Grades Of Nickel Research Articles

Effect of mineralogy on Co and Ni extraction from Brazilian limonitic laterites via bioleaching and chemical leaching

Iron-rich, limonitic laterites may contain economic grades of nickel and cobalt, but efficient extraction of these metals from such ores is still a challenge. In this study, four samples of limonitic laterites originating from the Barro Alto mine in Brazil were subjected to detailed quantitative mineralogical examination followed by bioleaching and chemical leaching tests including mineralogical leaching residue analyses. Bioleaching experiments with pure cultures and addition of elemental sulfur were conducted in 2L bioreactors under aerobic conditions with the sulfur-oxidizing acidophilic bacteria Acidithiobacillus (At.) thiooxidans and At. caldus, and under anaerobic conditions with At. ferrooxidans. Aerobic bioleaching of laterites with At. thiooxidans and At. caldus allowed for a lower pH of 1.0 and 1.1 respectively, and thus a higher Ni and Co extraction than anaerobic bioleaching with At. ferrooxidans at pH 1.5. Extraction of cobalt via bioleaching was in the range of 68–88 %, while extraction of nickel was between 17 % and 56 %. Mineralogical and geochemical analysis (XRD, SEM- MLA, DSC, LA-ICP-TOFMS, XRF) was conducted to (i) identify mineral phases, which are attacked by bioleaching and (ii) estimate the portions of Co and Ni, which are released by bioleaching of different mineral phases. Cobalt was mostly hosted by Mn-rich mineral phases, which were dissolved after reduction with ferrous iron generated by bacterial metabolism during oxidation of sulfur. Nickel was mostly hosted by goethite, the most abundant mineral phase, but nickel was also present in Mn-rich minerals (e.g. asbolane) and magnesium silicates (e.g. serpentine). Mineralogical and geochemical data revealed that goethite was almost unleached in all samples and nickel was mostly released from Mn-rich mineral phases and magnesium silicates. Results of this research were able to confirm reductive bioleaching of Mn-rich phases. Chemical leaching tests performed with different concentrations of sulfuric acid and with hydrochloric acid, and with sulfuric acid plus ferrous iron as a reducing agent supported bioleaching results. The results are not supporting published data on substantial reductive dissolution of goethite via ferric iron reduction activity of acidophilic bacteria.

Considering the action of frothers under degrading water quality

The stability of the froth is known to strongly affect flotation performance. Literature shows that both frothers and ions reduce bubble coalescence, and stabilise the bubbles that form, resulting in greater froth stability. Considering both variables act on the froth in a similar manner, it is becoming increasingly important to understand how frothers behave under conditions of increased ionic strength. Increasing the frother dosage stabilised the froth and increased the recovery of water and solids but had no impact on the recovery of copper and only a slightly positive influence on the recovery of nickel, with a simultaneous decrease in the grades of both copper and nickel. Increasing the ionic strength also stabilised the froth which increased the recovery of water and solids, but both the recoveries and grades of copper and nickel were unaffected. Examining both variables simultaneously revealed that ionic strength was more influential than frother dosage in the recovery of water with the opposite being true for the solids recoveries. This means that a simultaneous increase in ionic strength and decrease in frother dosage by the same amount will increase the water recoveries and decrease the solids recoveries. Such an increase will also slightly decrease the nickel recoveries while having no effect on the copper recoveries. Overall, managing the frother dosage under conditions of increased ionic strength, while still maintaining flotation performance, is possible. However, depending on the water quality, the frother dosage can be managed, this needs to be tailored to suit the requirements of the plant. Therefore, this study investigates the interrelationship between frother dosage and ionic strength within the context of flotation.

Production of Ferronickel Concentrate from Low-Grade Nickel Laterite Ore by Non-Melting Reduction Magnetic Separation Process

The production of ferronickel concentrate from low-grade nickel laterite ore containing 1.31% nickel (Ni) was studied by the non-melting reduction magnetic separation process. The sodium chloride was used as additive and coal as a reductant. The effects of roasting temperature, roasting duration, reductant dosage, additive dosage, and grinding time on the grade and recovery were investigated. The optimal reduction conditions are a roasting temperature of 1250 °C, roasting duration of 80 min, reductant dosage of 10%, additive dosage of 5%, and a grinding time of 12 min. The grades of nickel and iron are improved from 2.13% and 51.12% to 8.15% and 64.28%, and the recovery of nickel is improved from 75.40% to 97.76%. The research results show that the additive in favor of the phase changes from lizardite phase to forsterite phase. The additive promotes agglomeration and separation of nickel and iron.

Preparing Ferro-Nickel Alloy from Low-Grade Laterite Nickel Ore Based on Metallized Reduction–Magnetic Separation

Nickel, a valued metal, mainly exists as nickel oxide in laterite nickel ore. Furthermore, a large part of the laterite nickel ore is low-grade saprolitic ore. In this paper, a research on preparing ferro-nickel alloy from low-grade saprolitic laterite nickel ore using metallized reduction-magnetic separation was studied. In the research, the carbothermic reductions of iron oxide and nickel oxide were analyzed in terms of thermodynamics. The influences of reduction temperature, reduction time, carbon ratio, and CaO addition on the recoveries and grades of iron and nickel were experimentally investigated. To analyze and clarify the related mechanism, the microstructure of ferro-nickel alloy was observed by optical microscope (OM) and scanning electron microscope/energy dispersive spectrometer (SEM/EDS). Accordingly, the results showed that, increasing reduction temperature can improve the grades and recoveries of nickel and iron; appropriate reduction time, carbon ratio and CaO addition can favor aggregation and growing up of the ferro-nickel particles, improving the grades and recoveries of nickel and iron. The optimal process parameters obtained were a reduction temperature of 1350 °C, reduction time of 2 h, carbon ratio of 1.2, and CaO addition of 10%. In this case, the ferro-nickel alloy with nickel grade 7.90% and iron grade 77.32% was prepared successfully from the low-grade saprolitic ore with nickel content 1.82%. The nickel and iron recoveries were 89.36% and 95.87% respectively, which achieved the highly efficient recovery and utilization of iron and nickel of low-grade laterite nickel ore.

Solid-State Metalized Reduction of Magnesium-Rich Low-Nickel Oxide Ores Using Coal as the Reductant Based on Thermodynamic Analysis

The solid-state metalized reduction of magnesium-rich low-nickel oxide ore using coal as a reductant was studied based on thermodynamic analysis. The major constituent minerals of the ore were silicates and goethite. The former was the main nickel-bearing mineral, and the latter was the main iron-bearing mineral. Single factor tests were conducted to investigate the effects of reduction temperature, duration, and coal dosage on the beneficiation of nickel and iron such that optimal conditions were achieved. Considering the low recoveries of nickel and iron (Ni, 13.9 pct; Fe, 30.3 pct) under the obtained optimal conditions, an improved process, adding CaF2 before the reaction, was proposed to modify the solid-state metalized process. The results showed that the recoveries of nickel and iron reached to 96.5 and 73.4 pct, respectively, and that the grades of nickel and iron in the concentrate increased from 2.5 and 62.6 wt pct to 6.9 and 71.4 wt pct, respectively. Nickel and iron in the absence of CaF2 were metalized; nevertheless, the size of ferronickel particles was only 1 μm. Furthermore, alloys in the presence of CaF2 aggregated and exhibited bands with a length greater than 200 µm. These observations suggested that CaF2 could effectively reduce the surface tension of the newly generated alloy interface and promote the migration and polymerization of the alloy particles, which improves the beneficiation of nickel and iron by magnetic separation.

Microwave Enhanced Recovery of Nickel-Copper Ore: Communition and Floatability Aspects

A study describing the effect of microwave radiation, at a frequency of 2,450 MHz, on the processes of communition and flotation of a complex sulphide nickel-copper ore is presented. Ore communition has been investigated under standard radiation-free conditions and after ore treatment in a radiated environment as a function of ore size, exposure time to radiation, and microwave power. The findings show that communition is tremendously improved by microwave radiation with values of the relative work index as low as 23% at a microwave power of1.406 kW and after 10 s of exposure time. Communition is affected by exposure time and microwave power in a nontrivial manner. In terms of ore floatability, the experimental tests have been carried out on a sample of 75 μm in size under different exposure times. The results show that both ore concentrate recoveries and grades of nickel and copper are significantly enhanced after microwave treatment of the ore with relative increases in recovered concentrate, grade of nickel, and grade of copper of 26 wt%, 15 wt%, and 27%, respectively, at a microwave power of 1,330 kW and after 30 s of exposure time.

Use of ion implantation techniques to characterize the oxidation of elemental nickel

Factors affecting the adherence of protective alumina scales have been profitably studied employing ion implantation techniques. Alumina is considered to grow largely (but not exclusively) by short-circuit diffusion of oxygen down grain boundaries. Hence studies were conducted involving the oxidation of nickel (pure and Ni-270) because outward cation nickel diffusion is known to be important in the growth of nickel oxide. In contrast with alumina scales, neither sulfur nor argon implants produced scale exfoliation. Moreover implanted carbon did not produce excessive porosity associated with the formation of CO. Yttrium implants had two effects. In pure nickel, implanted yttrium hindered oxidation-related diffusion. For both grades of nickel, the implanted yttrium was found after oxidation to be at the interface between two layers in the final oxide, functioning there as a marker indicating the initial surface of the metal. Nickel particles were present within mature scales on nickel of both grades characterized here. Mechanisms responsible for these effects and their implications are discussed.

Effects of grain-boundary segregation and precipitation on the hydrogen susceptibility of nickel

The straining electrode tensile test was employed to study hydrogen embrittlement in three grades of nickel. Aging at intermediate temperatures (400 to 800 °C) after solution annealing caused sulfur segregation to grain boundaries in the materials. This sulfur segregation was found to influence intergranular hydrogen embrittlement, and the effect was most prominent when the surface supply of hydrogen was low and when the grain boundaries were free of graphite precipitates. Aging also induced graphite precipitation at the grain boundaries of one grade of nickel (Nickel 200). The presence of these grain-boundary particles reduced susceptibility to hydrogen embrittlement, but at the same time caused a form of aging embrittlement. The effect of the second-phase precipitate, when present, masked the effect of sulfur segregation on hydrogen susceptibility.

Grain boundary sliding in nickel wires having a bamboo structure

A technique for determining grain boundary sliding (GBS) rates by torsional deformation of wires with a bamboo structure is described and discussed. At low stresses, where strain rates within the grains are negligible, the average GBS viscosity of many grain boundaries can be determined from a single test. Results for two grades of nickel at 898 K indicate a low stress region in which sliding rates are approximately linear in the stress, suggesting diffusional accommodated sliding. At higher stresses, sliding rates are enhanced and depend more strongly on the stress, In this regime, sliding occurs faster in the purer of the two grades of nickel, presumably because the lower creep strength of the purer material results in an enhancement of deformation processes close to the boundaries.

Prevention and reversal of oxygen embrittlement in nickel

Abstract Attempts to reverse the oxygen embrittlement caused by high temperature air exposure of nickel of various purities are described. It is shown that reversal can be effected in certain reducing environments in those grades of nickel having very low concentrations of metallic impurities, except in regions where heavy cavitation has occurred owing to gas formation. Oxygen embrittlement can similarly be prevented by prior annealing in hydrogen, but again only in the absence of significant metallic impurities. These results are explained on the basis of three distinct phenomena leading to embrittlement, and their implications are considered for the similar embrittlement observed in superalloys.

The mechanism of cavity formation during high temperature oxidation of nickel

Three mechanisms have been advanced to account for the grain boundary voids observed in nickel following high temperature oxidation: vacancy injection, oxide growth stresses, and internal oxidation of carbon. A critical test to distinguish between the two former and the latter is developed by comparing the cavitation response of three grades of nickel to exposure at 1000°C in air and in a controlled, low oxygen partial pressure. The observation of similar cavitation at oxygen partial pressures below those required to form an external oxide discounts both vacancy injection and creep voiding in response to oxide growth stresses as possible mechanisms. However, this result supports the third possibility, that involving gas-bubble formation due to the internal oxidation of carbon. This is proved in three ways: firstly, by demonstrating the crucial role of carbon in promoting cavitation by systematically removing and then replacing this element before oxidation; secondly by producing cavitation when carbon was diffused into oxygen-containing nickel; and thirdly, by using mass spectrometry to identify the carbon dioxide, and possibly carbon monoxide, contained within the grain boundary pores. Consideration of these results leads to the conclusion that the reported cases of grain boundary voiding on oxidation are explained by gas forming reactions and are not evidence for vacancy injection or the existence of oxide growth stresses.

The embrittlement of nickel following high temperature air exposure

The embrittlement of three grades of nickel following air exposure at 1000 °C is reported. This embrittlement manifests itself in a dramatic loss in tensile ductility around the 800 °C range, and is accompanied by a transition to intergranular failure. Similar behavior has previously been reported in nickel-base superalloys, but is now shown to be a general property of nickel. Tests in a variety of atmospheres have established that the damaging species is oxygen, and that this can have a profound effect, even when present at very low partial pressures. Grain boundaries are observed to be pinned and recrystallization suppressed after oxygen exposure. This lack of boundary mobility has been used to explain the temperature dependence of the embrittlement observed, and has been related to some of the results seen in superalloys. Finally, a few implications for environment-property interactions are considered.

Void formation and denudation in ion-irradiated nickel

Abstract As a continuing investigation of the effect of carbon on void formation in metals, 4 MeV Ni++ ions were used to bombard three grades of nickel to 25 dpa at 594°C after helium implantation to 15 appm at room temperature. All irradiated specimens showed dense void formation irrespective of the carbon content. The present study thus reveals that the carbon effect disappears at high damage doses because too many vacancies are produced in comparison with the number of carbon atoms present in the matrix and also because the trapping of vacancies by the carbon atoms is not assisted by recombinations. Meanwhile, the dual-irradiated Ni specimens displayed unusual behavior of void formation and denudation along twin and grain boundaries. The one-side appearance of void denudation along many grain boundaries and the formation of unusually large voids at the edge of the denuded zone are particularly conspicuous and may have repercussions on the use of the denudation phenomenon to partially solve the swelling...

Oxidation of TD nickel at 1050 and 1200�C as compared to three grades of nickel of different purity

The oxidation of three nickels of different purity, Ni-200 (≈ 4000 ppm impurity), Ni-270 (≈200 ppm), and JM-Ni (≈30 ppm) was compared to that of TD-Ni (≈400 ppm with 24,000 ppm ThO2). The samples were isothermally oxidized in slowly flowing air at 1050 and 1200°C. All nickels were oxidized with major surfaces either polished, ground, annealed at 1120°C and polished, or annealed at 1240°C and polished. Weight change, metal thickness loss, scale thickness, microstructure, and scale texture were examined. In weight change, metal loss, and scale thickness, the TD-Ni was nearly the same as the higher purity grades, JM-Ni and Ni-270, while Ni-200 oxidized approximately twice as much as the others. Grinding and annealing had only second order effects on these aspects of oxidation behavior. On the other hand, in scale microstructure and texture TD-Ni was similar to the lower purity Ni-200 while Ni-270 was similar to JM-Ni. Grinding did not affect the textures of JM-Ni or Ni-270, which Were (001), but changed the textures of Ni-200 and TD-Ni from (Oil) to (031). Annealing did not affect the microstructure of the oxide layers. A two-layer scale was observed only on the TD-Ni and Ni-200. The presence of ThO2 in TD-Ni appears to act as an impurity in oxide scale orientation but does not substantially alter the extent of oxidation.

Dynamic strain aging of carbon doped Ni

Dynamic strain aging has been studied in pure nickel and in a commercial nickel alloy containing 0.1 to 0.2 wt.% carbon. Relaxation experiments were performed in tension as a function of plastic strain, strain rate and relaxation time. Sharp yield points were obtained in both grades of nickel upon reloading following relaxation, accompanied by an increase in flow stress. The strengthening of NiC alloy, for short relaxation times, follows a t 2 3 law indicating that a Cottrell-Bilby type point defect-dislocation interaction mechanism is operative. Activation volume measurements, however, indicate a dual mechanism process, the active mechanism being dependent on relaxation time and stress level. On account of the observation of yield points in the pure nickel and the correspondence between measured activation volumes, it is concluded that dislocation-dislocation interactions also have a strong role in the relaxation process.

Desulfurization of sulfur amino acids and proteins with Raney nickel

The reaction of amino acids with Raney nickel has been carefully studied and the conditions most suitable for specificity determined. Two different grades of Raney nickel have been compared. One grade was prepared by addition of sodium borohydride to nickel acetate and the other was W 6 Raney nickel. Reaction was studied at pH 5.0, 7.0 and 8.0 at 40°. The most efficient conditions were at pH 7.0 and 40°. Cystine was completely converted to alanine in 4 min. No appreciable differences were found in the rates of the desulfurization of methionine which were extremely low. At pH 7.0 and 22° or lower, the reaction showed a high degree of specificity for cystine which was completely desulfurized in 12 min (at 22°) while methionine was essentially unchanged even after 10 h of reaction. The reaction has been applied for the specific desulfurization of cysteine (or cystine) residues in hemoglobin, lysozyme and α-lactalbumin, respectively.

Degassing properties of nickel

The grades of nickel used in the electronic valve industry, containing magnesium, silicon and carbon among other impurities, have been found to have gas contents in the range 1.5 to 16 ml. torr g-1, the average value being about 5.0 ml. torr g-1. The total quantity of gas evolved is limited by the amount of oxygen present in the form of oxides of the impurities, particularly magnesium. These oxides have been found, both in wire and sheet, to be concentrated near the surface. In the case of sheet material 0.150 mm thick, 80% or more of the total gas content is in a skin 15μ thick. The diffusion constant of the gas desorbed from the nickel (largely carbon monoxide resulting from the reaction of carbon with the impurity oxides) has been measured in the temperature range 850° C to 975° C and, comparing the results with the diffusion of carbon in nickel, it is concluded that the evolution rate of carbon monoxide is largely controlled by the rate of carbon diffusion. In nickel which contains no stable impurity oxides the evolution of carbon monoxide proceeds at a slower rate and is controlled by the diffusion rate of the oxygen in the nickel lattice. The differences in evolution rate of carbon monoxide from the various grades of nickel can be explained in terms of the location of the oxygen in the nickel.