Saprolitic Ore Research Articles

Artificial Slags with Modulated Properties for Controlled Nickel Dissolution in Smelting Process

In pyrometallurgy process involving drying, calcination and reductive smelting steps, Saprolite ore is subjected in an electric arc furnace to produce Fe–Ni alloy and Ni matte. To optimize the nickel smelting step, the slag consisted of MgO–SiO2–FeO and having a lower viscosity and high fluidity is required. In this study, a number of new slag samples with varied degree of compositions are manufactured and used to examine the effect of their viscosity on nickel dissolution. Further correlation between the slag basicity and FeO addition on the smelting was also tested and simulated using Fe–Ni alloy from saprolite ore. As per the observations, the nickel dissolution increases with the increased content of FeO at a certain degree of activity which in turn can cause oxidation of nickel during the process. The slags with the ratio of MgO/SiO2 = 0.4–0.6, 30% fraction of FeO, and a viscosity of 1.8–1.06 poise in the olivine zone are found effective for the lowest dissolution rate of nickel with 0.021, 0.022, and 0.018 wt.%. The lowest dissolution rate is recorded for the slag with MgO/SiO2 ratio about 0.6. These slags with controlled amount of constituents could be used to recover precious metal from nickel smelter at a lower dissolution rate and thereby allowing to reduce the waste of the metal during smelting process.

MODEL OF LATERITE NICKEL DEPOSITS BASED ON LGSO AND HGSO VALUES PT MITRA KARYA AGUNG LESTARI

The laterite nickel deposit model provides information about the form of laterite nickel deposits below the surface, which can be used as one of the considerations in the implementation of mining activities. The purpose of conducting this research is to determine the distribution model of nickel laterite deposits in 3 dimensions (3D) and to determine the amount of nickel laterite reserves based on high-grade saprolite ore (HGSO) and low-grade saprolite ore (LGSO) values in the DH Block. In this research, Inverse Distance Weighted (IDW) is used to estimate nickel laterite resources, which are applied using mining software Surpac 6.3.2 to produce a model in 3D form. The data used are laterite nickel content data (assay), x, y, and z coordinate data (collar), survey data, and lithology data. Based on IDW estimation results with a Cut Off Grade (COG) value of 1.3 in the DH Block of PT Mitra Karya Agung Lestari, High-Grade Saprolite Ore (HGSO) values were obtained at Ni content 1.7 and Low-Grade Saprolite Ore (LGSO) at Ni content 1.3, with a tonnage value of 111.994 tons of HGSO and 371.044 tons of LGSO.

A novel and greener sequential column leaching approach for the treatment of two different Greek laterites

Τhe present study investigates, from an environmental protection viewpoint, the efficiency of sequential column leaching of two different Greek laterites, i.e. a limonitic ore from central and a saprolitic ore from northern Greece. First, the most refractory limonitic laterite is leached in the first column for 15 days and the obtained pregnant leach solution (PLS) is further used for the leaching of the easier to treat saprolitic ore in the second column, thus achieving a significantly reduced acid consumption. The main parameters affecting the process efficiency, i.e. acid molarity (1.5 or 3 mol/L H2SO4) and addition of sodium sulfite (Na2SO3) in the leaching solution were studied. The extraction of Ni, Co, Fe, Al, Mg, Mn and Ca was determined by Atomic Absorption Spectroscopy (AAS), while the characterization of the ores and final residues was carried out by X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA/DTA), and Scanning Electron Microscopy/Energy Dispersive X-Ray Spectroscopy (SEM-EDS) analysis. The results confirm the efficiency of the proposed green approach, which with the use of leaching solution containing 1.5 mol/L H2SO4 and 20 g/L Na2SO3 resulted in 73.8 % Ni, 71.6 % Co and 8.4 % Fe extraction after a short period of time (33 days), while the acid consumption, which is a serious environmental concern, was very low and did not exceed 300 kg/t ore. Overall, the proposed process not only improves the efficiency of leaching of different types of laterites for the recovery of both Ni and Co but also reduces the environmental impacts due to the significantly lower acid consumption.

Recovery of Rare Earth Elements Minerals in Complex Low-Grade Saprolite Ore by Froth Flotation

This study presented the first in a series of investigations currently underway to develop efficacious, cost-effective, and benign processing opportunities to produce rare earth elements (REE)–rich concentrate from an Australian complex low–grade saprolite ore [1.14% total rare earth oxides (TREO) grade], which is primarily exploited for its gold and copper values. This work specifically presented a preliminary flotation investigation carried out on the ore using sodium oleate as a collector. The relative effects of pulp pH, desliming, and depressants were investigated to ascertain any chance of recovering and upgrading REE minerals in saprolite ore using three different processing configurations. Based on the experimental results, flotation processes carried out on raw feed allowed the recovery of the majority of REE minerals (>50%), but the process was unselective, where clay and silicate gangue minerals reported into the flotation concentrate along with the REE minerals. However, desliming before flotation in the presence of depressants (starch and sodium silicate) improved REE minerals flotation selectivity, which produced concentrates assaying 5.87% and 4.22% TREO grades, with corresponding recoveries of 45% and 50% at pulp pH 9 and 10.5, respectively. Mineralogical analysis conducted on selected flotation concentrate indicated that silicate and clay gauge minerals were recovered via the synergistic act of surface activation and entrainment due to their fine to ultrafine nature. A comparison of all the test results revealed a haphazard grade–recovery relationship suggesting that there is an opportunity to further maximize both REE recovery and grade through further flotation studies where other process parameters may be investigated and optimized. The prospect of using magnetic separation has also been suggested.

Performance of Additive in Metal Separation from Nickel Ore

The potential resources and reserves of nickel ore in Indonesia is the third largest in the world. The potential quite large, but the nickel content found in nature is very small. To increase the added value of nickel ore, it is necessary to process/refine nickel ore. In addition, coal ratio parameter and process temperature in the reduction process, additive is also used as parameter for the composite reduction process. This research used 6 combination saprolite ore composite based on result of previous research. The objective of this research is to know the performance of additive in separation of metal from nickel ore based on result of XRD analysis. XRD analysis is used to know chemical compound saprolite ore composite after reduction process. This results from XRD analysis shown that additive CaCO3 has the best performance additive with higher Fe and Tetrataenite content with percentage of coal ratio of 30% in temperature of 1300 °C. For additive Ca2SO4 percentage coal ratio 15% have higher Fe and NiFeO content in temperature of 1200 °C and 1300 °C.

Development of a Low-Temperature Bloomery Process for Nickel and Cobalt Recovery from Saprolite Ores

The bloomery process in rotary kilns is used for reducing roasting of high-magnesia saprolite ores at relatively low temperatures (1200–1225°C). The influence of flux (limestone, bauxite, fluorite) and sulfur-containing (pyrite concentrate, elementary sulfur, gypsum) additives on the temperature of coarsening of metallic particles with the formation of coarse ferronickel grains is studied at a reducing roasting time of 30 min. The optimum charge composition is determined, and the simultaneous introduction of 2–3% CaF2 and 0.8–1.2% (based on sulfur) sulfur-containing additive into a charge at the optimum limestone and bauxite additives is shown to decrease the temperature of coarsening of metallic particles to 1200–1225°C. In this case, aggregates of metallic ferronickel grains bound by a sulfide phase form. According to electron-probe microanalysis data, 90–92% nickel concentrate in a metallic phase, 4–5% concentrate in a sulfide phase, and 4–6% nickel is retained in a slag. The accumulation of a sulfide phase as a binder between metallic grains and the presence of magnetic properties in both phases substantially facilitate their extraction into a magnetic phase during separation with high indices of nickel and cobalt recovery. The formation of metallic grain aggregates and a sulfide phase create favorable conditions for further processing of the magnetic product by high-pressure sulfuric acid leaching or a carbonyl method to produce called-for products (nickel sulfate, high-purity metallic powders).

Parent rock and climatic evolution control on the genesis of Ni-bearing clays in Ni-Co laterites: New inferences from the Wingellina deposit (Western Australia)

Oxide-type Ni-laterites seldom contain significant Ni-phyllosilicates reserves. This study is focused on the mineralogy of Ni-clays mainly occurring in the saprolite zone of the Wingellina oxide-type Ni-Co laterite deposit. Despite most of the Wingellina reserves occur in the oxide zone, the deposit also has a well-developed high Ni grade saprolite horizon. This study presents a mineralogical and chemical characterization of the Ni-phyllosilicates of the Wingellina saprolite ore, aimed to understand the role of diverse bedrocks (gabbro and serpentinite) and the influence of climate on the formation of different clay types.The main phyllosilicate in the gabbro-derived saprolite consists of dioctahedral Al- and Ni-montmorillonite, originated from the weathering of pyroxene. The genesis of Al- and Ni-rich montmorillonite from pyroxene can be explained by an open system alterative process, in which Al mainly derives from the dissolution of plagioclase. In the serpentinite-derived saprolite, the alteration pathway followed a multistage evolution: (i) lateritic alteration of serpentine I into Ni-serpentine II and tri- and dioctahedral smectites (saponite and nontronite); (ii) late precipitation of interstratified Ni-clays (chlorite-smectite and talc-smectite) as a replacement of former phyllosilicates and as neoformed minerals. The latest phenomenon may be related to the late Miocene shift from humid-and-acid (tropical climate) to saline-and-alkaline conditions (arid to semi-arid climate), and represents an example of post-lateritization processes, rarely observed in laterites located on stable cratons.The aridity-driven precipitation of Ni-rich interstratified clays in the Wingellina laterite can be seen as a new model for explaining the evolution of Ni-laterites in stable cratonic settings experiencing post-lateritization aridity.

Investigation of the reduction roasting of saprolite ores in the Caron Process: microstructure and thermodynamic analysis

ABSTRACT Studies have been undertaken to investigate the thermodynamic aspects of the reduction roasting of saprolite ores in the Caron Process. Reduction experiments have been conducted in controlled oxygen partial pressure conditions at selected temperatures. Detailed microstructure characterisation and thermodynamic analysis of reduced ore samples, focusing on the phase transformations, nickel recoveries and Ni-Fe alloy compositions produced, were carried out. Comparison has been made between the experimental results and FactSage thermodynamic predictions for these conditions. The differences between between the experimental and predicted results are discussed. It has been shown that the system below 700°C is approximated thermodynamically by considering the nickel–iron alloy product to be in chemical equilibrium with a metastable amorphous oxide phase.

Investigation of the reduction roasting of saprolite ores in the Caron process: effect of sulphur addition

ABSTRACT Laboratory studies have been undertaken to determine the mechanisms and kinetics of reactions occurring during the reduction roasting of saprolite ores with 1 wt% elemental sulphur addition. The reduction was undertaken using a 15%H2/85%N2 gas mixture at temperatures between 400 and 800°C; nickel was recovered by subsequent leaching in an ammoniacial aqueous solution. The effect of sulphur on dehydroxylation, reduction and sintering was investigated. Improvements in nickel recoveries were obtained when 1 wt% S was added to the nickel-bearing serpentine ore prior to the reduction roasting. Characterisation of the reduced and leached ore samples indicated that this improved Ni recovery with S addition is due to the formation of a leachable nickel sulphide phase, and the suppression of sintering and recrystallisation of the olivine phase formed at high reduction temperatures.

Bloomery Production of Ferronickel Using High-Iron Oxidized Magnesia Nickel Ores

The reducing roasting of low-grade high-iron saprolite ores in the temperature range 1300–1350°C is studied to form nickel-rich ferronickel balls. The nickel-lean (1.01%) high-iron (24.3% Fe) nature-mixed ore of the Buruktal deposit is analyzed. The influence of the amounts of a solid reducer (mixture of brown coal and coke) and flux additives (limestone, quartz sand, bauxite, kaolin clay, fluorite) on the limitation of the reduction of iron oxides from a silicate slag and on the coarsening of metallic particles in roasting is investigated. When 18–21% kaolin clay and 2–4% limestone are added to a charge, the reduction of iron from a slag to a metallic phase is strongly limited. The introduction of 1% fluorite into a charge leads to a noticeable decrease in the melting temperature and the viscosity of an acid silicate slag and creates favorable conditions for the coarsening of metallic particles during reducing roasting of the charge in the temperature range 1300–1325°C. As a result, the optimum charge composition and roasting parameters are determined. At these composition and parameters, metallic ferronickel granules rapidly form, and a slag becomes almost fully free of fine metallic particles because of a high surface tension between the slag and metallic phases. The nickel content in metallic granules reaches 10–13% under these roasting conditions in the presence of an excess solid reducer.

Investigation of the reduction roasting of saprolite ores in the Caron process: microstructure evolution and phase transformations

ABSTRACT Fundamental studies have been undertaken to determine the microstructural and phase transformations occurring during the reduction roasting of saprolite ores. Laboratory studies have been undertaken to simulate the conditions occurring during the reduction roast step of the Caron Process. Selected serpentine samples have been treated at temperatures between 500°C and 800°C in H2/N2 gas mixtures, and leaching tests on the reduced samples have been undertaken. Phase and microstructural changes have been characterised using X-ray Powder Diffraction (XRD), Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) techniques. A series of complex physical, microstructure and phase changes has been shown to occur during reduction roasting involving: (i) the dehydration of serpentine, (ii) the formation of a high-silica amorphous phase, (iii) the formation of Ni-Fe nanoparticles, and (iv) the nucleation, growth and recrystallisation of the forsterite (olivine) phase. The principal mechanism of removal of nickel from the reduced ore has been shown to occur through the selective leaching of the Ni-Fe alloy nano-particles from the surfaces in the product oxide.

Investigation of the reduction roasting of saprolite ores in the Caron process: reaction mechanisms and reduction kinetics

ABSTRACT Laboratory studies have been undertaken to investigate the mechanisms and kinetics of reactions occurring during the reduction roasting of saprolite ores. Reduction was undertaken using a H2/N2 gas mixture at temperatures between 400 and 800°C. The focus of the study was to determine the effect of dehydration, reduction, sintering and olivine recrystallisation reactions on nickel recovery. The effects of thermal history, temperature and time on the rates and extents of these processes have been investigated. The results provide valuable insights into the relative contributions of the elementary processes taking place during the reduction roast process, and help to explain some of the behaviour observed in industrial practice.

Application of Sulfide Copper Ores Oxidizing Roasting Products as Sulfidizing Agent During Melting Nickel Raw Materials To Matte

X-ray fluorescence analysis, X-ray powder diffraction, electron microprobe analysis, scanning electron microscopy, and thermal analysis are used to evaluate the material composition, structure and thermal properties of Dergamysh ore deposit and condensed roasted (750–850°C) products. Ore heating in air is accompanied by oxidation of sulfur and iron oxides, combustion and decomposition of sulfides, carbonate thermolysis, and decomposition of iron, copper, and zinc sulfates. Processes are generally completed up to 850°C. With desulfurization to the level of 60–94% sulfur the ore retains a porphyroblastic structure. Crystals (1–5 μm) of hexagonal and monoclinic pyrrhotites, corresponding to the general formula Fe0.80−0.93S, sphalerite and bornite border a mixture of fine (1 μm) olivine and spinel. In this case sulfides and oxides in contact with them achieve a similar concentration of non-ferrous metals, wt.%: up to 0.7 Co, 1.5–21.8 Cu, and 1.1–56.6 Zn. Heating a mixture of roasted (70–80% desulfurization) sulfide copper ore with nickeliferrous saprolite ore, calcium oxide and carbon in a weight ratio of 60:100:10:2.5 provides matte (4.1 wt. % Ni, 2.5 wt. % Cu, 0.38 wt. % Co, 2.1 g/ton Au, and 3.6 g/ton Ag) concentrating 90.3% nickel, 82.7% copper, 85.3% cobalt, and up to 99.0% of precious metals. The products of oxidation roasting of sulfide copper ores can be considered as an effective sulfiding agent and collector of valuable metals during smelting of nickeliferrous saprolite ores. The technology of joint reduction and sulfiding smelting of roasted copper ores and calcined saprolite ores is a promising way to use poor and mineral raw materials that are hard to enrich and to reduce SO2 emissions into the atmosphere.

Optimization of Saprolite Ore Composites Reduction Process Using Artificial Neural Network (ANN)

Indonesia is the third largest country that has laterite reserves. The potential for resources and nickel ore reserves is quite large in Indonesia, but nickel content in nature is very small. One type of laterite nickel ore is saprolite ore, which has small Fe and large Ni content (around 1.5 - 2.5%). In accordance with the Law No. 4 of 2009 concerning Mineral and Coal Mining in increasing the added value of nickel ore, it is necessary to process and refine nickel ore. One of the nickel ore processing/refining technologies is through Pyrometallurgy technique. Pyrometallurgy technique involves high temperature and large energy. The reduction process is one of the nickel ore processing process using the Pyrometallurgy technique. In addition to the reduction process, the use of composites which are mixing of saprolite ore, coal, additive and bentonite has an important role. There are several factors that influence the reduction process in saprolite ore composites. The results of this reduction process are analyzed using X Ray-Difference Fluorescence (XRF). The objective of this research is to obtain an optimal factor combination of the reduction process of saprolite ore composites, which is important to develop effective, efficient and systematic methods. This study utilises a neural network approach that will produce optimal factors with the estimate on the composition in the reduction process of saprolite ore composites. The optimal factor combination is a coal ratio of 15% with a type of additive Ca2SO4 or Composite SB15Ca10P2 with a temperature of 1200 0C and time duration of 3 hours.

Upgrading nickel in laterite ores by flotation

Nickel is sourced from sulphide and laterite ores. While 70% of the nickel resources are contained in laterites, these ores are often complex and expensive to treat using conventional methods. Therefore, upgrading the nickel content in laterite ores ahead of any recovery processes is economically desirable. Flotation has not been successful to recover nickel from laterite ores because of the fine-grain and low grade nickel. Nickel laterite deposits are generally divided into limonite (oxide), nontronite (clay) and saprolite (silicate) zones. A systematic study was conducted on the ore samples sourced from these three categories to see the effect of different mineralogies on the flotation behaviour of laterite ores. Pre-concentration of laterite ores by flotation was found to be possible, but it is highly determined by the ore mineralogy. In this study, no or minor upgrade in the nickel content was found for the limonite and nontronite samples. However, it was possible to obtain 40% upgrade in the nickel content (at 70% recovery) for the saprolite ore sample using flotation.

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.

Indirect bioleaching of low-grade nickel limonite and saprolite ores using fungal metabolic organic acids generated by Aspergillus niger

The objective of the present study was to investigate the indirect bioleaching of low-grade nickel limonite and saprolite ores using fungal metabolic organic acids generated by Aspergillus niger. The indirect bioleaching experiments were carried out in a 2000ml five-neck glass vessel containing 500ml of the culture filtrate comprising fungal metabolic organic acids (which were obtained from organic acid biogeneration experiments after filtration) supplemented with limonite or saprolite ores. For the organic acid biogeneration experiments, the highest generation of organic acids by A. niger was achieved for cassava starch as carbon source in the presence of KH2PO4, (NH4)2SO4 and MgSO4 under aeration condition, which were subsequently employed for the indirect bioleaching experiments. The highest nickel leaching efficiencies from saprolite and limonite ores were 88.9% and 84.9%, respectively, which were obtained at leaching temperature of 95°C, stirring speed of 400rpm, ore particle size of -177+149μm, and leaching time of 4h (for saprolite) and 24h (for limonite). Most importantly, the leaching using the biogenerated organic acids in this study is highly selective to magnesium (Mg) and is relatively selective to iron (Fe), thus supporting their potential industrial applications with respect to economic and environmental concerns.

A life cycle assessment of a new laterite processing technology

This paper presents a life cycle assessment (LCA) study of three nickel laterite processing technologies. The main goal was to quantify selected environmental impact categories and to compare and analyse each impact category for three different nickel feedstock for stainless steel production. The nickel laterite processing routes were (1) high pressure acid leaching (HPAL), (2) ferronickel, and (3) the newly developed Direct Nickel (DNi Process) that involves atmospheric leaching of nickel laterite using nitric acid. A cradle to gate approach was adopted. A functional unit of one tonne stainless steel was chosen. The scope covered was from laterite ore mining to final metal production. All inventory data was expressed in units per tonne nickel-based feedstock. The flow sheets for each technology were developed and the system boundaries were clearly defined. It was found that Ferronickel has the highest global warming potential and non-renewable energy scores whereas HPAL has the highest water depletion score. Overall, the DNi Process is found to be a more sustainable processing route as it produces less airborne emissions compared to the other two routes. Nitric acid is also less toxic compared to sulphuric acid used in HPAL. The DNi Process is also able to process different types of laterite ores (from limonitic to saprolitic ores) which is an important feature for future nickel production.

The accumulation of Ni in serpentines and garnierites from the Falcondo Ni-laterite deposit (Dominican Republic) elucidated by means of μXAS

Ni-bearing serpentines and garnierites (Ni-bearing Mg-phyllosilicates) are the main Ni ores in the Falcondo Ni-laterite deposit (Dominican Republic). In the present paper a set of garnierite samples and the associated Ni-bearing serpentines with characteristic mineral compositions and textures, from the saprolite horizon, were studied by EMPA, μXRF and μXAS. The ultimate goal is to elucidate, for the first time, the Fe speciation and the Ni local environment of saprolite ores from Ni-laterites of the Dominican Republic. The chemical composition of the minerals has been obtained by means of EMPA and the Ni, Fe and Cr elemental maps obtained by μXRF allowed distinguishing the saprolite fragments containing Ni-bearing serpentines and Fe oxyhydroxides from the garnierite veins. The Fe K-edge μXANES demonstrated that Fe in the Ni-poor primary serpentine is mostly in the Fe2+ form, whereas in the Ni-bearing serpentine constituting the bulk of the saprolite and in the Fe-bearing garnierite Type I Fe was in the form of Fe3+. In parallel, the local environment of Ni determined by means of Ni K-edge μEXAFS confirmed that in Ni-poor primary serpentines Ni formed a homogeneous Ni–Mg solid solution, in garnierites formed Ni–Ni clusters, and in Ni-bearing secondary serpentines Ni was found in Ni–Mg and Ni–Ni mixed sites. This paper explains the accumulation of Ni, the speciation of Fe in garnierites with various mineral compositions and in Ni-bearing serpentines from the saprolite horizon in Ni-laterite deposits.

Comparison of atmospheric citric acid leaching kinetics of nickel from different Indonesian saprolitic ores

Saprolitic ores from Sulawesi Island (SS ore) contain serpentine and goethite as major minerals, whereas the main minerals in saprolitic ore from Halmahera Island (SH ore) are talc and goethite. Most of the nickel was incorporated in a magnesium–silica-containing mineral. The effects on nickel extraction of leaching temperature, citric acid concentration, and ore particle size were determined to investigate the leaching performances and leaching kinetics of the two saprolitic ores. Nickel leaching efficiency from SS ore is always higher than that from SH ore under the same leaching conditions. The mineral contents of the ores significantly affected the leaching performances and mineral dissolution behaviors of the samples. The results of nickel leaching efficiency and analysis of the solid residues suggest that all dissolved nickel originated from serpentine, which is more easily leached than goethite and talc. The rate of nickel extraction for SS ore was faster than that for SH ore. Nickel leaching from SS ore and SH ore followed the shrinking-core model and was controlled by diffusion of a reactant or product through the solid product layer.