Ni-bearing Minerals Research Articles

Collaborative separation of nickel and iron from nickel laterite ore and red mud

ABSTRACT In this study, we investigated a nickel laterite ore with Ni content of 1.56 wt% and a red mud with Fe content of 20.98 wt%, the main Ni-bearing mineral in the nickel laterite ore was nickel-lizardite, and the main Fe-bearing mineral in the red mud was hematite. A novel process of roasting and magnetic separation was purposed to extract nickel and iron from the nickel laterite ore and red mud. The nickel laterite ore, red mud, calcium chloride, and coke were mixed and put in a roaster for roasting, and the ferronickel concentrate was obtained from the roasted ore by magnetic separation. The results showed that a ferronickel concentrate with Ni content of 7.97 wt%, Fe content of 73.09 wt%, iron recovery of 76.87%, and nickel recovery of 90.28% was obtained under the optimal conditions: a mass ratio of m (nickel laterite ore): m (red mud) : m (coke) : m (calcium chloride) : of 0.6:0.4:0.2:0.1, a roasting temperature of 1373 K, a roasting time of 90 min, a grinding fineness of − 0.045 mm occupying 90%, and a magnetic field strength of 0.20 T. The main minerals in the ferronickel product were metallic Fe and FeNi.

COMPORTAMENTO TÉRMICO DE 25°C A 1100°C DO MINÉRIO DE NÍQUEL DA MINA ONÇA-PUMA EM CARAJÁS

Ferronickel alloys are produced by pyrometallurgical processes from nickel-bearing hydrous magnesium silicates occurring in the saprolite in laterite deposit of the Serra de Onça-Puma/Pará-Brazil. The ore is treated by RKEF process. It consists of drying, calcination and reduction, however, the processing of lateritic nickel ore is quite difficult since the Ni-bearing minerals are finely disseminated in the ore bodies. In this work was studied the influence of thermal treatment between 25°C and 1100°C in nickel lateritic ore, evaluated through thermal analysis (Tg/DTA) and x-ray diffraction (XRD). The XRD analyses of raw samples without thermal treatment showed that they are mixture of serpentine, smectite and chlorite. After starting thermal treatment, the curves of Tg/DTA revealed to have two endothermic peaks at 60°C to180°C and 594°C to 613°C due to release the adsorbed and crystalline water, respectively, followed by an exothermic peak at 820ºC which can be attributed to the change in crystal structure and consequent formation of a new mineral phases. Weight differences can be observed when the adsorbed water removed, without phase changes in the range of 60°C to 180°C, indicated stability of nickel ore. Phase changes and weight loss were observed at 594°C to 613°C with clear crystalline breaking of the serpentines and smectite forming amorphous substances. Above this temperature new phases are crystallized until 820°C, when is formed forsterite (trevorite), enstatite and hematite, remaining unchanged quartz. On the analyzed conditions might infer that the pyrometallurgical to iron nickel production through this type of laterite ore effectively corresponds to RKEF process.

Sulfide mineralization in Sikhuran ophiolite complex, Esfandagheh, Iran: Implications from trace element composition of silicate and sulfides

The Sikhuran ophiolite complex in Esfandagheh, Kerman province, is considered one of the important chromite mining areas in southern Iran. The complex is comprised of mainly tectonized harzburgite of residual upper mantle, depleted harzburgite, chromitite, dunite, and orthopyroxenite of the transition zone, as well as upper cumulates of ultramafic-mafic rocks. Sulfide disseminations, i.e., pentlandite, chalcopyrite, chalcocite, millerite, and heazlewoodite are hosted by dunite and chromitite in the upper part of the transition zone. The abundance of Base Metal Sulfides (BMS) as interstitials of olivine shows early stage sulfur saturation in Mg-rich magmas. Low Ni contents of ubiquitous olivine indicate that Ni in the primary silicate melt is preferentially concentrated in the sulfide liquid. The high activity of Ni in the melt is evidenced by the dominance of Ni-rich pentlandite and other Ni-bearing minerals from the Sikhuran ophiolite complex. Major and trace element compositions indicate that pentlandite is the main PGE-carrier with ƩPGE up to 44 ppm. Palladium, the most abundant PGE, is partitioned into pentlandite by diffusion of Monosulfide Solid Solution (MSS). The factors affecting this mechanism include the initial concentration of Pd, low compatibility of Pd compared to IPGEs, and decreasing solubility of Pd in MSS with decreasing temperature. Generally, although no detailed studies have been conducted on the occurrence of sulfide minerals in Iran; sulfide mineralization with coarse sulfide minerals in the Sikhuran can be a new perspective for mining companies and economic geologists.

New insights into the distribution and speciation of nickel in a Myanmar laterite

Because ferromanganese oxides can host significant amounts of Ni during the weathering, the Fe- and Mn-oxide are resultantly considered as the important Ni-bearing minerals. However, little is known about the role of Mn species to influence the Ni behavior during this process. In this study, we employed the techniques of ICP-MS, XRF, XRD, XAFS (XANES and EXAFS), and μ-XRF to interpret the Ni behavior along a laterite profile in Myanmar. Nickel concentrations in the saprolite developed on peridotites can reach up to 11 wt% Ni mainly because of Ni precipitation as fracture-fillings and thin coatings on joints, which produce a promisingly and importantly economic mineral resource of this territory. In the peridotites, Fe and Mn species predominantly consisted of olivine (96%) and biotite (74%), respectively. Nickel XANES spectra indicated that Ni was primarily hosted by olivine (86%) in the protolith under reduction condition, lizardite (90%) and Ni-bearing goethite (10%) in the lower garnierite vein under strong oxidation condition, and lizardite (37%) and Ni-bearing goethite (63%) in the upper saprolite under medium oxidation condition. Accordingly, minerals of Fe and Mn were progressively oxidized toward Fe3+ and Mn4+, which occurred primarily as Fe3+-bearing goethite and Mn4+-bearing birnessite. The occurrence of Fe- and Mn-oxide plays an important role in Ni species and suggests that birnessite maybe facilitate the formation of Fe oxide precipitations by means of the oxidation of Fe2+ in the olivine to Fe3+ in the goethite. The results are of relevant importance, as it fills a gap in the knowledge of ore-formation processes occurring in Myanmar

High-Temperature microwave properties and phase transitions of ultramafic nickel ores

The mining of ultramafic ores is required to meet society’s continued demand for nickel. These deposits, however, are difficult to process due to their high serpentine content. Serpentine, a gangue mineral, increases slurry viscosity, slime-coats the valuable Ni-bearing mineral pentlandite, and reports to and dilutes the froth during flotation via the formation of bubble-fibre aggregates. Microwave pre-treatment can be used to convert the serpentine gangue to olivine, which should improve ore processing. However, the fundamental microwave properties and heating behaviour of ultramafic ores must be understood to develop a robust process. Microwave heating curves were developed for, and high temperature permittivity analysis was conducted on, two ultramafic nickel ores (Pipe and OK ore). Subsequently, TGA/DSC (thermogravimetric analysis/differential scanning calorimetry) and HTXRD (high-temperature x-ray diffraction) tests, along with a thermodynamic analysis using FactSage 7.3, were done to explain the heating behaviours and permittivity data. An unusual peak in the permittivity data was detected at 950 °C for the Pipe ore with both increasing and decreasing temperature; however, no phase transitions were detected in the TGA/DSC analysis. HTXRD of the Pipe ore revealed the presence of heazlewoodite at higher temperatures (950 to 1100 °C). Thermodynamic modeling of the Pipe ore system suggests that melting at higher temperatures is responsible for the decrease in the permittivities of this ore. To mitigate the melting and clumping of the ore particles, it is necessary to ensure that the processing temperature does not exceed 800 °C during microwave treatment. The OK ore, which contained less microwave response minerals than the Pipe ore, reached a maximum temperature of 500 °C after only 5 min of heating time, and therefore overheating was not an issue.

Mafic microgranular enclaves from the Tieshan batholith, eastern China: Implications for petrogenesis of magma associated with Fe-Cu skarn mineralization

Mineralogy, geochemistry, and geochronology of the mafic microgranular enclaves (MMEs) and their host diorite from the Tieshan batholith, Edong district, eastern China, were studied to constrain their petrogenesis and relationship with Fe-Cu skarn mineralization. The MMEs are diorite in composition and characterized by mixed apatite morphologies (elongated thin needles and stubby prismatic form) and bladed biotite, as well as clots of host diorite and megacrystic alkali-feldspar xenocrysts. The MMEs have similar zircon U-Pb age as their host diorite (~139 Ma). Most of the major and trace elements of the MMEs show a linear trend on Harker diagrams and plot along the low-silica trend of the host diorite. They are also characterized by enrichment of LREE and large ion lithophile elements (LILE), but are depleted in high field strength elements (HFSE). The MMEs display similar initial Sr isotopes and εNd(t), and slightly lower εHf(t) compared to that of host diorite. These results indicate that the Tieshan batholith formed via partial melting of an enriched lithospheric mantle, which is believed to be in equilibrium with a garnet-bearing residue (>50 km), followed by contamination of low crustal materials and fractional crystallization, whereas the MMEs appear to be the products of magma mixing. The presence of Cu- and Ni-bearing minerals in the MMEs probably indicates upper mantle or lower crust accumulation of sulfide which may have played a key role in controlling the formation of the parental magma associated with the skarn-porphyry Cu deposit (148 to 135 Ma) from the Middle-Lower Yangtze River metallogenic belt (MLYRMB). In contrast, the thinner, normal crust (~30 km) at ~ 130 Ma, believed to be in equilibrium with a plagioclase-rich residue, was either unsuitable for producing Cu-bearing accumulations or failed to transfer the deep accumulations to shallower levels to form Cu-bearing skarn systems, resulting in Fe-only mineralization. This may imply that skarn-porphyry Cu deposits prefer to form under > 50 km crustal settings, whereas Fe skarns may preferentially occur under normal (~30 km) crustal thickness.

The Influence of the Magmatic to Postmagmatic Evolution of the Parent Rock on the Co Deportment in Lateritic Systems: The Example of the Santa Fé Ni-Co Deposit (Brazil)

Abstract The Santa Fé Ni-Co deposit is a major undeveloped lateritic deposit located in the Goiás State of Central Brazil. The deposit comprises two properties that together have indicated resources of 35.7 million tonnes (Mt), grading 1.14% Ni and 0.083% Co, and inferred resources of 104.3 Mt at 1.03% Ni and 0.054% Co. The laterite was derived from Late Cretaceous alkaline ultramafic lithologies that experienced an initial silicification from Eocene to Oligocene, followed by lateritization and partial reworking in Miocene-Pliocene. The deposit is characterized both by oxide- and phyllosilicate-dominated ore zones. In the former, Ni- and Co-bearing hematite and goethite dominate the supergene mineralogical assemblage, while ore-bearing Mn oxyhydroxides occur as minor components. In the phyllosilicate-dominated horizons the major Ni-carrying phase is chlorite. Multivariate statistical analyses (factor analysis and principal components analysis) conducted on the drill core assay database (bulk-rock chemical analyses) showed that significant differences exist between Ni and Co distributions. The Ni distribution is not controlled by any clear geochemical correlation. This is because the highest Ni concentrations have been measured in the ferruginous and in the ochre saprolite zones, where Ni-bearing minerals (chlorite and goethite) are mostly associated with reworked material and only in a limited way, with zones affected by in situ ferrugination. Cobalt has an atypical statistical distribution at Santa Fé if compared with other laterites, correlated not only with Mn but also with Cr in the majority of the laterite facies. From microchemical analyses on several potential Co-bearing minerals, it was found that the Co-Cr association is related to elevated Co contents in residual spinels, representing unweathered phases of the original parent rock now included in the laterite. This element distribution is atypical for Ni-Co laterite deposits, where Co is normally associated with Mn in supergene oxyhydroxides. In the case of the Santa Fé laterite, the Co concentration in spinels is likely related to magmatic and postmagmatic processes that affected the original parent rock before lateritization, specifically (1) orthomagmatic enrichment of Co in chromite, due to its high affinity to spinels in alkaline melts, and (2) trace elements (i.e., Co, Mn, Ni, and Zn) redistribution during the hydrothermal alteration of chromite into ferritchromite. The Santa Fé deposit represents a good example of how the prelateritic evolution of a parent rock strongly affects the efficiency of Co mobilization and enrichment during supergene alteration. Based on the interpretation of metallurgical test work, a fraction of total Co between 20 and 50% is locked in spinels.

The Loma de Hierro Ni-laterite deposit (Venezuela): Mineralogical and chemical composition

Nickel laterite deposits developed on ultramafic rocks have traditionally been a significant source of Ni and Co and recently of Sc. Although the Loma de Hierro deposit (Venezuela) has been in operation for more than 50 years, it lacks detailed studies on the mineralogical and geochemical composition of the lateritic profile. In this study, we present a geochemical and mineral description of the main carrier phases of Ni and Co in a complete profile of the deposit. The selected weathering profile has been developed from a partially serpentinized harzburgitic protolith and has a well-developed saprolitic horizon covered by a thin limonitic horizon. The geochemical signature of the profile is characterized by a significant Mg and Si decrease towards the top of the saprolite, with a clearly visible Mg discontinuity. The main Ni-bearing minerals are secondary serpentine (1–4 wt.% NiO) and kerolite-pimelite-dominated garnierite mixtures with serpentine (18–22 wt.% NiO). Limonite is rich in goethite (0–1.85 wt. % NiO), gibbsite, and Mn-oxy-hydroxides. The latter have intermediate compositions between lithiophorite and asbolane (2–13 wt.% CoO). The highest Sc grades (40–68 ppm) were observed in the limonite with amounts positively correlated with Fe content. Rare earth elements are mainly concentrated in the upper part of the saprolite horizon (60–80 ppm), while they have a lower content in the limonite (7–45 ppm). In this horizon, rare earth elements are clearly associated with Fe, indicating adsorption and/or coprecipitation. This association was not observed in the saprolite, suggesting that other minerals (e.g., clay minerals) are controlling their concentration; more information is needed to identify the rare earth element-bearing minerals. The lateritic profile of Loma de Hierro can be classified as representative of hydrated Mg silicate deposits, and was formed in a context of continuous tectonic uplift and a low water table conditions favoring the development of a thick saprolitic horizon and the precipitation of kerolite-pimelite-dominated garnierites.

Extraction of Nickel from Garnierite Laterite Ore Using Roasting and Magnetic Separation with Calcium Chloride and Iron Concentrate

In this study, segregation roasting and magnetic separation are used to extract nickel from a garnierite laterite ore. The garnierite laterite ore containing 0.72% Ni, 0.029% Co, 8.65% Fe, 29.66% MgO, and 37.86% SiO2 was collected in the Mojiang area of China. Garnierite was the Ni-bearing mineral; the other main minerals were potash feldspar, forsterite, tremolite, halloysite, quartz, and kaolinite in the garnierite laterite ore. The iron phase transformations show that nickel is transformed from (Ni,Mg)O·SiO2·nH2O to a new nickel mineral phase dominated by [Ni]Fe solid solution; and iron changed from Fe2O3 and FeOOH to a new iron mineral phase dominated by metal Fe and Fe3O4 after segregation roasting. Ferronickel concentrate with Ni of 16.16%, Fe of 73.67%, and nickel recovery of 90.33% was obtained under the comprehensive conditions used: A roasting temperature of 1100 °C, a roasting time of 90 min, a calcium chloride dosage of 15%, an iron concentrate dosage of 30%, a coke dosage of 15%, a coke size of −1 + 0.5 mm, a magnetic separation grinding fineness of <45 μm occupying 90%, and a magnetic separation magnetic field intensity of H = 0.10 T. The main minerals in ferronickel concentrate are Fe, [Ni]Fe, Fe3O4, and a small amount of gangue minerals, such as CaO·SiO2 and CaO·Al2O3·SiO2.

Mineralogical characterization of low-grade nickel laterites from the North Oman Mountains: Using mineral liberation analyses – scanning electron microscopy-based automated quantitative mineralogy

Afterwards to the Late Cretaceous obduction of the Tethyan Semail ophiolite suite intense chemical weathering involved the Oman Mountains region. This weathering produced complex mineral and chemical assemblages that led to the formation of a Ni lateritic paleosol. In the present study, five laterite sections were sampled and studied by using a quantitative mineralogical and petrographic approach. Mineral liberation analyses (MLA) were carried out for the first time for several selected samples.The MLA results, supported by the Electron probe micro-analyzer (EPMA) and Energy-dispersive X-ray spectroscopy (EDX) analyses, revealed that the main ore minerals of the analyzed laterite are chlorite and goethite as the main Ni-bearing hosts. Magnetite and chromite are also present as by-product minerals.The Ni-bearing chlorite in the Saqah-3 and Al Russayl profiles have coarser grains compared to those in the other Saqah localities, while the goethite grains are coarse in most of the analyzed samples. The presence of approximately 60 to 80% of both the Ni-bearing minerals (chlorite and goethite) as liberated phases (>95% free) is a potential indicator for their future exploration.Chromite and magnetite grains are present in a wide range of grain sizes. Seventy percent of the chromite grains in Saqah-4 and Al Russayl profiles and 70% of the magnetite in Saqah-2 occur as liberated phases (>95%) compared to their presence in other profiles, where only half of them occur as liberated phases.The grain-size-liberation class relationships showed that Ni-bearing mineral phases (chlorite and goethite) are present as liberated phases (high-grade materials) followed by chromite and magnetite, which are interlocked with other phases to lower grade materials.A better understanding of the mineralogical and geochemical quantitative characterization, such as grain size, modal analyses, mineral association, and percentage of interlock between minerals in the deposit, can avoid the metallurgical problems, thus possibly reducing the operational costs and improving the recovery of metals.The above-obtained MLA parameters can build a good feasibility study during the exploration stage of these low-grade Ni deposits in the Northern Oman Mountains, as well as later during their beneficiation and processing methods, if other economic and mining factors are deemed favorable.

Weathering processes and crystal chemistry of Ni-bearing minerals in saprock horizons of New Caledonia ophiolite

This paper proposes a detailed study of the formation of the main Ni ore that is today mined in the saprock horizon of New Caledonia ophiolite. More specifically, this study aims at, i) characterizing the nature and the crystal chemistry of the main Ni-bearing phases, and ii) better understanding the weathering processes that lead to such nickel enrichment in these horizons. The study focuses on a boulder (~20 cm in diameter) sampled in the saprock facies of the Koniambo massif, reflecting the early stages of peridotite bedrock weathering. This boulder is explored with a large panel of techniques, from the centimeter to the nanometer scale, including micro-imaging and X-ray absorption spectroscopy at the Ni and Fe K-edges. A characterization along the cross section reveals important heterogeneities in textures, and a large concentration of nickel in the outer part through an intense and connected Ni-phyllosilicate network that develop at the expense of the primary lizardite network. The inner part is preserved from the weathering by supergene fluids. Primary lizardite initially contains about 0.4 wt% NiO, similarly to surrounding olivine and pyroxene. In the outer part, the main Ni-bearing phases are identified as polygonal serpentine (up to ~5 wt% NiO) and two successive generations of talc-like minerals that contain ~20 to 36 wt% NiO. In these two minerals, nickel is very likely to form nano-clusters in the octahedral layers. The Fe3+/Fetotal ratios in serpentine minerals increases regularly from ~0.5 in primary lizardite, to ~0.95 in polygonal serpentine, traducing increasing local oxygen fugacity with increasing weathering degree.From molecular modeling, we propose that the large excess of water systematically observed for these Ni-rich minerals can be explained by nanometer sized crystals, which potentially require many additional hydrogen bonds (i.e., mainly silanol groups) to passivate crystal edges and preserve electro-neutrality. On the other hand, the main driving force leading to important nickel accumulation in the saprock horizon is likely to be the strong pH gradient present at all scales in the regolith profile, including at the boulder scale, which have major effects on the hydroxide solubility. As the pH decreases in the phyllosilicate network, we observe, i) the weathering and oxidation of the primary lizardite network, ii) the formation of a newly formed lizardite, iii) the formation of Ni-rich polygonal serpentine, iv) the formation of successive generations of Ni-rich talc-like minerals.

Tredouxite, NiSb2O6: another new Ni-bearing mineral from the Bon Accord oxide body, South Africa

Tredouxite, NiSb2O6: another new Ni-bearing mineral from the Bon Accord oxide body, South Africa

Application of a selective dissolution protocol to quantify the terminal dissolution extents of pyrrhotite and pentlandite from pyrrhotite tailings

The recovery of valuable base metals from mining rejects presents an economical alternative to conventional hydrometallurgical processes. The reject of interest investigated in the present work is a nickeliferous, upgraded pyrrhotite tailings produced by Vale Base Metals in the Sudbury Basin of Ontario. A QEMSCAN™ analysis of the tailings showed a total Ni content of 1wt%, with 59% of the total Ni deported to pyrrhotite and 40% associated with pentlandite. The initial part of this study involved the development of a selective dissolution protocol to quantify the differential dissolution extents of the two Ni-bearing minerals. Application of this protocol to the pyrrhotite tailings sample showed that an acidity of 15wt% HCl, and a temperature of 80°C was adequate to selectively dissolve 96% of pyrrhotite from the tailings. Subsequently, an anoxic acidic leach of the tailings at pH1.5, and at 5% (w/v) solids loading showed minimal dissolution of Fe and Ni from pentlandite in tests with and without pH control. The extent of Ni dissolution was next evaluated as a function of pH during an oxic acid leach. The testing protocol involved leaching the tailings under two pH regimes: fixed and uncontrolled pH. The results showed that operation at a fixed pH increases the extent of Ni dissolution due to the higher concentration of the oxidant Fe(III) in solution. Finally, an oxic ferric leach showed that the terminal dissolution extents of pyrrhotite and pentlandite were comparable at 46% total Ni extraction.

Stream sediment geochemical patterns around an ancient gold mine in the Wadi El Quleib area of the Allaqi region, south Eastern Desert of Egypt: Implications for mineral exploration and environmental studies

The investigation of geochemical patterns in stream sediments around the newly discovered ancient gold mine in the Wadi El Quleib area is aimed at economic evaluation and environmental assessment of catchment sediments. For these reasons, forty stream sediment's composite samples were collected from the area covered by the metamorphosed ultramafic and their derivatives, volcanogenic metasediments, granitoid plutons, sand stones, and unconsolidated sediments. Fifty three chemical elements were analyzed using inductively coupled plasma–mass spectrometry. They were processed using various mathematical computations, graphical plots, and mapping techniques. The results revealed that the multiple populations within data set were caused by natural and ancient mining activities. Both geogenic and anthropogenic sources could influence on the dispersion of the elements of interest in the stream sediments. Despite sediments' materials were predominantly generated from metabasic and ultramafic provenance rather than mixed and flesic sources, and the area may have been subjected to more than one weathering cycle, they did not follow the sedimentary sorting and recycling trend. The lack of Au content and the negative correlation of Au with other elements are due to ancient human works and thus, the combined elements Ag+As, Ag+Hg, and Ag+Hg+As are considered the pathfinder for Au mineralization. The metamorphosed ultramafic and their derivatives, volcanogenic metasediments and their thrust contact host Au-mineralization, Cr-mineralization, and Ni-bearing minerals. Environmentally, the low values of contamination degrees and potential ecological risk indices of heavy metal(loid)s indicated that the sediment materials are good in quality and possess no actual hazard to human health. In general, the study area is more promising for Au mineralization and accepted as safe environment for the urban renewal purposes and land-use management in the future.

Leaching potential of geogenic nickel in serpentine soils from Taiwan and Austria

Serpentine soils may be natural sources of metal leaching and pollution. In this study, two contrasting serpentine soils from Taiwan and Austria were selected to evaluate the leaching potential of geogenic nickel (Ni). We applied selective sequential extractions and dissolution kinetics with three inorganic acids (HCl, HNO3, and H2SO4) and three organic acids (citric, acetic, and oxalic acids) in concentrations ranging from 0.05 to 10 mM to determine the release rate of Ni in the soils with respect to pH and acid types. Chlorite and serpentine were the major Ni-bearing minerals in the studied soils. Ni was dominantly bound in unavailable forms within these silicate minerals, but smaller fractions of acid-soluble, Fe–Mn oxide-bound, and organically bound Ni represented more labile Ni sources in the soils. The release rate of Ni from the soils increased with decreasing pH in all acids. However, the organic acids caused stronger pH dependences than the inorganic acids, likely because of ligand-promoted dissolution. The maximum total rate of Ni dissolution occurred with citric acid in both soils. The dissolution of Ni strongly increased when the ionic strength in the background solutions increased. We observed marked differences in dissolution rates and ligand effects between the Austrian and Taiwanese soils, which reflect differences in labile Ni pools, especially in the organically bound fraction. Our results demonstrate that labile fractions control the leaching potential of Ni in serpentine soils and that Ni associated with soil organic matter may contribute to leaching at moderately acidic pH levels.

Nickel in a serpentine-enriched Fluvisol: Redox affected dynamics and binding forms

We determined redox-induced (im)mobilization of geogenic nickel (Ni) as well as binding forms of Ni in a Fluvisol at the River Velika Morava valley (Serbia), enriched with serpentine minerals. The selected site is representative for intensive agricultural land use in the area and susceptible to dynamic redox conditions due to periodical flooding. A seven-step sequential extraction, grain-size and light-liquid separation as well as mineralogical analyses were used, first, to assess binding forms of Ni and second, to determine relationships between grain-size fractions, abundance of heavy density minerals, and Ni concentration in the bulk soil. The sequential extraction revealed that the majority of Ni was in the residual fraction, followed by organic matter and Fe oxides. Fine grain-size fraction (<63μm) was the major location of accumulation of Ni in the soil. Minerals which are characteristic for serpentine soils such as serpentine, spinels, hematite, and magnetite were found in silt and in the heavy density fraction (>2.9gml−1) of the medium and fine sand. However, the light minerals quartz, chlorite, micas, and secondary clay minerals dominate the soil mineral composition. Thus, total Ni concentration in the soil is derived from the content of Ni-bearing minerals and diluted by the minerals which are low in Ni.We simulated flooding using an automated biogeochemical microcosm system and determined the release dynamics of Ni at controlled redox potentials (EH) in soil slurries. Pre-defined redox-windows were systematically created in steps of approximately 100mV from reducing to oxidizing conditions while EH and pH were continuously monitored. In parallel, the release dynamics of soluble nickel (Ni), iron (Fe), magnesium (Mg), manganese (Mn), dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), and sulfate (SO42−) were measured at each EH-window. Our results highlighted that geogenic Ni can be mobilized to a considerable amount during low EH, while elevating EH from reducing to oxidizing conditions generated an immobilization Ni. We suggested that mobilization of Ni has been primarily affected by formation of Ni–DOC complexes at low EH, whereas Ni seems to be immobilized as a result of formation of Fe/Mn (hydro)oxides and the linked co-precipitation of Ni during oxidation. Factor analysis (FA) as multivariate statistical method explained 85.08% of the variance (67.89% and 17.19% component Nos. 1 and 2, respectively). The FA reveals that soluble Ni, Fe, DOC, Mn, and Mg were clustered in one group which indicate that the combined effect of DOC together with the chemistry of Fe, Mn, and Mg might be linked to the redox-induced release dynamics of Ni. The practical perspective of the study was to draw attention to dynamics of soluble Ni in fluctuating conditions for a better ecological risk assessment of floodplain sites under agricultural use. Nevertheless, similar studies should be conducted with further serpentine soils from various sites world-wide to verify the detected dynamics and processes.

The Yatela gold deposit in Mali, West Africa: The final product of a long-lived history of hydrothermal alteration and weathering

The Yatela gold deposit is located in the Kédougou-Kénieba inlier (KKI), a window of ca. 2200-2050 Ma rocks that are exposed in eastern Senegal and western Mali. The geology of the KKI differs from other Paleoproterozoic granite-greenstone belts and sedimentary basins by the abundance of carbonate rocks. The Yatela deposit occurs within 8 km of the regional-scale Senegal–Mali Shear Zone. Country rocks in the Yatela region have been subjected to polycyclic deformation and regional greenschist-facies metamorphism. A syn-kinematic diorite stock has intruded the metasedimentary sequences in the open pit and is associated with a hornblende-hornfels contact aureole. Field relationships and micro-textural data indicate that the primary gold mineralisation is shear-hosted. The similar relative timing and structural setting between the Yatela primary gold mineralisation and other world-class deposits in the region (e.g., Loulo, Lawrence et al., 2013a; Massawa, Treloar et al., 2014; Sadiola Hill, Masurel et al., in press) suggest that regional orogenic gold mineralisation occurred during a period of transcurrent tectonics, after the cessation of regional compressional deformation. The primary gold mineralisation at Yatela, however, is low-grade and sub-economic. It is hosted by marbles and, to a lesser extent, diorite. The primary ore is pyrite-rich, with abundant chalcopyrite, minor arsenopyrite and accessory Zn–Pb–Sb–Fe–Ag–Co–Ni-bearing mineral species. Post-Birimian surficial dissolution of hydrothermally altered and mineralised host marbles resulted in the creation of troughs, which were draped and infilled with a ferruginous dissolution residue enriched in gold. This auriferous residuum formed the economic resource mined at Yatela until decommissioning in 2013. The Yatela gold deposit is unique with respect to mineralisation types encountered in West Africa because an auriferous residuum of economic interest (>1 Moz) derives from an underlying sub-economic Birimian occurrence. This study provides a new appreciation for the economic interest of Yatela-style orebodies and their prospectivity in other gold provinces of the West African Craton where carbonates are present, such as in the Siguiri basin in Guinea and the Ity region in western Côte d’Ivoire.

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.

Nickel isotope fractionation during tropical weathering of ultramafic rocks

Although Ni isotopes have been shown to be significantly fractionated in terrestrial samples, their use in continental environmental studies has not yet been evaluated. The present study focuses on an ultramafic (UM) massif (Barro Alto, Goiás, Brazil) because such areas are naturally rich in Ni. We present developed lateritic weathering profiles. The goal of the study is to evaluate the potential of using Ni isotopes in environmental continental studies by combining its isotopic signature with mineralogy, in order to better understand the geochemical cycling of Ni in UM settings during weathering. As such, Ni isotope values were measured in samples from the Barro Alto UM complex in the main stages of the lateritic weathering profile of UM rocks, including bedrock, ores (saprolitic and lateritic samples) and soil. The mineralogical composition of the samples, with a focus on the different Ni-bearing minerals, was also determined to decipher the potential links between isotopic fractionation and weathering dynamics. Isotopic signatures (δ60Ni) from the natural Ni geochemical cycle include: bedrock samples (δ60Ni=0.28±0.08‰), ore samples (saprolitic and lateritic, δ60Ni from −0.60 to 0.30‰) and soil samples (δ60Ni from −0.19 to −0.02‰). An overall trend of heavier isotope depletion was observed in the solid phase during weathering (Δ60NiSoil–Bedrock=−0.47‰). The mineralogical results were consistent with the literature and showed that the mineralogy of the lateritic part and soil was dominated by Fe-oxides, whereas clay minerals were the primary Ni phase scavengers in the saprolitic part of the profile. Thus, the formation of Ni-bearing clay minerals and Fe-oxides appeared to lead to depletion in heavier isotopes, which indicates preferential export of heavy isotopes in the dissolved phase. This result is consistent with isotopic signatures measured in the exchangeable pool of the solid phase (Δ60Niexch-total up to 0.47‰), and Ni isotopes appear to be a promising tracer to better understand the biogeochemical Ni cycling on the Earth's surface.

Genesis and mineralogical classification of Ni-laterites, Oman Mountains

The laterite profiles investigated in the present study developed after the emplacement of a slab of oceanic crust and upper mantle sequence (the Semail ophiolite) onto the East Arabian margin during the Late Cretaceous. The laterites formed as a result of prolonged weathering of the ophiolitic assemblage under tropical to subtropical conditions.Nine laterite profiles have been examined for their Ni potential along a NW–SE segment of the Oman Mountains. The profiles show a vertical succession from bedrock protolith through saprolite, oxide laterite, to clay laterite.A significant enrichment in Ni and Co occurred as a result of the lateritization process. Ni concentrations average 0.63% (Ibra), 0.72% (3 profiles, East Ibra), 0.67% (3 profiles, Al-Russayl), and 0.33% (2 profiles, Tiwi). Electron microprobe analyses showed that goethite, chlorite, kaolinite, serpentine and talc are the main Ni-bearing minerals. This study showed that the Ibra, East Ibra and Tiwi laterites are similar to the other hydrous Mg-silicates (type A) Ni deposits, where nickel-bearing talc (willemseite) or chlorite, and serpentine (nepouite, chrysotile, and antigorite) are the main constituents. Al-Russayl laterite is however, similar to the oxide type (Type C), where most likely the nickel is included in the oxyhydroxides (mainly goethite) minerals.