Ni Laterite Ores Research Articles

Ni(Co) Laterite Deposits of Southeast Asia: A Review and Perspective

Southeast Asia has great potential for mineral exploration, and this region is well-known to host huge economic ore deposits located in complex tectonic terranes. Amongst these ore deposits, the Ni(Co) laterite deposits are mainly distributed in Indonesia, the Philippines, and Myanmar. There are two main types of Ni(Co) laterite deposits consisting of hydrous Mg silicate (or garnierite) and oxide ores, with limited development of clay silicate type. These deposits are influenced and controlled by the lithology of ultramafic bedrock, topography, climate, weathering, structures, and tectonic environment. The degree of bedrock serpentinization has an important influence on the grade of Ni laterite ore. Given the growing demand of modern society for Ni(Co) ore resources, deep research should be focused on a better understanding of the genesis of this laterite deposit and geological features of Ni(Co) ore, as well as its exploration applications in southeastern Asia. Improving current research and exploration methods by means of cutting-edge technologies can enhance the understanding of the Ni(Co) enrichment mechanism in weathered laterite and lead to the discovery of new deposits in Southeast Asia. Ni(Co) laterite deposits from this region, especially Indonesia and the Philippines, have the potential to be a source of scandium, rare earth elements, and platinum group elements.

Utilization of laterite ore as an oxygen carrier in chemical looping reforming of methane for syngas production

Growing energy demands in various sectors have resulted in overusing fossil fuel sources and rise in greenhouse gases in the atmosphere. This necessitates the need for reducing greenhouse gases and shifting to cleaner, renewable energy sources like H2. Chemical looping is one such renewable method to produce clean H2. The efficiency of this process depends on the oxygen carrier. Generally, oxygen carriers (OC) are transition metal oxides (Fe2O3 or NiO) or some complex metal oxides like spinel or perovskites, but usage of these OCs are restricted due to their availability and redox performance. One solution for selecting OCs can be using industrial waste like slag or low-grade ores because of their composition, which consists of metal oxides. One such low-grade ore is Ni-laterite ore or chromite overburden, a mining waste found in the chromite mines of Sukinda (India). In this work, we have focused on utilizing this laterite ore as an OC for the chemical looping reforming of methane to produce syngas. The reactivity analysis of laterite ore with CH4 was performed in DSC-TG and the reaction products were analyzed in gas chromatography along with microscopy and spectroscopic techniques. Results showed the formation of H2 and CO gases along with reduced metallic phases. The total H2 yield at 750 °C is determined to 53.67 (±1.09) ml/g of OC which is comparable or even higher than existing CeO2 based OCs. Further, thermodynamic calculations are presented to calculate the theoretical yield for our process and compared with the experimental H2 yield. This study effectively demonstrates the performance of laterite ore as an OC for generating clean and renewable energy through chemical looping technique.

Enhancement of nickel laterite ore bioleaching by Burkholderia sp. using a factorial design

Interest in low-grade Ni-laterite ores has increased in recent years; however, the laterite process has proven technically difficult and costly, and the development of alternative low-cost biotechnologies for Ni solubilization has been encouraged. In this context, for the first time, a sample of Brazilian Ni-laterite ore was subjected to microbial bioleaching using a heterotrophic Burkholderia sp. strain. Experiments were performed in a 23 two-level full factorial design by determining the influence of glucose concentration (5–15%, w/v), Ni-laterite ore concentration (0.25–0.75%, w/v), and cultivation period (14–42 days) on Ni solubilization. The variable more important for Ni-laterite bioleaching was the glucose concentration (x1). Bioleaching batch experiments demonstrated that about 87% Ni (7.5 mg Ni/g ore) were solubilized by Burkholderia sp. after 42 days. This study's significance is that it has opened up an opportunity for the potential application of potassium-solubilizing bacterial strains to process low-grade Ni-laterite ores.

Multiscale physical–chemical analysis of the impact of fracture networks on weathering: Application to nickel redistribution in the formation of Ni-laterite ores, New Caledonia

Supergene processes related to downward water migration and dissolution of primary minerals in the New Caledonian peridotites result in Ni enrichment at the bottom of the lateritic profile near bedrock. However, the combined effects of relief, lateral fluid flow, and complex inherited discontinuity networks filled by serpentine generate a more complex Ni distribution than a simple flat horizon. In surficial environments, fluid flow and mass transfer are not limited to the vertical scale; they can also be related to lateral fluid circulation and local drainage along damage zones in the vicinity of faults. In this study, we present new structural, petrophysical and geochemical data for core samples to shed light on the impact of a fracture network on the alteration and progression of the Ni-enrichment front during weathering. The analysis of element redistribution by XRF mapping coupled with fracture extraction from computed tomography (CT) establishes that the serpentine fracture network comprises sets of sub-orthogonal fractures whose orientations are potentially determined by pre-existing magmatic foliation. The progression of the olivine dissolution front leads to the redistribution and concentration of Ni into the serpentine fracture network as secondary Mg-Ni talc-like phases. The increase in porosity from < 1 % in the bedrock to > 10 % in the saprock is mainly driven by the formation of nanopores. Nanoporosity may control the development of the weathering front and the redistribution of Ni by small-scale diffusion. Structural and geochemical characteristics identified at the sample scale are analogous to those observed on the larger scale of the outcrop and deposit. Scale invariance in the structural organization and geochemical evolution indicates the potential upscaling of the processes involved in the redistribution of Ni.

Chemo-physical concentration of a Low-grade nickel laterite ore

• A novel method for the beneficiation of limonitic Ni laterites . • Long-term oxalic acid leaching of a low-grade Ni laterite ore from Iran. • A dissolution-precipitation behavior for Ni in contrast to leachability of Fe. • Fast dissolution for Ni and Fe but delayed precipitation for Ni at high temperature. • Collection of nickel oxalate particles in the fine fraction of the leach residue. Extraction of nickel from laterites is a challenging task due to the lack of an efficient nickel concentration method. Current efforts on the beneficiation of nickel laterites–especially low-grade ones– are mainly focused on atmospheric leaching methods using mineral acids, organic acids, or a mixture of them. The aim of the present paper is developing a novel hydrometallurgical approach to concentrate nickel from laterites based on a long-term oxalic acid leaching followed by size separation of the leach residue. A limonitic laterite sample from Sarchahan deposit (Fars province, Iran) containing 0.8% Ni and 27.3% Fe was used for the experiment and dissolution behavior of nickel and iron during the course of long time leaching runs (52 h) was studied under the influence of temperature (60–90 °C) and oxalic acid concentration (0.75–1.25 M). The results show that nickel initially dissolves, but subsequently precipitates with the presence of oxalate ions as NiC 2 O 4 ·2H 2 O. In addition, iron steadily dissolves as ferric oxalate and maintained in solution so long as light-protected. However, it tends to precipitate as FeC 2 O 4 ·2H 2 O at higher temperatures and long retention times. The leach residue was separated into a fine and a coarse fraction via wet classification using a cut point of 44 μm. Phase and chemical analysis confirmed accumulation of nickel in the fine fraction yielding a Ni concentrate as an intermediate product. The concentrate obtained at 60 °C and 1.25 M oxalic acid concentration contained 3.2% Ni (∼10% NiC 2 O 4 ·2H 2 O) and 3.5% Fe with a corresponding concentration ratio of 4.05, enrichment ratio of 3.44 and nickel recovery of 84%. The proposed method appears to provide a promising prospect for exploiting low-grade nickel laterites, as the obtained concentrate could be a suitable feedstock for both pyro- and hydrometallurgical processing to yield a marketable Ni product.

Recommendation for lateritic Ni-ore processing: garnierite mineralogical and geochemical approach

The objective of this study is to analyze the mineralogy and geochemistry of garnierite and its implication for Ni laterite processing. Mineralogical analysis using optical microscopic and X-ray diffraction (XRD) methods were performed, whereas chemical composition was obtained by X-ray fluorescence (XRF) method. Genetically, Ni in laterite ore is associated with SiO2 and MgO and is not accompanied by the elements of Co, Fe, Cr, Al, Mn, and Ca. In this study, Ni-laterite ore has Ni content of 2.1%, SiO2 25.42%, S/M ratio 3.7, and Fe/Ni ratio 15.5, meaning that it is more suitable to be processed by pyrometallurgical route. However, there are some characters that still have to go through treatment, namely reducing of Fe from 32.63% to 20%, increasing MgO, and reducing SiO2 by blending. Result of mineralogical analysis shows that the dominant mineral is quartz (44.8%) and talc (38.85%) with small amount of lizardite (16.35%). The high content of quartz and talc and the low in lizardite of the Ni-laterite ore in the study area indicated that it is recommended for pyrometallurgical processing which is also in accordance with its geochemical characteristics.

Origin of Critical Metals in Fe–Ni Laterites from the Balkan Peninsula: Opportunities and Environmental Risk

As the global energy sector is expected to experience a gradual shift towards renewable energy sources, access to special metals in known resources is of growing concern within the EU and at a worldwide scale. This is a review on the Fe–Ni ± Co-laterite deposits in the Balkan Peninsula, which are characterized by multistage weathering/redeposition and intense tectonic activities. The ICP-MS analyses of those laterites indicated that they are major natural sources of Ni and Co, with ore grading from 0.21 to 3.5 wt% Ni and 0.03 to 0.31 wt% Co, as well as a significant Sc content (average 55 mg/kg). The SEM-EDS analyses revealed that fine Fe-, Ni-, Co-, and Mn-(hydr)oxides are dominant host minerals and that the enrichment in these elements is probably controlled by the post-formation evolution of initial ore redeposition. The paucity of rare earth element (REE) within the typical Fe–Ni laterite ore and the preferential occurrence of Co (up to 0.31 wt%), REE content (up to 6000 mg/kg ΣREE), and REE-minerals along with Ni, Co, and Mn (asbolane and silicates) towards the lowermost part of the Lokris (C. Greece) laterite ore suggest that their deposition is controlled by epigenetic processes. The platinum-group element (PGE) content in those Fe–Ni laterites, reaching up to 88 μg/kg Pt and 26 μg/kg Pd (up to 186 μg/kg Pd in one sample), which is higher than those in the majority of chromite deposits associated with ophiolites, may indicate important weathering and PGE supergene accumulation. Therefore, the mineralogical and geochemical features of Fe–Ni laterites from the Balkan Peninsula provide evidence for potential sources of certain critical metals and insights to suitable processing and metallurgical methods. In addition, the contamination of soil by heavy metals and irrigation groundwater by toxic Cr(VI), coupled with relatively high Cr(VI) concentrations in water leachates for laterite samples, altered ultramafic rocks and soils neighboring the mining areas and point to a potential human health risk and call for integrated water–soil–plant investigations in the basins surrounding laterite mines.

Chromium occurrence in a nickel laterite profile and its implications to surrounding surface waters

Ultramafic rocks are considered as the most important geogenic sources of Cr whose hexavalent species is of environmental concern. In tropical to subtropical areas (e.g. New Caledonia, Brazil, Philippines), prolonged and pervasive weathering of ultramafic rocks produces Ni laterite ores which are further enriched in Cr. While elevated levels of Cr have been identified in Ni laterites, Cr availability and export from these deposits and its contribution to natural waters remain poorly understood. Therefore, this study examined the speciation and flux of Cr in a Ni laterite profile through sequential extraction and leaching experiments coupled with physical, mineralogical, and geochemical characterization. These were correlated to the behavior and export of Cr in surrounding surface waters studied through hydrochemical investigation. This work demonstrates, through the example of the Rio Tuba Ni laterite deposit, that pervasive weathering of ultramafic rocks in tropical areas generate very important reservoirs of Cr(VI). Although Cr is primarily fixed in insoluble fractions (>89%) and least in bioavailable and easily mobilizable phases (<1%), due to the inherent elevated Cr content (up to 2.9 wt%) of the Ni laterites, the latter still provided water-extractable Cr(VI) contents surpassing drinking water and freshwater standards. By comparison with the silicate-rich saprolite unit, the overlying Fe-(oxyhydr)oxide dominated laterite layer yielded lower Cr(VI) contents due to its acidic nature and higher amounts of organic matter and Fe-(oxyhydr)oxides which promote reduction and readsorption of Cr(VI). During water infiltration, Cr(VI) migrates downward along the profile at a rate of 62 to 3446 t/km2/yr. While the alkaline and oxidizing conditions of the surrounding surface waters favor Cr(VI) mobilization, only a fraction of Cr(VI) from the Ni laterites reaches these water bodies. Cr(VI) concentrations (≤213 μg/L) and fluxes (mostly ≤50 kg/km2/yr) in the surface waters being significantly lower than that of the Ni laterites reflect the action of processes (e.g. dilution, reduction, adsorption) that attenuate the release of this species along water flow paths.

Kinetics study on non-isothermal carbothermic reduction of nickel laterite ore in presence of Na2SO4

Sodium sulfate has proven to be an effective additive for enhancing the reduction and metal aggregation during the carbothermic reduction of Ni laterite ore. In this study, the effect of Na2SO4 on the non-isothermal reduction kinetics of Ni laterite ore with solid C was investigated. The kinetic parameters and mechanism function were determined. The reduction mechanism was also analyzed by combining X-ray diffraction analysis with evolved-gas analysis. The results indicated that the reduction process was divided into three stages on the basis of the conversion degree. The average activation energy was 323.0 kJ/mol for the initial stage of α = 0–0.40, 161.2 kJ/mol for the middle stage of α = 0.40–0.80, and 161.3 kJ/mol for the decaying stage of α = 0.80–1.00. Three-dimensional diffusion equation was determined as the mechanism function in the initial and middle stage. The chemical reaction function exhibited the best fit in the decaying stage.

Extraction of nickel and cobalt from a laterite ore using the carbothermic reduction roasting-ammoniacal leaching process

The carbothermic reduction roasting followed by ammoniacal leaching of a Ni-laterite ore from Bajaur (Pakistan) has been studied first time for its potential exploitation via the Caron process. The use of fuel oil as reductant can be costly in Pakistan, therefore, plenty available coal was employed in this study. The roasting parameters like coal mixing proportion (5–15 wt%), temperature (600–900 °C), additive dosage (3–12 wt%), and time (15–180 min) were varied to optimize the selective reduction of Ni and Co. The extent of goethite phase transformation of roasted products characterized through the X-ray diffraction (XRD) analysis could depict sharp peaks for the formation of Ni-Fe alloy phase in the presence of an additive, Na2SO4. The optimal reduction condition was observed to be laterite ore mix with 10 wt% coal and 9 wt% Na2SO4, and roasted at 800 °C for 120 min. Leaching of the roast-reduced product performed in NH4OH–(NH4)2CO3 solutions (150 g/L total NH3) was influenced by carbonate ion concentration and yielded >90% Ni and 67% Co. The apparent activation energy of Ni, 21.2 kJ/mole and Co, 7.6 kJ/mole indicated to follow intermediate-controlled and diffusion-controlled mechanism, respectively. Furthermore, the leach liquor was pre-oxidized and contacted to 10 vol% of LIX 84-I; yielding a selective extraction of >97% Ni over Co at the organic-to-aqueous ratio of 1. Results presented in this paper suggest that the extraction of Ni and Co from Bajaur lateritic ore is technically feasible through the Caron process, and can be useful to others as well.

Characterization and bioleaching of nickel laterite ore using Bacillus subtilis strain.

There are two principal types of nickel (Ni) deposits: sulfide and laterite ores. Interest in low-grade Ni-laterite ores has increased in recent years as high-grade Ni-sulfide deposits are being quickly depleted. However, processing of Ni laterites has proven technically difficult and costly, and the development of alternative low-cost biotechnologies for Ni solubilization has been encouraged. In this context, by the first time, a sample of Brazilian Ni-laterite ore was analyzed mineralogically and subjected to bioleaching tests using a heterotrophic Bacillus subtilis strain. SEM-analysis indicated that the primary Ni carrier mineral is goethite. Chemical analysis of different grain size fractions indicated a homogeneous distribution of Ni. XRF-analysis showed that the ore consists mainly in lizardite (32.6% MgO) and contains1.0% NiO (0.85% Ni). Bioleaching batch experiments demonstrated that about 8.1% Ni (0.7 mg Ni/g ore) were solubilized by the B. subtilis after 7 days. Application of microwave heating as a Ni-laterite pretreatment was also tested. This pretreatment increased the bioextraction of Ni from 8% to 26% (2.3 mg Ni g-1 ore).

New insights into nanomineralogy and geochemistry of Ni-laterite ores from central Greece (Larymna and Evia deposits)

Nickeliferous laterite ores from two typical central Greece deposits (Larymna and Evia), currently used in the LARCO GMMSA smelting plant to produce ferronickel, were characterized using a combination of diffraction, microscopic, and analytical techniques. X-ray diffraction patterns of various fractions, with emphasis to the clayey material (<2 μm), after glycolation and heating at 550 °C, indicated that both materials contain crystalline Fe3+ oxide (hematite) and chlorite-group phyllosilicates, whereas the Evia sample contains additional illite. Transmission electron microscopy investigations revealed that the LARCO laterite ores consist of complex nanoscale aggregates of the above-mentioned phases. Different Ni-bearing Mg-Fe-phyllosilicates (mainly chlorite-group minerals), occur in mixture with hematite. Nickel is present in all examined phases, and therefore the separation of pure Ni-phases, by physical or chemical methods, is practically unfeasible. Trace element bulk analyses showed that there no significant differences, with regarding to Ni content concentrations (ca. 0.6–0.7 wt.%), between the initial ore and the clay fraction, for both the Larymna and Evia laterites (ca. 30% and 26% wt.% enrichment respectively). However, the Larymna ore contains double quantities of Co and it is enriched in rare earths compared to Evia (ΣREE = 774 ppm and 76 ppm respectively), while Sc concentrations are comparable in both mining areas (64 ppm and 42 ppm respectively). Discrimination diagrams (e.g. Th/Sc vs. Zr/Sc and Ce/Ce* vs. Eu/Eu*) showed that LARCO laterite Ni-ores do not exclusively originate in ultrabasic -ophiolitic- rocks as previously considered.

Reactive Transport Modeling Applied to Ni Laterite Ore Deposits in New Caledonia: Role of Hydrodynamic Factors and Geological Structures in Ni Mineralization

AbstractThis study is devoted to understanding the impact of topography and hydrodynamics on the formation of high‐grade supergene nickel deposits. The investigation proposes a new conceptual mineralization model that describes the formation of various exceptionally Ni‐enriched hot spots observed in lateritic profiles. Numerical analysis of the effects of local hydrodynamics on deposits formation is performed by means of PHREEQC geochemical simulator and COMSOL Multiphysics software. These are coupled through an iCP Java interface that allows to code their level of interaction and facilitates the exchange of parameters. The model developed extends the currently existing geochemical formulation of nickeliferous laterite formation from peridotite carried out in 1‐D and is additionally capable of simulating mass solute transport and geochemical processes within complex fractured‐porous systems. The simulations improve our understanding of metal enrichment in saprolite and bedrock zones. It was shown that, although the initial development of nickel lateritic ores takes a few million years, they are prone to relatively quick leaching and subsequent redistribution of Ni when the topography changes in response to tectonic processes. The latter leads to the formation of rich nickel deposits at the bottom of the slope, mostly due to leaching of the saprolite material. In addition to the role of changes in topography, the critical impact of fractures and fracture networks on metal mobility and distribution was identified. The model developed provides significant insight into the distribution of mineral resources, in particular Ni deposits, and can be of great help for future mineral prospecting in industry.

Concentration and Separation of Scandium from Ni Laterite Ore Processing Streams

The presence of a considerable amount of scandium in lateritic nickel-cobalt ores necessitates the investigation of possible processing alternatives to recover scandium as a byproduct during nickel and cobalt production. Therefore, in this study, rather than interfering with the main nickel-cobalt production circuit, the precipitation-separation behavior of scandium during a pH-controlled precipitation process from a synthetically prepared solution was investigated to adopt the Sc recovery circuit into an already existing hydrometallurgical nickel-cobalt hydroxide processing plant. The composition of the synthetic solution was determined according to the hydrometallurgical nickel laterite ore processing streams obtained from a HPAL (high-pressure sulphuric acid leaching) process. In order to selectively precipitate and concentrate scandium with minimum nickel and cobalt co-precipitation, the pH of the solution was adjusted by CaCO3, MgO, Na2CO3, and NaOH. It was found that precipitation with MgO or Na2CO3 is more advantageous to obtain a precipitate containing higher amounts of scandium with minimum mass when compared to the CaCO3 route, which makes further processing more viable. As a result of this study, it is proposed that by a simple pH-controlled precipitation process, scandium can be separated from the nickel and cobalt containing process solutions as a byproduct without affecting the conventional nickel-cobalt hydroxide production. By further processing this scandium-enriched residue by means of leaching, SX (solvent extraction), and precipitation, an intermediate (NH4)2NaScF6 product can be obtained.

Overcoming the bacteriostatic effects of heavy metals on Acidithiobacillus thiooxidans for direct bioleaching of saprolitic Ni laterite ores

In this study, the adaptation of Acidithiobacillus thiooxidans to heavy metals leached from saprolitic Ni laterite ores from Riverina, Australia, was performed by gradual acclimatisation. The microorganism was cultivated in heavy metals (Ni, Co, Fe, Mg, Cr and Mn) with total concentrations of 2400 to 24,000ppm equivalent to total dissolution of 1 to 10% (w/v) pulp densities of the saprolitic Ni laterite ore. Adaptation evolution mapped from its tolerance index was found to be dependent on metal concentration, acid generation, and period of adaptation. Bio-stimulation of cell growth and acid production was promoted by heavy metal stress on the bacteria. Pre-established heavy metal tolerance of the bacterial strain improved the leaching rate in its early phase; 20% and 7% increase in Ni and Co metal recoveries were observed in using adapted bacteria. However heavy metal tolerance was also achieved by the bacterium during the leaching process, albeit delayed by a lag phase. These results confirm the robust nature and suitability of A. thiooxidans in direct bioleaching of Ni ores.

Overcoming the Bacteriostatic Effects of Heavy Metals on &lt;i&gt;A.&lt;/i&gt; &lt;i&gt;thiooxidans&lt;/i&gt; Direct Bioleaching of Saprolitic Ni Laterite Ores

In this study, the adaptation of A. thiooxidans to heavy metals leached from saprolitic Ni laterite ores was performed by gradual acclimatisation. The bacteria was cultivated in heavy metals (Ni, Co, Fe, Mg, Cr and Mn) with total concentrations of 2400 to 24000 ppm equivalent to total dissolution of 1 to 10% (w/v) pulp densities of the saprolitic Ni laterite ore. Adaptation evolution mapped from its tolerance index was found to be dependent on metal concentration, acid generation, and period of adaptation. Bio-stimulation of cell growth and acid production was promoted by heavy metal stress on the bacteria. Pre-established heavy metal tolerance of the bacteria improved the leaching rate in its early phase; 20% and 7% increase in Ni and Co metal recoveries were observed in using adapted bacteria. However heavy metal tolerance was also achieved by the bacteria during the leaching process, albeit delayed by a lag phase. These results confirm the robust nature and suitability of A. thiooxidans in direct biomining of Ni ores.

Nickel isotope fractionation during laterite Ni ore smelting and refining: Implications for tracing the sources of Ni in smelter-affected soils

Nickel isotope ratios were measured in ores, fly ash, slags and FeNi samples from two metallurgical plants located in the Goiás State, Brazil (Barro Alto, Niquelândia). This allowed investigating the mass-dependent fractionation of Ni isotopes during the Ni-laterite ore smelting and refining. Feeding material exhibits a large range of δ60Ni values (from 0.02 ± 0.10‰ to 0.20 ± 0.05‰, n = 7), explained by the diversity of Ni-bearing phases, and the average of δ60Nifeeding materials was found equal to 0.08 ± 0.08‰ (2SD, n = 7). Both δ60Ni values of fly ash (δ60Ni = 0.07 ± 0.07‰, n = 10) and final FeNi produced (0.05 ± 0.02‰, n = 2) were not significantly different from the feeding materials ones. These values are consistent with the very high production yield of the factories. However, smelting slags present the heaviest δ60Ni values of all the smelter samples, with δ60Ni ranging from 0.11 ± 0.05‰ to 0.27 ± 0.05‰ (n = 8). Soils were also collected near and far from the Niquelândia metallurgical plant, to evaluate the potential of Ni isotopes for tracing the natural vs anthropogenic Ni in soils. The Ni isotopic composition of the non-impacted topsoils developed on ultramafic rocks ranges from −0.26 ± 0.09‰ to −0.04 ± 0.05‰ (n = 20). On the contrary, the Ni isotopic composition of the non-ultramafic topsoils, collected close to the plant, exhibit a large variation of δ60Ni, ranging from −0.19 ± 0.13‰ up to 0.10 ± 0.05‰ (n = 4). This slight but significant enrichment in heavy isotopes highlights the potential impact of smelting activity in the surrounding area, as well as the potential of Ni isotopes for discerning anthropogenic samples (heavier δ60Ni values) from natural ones (lighter δ60Ni values). However, given the global range of published δ60Ni values (from −1.03 to 2.5‰) and more particularly those associated to natural weathering of ultramafic rocks (from −0.61 to 0.32‰), the use of Ni isotopes for tracing environmental contamination from smelters will remain challenging.

Preconcentration strategies in the processing of nickel laterite ores part 3: Flotation testing

The preconcentration of nickel (Ni) laterite ores ahead of Ni recovery by hydrometallurgical processing makes good economic sense. Since Ni-bearing minerals are often finely disseminated through laterite ores, liberation of minerals either high and/or low in Ni content is a prerequisite prior to any form of separation process. It is the purpose of this paper to investigate the use of flotation to generate products either high or low in Ni-bearing minerals from a sample of Ni laterite with the generic description of “siliceous goethitic”. Previous attempts showed that upgrading of Ni laterites has only been conducted in laboratory or pilot plant scale, not adopted commercially. A number of feed preparation techniques ahead of flotation were attempted at laboratory scale on a sample of Ni laterite containing predominantly goethite and quartz. Flotation tests even on closely sized particles (38–75μm) failed to yield significant Ni upgrades using the reagents tested in this study, based on those used commercially for processing iron oxide ores. The best result was an increase in Ni content from 1.0% to 1.4% at a Ni recovery of 43%. This was obtained using 400g/t of an amine collector and 300g/t of starch at pH 10 on a sample of hydrocyclone underflow. This paper was designed to provide some lessons learnt for future researchers from laboratory flotation testing of a complex Ni laterite ore.

Preconcentration strategies in the processing of nickel laterite ores part 2: Laboratory experiments

A number of physical separation techniques for nickel (Ni) laterites have been investigated at laboratory and pilot plant scale and reported in the open literature. These included sink–float (or dense media) separation, gravity separation, magnetic separation, electrostatic separation, (roasting) and flotation. The information located so far and reported in the literature review by Quast et al. (2015) suggests that all these techniques, although providing some degree of upgrading, have not been incorporated into full plant operations as yet. The only successful preconcentration technique incorporated into some commercial operations has been the removal of a coarse product containing lower Ni values than the feed. In this work, the application of a number of physical separation techniques (screening, gravity and magnetic separation with and without roasting) has been investigated in the laboratory for upgrading three Western Australian low-grade Ni laterites (goethitic, siliceous goethitic and saprolitic). Roasting of the goethitic laterite caused a noticeable increase in Ni and Co (and corresponding mass) recovery into the magnetic product with temperature up to a certain point, but this effect was reversed at 650°C. Overall, the application of the selected techniques failed to produce any significant Ni grade enhancement for these three laterite ores. These tests confirm that the complex mineralogy of these three Ni laterite ores compromises any significant upgrading in Ni values by standard physical separation techniques.

Preconcentration strategies in the processing of nickel laterite ores Part 4: Preliminary dewatering studies

The aim of this paper is to address primary dewatering of nickel (Ni) slurry streams resulting from any form of aqueous processing. The test work was conducted to investigate primary dewatering of screened products from either stirred milling or overflows from a hydrocyclone. Settling tests for the stirred mill products were conducted in 2M NaCl to simulate expected process water quality where these laterite processes are located. Primary dewatering of 10wt.% <38μm stirred mill products can be successfully implemented for the three Ni laterite ores in 2M NaCl solutions. Sediment solid contents of>20wt.% have been achieved for all three ore types without raking. Sediment consolidation was significantly increased in further tests using low shear rate raking at 0.1rpm. Zeta potentials were measured as a function of pH for all the fine laterite samples and compared to the characteristics for some of the major ore components. The more rapid settling behaviour observed for the goethitic laterite slurries was explained by little particle–particle repulsion due to the tests being conducted close to the isoelectric point. The zeta potentials measured at the pH values where the settling tests were conducted for laterites containing higher amounts of silica and silicates were much higher, requiring higher additions of flocculant and settling to lower sediment solids densities. The high salt content (2M NaCl) is expected to screen electrostatic interactions between the particles and enhance settling behaviour.