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Leaching and ion exchange based recovery of nickel and cobalt from a low grade, serpentine-rich sulfide ore using an alkaline glycine lixiviant system
Minerals Engineering 145 (2020) 106073
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Leaching and ion exchange based recovery of nickel and cobalt from a low grade, serpentine-rich sulfide ore using an alkaline glycine lixiviant system
T
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J.J. Eksteena, , E.A. Orabya,b, V. Nguyena a
Faculty of Science and Engineering, Western Australian School of Mines: Minerals, Energy and Chemical Engineering, Curtin University, GPO Box U1987, Perth, WA 6845, Australia b Department of Mining and Metallurgical Engineering, Faculty of Engineering, Assiut University, Egypt
A R T I C LE I N FO
A B S T R A C T
Keywords: Glycine Nickel Cobalt Leaching Batteries
The paper presents the outcomes of exploratory research relating to the atmospheric pressure and ambient temperature leaching of nickel and cobalt from a Western Australian low grade, disseminated, nickel-cobalt sulfide ore, and the subsequent recovery using ion exchange (IX) using alkaline glycine solutions in mildly oxidizing environments. The results present a foundation for a direct leach approach at ambient conditions, particularly if upstream opportunities are considered (heap leach, in-situ leach, or vat leach, or bulk ore leach) from low grade Ni-Co resources. The results for cobalt are particularly exciting given the low recovery of cobalt in most smelting operations and the loss of cobalt to converter slags in conventional approaches. In addition, significant nickel losses are often incurred to flotation cleaner tailings to make a smeltable concentrate at an acceptable level of magnesium. The study showed that even though glycine-based leach rates for Ni and Co are slow, no passivation was observed and about 83.5% Ni and 76.3% Co were extracted at room temperature using conventional bottle rolls over a 672 h period using a multistage extraction (i.e. leachate decant and reagent refresh with either new reagent or recycled barren raffinate). The ore contained cobalt-bearing pentlandite as the predominant Ni-Co mineralization, with Kaolinite-serpentine group, magnesite and hydrotalcite the predominant oxide and pyrrhotite as the predominant sulfide gangue minerals. The effects of glycine concentration, pH and temperature have been studied. It was found that leaching at pH 10.0 gave significant better leach Ni and Co extraction than operating at higher pH of 11.5. In glycine leach campaigns, the dissolution of iron, magnesium, silicon, manganese and other impurities were insignificant. This is particularly important for iron removal which would normally have posed a significant solid-liquid separation and waste disposal cost and magnesium, given the very high levels of magnesium that would normally have dissolved from such ores in acidic systems. Excellent recovery of Ni and Co from leach solutions was achieved by a selected ion exchange resin (Purolite S930Plus) and high Ni and Co dissolution was achieved using recycle glycine solutions after metals adsorption and pH adjustment.
1. Introduction Nickel is a critically important base metal that exhibits high corrosion resistant and durability properties and is used to manufacture corrosion-resistant alloys such as stainless steel and other superalloys (Crundwell et al., 2011). The market for battery grade nickel salts is growing rapidly as it used to prepare precursors in Lithium-ion Batteries (LiBs) and other rechargeable batteries. High nickel use is predicted for the Nickel-Manganese-Cobalt (NMC) LiBs with NMC ratios of 811 and 622, which are the preferred cathode chemistries for LiBs used in electric vehicles for the projected future. Nickel is found primarily in two types of ores namely laterite (oxide) and sulphide ores. The sulfide
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ores are normally associated with mafic and ultramafic ores which are inherently basic and tend to be magnesium rich and are typically mineralised in either a massive sulfide or a disseminated form in these rock types. Two significant Ni minerals in sulphide ores are pentlandite [(Ni,Fe)9S8] and nickeliferous pyrrhotite. There are several different techniques that can be used in the extraction of nickel and cobalt from various ore minerals. Sulphide ores that are mined for Ni and Co contain between 1.5 and 3.0% Ni and 0.05–1.0% Co (Crundwell et al., 2011). Traditional processing of these ores is through processing in a concentrator and smelter. The matte-smelting process and ancillary processes involves a combination of grinding, froth flotation, smelting, converting and refining, which may include pressure leaching and
Corresponding author. E-mail address: [email protected] (J.J. Eksteen).
https://doi.org/10.1016/j.mineng.2019.106073 Received 16 June 2019; Received in revised form 1 September 2019; Accepted 6 October 2019 0892-6875/ © 2019 Elsevier Ltd. All rights reserved.
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consists of crushing and leaching by heap or dump leach approaches. The refinery at Fort Saskatchewan was one of the first to utilise ammonia as a leaching reagent (Cooper and Mihaylov, 1997). The ammoniacal process involves pressure leaching of the nickel concentrate and matte with ammonia and oxygen in a series of autoclaves operating at 105–120 °C (Crundwell et al., 2011). This process aims to maximise the efficiency of leaching nickel and cobalt in addition to the oxidation of cobalt into solution as cobaltic hexamine. The process involves leaching of mixed Ni-Co sulphide precipitates in (NH4)2SO4 using ammonia and oxygen according to Eqs. (1) and (2).
pressurised Ni reduction by hydrogen or electrowinning (Crundwell et al., 2011; Burkin, 2001), e.g. the using the Sherritt process. In general there is a great similarity between the nickel sulfide ores with platinum group metals (PGMs) as a by-product, such as in Western Australia, and PGM ores where nickel is the by-product such as found in South Africa (Mpinga et al., 2015). Non-traditional processing often refers to hydrometallurgical methods, which can directly treat the bulk of the concentrate, instead of smelting it to a matte. Other hyrometallurgical alternatives also include the treatment of the bulk ore itself, or various waste products such as flotation cleaner tailings. A hydrometallurgical option, should it proven to be effective, would allow relaxation of the concentrate grade specifications in a flotation circuit to produce a smeltable concentrate and allows relation of the mass pull in flotation circuits to ensure a higher nickel and cobalt recovery. This was the basis for the heap bioleaching of Jinchuan Ni ores (Qin et al., 2009; Zhen et al., 2009) also known for their high magnesium content, where the magnesium was mineralised as olivine, chlorite and antigorite (i.e. all silicate minerals). Mwase et al. (2012a, 2012b) have applied a heap bioleach approach for Ni extraction to ultramafic PGM sulfide concentrate and subsequently on the bulk ore itself (Mwase et al., 2014) derived from South African Platreef ore. Like the Jinchuan ore example, the Platreef ore had Ni mineralised as silicates with olivine, serpentine and talc being predominant. In both the cases the acidic heap leach approach led to significant iron and magnesium dissolution. For Western Australian nickel concentrates, magnesium minerals are quite problematic (Lotter et al., 2008) as they significantly raise the liquidus temperature of the slag leading to high slag viscosity and poor matteslag disengagement. This has been shown by Ritchie and Eksteen (2011) and Eksteen et al. (2011) to cause significant operational challenges in matte smelting furnaces. Significant nickel and associated cobalt losses (up to 40%) may occur to keep the magnesium levels and pyrrhotite levels under control (Peng and Seaman, 2011, 2012) to produce a smeltable concentrate. Matte entrainment in slag leads to further losses. Matte converting, which is accompanied by air or oxygen injection, lead to significant cobalt oxidation. This leads to the formation of cobalt oxides and silicates (similar to the formation of magnetite and iron silicate or fayalite) in the converter slag which is difficult to recover subsequently even with good endpoint control (Bezuidenhout et al., 2017). Bezuidenhout et al. (2017) further notes that for Ni matte converting operations in South Africa, 70% of the cobalt in the furnace matte (prior to converting) can be lost as silicates to converter slag and slag-suspended spinel phases. It is therefore clear that significant Ni and Co metal losses occur across the nickel processing value chain. The “smearing” effect of iron across the value chain through sequential deportment from the ore into the flotation concentrate, and subsequently into furnace matte, converter matte and various stages of refining is particularly problematic, particularly when battery grade nickel and cobalt sulfates are targeted, where the presence of ppm levels of iron is problematic. Further challenges arise due to the SO2 and SO3 produced during smelting and converting, particularly with fugitive emissions from the converting aisle where unsteady state SOx production lead to poor acid plant stability and often has to be scrubbed to meet environmental standards (Bezuidenhout et al., 2012). Given the focus on lessened environmental impact (Shen et al., 2008) and the metals losses incurred in conventional processing as explained above, there is a significant drive to consider alternative options. Hydrometallurgical approaches to date typically involve the use of different reagents such as ammonia, or sulphuric acid or hydrochloric acid, or bioleach approaches as mentioned above. In recent years, there have been promising advancements in the development of a new method which uses glycine in an alkaline environment as a lixiviant for base and precious metals (Eksteen et al., 2017a, 2017b; Tanda et al., 2017; Mpinga et al., 2015; Oraby and Eksteen, 2014) from their sulfide, oxide and native metal resources. A high level block diagram of the traditional extraction process and its relation to the proposed method for this study is provided in Fig. 1. The proposed process mainly
NiS(s) + 2O2(g ) + 6NH3(l) → Ni(NH3)6 SO4(aq)
(1)
2CoS(s) + 4.5O2(g ) + 10NH3(l) + (NH 4)2 SO4(aq) → [Co(NH3)6]2 (SO4 )3(aq) + H2 O(l)
(2)
There are also several refineries that use sulphuric acid and oxygen as a leaching reagent. These include the Harjavalta refinery in Finland, mixed Ni-Co plants from Murrin and most platinum-group metal refineries that process converter mattes (Crundwell et al., 2011). Acids react with a number of gangue minerals that predominate in the ore and concentrates, particularly at a higher temperature. Due to this, the sulphate method is efficient, but is largely regarded as relatively nonselective and reagent consuming. The Nikkelverk process is one refinery that uses a chlorine-based system for refining sulphide mattes and mixed sulphide precipitates (Crundwell et al., 2011; Budac et al., 2009; Stensholt et al., 1986; Moats and William, 2014). Roughly 90% of the matte is leached in the tank and autoclave, and the remaining matte is used to precipitate the copper sulphide (Budac et al., 2009; Stensholt et al., 1986). Chlorine gas is an effective in this process because it is a strong oxidant, however chlorine gas is a poisonous gas. Chlorine would be more suitable for high grade materials such as concentrates than ores. Glycine has been suggested as a lixiviant under alkaline conditions that can be used to leach metals directly from crushed ore. This could dramatically improve the efficiency of the process for extracting metals – since it allows for the bypassing of the froth flotation, smelting and converting stages in traditional processing (see Fig. 1), as well as any pressure leaching processes. Previous investigations have suggested that glycine is a suitable lixiviant for leaching gold, silver, nickel, cobalt and copper from a variety of ore types, particularly when precious and base metal polymetallic ores need to be treated (Eksteen et al., 2018; Eksteen et al., 2017a,b; Tanda et al., 2017; Eksteen and Oraby, 2016; Mpinga et al., 2015; Oraby and Eksteen, 2014, 2015). It has also been demonstrated as a suitable lixiviant for polymetallic electronic waste (Oraby et al., 2019). Alkaline leaching using glycine as lixiviant has many advantages over traditional processing and other hydrometallurgical extraction reagents. In addition to being relatively cheap and widely available, its primary advantage is that it is significantly less harmful compared to other reagents that are used in industry. Preliminary tests also suggest that it can be used to extract metals at ambient temperature and pressure, making it more cost effective than traditional methods since there is no need to add energy into the system to raise the temperature (Oraby and Eksteen, 2014; Eksteen et al., 2017b). Glycine leaching shows strong potential for direct leaching of slag, concentrate and crushed ore (Eksteen et al., 2018). These results strongly suggest that glycine can be a suitable choice for recovering nickel and cobalt from waste products – and point toward glycine as a suitable lixiviant for selective recovery of these metals in other process streams. It also confirmed that selective leaching of chalcophile metals such as Cu, Ni, Co, Zn, and Pb over Fe, Al, Mg, Mn, and Si was possible. This could result in a significant reduction in the number of process steps, which would reduce the overall losses and hence improve the overall recovery of the desired metals. The reactions of Ni, Co from pentlandite and Cu from chalcopyrite with glycine at alkaline pH can form metal glycinate 2
Minerals Engineering 145 (2020) 106073
J.J. Eksteen, et al.
Fig. 1. Block diagram for the conventional and proposed processes.
compositions of the ore sample was analysed by Quantitative X-ray Diffraction (Q-XRD) technique. The chemical analysis for the targeted base metals and other elements was conducted by X-ray Fluorescence (XRF) technique. Liquor samples were analysed by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and Atomic Absorption Spectroscopy (AAS). Particle size distribution was analysed with Malvern laser particle size analyser and the total sulfur content by Leco combustion analyser.
Table 1 Bulk mineralogical analysis of the tested ore sample. Mineral
Wt.%
Kaolinite-serpentine group Hydrotalcite group Chlorite group Spinel group Dolomite group Magnesite Brucite Pentlandite group - Pentlandite
80 5 <1 2 2 7 2 1
Total
100
2.2. Leaching All experiments were carried out using solutions prepared from analytical grade reagents and deionised water. Unless specified, all experiments were conducted using a bottle roller. The ore and glycine solutions were placed in a 2.0 L plastic bottles with a 5 mm hole in the lid to allow for air exchange. After pH adjustment, the leach slurries were both rolled at 100 rpm. At the different sampling times, solution samples of the leach solution at different times were collected after vacuum filtration using a 0.45 µm filter paper. The solids were returned back to the leach bottle and the filtrates were analysed for Ni, Co and Cu by using atomic absorption spectrometry (AAS). The metal content in the sub-sample solutions and changing in leach solution volume were considered in the metals recovery calculations. The final leach filtrates were analysed for different elements by ICP-OES. All the solid residues were sent in duplicates for XRF analysis. Assays (XRF and ICP-OES) were performed by the internationally recognised and certified laboratory Bureau Veritas (https://www.bureauveritas.com.au/) in Perth, WA.
complexes using as caustic as a pH modifier. These reactions are shown in Eqs. (3), (4) and (5) respectively.
2(FeS. NiS) + 6(NH2 CH2 COOH) + 8(NaOH) + 8O2 → 2[Ni(NH2 CH2 COO)3] + 4(Na2SO4 ) + 7H2 O + Fe2 O3
(3)
2(FeS. CoS) + 6(NH2 CH2 COOH) + 8(NaOH) + 8O2 → 2[Co(NH2 CH2 COO)3] + 4(Na2SO4 ) + 7H2 O + Fe2 O3
(4)
CuFeS2 + 2(NH2 CH2 COOH) + 4(NaOH) + 5O2 → 2[Cu(NH2 CH2 COO)2] + 2(Na2SO4 ) + 3H2 O + Fe2 O3
(5)
Glycine has been shown to be an effective reagent that is able to selectively leach a variety of metals from a range of minerals under alkaline conditions at a range of ambient temperatures (Oraby and Eksteen, 2014; Eksteen and Oraby, 2016; Tanda et al., 2017). This supports the proposal of glycine as an attractive alternative to the harmful reagents used in the current leaching industrial processes. The successful exploratory tests into extracting nickel and cobalt from concentrates (Eksteen et al., 2018) which forms the basis of the investigation into leaching nickel and cobalt from crushed low-grade sulphide ores using glycine. Some key variables will be tested in this research study are glycine concentration, the leach pH, temperature, and the impact of regenerating or recycling the glycine for further metals leaching.
3. Results and discussion Tables 1 and 2 show the quantitative X-ray diffraction (Q-XRD) and X-ray fluorescence (XRF) analyses of the tested ore samples respectively. The mineralogy showed that kaolinite-serpentine group is the main mineral present and magnesite represents about 7%, hydrotaclite 5% and dolomite and brucite about 2% each of the tested samples. The presence of such high percentages of hydroxide and carbonate minerals will clearly make the direct leach of such ore sample by conventional sulfuric acid uneconomic due to the high acid consumption and high impurities in the final leach solutions. The use of any acidic leaching approach is bound to be highly reagent consuming. The elemental analysis confirms the high percentage of Mg in the ore which would lead the formation of MgSO4 if leached with sulphuric acid. Other than the obviously acid soluble minerals such magnesite, brucite and hydrotalcite, the predominant mineral, chrysotile is partially acid soluble (leaving silica gel behind), even in fairly mildly acidic environments as shown by Morgan (1997a, 1997b). The particle size distribution of the treated sample has been analysed by Malvern laser analyser and the results are shown in Fig. 2. The
2. Experimental 2.1. Samples preparation Low grade nickel ore sample from a Western Australian deposit has been used to conduct this research program. The sample was obtained from a cyclone overflow from the mine site and tested after drying and splitting to different subsample portions. The sample was treated as received to evaluate the glycine soluble nickel, cobalt and copper from such ore sample at different leach conditions. The mineralogical Table 2 Elemental analysis of the tested ore sample. Sample Units Ore Sample
Si % 15.6
Al % 0.25
Ca % 0.31
Fe % 5.2
Mg % 23.5
Na % 0.27
S % 1.02
3
Mn % 0.06
Ni % 0.66
Cu % 0.02
Pb % BDL
Zn % 0.002
As % 0.004
Co % 0.014
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Fig. 2. Particle size distribution of the tested ore sample.
nickel, cobalt and copper and other chalcophile metals from different ore sources (Eksteen and Oraby, 2016) in an alkaline environment. Glycine is the simplest α-amino acid that has the chemical formula C2H5NO2. Since it contains a basic amine group (NH2) and an acidic carboxyl group (COOH), it can exist as a zwitterion, depending on how alkaline or acidic its environment is. At alkaline environment, the glycine exists in an anion form (Glycinate) as shown in Eq. (6).
P80 pass size of the ground sample was 170 µm and 61.7% of the particles was passing 75 µm. 3.1. Acid leach Preliminary experiments were conducted as control tests to evaluate the possibility of leaching the ore by conventional acid processes. This was done using acid solutions containing 50 g/L and 200 g/L sulfuric acid. Due to the high acid consumable impurities in the ore sample, both acid tests did not extract Ni or Co and high silica gel suspension was observed during the high acid leach test. Fig. 3 shows the metals recovery from leaching the ore sample by 200 g/L acid and the maximum Ni and Co recovery was only 5.98% and 1.13%, respectively. The low metals recovery is due to most of the acid been consumed by the high acid soluble gangue minerals present in the ore sample.
−H+
(H3 N+ − CH2 − CO2−) + OH− → (H2 N − CH2 − CO2−) + H2 O
(6)
This negatively charged glycinate anion can form complexes with the target metals (Ni2+, Co2+ and Cu2+) in the ore according to Equation (7).
4M + 4(x + 1)HL + 4NaOH + xO2 → 4Na[ML(x + 1)] + 2(x + 2)H2 O (7) where M is precious or chalcophile metal, x represents the valence of the metal ions and L− stands for glycine anion (NH2CH2COO−). The following sections cover the systematic evaluation of leach conditions and parameters for Ni, Co and Cu extraction by alkaline glycine solutions. The effects of pH, glycine concentration, and
3.2. Glycine leaching (GlyLeach™) GlyLeach™ process is a hydrometallurgical process that utilised amino acids in general and glycine in particular to leach gold, silver,
Fig. 3. Nickel, Cobalt and Copper extraction from low grade nickel ore sample at 200 g/L acid, 3 g/L ferric, 40% solids, and room temperature. 4
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Fig. 4. Effect of glycine concentration on nickel extraction from low grade nickel ore at 40% solids, pH 10.0 and room temperature.
be clearly seen that Co leaching is proportional to nickel leaching during leaching and the cobalt extraction increases concurrently over the time. Maximum cobalt extraction was 66.6% after 336 h leaching at 46.3 g/L glycine. The Cu dissolution is much lower than Ni and Co as the copper present as chalcopyrite which leaches much slower in glycine solutions at room temperature and the absence of strong oxidants (Oraby and Eksteen, 2014). Recent research published by Tanda et al. (2019) and O’Connor et al. (2018) confirmed the need for higher temperature and stronger oxidation conditions (than maintained in this work) and the semiconductor behaviour of chalcopyrite in alkaline glycine solutions. Table 3 shows the impurities dissolution at different glycine levels. The results show the selectivity of leaching Ni and Co over Fe, Si, Al, and Mg which is another important advantage of alkaline glycine leaching and significantly simplifying downstream purification requirements and associated costs. The Mg dissolution slightly increases by increasing the glycine concentration, however the magnesium dissolution percentage is less than 0.08% of the total Mg present in the ore. Even more important, the iron levels remained below detection limits of the ICP-OES. This is of particular importance as iron is particularly problematic if nickel and cobalt are targeted for battery grade cathode precursors. In conventional processing iron is “smeared” across the process as the flotation cleaner process, the smelter furnace and
temperature have also been studied and discussed. Multi-contact leach tests were conducted using fresh and recycle glycine solutions to show the leaching continuity and glycine recyclability. 3.2.1. Effect of glycine concentration As glycine is the main lixiviant for the nickel, cobalt and copper leaching during the GlyLeach™ process, it is important to evaluate the effect of varying glycine concentrations on the metals extraction and impurities dissolution. Fig. 4 shows the effect of glycine concentration on Ni, Co and Cu extraction at pH 10.0, 40% solids and room temperature. Three levels of glycine concentration were tested 17.3 g/L [Gly: (Ni + Co + Cu) = 3:1], 28.9 g/L [Gly: (Ni + Co + Cu) = 5:1], and 46.3 g/L [Gly: (Ni + Co + Cu) = 8:1]. At such high concentrations, glycine should be recycled back to the leach step after metals recovery from solutions. The results shown in Figs. 4 and 5 indicate the glycine concentration should be maintained at a level of glycine to total metal molar ratio 5:1 or above. The kinetic curve of nickel extraction (Fig. 4) indicates the extraction kinetics is slow and is not suitable for tank leach applications at room temperature. Maximum nickel recovery achieved after 336 h (14 days) was 73.8%. Despite the slow leach rate, the kinetic curve indicates that there is no surface passivation and the nickel and Co leaching increases over the leach time. Fig. 5 shows the cobalt recovery at different levels of glycine. It can
Fig. 5. Effect of glycine concentration on cobalt extraction from low grade nickel ore at 40% solids, pH 10.0 and room temperature. 5
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Table 3 Impurities dissolution at different glycine levels after 336 h leaching of nickel ore by Glyleach™ process (BDL = Below Detection Limit). Glycine g/L
Al mg/L
As mg/L
Co mg/L
Cu mg/L
Fe mg/L
Mg mg/L
Ni mg/L
Pb mg/L
S mg/L
Si mg/L
Zn mg/L
17.3 28.9 46.3
BDL BDL BDL
BDL BDL BDL
4.74 55.4 65.0
21.8 15.7 18.1
BDL BDL BDL
15.6 42.5 124
372 2960 3300
BDL BDL BDL
726.5 5395 5640
BDL BDL BDL
3.0 3.0 3.5
Fig. 6. Effect of pH on nickel extraction from low grade nickel ore at 40% solids, pH 10.0 and room temperature.
converter and first refining steps in a conventional Sherritt® process are all in place to reject iron. This leach therefore achieves iron rejection right from the start.
extractions than operating at higher pH’s (pH of 11.5) which is opposite to the behaviour of copper sulfides such as chalcopyrite, which showed improved the copper extraction at pH 11.5 (Oraby and Eksteen, 2014; Eksteen et al., 2017b). Table 4 shows the impurities dissolution at different leach pHs. Mg dissolution increases by leaching at lower pH (pH 9.0) so pH 10 was selected as an optimum leach pH for Ni and Co.
3.2.2. Effect of pH The effect of leach solution pH on nickel, Co and Cu has been studied at different pH levels. It can be seen that there is a negative impact of increasing the leach pH from 10 to 11.5 on nickel extraction as shown in Fig. 6. Nickel extraction decreases from 73.8 to 29.8% by increasing the pH from 10 to 11.5. This results can attributed to the precipitation of Ni as nickel hydroxide by increasing the leach pH. Similar finding was observed for Co extraction as shown in Fig. 7. The Cu dissolution is much lower than Ni and Co and Cu behaves quite different to Ni and Co. It was found that running the leach at milder alkaline pH (pH 10) gave significantly better Ni and Co
3.2.3. Effect of temperature Tanda et al. (2018), showed that temperature enhanced the copper dissolution by glycine from different copper sulfide minerals. Oraby and Eksteen (2014, 2015); Eksteen and Oraby (2015), found also temperature is a key parameter in the precious metals dissolution by glycine. To evaluate the effect of temperature on Ni and Co extractions, two temperature levels were tested to evaluate the effect of temperature on metals extraction from the tested ore. Fig. 8 shows the Ni extraction
Fig. 7. Effect of pH on cobalt extraction from low grade nickel ore at 40% solids, pH 10.0 and room temperature. 6
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Table 4 Impurities dissolution at different leach pHs after 336 h leaching of nickel ore by Glyleach™ process (BDL = Below Detection Limit). Leach pH
Al mg/L
As mg/L
Co mg/L
Cu mg/L
Fe mg/L
Mg mg/L
Ni mg/L
Pb mg/L
S mg/L
Si mg/L
Zn mg/L
9.0 10 11.5
BDL BDL BDL
BDL BDL BDL
52.9 65.0 22.6
16.4 18.1 31.8
BDL BDL BDL
1420 124 3.0
2860 3300 1350
BDL BDL BDL
4120 5640 3920
BDL BDL BDL
3.0 3.5 3.6
Fig. 8. Effect of glycine concentration on nickel extraction from low grade nickel ore at 40% solids, pH 10.0 and two levels of temperature.
Fig. 9. Effect of temperature on cobalt extraction from low grade nickel ore 40% solids, pH 10.0 and room temperature.
cycles using a fresh glycine solution at each cycle. The required volume of leach solution containing 46.3 g/L glycine at pH 10 was mixed with solids to produce 40% solids. The results of Ni and Co extraction from these cycle tests are shown in Fig. 10. The results indicate that Ni and Co extraction increases by time and the maximum Ni recovery reaches 83.5% after 672 h leaching. It is interesting to note the Co dissolution kinetics is congruent with the Ni recovery and the maximum Co recovery was 76.2% after 672 h period. It would imply that the cobalt is probably in solid solution in the pentlandite matrix and fairly homogenously distributed throughout the pentlandite grains. The copper in such ore is a “nuisance” copper and does not play a role in the economics of this deposit. However, the accumulative Cu recovery reaches 23.7% during the four cycle tests. The long leach times to achieve good recoveries implies that the leach approach is more suitable for an alkaline heap leach environment rather than a tank leach of the ore sample.
at different levels of temperature, it is clear that the higher temperature only improves the initial Ni leach rate, however the overall Ni extraction was higher at room temperature. The Ni extraction after 336 h decreases from 73.8% to 56.3% by increasing temperature from room temperature (23 °C) to 55 °C, respectively. Fig. 9 shows the Co extraction at different levels of temperature, it is clearly confirmed that the temperature also improves the initial Co leach rate, however the overall Co extraction was also higher at room temperature. The Co extraction after 336 h decreases from 66.7% to 41.0% by increasing temperature from room temperature (23 °C) to 55 °C, respectively. The results proved the temperature improves the Cu dissolution which is in consistent with the previous studies (Oraby and Eksteen, 2014; Eksteen et al., 2017b). 3.2.4. Multi contact leach – Fresh solution Multi-contact leach test of the ore sample was carried out for 4 7
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Fig. 10. Effect of multi-contact glycine leaching on nickel and cobalt extraction from low grade nickel ore at 46.3 g/L glycine, 40% solids, pH 10.0 and room temperature.
Fig. 11 shows the cumulative recovery of Ni, Co and Cu during the multi contact with barren solutions. It can be clearly seen that Co and Ni dissolution is concurrent (and that the cobalt is in solid solution in the pentlandite). The results supports the conclusion that the leaching of Ni and Co continues over time using recycled barren leach solution, where the solution contains glycine at the target leach pH, and that the glycine is regenerated. Table 6 shows the metals concentration at the end of each cycles before and after adsorption on 55.0 g/L resin. It can be seen the resin was very effective to adsorb more than 97% of Ni, 65% of Co and 99.0% of Cu. The Co adsorption efficiency increases by increasing of the accumulated Co concentration in the barren solution. Table 7 shows the cumulative metals recovery after each cycle. This would align with a real system heap leach system where barren raffinate solution, where the glycine has been regenerated is reused to leach the metals.
Table 5 Leach conditions for glycine recycle test. Factor
Barren Solution Leach
Glycine (g/L) Solids (%) Grind size p80 (µm) Temperature (°C) Target pH Water
46.3 40.0 169.6 Ambient in bottle roll 10.0 Perth Tap Water
3.2.5. Multi leach – Recycled barren solution A leach test was conducted to show the effectiveness of continues leaching of metals using barren/recycle glycine solutions after metals adsorption onto ion exchange resin. The leach solution was periodically filtered, and a Purolite S930Plus resin was used to adsorb the metals from the solution after certain time and nickel concentration reached a certain value (adsorption cycles occurred approximately every 72 h). A total of four cycles were carried out for the duration of the test. Table 5 shows the leach conditions for the multi leach-recycle glycine solutions test.
3.3. Optimum leach conditions From the results, it can be observed that pH and glycine
Fig. 11. Effect of multi-contact recycle glycine solutions on nickel and cobalt extraction from low grade nickel ore at 46.3 g/L glycine, 40% solids, pH 10.0 and room temperature. 8
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Table 6 Ni, Co and Cu concentration before and after adsorption for each cycle of leaching using recycle glycine solutions. Ni
Co
Cu
#
Time (hr)
Fresh (mg/L)
Barren (mg/L)
Adsorp. (%)
Fresh (mg/L)
Barren (mg/L)
Adsorp. (%)
Fresh (mg/L)
Barren (mg/L)
Adsorp. (%)
Clycle1 Clycle2 Clycle3 Clycle4
72 72 72 144
1540 910 621 374
32 25.0 33.2 12.5
97.9 97.3 95.0 96.6
38.4 35.5 22.4 23.2
14.0 10.5 8.9 8.5
63.5 70.4 60.3 63.4
14.53 4.1 4.0 6
0.125 0.1 0.13 0.15
99.4 97.5 96.7 97.5
sulfide resources using a benign alkaline leach technology, non-toxic, non-volatile and cost effective reagents, where the reagents can be recycled to the leach after resetting the pH. Further work to simulate the actual metals recovery from coarse particles by column leach to simulate the heap leach applications are required.
Table 7 Ni, Co and Cu accumulative extraction after each cycle of leaching using recycle glycine solutions. Final Cumulative Extraction
Cycle1
Cycle2
Cycle3
Cycle4
Nickel Extraction (%) Cobalt Extraction (%) Copper Extraction (%)
34.3 35.7 15.0
55.6 59.0 18.9
65.6 65.5 22.2
73.7 74.6 27.8
4. Conclusions An alkaline glycine leaching research study for a highly acid consuming low grade nickel sulfide ore containing 0.67% Ni has been conducted to evaluate the amenability of such ore for the eventual application of heap, vat and in-situ leaching modes using glycine. In this study, different parameters have been evaluated to extract Ni and Co from the low grade ore. The effects of pH, glycine concentration, and temperature have been studied. The results indicate that leaching such a high acid consumable nickel ore with conventional sulphuric acid leaching is uneconomic and about 250 kg/t acid was consumed with only 6% Ni was extracted. The study showed that glycine-based Ni and Co leach rates are slow and about 83.5% Ni and 76.3% Co were
concentration are the controlling factors of nickel and cobalt extraction in alkaline glycine solutions. Optimum conditions to leach such ore are summarised form this research study to be 46.3 g/L glycine (8:1 Gly: total metals content), pH 10.0, 40% solids and room temperature. The proposed flowsheet for Ni leaching from such low grade ore by alkaline glycine leaching consists mainly of heap leaching followed by metals recovery (Ni, Co and Cu) by resin in column (CIC) and recycling glycine solution to the leaching step. Fig. 12 shows the proposed simulated heap application set up to treat such deposits. Bench scale results will provide a basis to investigate nickel and cobalt recovery from various
Fig. 12. Column leach set up for heap leach applications. 9
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Fig. 13. Conceptual block diagram flowsheet for the production of nickel and cobalt sulfates from low grade sulfide ores or tailings using an alkaline glycine leach process.
extracted in 672 h. The results showed that increasing glycine concentration at pH 10.0 and room temperature have significant roles in maximising the Ni and Co recovery. It was found temperature improves the initial metals extraction, however leaching at room temperature provided a higher overall metals recovery. Selective leaching of Ni and Co by glycine solutions over other impurities such as Si, Mg, Fe and Al was proved in this research study. Overall, using glycine as a leaching reagent has successfully been proven to be feasible and highly selective. It is a safer alternative to the traditional smelting method, and is highly suitable for the extraction of nickel, cobalt and copper from crushed low-grade sulphide ores. A conceptual block process flow diagram can be postulated (shown in Fig. 13) whereby the nickel and cobalt are co-extracted in a heap leach (or vat leach or in-situ leach), and co-adsorbed onto a cation exchanger (IX) and the barren raffinate is recycled back to the leach. The Ni and Co can be eluted from the resin by a strong sulfuric acid solution at 180 g/L. Separation of the Ni and Co in acidic IX eluate can be done by extracting Co by solvent in a two stage extraction (SX) process (Olivier et al., 2012) and recovering the Ni for the SX raffinate using IX and recycling the final barren raffinate. The refined CoSO4 and NiSO4 can then be crystallised, centrifuged, dried and shipped to a cathode precursor refinery to produce NCM / NCA mixed hydroxide precipitates or lithiated cathode active materials.
Elsevier, Oxford. Eksteen, J.J., Bezuidenhout, G.A., Van Beek, B., 2011. Cracking a hard nut: an overview of Lonmin’s operations directed at smelting of UG2-rich concentrate blends. J. South Afr. Inst. Min. Metall. 111 (10), 681–690. Eksteen, J.J., Oraby, E.A., Lombard, L., Di Prinzio, L., 2018. Leaching of cobalt bearing nickel sulfide (cobalt bearing pentlandite concentrates) and furnace and converter mattes with alkaline glycine, and Subsequent SX and IX. ALTA, Nickel-Cobalt-Copper, Uranium-REE and Gold-PM Conference, Perth, Australia, 19-26 May 2018. Perth, Australia. Eksteen, J.J., Oraby, E.A., 2016. A process for selective recovery of chalcophile group elements, PCT/AU2016/050171. Eksteen, J.J., Oraby, E.A., Tanda, B.C., Tauetsile, P.J., Bezuidenhout, G.A., Newton, T., Trask, F., Bryan, I., 2017a. Towards industrial implementation of glycine-based leach and adsorption technologies for gold-copper ores. Can. Metall. Q. 57 (4), 390–398. Eksteen, J.J., Oraby, E.A., 2015. The leaching and adsorption of gold using low concentration amino acids and hydrogen peroxide: effect of catalytic ions, sulphide minerals and amino acid type. Miner. Eng. 70, 36–42. Eksteen, J.J., Oraby, E.A., Tanda, B.C., 2017b. A conceptual process for copper extraction from chalcopyrite in alkaline glycinate solutions. Miner. Eng. 108, 53–66. Lotter, N.O., Bradshaw, D.J., Becker, M., Parolis, L.A.S., Kormos, L.J., 2008. A discussion of the occurrence and undesirable flotation behaviour of orthopyroxene and talc in the processing of mafic deposits. Miner. Eng. 21, 905–912. Moats, M.S., William, G.D., 2014. Chapter 2.2 - Nickel and Cobalt Production A2 Seetharaman, Seshadri. In: Treatise on Process Metallurgy, pp. 625–669. Morgan, A., 1997a. Acid leaching studies of chrysotile asbestos from mines in the Coalinga region of California and from Quebec and British Columbia. Ann. Occup. Hygiene 41 (3), 249–268. Morgan, A., 1997b. Acid leaching studies of neutron-irradiated chrysotile asbestos. Ann. Occup. Hygiene 41 (3), 269–279. Mpinga, C.N., Eksteen, J.J., Aldrich, C., Dyer, L., 2015. Direct leach approaches to Platinum Group Metal (PGM) ores and concentrates: a review. Miner. Eng. 78, 93–113. Mwase, J.M., Petersen, J., Eksteen, J.J., 2014. A novel sequential heap leach process for treating crushed Platreef ore. Hydrometallurgy 141, 97–104. Mwase, J.M., Petersen, J., Eksteen, J.J., 2012a. A conceptual flowsheet for heap leaching of platinum group metals (PGMs) from a low-grade ore concentrate. Hydrometallurgy 111–112, 129–135. Mwase, J.M., Petersen, J., Eksteen, J.J., 2012b. Assessing a two stage heap leaching process for Platreef flotation concentrate. Hydrometallurgy 129–130, 74–81. O’Connor, G.M., Lepkova, K., Eksteen, J.J., Oraby, E.A., 2018. Electrochemical behaviour and surface analysis of chalcopyrite in alkaline glycine solutions. Hydrometallurgy 182, 32–43. Olivier, M., Dorfling, C., Eksteen, J.J., 2012. Evaluating a solvent extraction process route incorporating nickel preloading of Cyanex 272 for the removal of cobalt and iron from nickel sulphate solutions. Miner. Eng. 27–28, 37–51. Oraby, E.A., Eksteen, J.J., 2014. The selective leaching of copper from a gold–copper concentrate in glycine solutions. Hydrometallurgy 150, 14–19. Oraby, E.A., Eksteen, J.J., 2015. The leaching of gold, silver and their alloys in alkaline glycine–peroxide solutions and their adsorption on carbon. Hydrometallurgy 152, 193–203. Oraby, E.A., Li, H., Eksteen, J.J., 2019. An alkaline glycine-based leach process of base and precious metals from powdered waste printed circuit boards. Waste and Biomass Valorization 1–13. https://doi.org/10.1007/s12649-019-00780-0. In Press. Peng, Y., Seaman, D., 2011. The flotation of slime–fine fractions of Mt. Keith pentlandite ore in de-ionised and saline water. Miner. Eng. 24, 479–481. Peng, Y., Seaman, D., 2012. Effect of feed preparation on copper activation in flotation of
Acknowledgements The authors would like to express their gratitude towards Curtin University for their support of this research. References Budac, J.J., Fraser, R., Mihaylov, I., 2009. Hydrometallurgy of nickel and cobalt 2009. Proceedings of 39th Annual Hydrometallurgy Meeting held in conjunction with the 48th Conference of Metallurgists. Canadian Institute of Mining, Sudbury, Ontario. Bezuidenhout, G.A., Davis, J., Van Beek, B., Eksteen, J.J., 2012. Operation of a concentrated mode Dual-Alkali scrubber plant at the Lonmin smelter. J. South Afr. Inst. Min. Metall. 112 (7), 657–665. Bezuidenhout, G.A., Eksteen, J.J., Akdogan, G. Van, Beek, B., Wendt, W., Persson, W., 2017. Implementation of flame optical emission spectroscopy system for converter Fe end-point control associated with Ni-Cu-S-PGM converter mattes. Miner. Eng. 100, 132–143. Burkin, A.R., 2001. Chemical Hydrometallurgy Theory and Principles. Imperial College Press. Cooper, W.C., Mihaylov, I., 1997. Hydrometallurgy and refining of nickel and cobalt. Nickel and Cobalt 1997 (1), 335–369. Crundwell, F.K., Michael, S.M., Venkoba, R., Timothy, G.R., William, G.D., 2011. Chapter 1 - Overview. Extractive Metallurgy of Nickel, Cobalt and Platinum Group Metals.
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of copper oxide minerals in aqueous alkaline glycine solutions. Hydrometallurgy 167, 153–162. Tanda, B.C., Eksteen, J.J., Oraby, E.A., O’Connor, G.M., 2019. The kinetics of chalcopyrite leaching in alkaline glycine/glycinate solutions. Miner. Eng. 135, 118–128. Qin, W., Zhen, S., Yan, Z., Campbell, M., Wang, J., Liu, K., Zhang, Y., 2009. Heap bioleaching of a low-grade nickel-bearing sulfide ore containing high levels of magnesium as olivine, chlorite and antigorite. Hydrometallurgy 98, 58–65. Zhen, S., Yan, Z., Zhang, Y., Wang, J., Campbell, M., Qin, W., 2009. Column bioleaching of a low grade nickel-bearing sulfide ore containing high magnesium as olivine, chlorite and antigorite. Hydrometallurgy 96, 337–341.
Mt Keith pentlandite. Mineral Process. Extract. Metal. (Trans. Inst. Min Metall. C) 121 (3), 11–139. Ritchie, S., Eksteen, J.J., 2011. Investigating the effect of slag bath conditions on the existence of “mushy” zones in PGM smelting furnaces using computational fluid dynamics. Miner. Eng. 24 (7), 661–675. Shen, Y.F., Xue, W.Y., Li, W., Tang, Y.L., 2008. Selective recovery of nickel and cobalt from cobalt-enriched Ni–Cu matte by two-stage counter-current leaching. Sep. Purif. Technol. 60 (2), 113–119. Stensholt, E.O., Dotterud, O.M., Henriksen, E.E., 1986. Falconbridge chlorine leach process. Section C. Trans. Inst. Min. Metal. 5, C10–C16. Tanda, B.C., Eksteen, J.J., Oraby, E.A., 2017. An investigation into the leaching behaviour
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Leaching and ion exchange based recovery of nickel and cobalt from a low grade, serpentine-rich sulfide ore using an alkaline glycine lixiviant system
T
⁎
J.J. Eksteena, , E.A. Orabya,b, V. Nguyena a
Faculty of Science and Engineering, Western Australian School of Mines: Minerals, Energy and Chemical Engineering, Curtin University, GPO Box U1987, Perth, WA 6845, Australia b Department of Mining and Metallurgical Engineering, Faculty of Engineering, Assiut University, Egypt
A R T I C LE I N FO
A B S T R A C T
Keywords: Glycine Nickel Cobalt Leaching Batteries
The paper presents the outcomes of exploratory research relating to the atmospheric pressure and ambient temperature leaching of nickel and cobalt from a Western Australian low grade, disseminated, nickel-cobalt sulfide ore, and the subsequent recovery using ion exchange (IX) using alkaline glycine solutions in mildly oxidizing environments. The results present a foundation for a direct leach approach at ambient conditions, particularly if upstream opportunities are considered (heap leach, in-situ leach, or vat leach, or bulk ore leach) from low grade Ni-Co resources. The results for cobalt are particularly exciting given the low recovery of cobalt in most smelting operations and the loss of cobalt to converter slags in conventional approaches. In addition, significant nickel losses are often incurred to flotation cleaner tailings to make a smeltable concentrate at an acceptable level of magnesium. The study showed that even though glycine-based leach rates for Ni and Co are slow, no passivation was observed and about 83.5% Ni and 76.3% Co were extracted at room temperature using conventional bottle rolls over a 672 h period using a multistage extraction (i.e. leachate decant and reagent refresh with either new reagent or recycled barren raffinate). The ore contained cobalt-bearing pentlandite as the predominant Ni-Co mineralization, with Kaolinite-serpentine group, magnesite and hydrotalcite the predominant oxide and pyrrhotite as the predominant sulfide gangue minerals. The effects of glycine concentration, pH and temperature have been studied. It was found that leaching at pH 10.0 gave significant better leach Ni and Co extraction than operating at higher pH of 11.5. In glycine leach campaigns, the dissolution of iron, magnesium, silicon, manganese and other impurities were insignificant. This is particularly important for iron removal which would normally have posed a significant solid-liquid separation and waste disposal cost and magnesium, given the very high levels of magnesium that would normally have dissolved from such ores in acidic systems. Excellent recovery of Ni and Co from leach solutions was achieved by a selected ion exchange resin (Purolite S930Plus) and high Ni and Co dissolution was achieved using recycle glycine solutions after metals adsorption and pH adjustment.
1. Introduction Nickel is a critically important base metal that exhibits high corrosion resistant and durability properties and is used to manufacture corrosion-resistant alloys such as stainless steel and other superalloys (Crundwell et al., 2011). The market for battery grade nickel salts is growing rapidly as it used to prepare precursors in Lithium-ion Batteries (LiBs) and other rechargeable batteries. High nickel use is predicted for the Nickel-Manganese-Cobalt (NMC) LiBs with NMC ratios of 811 and 622, which are the preferred cathode chemistries for LiBs used in electric vehicles for the projected future. Nickel is found primarily in two types of ores namely laterite (oxide) and sulphide ores. The sulfide
⁎
ores are normally associated with mafic and ultramafic ores which are inherently basic and tend to be magnesium rich and are typically mineralised in either a massive sulfide or a disseminated form in these rock types. Two significant Ni minerals in sulphide ores are pentlandite [(Ni,Fe)9S8] and nickeliferous pyrrhotite. There are several different techniques that can be used in the extraction of nickel and cobalt from various ore minerals. Sulphide ores that are mined for Ni and Co contain between 1.5 and 3.0% Ni and 0.05–1.0% Co (Crundwell et al., 2011). Traditional processing of these ores is through processing in a concentrator and smelter. The matte-smelting process and ancillary processes involves a combination of grinding, froth flotation, smelting, converting and refining, which may include pressure leaching and
Corresponding author. E-mail address: [email protected] (J.J. Eksteen).
https://doi.org/10.1016/j.mineng.2019.106073 Received 16 June 2019; Received in revised form 1 September 2019; Accepted 6 October 2019 0892-6875/ © 2019 Elsevier Ltd. All rights reserved.
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consists of crushing and leaching by heap or dump leach approaches. The refinery at Fort Saskatchewan was one of the first to utilise ammonia as a leaching reagent (Cooper and Mihaylov, 1997). The ammoniacal process involves pressure leaching of the nickel concentrate and matte with ammonia and oxygen in a series of autoclaves operating at 105–120 °C (Crundwell et al., 2011). This process aims to maximise the efficiency of leaching nickel and cobalt in addition to the oxidation of cobalt into solution as cobaltic hexamine. The process involves leaching of mixed Ni-Co sulphide precipitates in (NH4)2SO4 using ammonia and oxygen according to Eqs. (1) and (2).
pressurised Ni reduction by hydrogen or electrowinning (Crundwell et al., 2011; Burkin, 2001), e.g. the using the Sherritt process. In general there is a great similarity between the nickel sulfide ores with platinum group metals (PGMs) as a by-product, such as in Western Australia, and PGM ores where nickel is the by-product such as found in South Africa (Mpinga et al., 2015). Non-traditional processing often refers to hydrometallurgical methods, which can directly treat the bulk of the concentrate, instead of smelting it to a matte. Other hyrometallurgical alternatives also include the treatment of the bulk ore itself, or various waste products such as flotation cleaner tailings. A hydrometallurgical option, should it proven to be effective, would allow relaxation of the concentrate grade specifications in a flotation circuit to produce a smeltable concentrate and allows relation of the mass pull in flotation circuits to ensure a higher nickel and cobalt recovery. This was the basis for the heap bioleaching of Jinchuan Ni ores (Qin et al., 2009; Zhen et al., 2009) also known for their high magnesium content, where the magnesium was mineralised as olivine, chlorite and antigorite (i.e. all silicate minerals). Mwase et al. (2012a, 2012b) have applied a heap bioleach approach for Ni extraction to ultramafic PGM sulfide concentrate and subsequently on the bulk ore itself (Mwase et al., 2014) derived from South African Platreef ore. Like the Jinchuan ore example, the Platreef ore had Ni mineralised as silicates with olivine, serpentine and talc being predominant. In both the cases the acidic heap leach approach led to significant iron and magnesium dissolution. For Western Australian nickel concentrates, magnesium minerals are quite problematic (Lotter et al., 2008) as they significantly raise the liquidus temperature of the slag leading to high slag viscosity and poor matteslag disengagement. This has been shown by Ritchie and Eksteen (2011) and Eksteen et al. (2011) to cause significant operational challenges in matte smelting furnaces. Significant nickel and associated cobalt losses (up to 40%) may occur to keep the magnesium levels and pyrrhotite levels under control (Peng and Seaman, 2011, 2012) to produce a smeltable concentrate. Matte entrainment in slag leads to further losses. Matte converting, which is accompanied by air or oxygen injection, lead to significant cobalt oxidation. This leads to the formation of cobalt oxides and silicates (similar to the formation of magnetite and iron silicate or fayalite) in the converter slag which is difficult to recover subsequently even with good endpoint control (Bezuidenhout et al., 2017). Bezuidenhout et al. (2017) further notes that for Ni matte converting operations in South Africa, 70% of the cobalt in the furnace matte (prior to converting) can be lost as silicates to converter slag and slag-suspended spinel phases. It is therefore clear that significant Ni and Co metal losses occur across the nickel processing value chain. The “smearing” effect of iron across the value chain through sequential deportment from the ore into the flotation concentrate, and subsequently into furnace matte, converter matte and various stages of refining is particularly problematic, particularly when battery grade nickel and cobalt sulfates are targeted, where the presence of ppm levels of iron is problematic. Further challenges arise due to the SO2 and SO3 produced during smelting and converting, particularly with fugitive emissions from the converting aisle where unsteady state SOx production lead to poor acid plant stability and often has to be scrubbed to meet environmental standards (Bezuidenhout et al., 2012). Given the focus on lessened environmental impact (Shen et al., 2008) and the metals losses incurred in conventional processing as explained above, there is a significant drive to consider alternative options. Hydrometallurgical approaches to date typically involve the use of different reagents such as ammonia, or sulphuric acid or hydrochloric acid, or bioleach approaches as mentioned above. In recent years, there have been promising advancements in the development of a new method which uses glycine in an alkaline environment as a lixiviant for base and precious metals (Eksteen et al., 2017a, 2017b; Tanda et al., 2017; Mpinga et al., 2015; Oraby and Eksteen, 2014) from their sulfide, oxide and native metal resources. A high level block diagram of the traditional extraction process and its relation to the proposed method for this study is provided in Fig. 1. The proposed process mainly
NiS(s) + 2O2(g ) + 6NH3(l) → Ni(NH3)6 SO4(aq)
(1)
2CoS(s) + 4.5O2(g ) + 10NH3(l) + (NH 4)2 SO4(aq) → [Co(NH3)6]2 (SO4 )3(aq) + H2 O(l)
(2)
There are also several refineries that use sulphuric acid and oxygen as a leaching reagent. These include the Harjavalta refinery in Finland, mixed Ni-Co plants from Murrin and most platinum-group metal refineries that process converter mattes (Crundwell et al., 2011). Acids react with a number of gangue minerals that predominate in the ore and concentrates, particularly at a higher temperature. Due to this, the sulphate method is efficient, but is largely regarded as relatively nonselective and reagent consuming. The Nikkelverk process is one refinery that uses a chlorine-based system for refining sulphide mattes and mixed sulphide precipitates (Crundwell et al., 2011; Budac et al., 2009; Stensholt et al., 1986; Moats and William, 2014). Roughly 90% of the matte is leached in the tank and autoclave, and the remaining matte is used to precipitate the copper sulphide (Budac et al., 2009; Stensholt et al., 1986). Chlorine gas is an effective in this process because it is a strong oxidant, however chlorine gas is a poisonous gas. Chlorine would be more suitable for high grade materials such as concentrates than ores. Glycine has been suggested as a lixiviant under alkaline conditions that can be used to leach metals directly from crushed ore. This could dramatically improve the efficiency of the process for extracting metals – since it allows for the bypassing of the froth flotation, smelting and converting stages in traditional processing (see Fig. 1), as well as any pressure leaching processes. Previous investigations have suggested that glycine is a suitable lixiviant for leaching gold, silver, nickel, cobalt and copper from a variety of ore types, particularly when precious and base metal polymetallic ores need to be treated (Eksteen et al., 2018; Eksteen et al., 2017a,b; Tanda et al., 2017; Eksteen and Oraby, 2016; Mpinga et al., 2015; Oraby and Eksteen, 2014, 2015). It has also been demonstrated as a suitable lixiviant for polymetallic electronic waste (Oraby et al., 2019). Alkaline leaching using glycine as lixiviant has many advantages over traditional processing and other hydrometallurgical extraction reagents. In addition to being relatively cheap and widely available, its primary advantage is that it is significantly less harmful compared to other reagents that are used in industry. Preliminary tests also suggest that it can be used to extract metals at ambient temperature and pressure, making it more cost effective than traditional methods since there is no need to add energy into the system to raise the temperature (Oraby and Eksteen, 2014; Eksteen et al., 2017b). Glycine leaching shows strong potential for direct leaching of slag, concentrate and crushed ore (Eksteen et al., 2018). These results strongly suggest that glycine can be a suitable choice for recovering nickel and cobalt from waste products – and point toward glycine as a suitable lixiviant for selective recovery of these metals in other process streams. It also confirmed that selective leaching of chalcophile metals such as Cu, Ni, Co, Zn, and Pb over Fe, Al, Mg, Mn, and Si was possible. This could result in a significant reduction in the number of process steps, which would reduce the overall losses and hence improve the overall recovery of the desired metals. The reactions of Ni, Co from pentlandite and Cu from chalcopyrite with glycine at alkaline pH can form metal glycinate 2
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Fig. 1. Block diagram for the conventional and proposed processes.
compositions of the ore sample was analysed by Quantitative X-ray Diffraction (Q-XRD) technique. The chemical analysis for the targeted base metals and other elements was conducted by X-ray Fluorescence (XRF) technique. Liquor samples were analysed by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and Atomic Absorption Spectroscopy (AAS). Particle size distribution was analysed with Malvern laser particle size analyser and the total sulfur content by Leco combustion analyser.
Table 1 Bulk mineralogical analysis of the tested ore sample. Mineral
Wt.%
Kaolinite-serpentine group Hydrotalcite group Chlorite group Spinel group Dolomite group Magnesite Brucite Pentlandite group - Pentlandite
80 5 <1 2 2 7 2 1
Total
100
2.2. Leaching All experiments were carried out using solutions prepared from analytical grade reagents and deionised water. Unless specified, all experiments were conducted using a bottle roller. The ore and glycine solutions were placed in a 2.0 L plastic bottles with a 5 mm hole in the lid to allow for air exchange. After pH adjustment, the leach slurries were both rolled at 100 rpm. At the different sampling times, solution samples of the leach solution at different times were collected after vacuum filtration using a 0.45 µm filter paper. The solids were returned back to the leach bottle and the filtrates were analysed for Ni, Co and Cu by using atomic absorption spectrometry (AAS). The metal content in the sub-sample solutions and changing in leach solution volume were considered in the metals recovery calculations. The final leach filtrates were analysed for different elements by ICP-OES. All the solid residues were sent in duplicates for XRF analysis. Assays (XRF and ICP-OES) were performed by the internationally recognised and certified laboratory Bureau Veritas (https://www.bureauveritas.com.au/) in Perth, WA.
complexes using as caustic as a pH modifier. These reactions are shown in Eqs. (3), (4) and (5) respectively.
2(FeS. NiS) + 6(NH2 CH2 COOH) + 8(NaOH) + 8O2 → 2[Ni(NH2 CH2 COO)3] + 4(Na2SO4 ) + 7H2 O + Fe2 O3
(3)
2(FeS. CoS) + 6(NH2 CH2 COOH) + 8(NaOH) + 8O2 → 2[Co(NH2 CH2 COO)3] + 4(Na2SO4 ) + 7H2 O + Fe2 O3
(4)
CuFeS2 + 2(NH2 CH2 COOH) + 4(NaOH) + 5O2 → 2[Cu(NH2 CH2 COO)2] + 2(Na2SO4 ) + 3H2 O + Fe2 O3
(5)
Glycine has been shown to be an effective reagent that is able to selectively leach a variety of metals from a range of minerals under alkaline conditions at a range of ambient temperatures (Oraby and Eksteen, 2014; Eksteen and Oraby, 2016; Tanda et al., 2017). This supports the proposal of glycine as an attractive alternative to the harmful reagents used in the current leaching industrial processes. The successful exploratory tests into extracting nickel and cobalt from concentrates (Eksteen et al., 2018) which forms the basis of the investigation into leaching nickel and cobalt from crushed low-grade sulphide ores using glycine. Some key variables will be tested in this research study are glycine concentration, the leach pH, temperature, and the impact of regenerating or recycling the glycine for further metals leaching.
3. Results and discussion Tables 1 and 2 show the quantitative X-ray diffraction (Q-XRD) and X-ray fluorescence (XRF) analyses of the tested ore samples respectively. The mineralogy showed that kaolinite-serpentine group is the main mineral present and magnesite represents about 7%, hydrotaclite 5% and dolomite and brucite about 2% each of the tested samples. The presence of such high percentages of hydroxide and carbonate minerals will clearly make the direct leach of such ore sample by conventional sulfuric acid uneconomic due to the high acid consumption and high impurities in the final leach solutions. The use of any acidic leaching approach is bound to be highly reagent consuming. The elemental analysis confirms the high percentage of Mg in the ore which would lead the formation of MgSO4 if leached with sulphuric acid. Other than the obviously acid soluble minerals such magnesite, brucite and hydrotalcite, the predominant mineral, chrysotile is partially acid soluble (leaving silica gel behind), even in fairly mildly acidic environments as shown by Morgan (1997a, 1997b). The particle size distribution of the treated sample has been analysed by Malvern laser analyser and the results are shown in Fig. 2. The
2. Experimental 2.1. Samples preparation Low grade nickel ore sample from a Western Australian deposit has been used to conduct this research program. The sample was obtained from a cyclone overflow from the mine site and tested after drying and splitting to different subsample portions. The sample was treated as received to evaluate the glycine soluble nickel, cobalt and copper from such ore sample at different leach conditions. The mineralogical Table 2 Elemental analysis of the tested ore sample. Sample Units Ore Sample
Si % 15.6
Al % 0.25
Ca % 0.31
Fe % 5.2
Mg % 23.5
Na % 0.27
S % 1.02
3
Mn % 0.06
Ni % 0.66
Cu % 0.02
Pb % BDL
Zn % 0.002
As % 0.004
Co % 0.014
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Fig. 2. Particle size distribution of the tested ore sample.
nickel, cobalt and copper and other chalcophile metals from different ore sources (Eksteen and Oraby, 2016) in an alkaline environment. Glycine is the simplest α-amino acid that has the chemical formula C2H5NO2. Since it contains a basic amine group (NH2) and an acidic carboxyl group (COOH), it can exist as a zwitterion, depending on how alkaline or acidic its environment is. At alkaline environment, the glycine exists in an anion form (Glycinate) as shown in Eq. (6).
P80 pass size of the ground sample was 170 µm and 61.7% of the particles was passing 75 µm. 3.1. Acid leach Preliminary experiments were conducted as control tests to evaluate the possibility of leaching the ore by conventional acid processes. This was done using acid solutions containing 50 g/L and 200 g/L sulfuric acid. Due to the high acid consumable impurities in the ore sample, both acid tests did not extract Ni or Co and high silica gel suspension was observed during the high acid leach test. Fig. 3 shows the metals recovery from leaching the ore sample by 200 g/L acid and the maximum Ni and Co recovery was only 5.98% and 1.13%, respectively. The low metals recovery is due to most of the acid been consumed by the high acid soluble gangue minerals present in the ore sample.
−H+
(H3 N+ − CH2 − CO2−) + OH− → (H2 N − CH2 − CO2−) + H2 O
(6)
This negatively charged glycinate anion can form complexes with the target metals (Ni2+, Co2+ and Cu2+) in the ore according to Equation (7).
4M + 4(x + 1)HL + 4NaOH + xO2 → 4Na[ML(x + 1)] + 2(x + 2)H2 O (7) where M is precious or chalcophile metal, x represents the valence of the metal ions and L− stands for glycine anion (NH2CH2COO−). The following sections cover the systematic evaluation of leach conditions and parameters for Ni, Co and Cu extraction by alkaline glycine solutions. The effects of pH, glycine concentration, and
3.2. Glycine leaching (GlyLeach™) GlyLeach™ process is a hydrometallurgical process that utilised amino acids in general and glycine in particular to leach gold, silver,
Fig. 3. Nickel, Cobalt and Copper extraction from low grade nickel ore sample at 200 g/L acid, 3 g/L ferric, 40% solids, and room temperature. 4
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Fig. 4. Effect of glycine concentration on nickel extraction from low grade nickel ore at 40% solids, pH 10.0 and room temperature.
be clearly seen that Co leaching is proportional to nickel leaching during leaching and the cobalt extraction increases concurrently over the time. Maximum cobalt extraction was 66.6% after 336 h leaching at 46.3 g/L glycine. The Cu dissolution is much lower than Ni and Co as the copper present as chalcopyrite which leaches much slower in glycine solutions at room temperature and the absence of strong oxidants (Oraby and Eksteen, 2014). Recent research published by Tanda et al. (2019) and O’Connor et al. (2018) confirmed the need for higher temperature and stronger oxidation conditions (than maintained in this work) and the semiconductor behaviour of chalcopyrite in alkaline glycine solutions. Table 3 shows the impurities dissolution at different glycine levels. The results show the selectivity of leaching Ni and Co over Fe, Si, Al, and Mg which is another important advantage of alkaline glycine leaching and significantly simplifying downstream purification requirements and associated costs. The Mg dissolution slightly increases by increasing the glycine concentration, however the magnesium dissolution percentage is less than 0.08% of the total Mg present in the ore. Even more important, the iron levels remained below detection limits of the ICP-OES. This is of particular importance as iron is particularly problematic if nickel and cobalt are targeted for battery grade cathode precursors. In conventional processing iron is “smeared” across the process as the flotation cleaner process, the smelter furnace and
temperature have also been studied and discussed. Multi-contact leach tests were conducted using fresh and recycle glycine solutions to show the leaching continuity and glycine recyclability. 3.2.1. Effect of glycine concentration As glycine is the main lixiviant for the nickel, cobalt and copper leaching during the GlyLeach™ process, it is important to evaluate the effect of varying glycine concentrations on the metals extraction and impurities dissolution. Fig. 4 shows the effect of glycine concentration on Ni, Co and Cu extraction at pH 10.0, 40% solids and room temperature. Three levels of glycine concentration were tested 17.3 g/L [Gly: (Ni + Co + Cu) = 3:1], 28.9 g/L [Gly: (Ni + Co + Cu) = 5:1], and 46.3 g/L [Gly: (Ni + Co + Cu) = 8:1]. At such high concentrations, glycine should be recycled back to the leach step after metals recovery from solutions. The results shown in Figs. 4 and 5 indicate the glycine concentration should be maintained at a level of glycine to total metal molar ratio 5:1 or above. The kinetic curve of nickel extraction (Fig. 4) indicates the extraction kinetics is slow and is not suitable for tank leach applications at room temperature. Maximum nickel recovery achieved after 336 h (14 days) was 73.8%. Despite the slow leach rate, the kinetic curve indicates that there is no surface passivation and the nickel and Co leaching increases over the leach time. Fig. 5 shows the cobalt recovery at different levels of glycine. It can
Fig. 5. Effect of glycine concentration on cobalt extraction from low grade nickel ore at 40% solids, pH 10.0 and room temperature. 5
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Table 3 Impurities dissolution at different glycine levels after 336 h leaching of nickel ore by Glyleach™ process (BDL = Below Detection Limit). Glycine g/L
Al mg/L
As mg/L
Co mg/L
Cu mg/L
Fe mg/L
Mg mg/L
Ni mg/L
Pb mg/L
S mg/L
Si mg/L
Zn mg/L
17.3 28.9 46.3
BDL BDL BDL
BDL BDL BDL
4.74 55.4 65.0
21.8 15.7 18.1
BDL BDL BDL
15.6 42.5 124
372 2960 3300
BDL BDL BDL
726.5 5395 5640
BDL BDL BDL
3.0 3.0 3.5
Fig. 6. Effect of pH on nickel extraction from low grade nickel ore at 40% solids, pH 10.0 and room temperature.
converter and first refining steps in a conventional Sherritt® process are all in place to reject iron. This leach therefore achieves iron rejection right from the start.
extractions than operating at higher pH’s (pH of 11.5) which is opposite to the behaviour of copper sulfides such as chalcopyrite, which showed improved the copper extraction at pH 11.5 (Oraby and Eksteen, 2014; Eksteen et al., 2017b). Table 4 shows the impurities dissolution at different leach pHs. Mg dissolution increases by leaching at lower pH (pH 9.0) so pH 10 was selected as an optimum leach pH for Ni and Co.
3.2.2. Effect of pH The effect of leach solution pH on nickel, Co and Cu has been studied at different pH levels. It can be seen that there is a negative impact of increasing the leach pH from 10 to 11.5 on nickel extraction as shown in Fig. 6. Nickel extraction decreases from 73.8 to 29.8% by increasing the pH from 10 to 11.5. This results can attributed to the precipitation of Ni as nickel hydroxide by increasing the leach pH. Similar finding was observed for Co extraction as shown in Fig. 7. The Cu dissolution is much lower than Ni and Co and Cu behaves quite different to Ni and Co. It was found that running the leach at milder alkaline pH (pH 10) gave significantly better Ni and Co
3.2.3. Effect of temperature Tanda et al. (2018), showed that temperature enhanced the copper dissolution by glycine from different copper sulfide minerals. Oraby and Eksteen (2014, 2015); Eksteen and Oraby (2015), found also temperature is a key parameter in the precious metals dissolution by glycine. To evaluate the effect of temperature on Ni and Co extractions, two temperature levels were tested to evaluate the effect of temperature on metals extraction from the tested ore. Fig. 8 shows the Ni extraction
Fig. 7. Effect of pH on cobalt extraction from low grade nickel ore at 40% solids, pH 10.0 and room temperature. 6
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Table 4 Impurities dissolution at different leach pHs after 336 h leaching of nickel ore by Glyleach™ process (BDL = Below Detection Limit). Leach pH
Al mg/L
As mg/L
Co mg/L
Cu mg/L
Fe mg/L
Mg mg/L
Ni mg/L
Pb mg/L
S mg/L
Si mg/L
Zn mg/L
9.0 10 11.5
BDL BDL BDL
BDL BDL BDL
52.9 65.0 22.6
16.4 18.1 31.8
BDL BDL BDL
1420 124 3.0
2860 3300 1350
BDL BDL BDL
4120 5640 3920
BDL BDL BDL
3.0 3.5 3.6
Fig. 8. Effect of glycine concentration on nickel extraction from low grade nickel ore at 40% solids, pH 10.0 and two levels of temperature.
Fig. 9. Effect of temperature on cobalt extraction from low grade nickel ore 40% solids, pH 10.0 and room temperature.
cycles using a fresh glycine solution at each cycle. The required volume of leach solution containing 46.3 g/L glycine at pH 10 was mixed with solids to produce 40% solids. The results of Ni and Co extraction from these cycle tests are shown in Fig. 10. The results indicate that Ni and Co extraction increases by time and the maximum Ni recovery reaches 83.5% after 672 h leaching. It is interesting to note the Co dissolution kinetics is congruent with the Ni recovery and the maximum Co recovery was 76.2% after 672 h period. It would imply that the cobalt is probably in solid solution in the pentlandite matrix and fairly homogenously distributed throughout the pentlandite grains. The copper in such ore is a “nuisance” copper and does not play a role in the economics of this deposit. However, the accumulative Cu recovery reaches 23.7% during the four cycle tests. The long leach times to achieve good recoveries implies that the leach approach is more suitable for an alkaline heap leach environment rather than a tank leach of the ore sample.
at different levels of temperature, it is clear that the higher temperature only improves the initial Ni leach rate, however the overall Ni extraction was higher at room temperature. The Ni extraction after 336 h decreases from 73.8% to 56.3% by increasing temperature from room temperature (23 °C) to 55 °C, respectively. Fig. 9 shows the Co extraction at different levels of temperature, it is clearly confirmed that the temperature also improves the initial Co leach rate, however the overall Co extraction was also higher at room temperature. The Co extraction after 336 h decreases from 66.7% to 41.0% by increasing temperature from room temperature (23 °C) to 55 °C, respectively. The results proved the temperature improves the Cu dissolution which is in consistent with the previous studies (Oraby and Eksteen, 2014; Eksteen et al., 2017b). 3.2.4. Multi contact leach – Fresh solution Multi-contact leach test of the ore sample was carried out for 4 7
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Fig. 10. Effect of multi-contact glycine leaching on nickel and cobalt extraction from low grade nickel ore at 46.3 g/L glycine, 40% solids, pH 10.0 and room temperature.
Fig. 11 shows the cumulative recovery of Ni, Co and Cu during the multi contact with barren solutions. It can be clearly seen that Co and Ni dissolution is concurrent (and that the cobalt is in solid solution in the pentlandite). The results supports the conclusion that the leaching of Ni and Co continues over time using recycled barren leach solution, where the solution contains glycine at the target leach pH, and that the glycine is regenerated. Table 6 shows the metals concentration at the end of each cycles before and after adsorption on 55.0 g/L resin. It can be seen the resin was very effective to adsorb more than 97% of Ni, 65% of Co and 99.0% of Cu. The Co adsorption efficiency increases by increasing of the accumulated Co concentration in the barren solution. Table 7 shows the cumulative metals recovery after each cycle. This would align with a real system heap leach system where barren raffinate solution, where the glycine has been regenerated is reused to leach the metals.
Table 5 Leach conditions for glycine recycle test. Factor
Barren Solution Leach
Glycine (g/L) Solids (%) Grind size p80 (µm) Temperature (°C) Target pH Water
46.3 40.0 169.6 Ambient in bottle roll 10.0 Perth Tap Water
3.2.5. Multi leach – Recycled barren solution A leach test was conducted to show the effectiveness of continues leaching of metals using barren/recycle glycine solutions after metals adsorption onto ion exchange resin. The leach solution was periodically filtered, and a Purolite S930Plus resin was used to adsorb the metals from the solution after certain time and nickel concentration reached a certain value (adsorption cycles occurred approximately every 72 h). A total of four cycles were carried out for the duration of the test. Table 5 shows the leach conditions for the multi leach-recycle glycine solutions test.
3.3. Optimum leach conditions From the results, it can be observed that pH and glycine
Fig. 11. Effect of multi-contact recycle glycine solutions on nickel and cobalt extraction from low grade nickel ore at 46.3 g/L glycine, 40% solids, pH 10.0 and room temperature. 8
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Table 6 Ni, Co and Cu concentration before and after adsorption for each cycle of leaching using recycle glycine solutions. Ni
Co
Cu
#
Time (hr)
Fresh (mg/L)
Barren (mg/L)
Adsorp. (%)
Fresh (mg/L)
Barren (mg/L)
Adsorp. (%)
Fresh (mg/L)
Barren (mg/L)
Adsorp. (%)
Clycle1 Clycle2 Clycle3 Clycle4
72 72 72 144
1540 910 621 374
32 25.0 33.2 12.5
97.9 97.3 95.0 96.6
38.4 35.5 22.4 23.2
14.0 10.5 8.9 8.5
63.5 70.4 60.3 63.4
14.53 4.1 4.0 6
0.125 0.1 0.13 0.15
99.4 97.5 96.7 97.5
sulfide resources using a benign alkaline leach technology, non-toxic, non-volatile and cost effective reagents, where the reagents can be recycled to the leach after resetting the pH. Further work to simulate the actual metals recovery from coarse particles by column leach to simulate the heap leach applications are required.
Table 7 Ni, Co and Cu accumulative extraction after each cycle of leaching using recycle glycine solutions. Final Cumulative Extraction
Cycle1
Cycle2
Cycle3
Cycle4
Nickel Extraction (%) Cobalt Extraction (%) Copper Extraction (%)
34.3 35.7 15.0
55.6 59.0 18.9
65.6 65.5 22.2
73.7 74.6 27.8
4. Conclusions An alkaline glycine leaching research study for a highly acid consuming low grade nickel sulfide ore containing 0.67% Ni has been conducted to evaluate the amenability of such ore for the eventual application of heap, vat and in-situ leaching modes using glycine. In this study, different parameters have been evaluated to extract Ni and Co from the low grade ore. The effects of pH, glycine concentration, and temperature have been studied. The results indicate that leaching such a high acid consumable nickel ore with conventional sulphuric acid leaching is uneconomic and about 250 kg/t acid was consumed with only 6% Ni was extracted. The study showed that glycine-based Ni and Co leach rates are slow and about 83.5% Ni and 76.3% Co were
concentration are the controlling factors of nickel and cobalt extraction in alkaline glycine solutions. Optimum conditions to leach such ore are summarised form this research study to be 46.3 g/L glycine (8:1 Gly: total metals content), pH 10.0, 40% solids and room temperature. The proposed flowsheet for Ni leaching from such low grade ore by alkaline glycine leaching consists mainly of heap leaching followed by metals recovery (Ni, Co and Cu) by resin in column (CIC) and recycling glycine solution to the leaching step. Fig. 12 shows the proposed simulated heap application set up to treat such deposits. Bench scale results will provide a basis to investigate nickel and cobalt recovery from various
Fig. 12. Column leach set up for heap leach applications. 9
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Fig. 13. Conceptual block diagram flowsheet for the production of nickel and cobalt sulfates from low grade sulfide ores or tailings using an alkaline glycine leach process.
extracted in 672 h. The results showed that increasing glycine concentration at pH 10.0 and room temperature have significant roles in maximising the Ni and Co recovery. It was found temperature improves the initial metals extraction, however leaching at room temperature provided a higher overall metals recovery. Selective leaching of Ni and Co by glycine solutions over other impurities such as Si, Mg, Fe and Al was proved in this research study. Overall, using glycine as a leaching reagent has successfully been proven to be feasible and highly selective. It is a safer alternative to the traditional smelting method, and is highly suitable for the extraction of nickel, cobalt and copper from crushed low-grade sulphide ores. A conceptual block process flow diagram can be postulated (shown in Fig. 13) whereby the nickel and cobalt are co-extracted in a heap leach (or vat leach or in-situ leach), and co-adsorbed onto a cation exchanger (IX) and the barren raffinate is recycled back to the leach. The Ni and Co can be eluted from the resin by a strong sulfuric acid solution at 180 g/L. Separation of the Ni and Co in acidic IX eluate can be done by extracting Co by solvent in a two stage extraction (SX) process (Olivier et al., 2012) and recovering the Ni for the SX raffinate using IX and recycling the final barren raffinate. The refined CoSO4 and NiSO4 can then be crystallised, centrifuged, dried and shipped to a cathode precursor refinery to produce NCM / NCA mixed hydroxide precipitates or lithiated cathode active materials.
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