is good, and cyanide is clearly the most efficient lixiviant for precious metals. Indeed, the relatively short lifetime for cyanide in the environment renders it one of the less problematic chemicals used for extraction of gold from ore. Mercury amalgamation or use of bromide as a lixiviant are certainly much more problematic. What, then, is the basis f~r the international concern about precious metals mines that use cyanide. Ifuse of cyanide for gold recovery is to continue, what additional infom1ation needs to be developed that will allow a better management of the risks of cyanide? Which of the concerns are directly related to cyanide, and which are indirect concerns that more related to effects of open pit mining. Under what conditions should use of cyanide be discouraged? DUl::ing June of 2000 the United Nations Environmental Program conducted a two-day workshop on cyanide use in mining that was attended by persons from the mining industry, regulators and environmental community. Support and attendance at this workshop reflected concerns by all three groups on further restrictions for cyanide use and the emerging potential for guidelines for better management of the catastrophic release of cyanide-containing mining waste. The following discussion is meant to focus-on those risks and explore the basis for an often negative reaction to precious metals mining using cyanide. It is presented in the format of a statement, followed by a discussion. While admittedly provocative, the statements are meant to express the concerns? of the public regarding cyanide and the mining industry.

Jan 1, 1998

By Kazutoshi Haga, Atsushi Shibayama, Altansukh Batnasan

This study presents a viable approach for recovery of precious metals such as gold (Au), silver (Ag), palladium (Pd), and base metals, including copper (Cu), nickel (Ni), cobalt (Co), lead (Pb) and zinc (Zn) from waste printed circuit boards (WPCBs) via iodine-iodide leaching and precipitation. The behaviours of dissolution and precipitation of precious and base metals during iodine-iodide leaching and precipitation processes were discussed. Sodium hydroxide (NaOH) was used to remove base metal impurities exist in the pregnant leach solution under alkaline conditions. Precious metals remained in the resulting solution from NaOH precipitation were recovered by reduction using ascorbic acid (L-AA) solution. Results show that under optimum leaching conditions, almost all (> 99%) of Au was dissolved in an iodine-iodide solution when the dissolution efficiencies of other precious metals (Ag, Pd) and base metals, besides calcium (leaching of 25%) were less than 1 and 6%, respectively. The study revealed that more than 95% of Cu, Ni, Pb, Zn, Fe and Mn were initially removed from the pregnant leach solution at pH of 9.3 with addition of 0.1 M NaOH. Then 99.8% Au, 81.7% Ag and 74% Pd were precipitated from the obtained solution after NaOH precipitation while L-AA dose was 0.6 ml/ml at the condition. It can be concluded that the precious and base metals could be recovered selectively and economically from WPCBs via iodine-iodide leaching followed by precipitation using NaOH and L-AA.

Mar 1, 2018

By Alex Luyima, Jaan Kers, Lifeng Zhang

"The pyrolysis of PWBs was investigated by a TG-DTA-MS furnace at 300–1173 K. The kinetics and the control of emitted gas during the pyrolysis of PWBs with and without chemical additives were studied. Moreover, the possibility of controlling the amount of toxic exhaust gases like HBr, C6H6, Br2, Cl2, HCl gas and recovering beneficial gaseous fuels like CH4 and H2 from pyrolysis process is discussed. The MS data for each PWB sample were examined as a function of temperature and particular m/z values could be associated with the mass loss steps in the TG data. The degradation of the organic material was characterized by m/z = 2, 16, 18, 28, 36, 44, 71, 78, 81, and 160. Fe2O3 was the best inhibitor of toxic HBr and C6H6 when compared to Al2O3, CaO Y-zeolite and ZSM-5. Moreover, it had no significant effect on the valuable H2 and CH4 gas evolution. This selective inhibition of toxic gases while maintaining the valuable ones make Fe2O3 the best candidate among the investigated additives in controlling gas emissions from PWB pyrolysis process.IntroductionThe electronic and electric industry is one of the world’s largest and fastest growing manufacturing sectors. As a consequence of this growth, electrical and electronic waste (e-waste), such as computers, washing machines, printers, mobile phones, television sets, stereos, radios, etc., is generated in large quantities around the world. Printed wiring boards (PWBs) are a common component of many electronic and electric systems.[1]. The rapid development and expansion of the electronics industry over the past several decades have led to a dramatic increase in the production of PWBs and a corresponding increase in the amount of waste generated from both production and disposal. The environmental impacts of the treatment and recycling of PWBs waste have become a major concern [1-2]. PWBs are particularly problematic to recycle because of the heterogeneous mix of organic material, metals, and glass fiber [1]."

Jan 1, 2012

By Jinxing Ji

Several fundamental aspects related to the nickel electrowinning from chloride electrolytes have been addressed in this paper. The thermodynamic study includes the activity coefficient of the hydrogen ion and the speciation diagram of NiCI2 solutions. The activity coefficient of the hydrogen ion (YH+) was calculated and estimated experimentally using a combination glass pH electrode. It was found that YH+ was greater than one in concentrated NiCl2 solutions and increased significantly with increasing NiCl2 concentration. The speciation diagram for NiCl2 solutions was plotted with YH+ and the effect of the ionic strength on the equilibrium constants being taken into account. It was discovered that the predominant nickel species in the acidic region were Ni2+ and NiCI+ in 0.937 M NiCl2 solution at 25°C. Electrodeposition tests demonstrated that higher Nit' concentration in the electrolyte improved the current efficiency of nickel electrodeposition (CENi). The additions of H3BO3, and NH4Cl increased very little the current efficiency of nickel electrodeposition at pH 1.5 and temperature 60°C. However, the addition of sulfate decreased the current efficiency of nickel electrodeposition. Nickel electrodeposition was also found to be a steady-state process since the amount of acid added to the electrolyte at a constant pH increased linearly with time during galvanostatic electrodeposition. The cathode surface pH during nickel electrodeposition was measured using a flat-bottom combination glass pH electrode and a 500-mesh gold gauze as cathode. The cathode surface pH was found always to be higher than the pH in the bulk electrolyte, and if the current density was sufficiently large, it would eventually reach a level causing precipitation of insoluble Ni(OH)2(s) on the cathode surface. Rotating disc electrode studies revealed that the rate of nickel electrodeposition was first order with respect to the activity of nickel ion and zero order with respect to the activities of chloride and hydrogen ions. The rate of hydrogen evolution was found to be first order with respect to the activity of hydrogen ion and to be zero order with respect to the activities of nickel and chloride ions. These findings indicate that nickel deposition and hydrogen evolution proceed independently.

Jan 1, 1995