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Upgrading nickel in laterite ores by flotation
Minerals Engineering 121 (2018) 100–106
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Upgrading nickel in laterite ores by flotation Saeed Farrokhpay a b c
a,b,⁎
a,c
, Daniel Fornasiero , Lev Filippov
T
a
Université de Lorraine, GeoRessources Laboratory, CNRS, CREGU, UMR 7359, 2 rue du Doyen Marcel Roubault, 54518 Vandœuvre-lès-Nancy, France School of Chemical Engineering, University of Queensland, St. Lucia, Queensland 4072, Australia Future Industries Institute, University of South Australia, Mawson Lakes, SA 5095, Australia
A R T I C LE I N FO
A B S T R A C T
Keywords: Nickel Laterite ore 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.
1. Introduction Nickel is an important metal with the total global consumption of about 2 million tons per year which has grown rapidly since the 1940s (Fig. 1) (Mackey, 2011). Nickel is sourced from two different types of ores, sulphide and laterite. The majority of the world’s nickel resources occur as laterite ores (about 70%) which are complex and low grade, and therefore expensive to treat using conventional smelting and high temperature and/or high pressure autoclave methods (Xu et al., 2013). These days, nickel laterites are more attractive for production of nickel as the amount of high grade nickel sulphide ores has diminished (Janwong, 2012). Therefore more economic processes to recover nickel from these resources should be developed. It should be noted that nickel laterite mineralogy is complex, and nickel often presents as ultrafine inclusions in a number of mineral phases. The CSIRO researchers (Elliot et al., 2009; Watling et al., 2011) have examined the composition of 50 nickel laterite ore samples and noted an extreme variability in both their elemental and mineralogical characteristics. Because of the low nickel concentration and variable distribution in these phases, effective upgrading by physical separation processes would be challenging. In addition, laterite ores often contain phyllosilicate minerals such as talc, serpentine and smectite. Therefore, a good knowledge of phyllosilicates is helpful to understand the mineralogy of such laterite ores. Recent papers on the classification of phyllosilicate minerals and their effect in mineral processing are
⁎
available (Ndlovu et al., 2013; Ndlovu et al., 2014). Researchers have tried to improve nickel laterite flotation recovery by using a number of feed preparation techniques. A summary of the nickel grades obtained using flotation reported in the literature is presented in Table 1. It can be seen that only minor nickel upgrades have been reported. Quast et al. (2015a) have concluded that the complex mineralogy of nickel laterite ores makes it difficult to achieve any significant nickel upgrading by physical techniques, including flotation. They achieved 40% increase in the nickel content (from 1.0% to 1.4%) at a nickel recovery of 43% (Quast et al., 2015c). However, flotation is the most widely used separation technique in mineral processing. It will be beneficial both economically and technically if we could increase the nickel grade of laterite ores using flotation prior to hydro or pyro metallurgy processes. A recent comprehensive review on topics influencing nickel laterite flotation has shown that further investigations in the flotation of laterite ores are undoubtedly warranted (Farrokhpay and Filippov, 2016). David (2008) has highlighted that the lack of success in upgrading nickel in laterites via flotation is due to the absence of a specific nickel rich phase in laterite ores. In fact, nickel is present in a number of soft minerals which can easily report to the slimes during milling. Since flotation relies on selective adsorption of collectors on the surfaces of specific minerals, the low percentage of nickel and its fine-grained distribution can compromise the recovery of a high grade concentrate. This work aims to instigate upgrading the nickel content in laterite
Corresponding author at: Université de Lorraine, GeoRessources Laboratory, 2 rue du Doyen Marcel Roubault, 54518 Vandœuvre-lès-Nancy, France. E-mail address: [email protected] (S. Farrokhpay).
https://doi.org/10.1016/j.mineng.2018.02.021 Received 26 December 2017; Received in revised form 21 February 2018; Accepted 22 February 2018 0892-6875/ © 2018 Elsevier Ltd. All rights reserved.
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Fig. 1. World nickel consumption (after Mackey, 2011).
Table 1 Various attempt of upgrading nickel in laterite ores by flotation (modified from Farrokhpay and Filippov, 2016). Ore source
Conditions
Ni head grade
Ore type
Best Ni grade (%)
@ Ni Rec (%)
Brazil New Caledonia
Synthesized 2,3 octanedione dioxim as collector Micro-flotation of 53–74 μm fraction using a variety of reagents. Best selectivity by using cetyl trimethyl ammonium bromide (CTAB) or sodium NaOl Anionic collectors plus sodium silicate Sodium lauryl methylamino acetic acid and sodium salt of modified carboxylic acid A number of feed preparation techniques before flotation
1.2%
Saprolite Saprolite
63 –
0.6% 0.5% 1.0%
Lemonite Lemonite Lemonite
1.4 No or minor change 1.6 1.0 1.4
India India Australia
ore using flotation. After careful characterisation, the laterite samples were treated with different collectors, and at different flotation conditions. The results will be discussed in conjunction with the ores mineralogy.
60 70–80 43
USA), which is a commercial sample of hydroxamate (HDMA), were used as collectors. Methyl isobutyl carbinol (MIBC) was used as frother. The pH was adjusted using NaOH and/or HCl diluted solutions when needed. 600 g sample of laterite ore was mixed with tap water and placed in a 2 L cell attached to a rotor-stator type MINEMET laboratory flotation machine. Flotation tests were conducted at various pH values using different collectors. Conditioning time was 3 min and aeration rate was 4 L/min. Flotation time varied between 5 and 15 min. In addition to chemical assays, selected flotation products were analysed using XRD and infrared spectroscopy. All tests were done in triplicate, and the average experimental error was ± 5%. Diffuse reflectance (DRIFT) spectra were recorded with a 2 cm−1 spectral resolution using a Fourier-transform infrared spectrometer (BRUKER IFS 55) equipped with a large-band mercury cadmium telluride (MCT) detector cooled at 77 °K and associated with a diffuse reflectance attachment (Harrick Corporation). Sample preparation involves mixing 50 mg of sample with 320 mg of KBr. The infrared spectrum of each sample was scanned 200 times. The total amount of carbon was determined by heating the samples in an O2 atomosphere at 1150 °C, and then the formed CO2 was measured with an IR-detector. The amount of organic carbon was measured by heating the sample in HCl. The difference between the total amount of C and the amount of organic carbon is the amount of inorganic C (present as carbonate).
2. Material and experimental methods Nickel laterite ores with different mineralogies from South East Asia were used in this study. The ores were representative of different laterite zones of a particular mine with different feed grades. The ore samples will be named as L (i.e. limonite), S (i.e. saprolite), and I (i.e. intermediate) to identify their geological origin. The QEMSCAN (Fig. 2a) data as well as XRD spectra (Fig. 2b) showed that the “S” laterite sample is composed of serpentine, goethite, siderite, spinel, quartz, olivine and clays (nontronite, saponite), and nickel is mainly carried by serpentine, goethite and clays. The “L” and “I” laterite samples contain mainly spinel, goethite and quartz, with less amount of serpentine, olivine, and clays. Nickel is mainly carried by goethite in the I and L laterite samples. The size fraction of −300 µm was examined due to the ore supplier interest. This size fraction corresponds to a P80 of about 140 µm which is appropriate for flotation tests. The nickel head grade of samples L, I and S (at the −300 µm size fraction) was found to be 1.2%, 1.1%, and 3.0%, respectively. Nickel was found, more or less, at the same grade in all size fractions in these laterite ore samples. This is different from the result of a previous study of a laterite ore from an Australian deposit where nickel content increased with decreasing particle size (Quast et al., 2015b). The assays of the laterite samples is provided in Table 2 (measured by XRD). Sodium oleate (NaOl), dodecylamine (DDA) and Aero 6493 (Cytec, 101
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Quartz Olivine 0
20
40
60
80
100
Serpentine Pyroxene-Amphibole Feldspar Clay Minerals Goethite
0
20
40
60
80
100
Hematite/Magnetite Siderite Spinel(CrFeMgAlV) Asbolane
0
20
40
60
80
100
MnO - (OH)
Fig. 2a. QEMSCAN results of the (top) S, (middle) I and (bottom) L laterite samples. The coloured boxes correspond to the various minerals present in these samples obtained from the database (as shown in the right side).
3. Results and discussion
3.2. Flotation results
3.1. Infrared analysis of ore samples
For the limonite sample (ore L), no upgrade in the nickel content was found after flotation using different collectors at different conditions. This is not surprising as similar results have been previously reported for laterite ores with similar mineralogy (see Table 1). However, for the saprolite sample (ore S) the flotation results are promising, especially with the hydroxamate collector (HDMA), as the nickel content was upgraded to various levels (see Table 3). Table 3 also shows the nickel upgrading after flotation of the intermediate sample ore I. The best flotation result was for the S ore sample where nickel upgraded from 3.0% up to 4.2% (i.e. by 40%) at around 70% when HDMA was used. This is considerably better than nickel flotation grade and recovery data reported in the literature for this type of ores (i.e. saprolite) (Table 1). Based on these data, the best condition to upgrade nickel in the current study was obtained by using the HDMA collector at pH 10. On the other hand, NaOl and DDA (results not shown) produced nickel concentrates with a lower grade and recovery compared to HDMA. While Table 3 shows the changes in the Ni grade data, it should be mentioned that the grade of the other elements in the ores remained more or less similar after flotation (data not provided; only grade of iron slightly decreased from 18.7% to 17.1%). To better understand the flotation results, the concentrates and tailings obtained for the two best flotation results for the ore S (using NaOl at pH 4.5 and HDMA at pH 10.0) were analysed using XRD (Fig. 4). The concentrate and tailing of the flotation experiment with NaOl show relatively similar diffractograms, which makes it difficult to compare which minerals are floating. However, when hydroxamate was used as collector, the XRD results show that more serpentine (peaks at 7.29°), but less quartz (peaks at 3.34°) or siderite (peaks at 2.78° and 1.73°) are present in the flotation concentrate. Furthermore, goethite is observed in both flotation products (peaks at 4.56°). While it is often suggested that HDMA acts as a chelating agent for iron, the result of the current study shows the opposite where siderite (i.e. iron carbonate) being not floated. According to Miller et al. (2002), metal hydroxamate has a lower stability with Fe(II) compared to Fe(III) ions. Since siderite consists of Fe(II), this might explain the lower selectivity for siderite compared to serpentine (as the latter contains both Fe(II) and Fe(III) due to the replacement of Mg with Fe in the serpentine). Furthermore, Agrawal et al. (2001) showed that hydroxamate has a better stability with Ni2+ compared to Fe2+. However, to prove this hypothesis, further study of the adsorption of hydroxamic acid onto serpentine and iron carbonate is needed.
The infrared spectra of the ore samples in Fig. 3 show some similarities, as expected from their comparable mineral composition. In the higher wavenumber region a sharp peak at 3683, 3695 and 3685 cm−1 is present for the S, I and L samples, respectively, together with less defined peaks at 3571, 3619 and 3645 cm−1. All these peaks are characteristic of stretching vibrations of outer hydroxyl groups coordinated to metal ions such as magnesium or aluminium (Farmer and Russell, 1966; Mellini et al., 2002; Foresti et al., 2009; Liu et al., 2010). The very broad peak between 3500 and 3100 cm−1 is attributed to the water adsorbed on the minerals (Prost and Chaussidon, 1969; Sposito et al., 1983). The peak at 2509–2507 cm−1 is only observed in the S and I samples, and it is attributed to the combination IR bands of CO3 vibrations associated with for example Zn, Ca and Mg (Foresti et al., 2009; Chukanov, 2014). In the intermediate wavenumber region, a series of peaks are present: at around 1975 cm−1, 1863 cm−1 and 1805–1791 cm−1 combination bands of CO3 vibrations (Farmer, 1975; Okazaki, 1983; Ren et al., 2014; Van Olphen and Fripiat, 1979); at 1653–31 cm−1 due to OH or CO3 vibrations (Motlagh et al., 2011); and at 1443–39 cm−1 due to ν3CO3 (Dubrawski and Channon, 1989). These peaks have variable intensities in the samples; but the only difference is the absence of the 1443–39 cm−1 peak in the L sample. In the lower wavenumber region, a strong and broad peak is observed at around 1000 cm−1 for the L and S samples. The spectrum of sample I shows the presence of smaller peaks at 1106, 1032, 903 cm−1 which are also present in the spectra of the L and S samples and identified as shoulders in the 1000 cm−1 broad peak. These peaks and those at 802–798 and 646–21 cm−1 are all attributed to the Si-O vibrations (Lippincott et al., 1958; Hlavay et al., 1977; Hofmeister and Bowey, 2006; Foresti et al., 2009). Peaks at 868–7 and 739 cm−1 for samples S and I are attributed to the CO3 vibrations (Dubrawski and Channon, 1989; Regnier et al., 1994). The infrared results have confirmed the presence of magnesium and aluminium silicate and carbonate minerals in these ore samples; however, the carbonate component in the L sample is either absent or very low (compared to the other two samples). The carbonate peaks observed for the saprolite sample in the current study were absent in other saprolite ores from the same region which the authors have studied previously (Farrokhpay and Filippov, 2017), indicating the presence of metal carbonates (probably, siderite FeCO3) in the current sample as suggested by the QEMSCAN and XRD analyses. 102
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Fig. 2b. XRD results of the (top) S, (middle) I and (bottom) L laterite samples. The coloured vertical lines correspond to XRD patterns of various elements obtained from the XRD database.
saprolite ore sample when floated with HDMA. The XRD diffractograms of S ore sample (Fig. 2b) were compared with those of the flotation concentrates when NaOl and HDMA were used as collector (Fig. 4). It was noticed that several peaks are missing (or are largely reduced) in the flotation concentrate when HDMA was used (compared to the S ore sample). These peaks are at 4.24, 3.59, 3.33, 1.81 2.34, 2.12, 1.96° (related to quartz) and at 2.78 and 1.73°
Moreover, carbon analysis indicated the presence of 1.3%, 0.3% and 1.8% of inorganic carbon in the S ore feed, and flotation concentrate and tail products, respectively when HDMA was used as collector. If the carbon only originates from carbonate, these numbers correspond to about 12%, 3% and 18% siderite in the feed, flotation concentrate and tail samples, respectively. These data confirm the XRD results with the presence of a much higher amount of siderite in the flotation tail for the 103
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Table 2 The assays of major elements in laterite samples (% as measured by XRD).
Ni Si Al Fe Mn Mg Cr Co
Table 3 A summary of the flotation results for the saprolite and intermediate ores (sample S and I, respectively) (The Ni grades for sample S and I are 3.0% and 1.1%, respectively).
I
S
L
1.1 10.8 3.0 18.4 0.2 5.2 2.5 0.2
3.0 9.5 0.5 18.4 0.5 2.5 0.5 0.1
1.2 5.2 1.6 43.3 0.5 1.5 1.5 –
Ore
pH
Collector
Dosage (g/t)
Ni Rec (%)
Ni grade (%)
Ni upgrade (%)
S S S S S
4.5 4.5 10 10 10
NaOl NaOl HDMA HDMA HDMA
500 1000 500 1000 1500
39 17 44 60 70
3.4 3.5 4.2 4.1 4.2
16 17 40 40 40
I I I
4.5 9 10
NaOl NaOl HDMA
500 500 500
40 65 72
1.2 1.2 1.3
10 10 20
Fig. 3. DRIFT spectra of the (top) S, (middle) I and (bottom) L laterite samples.
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Fig. 4. XRD results of the flotation products of S ore sample: a and b, concentrate and tail respectively, when NaOl used as collector; c and d, concentrate and tail respectively, when HDMA was used as collector.
Fig. 5. Infrared spectra of the flotation products of the S sample floated with (top) NaOl (black: concentrate, red: tail) at pH 4.5 or (bottom) HDMA (blue: concentrate, green: tail) at pH 10.0. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
affinity, and provided strong flotation performances, for minerals containing trivalent transition metals such as Fe(III) in hematite and goethite (Han et al. 1973; Quast, 2000) because it can form an octahedral complex with them compared to a less stable square planar structure with divalent transition metals such as Cu(II) and Pt(II) (Codd, 2008). It should be also mentioned that the flotation test with HDMA was conducted at pH 10.0, and it has been reported that siderite is stable in aqueous solutions between pH 7 to 11 (Ignatow, 1975) These results have clearly shown that in the flotation of the S ore sample, HDMA is selective against siderite as this mineral was mainly found in the tailing. Since nickel is not present in siderite, this results in an increase in nickel grade after flotation, as discussed.
(related to siderite) (ICDD, 1992). Infrared spectroscopy analysis of the concentrate and tail products after flotation of the S sample using NaOl or HDMA collector was also conducted to confirm the above observations. The infrared spectra of these products (Fig. 5) look similar to the spectrum of the feed in Fig. 3, expect for the disappearance of the carbonate peaks (at 2503, 1801, 1441, 866 and 739 cm−1) in the concentrate when hydroxamate was used as collector, or their slight decrease in intensity when oleate was used. This indicates that hydroxamate is a very selective collector against the carbonate minerals present in this ore sample at pH 10.0, which could explain the increase in Ni grade after flotation of ore S, using this collector (Table 3). QEMSCAN data showed the absence of nickel in the siderite phase. If siderite is the main carbonate mineral in sample S, its low flotation can be explained by its low affinity to the hydroxamate collector because iron in siderite is mainly in Fe(II) state (Miller et al., 2002). Hydroxamate has previously shown a strong
4. Conclusions In this study, upgrading nickel by flotation in three laterite ore 105
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samples, limonite, saprolite and intermediate, from different geology zones, was investigated. It was possible to upgrade the nickel grade in the saprolite sample by about 40% at more about 70% recovery using a hydroxamate collector at pH 10. These grade and recovery results are considerably higher than the values previously reported in the literature for saprolite ores, and they were attributed to the flotation of the nickel-bearing minerals of serpentine and goethite with hydroxamate collector and the rejection of iron carbonate (siderite) present in this ore sample. The nickel content was slightly upgraded for the intermediate ore sample. However, no upgrading in nickel content was observed for the limonite ore. The findings of this project will help to unlock a substantial volume of nickel in laterite resources with significant economic value.
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Acknowledgements The financial support from Labex “Ressources 21” (Strategic Metals in the 21st Century) is gratefully acknowledged (Investissements d’Avenir-grant agreement no. ANR-11-LABX-0030). Frima Dhani is acknowledged for his contribution during his Master project (EMerald Erasmus Mundus Master in Georesources Engineering). The authors gratefully acknowledge the valuable discussion with Professor Jacques Yvon for XRD analysis. D. Fornasiero acknowledges the financial support provided by the Région Lorraine (FEDER) and EU’s Emerald program. References Agrawal, Y.K., Menon, S.K., Parekh, P.C., 2001. Mixed-ligand stability constants of divalent metal ions with glycine and hydroxamic acids. Indian J. Chem.– Sect. A Inorg. Phys. Theor. Anal. Chem. 40 (12), 1313–1318. Chukanov, N.V., 2014. Infrared Spectra of Mineral Species: Extended Library, vol I Springer. Codd, R., 2008. Traversing the coordination chemistry and chemical biology of hydroxamic acids. Coord. Chem. Rev. 252, 1387–1408. David, D. 2008, Beneficiation of nickel laterites for HPAL processing, in: Proceedings of the Metallurgical Plant Design and Operating Strategies (MetPlant), AusIMM, pp. 223–232. Dubrawski, J.V., Channon, A.L., 1989. Examination of the siderite-magnesite mineral series by Fourier transform infrared spectroscopy. Am. Mineral. 74, 187–190. Elliot, A., Fletcher, H., Li, J., Watling, H., Robinson, D.J. 2009, Heap leaching of nickel laterites-a challenge and an opportunity, in: Conference of Metallurgists, Sudbury. Farmer, V.C., Russell, J.D., 1966, Infrared absorption spectrometry in clay studies, in: Clays & Clay Minerals Conference Proceeding, pp. 121–142. Farrokhpay, S., Filippov, L., 2017. Aggregation of nickel laterite ore particles using polyacrylamide homo and copolymers with different charge densities. Powder Technol. 318, 206–213. Farrokhpay, S., Filippov, L., 2016. Challenges in processing nickel laterite ores by flotation. Int. J. Miner. Process. 151, 59–67. Foresti, E., Fornero, E., Lesci, I.G., Rinaudo, C., Zuccheri, T., Roveri, N., 2009. Asbestos health hazard: a spectroscopic study of synthetic geoinspired Fe-doped chrysotile. J. Hazard. Mater. 167, 1070–1079. Han, K.N., Healy, T.W., Fuerstenau, D.W., 1973. The mechanism of adsorption of fatty acids and other surfactants at the oxide-water interface. J. Colloid Interface Sci. 44 (3), 407–414.
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Minerals Engineering journal homepage: www.elsevier.com/locate/mineng
Upgrading nickel in laterite ores by flotation Saeed Farrokhpay a b c
a,b,⁎
a,c
, Daniel Fornasiero , Lev Filippov
T
a
Université de Lorraine, GeoRessources Laboratory, CNRS, CREGU, UMR 7359, 2 rue du Doyen Marcel Roubault, 54518 Vandœuvre-lès-Nancy, France School of Chemical Engineering, University of Queensland, St. Lucia, Queensland 4072, Australia Future Industries Institute, University of South Australia, Mawson Lakes, SA 5095, Australia
A R T I C LE I N FO
A B S T R A C T
Keywords: Nickel Laterite ore 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.
1. Introduction Nickel is an important metal with the total global consumption of about 2 million tons per year which has grown rapidly since the 1940s (Fig. 1) (Mackey, 2011). Nickel is sourced from two different types of ores, sulphide and laterite. The majority of the world’s nickel resources occur as laterite ores (about 70%) which are complex and low grade, and therefore expensive to treat using conventional smelting and high temperature and/or high pressure autoclave methods (Xu et al., 2013). These days, nickel laterites are more attractive for production of nickel as the amount of high grade nickel sulphide ores has diminished (Janwong, 2012). Therefore more economic processes to recover nickel from these resources should be developed. It should be noted that nickel laterite mineralogy is complex, and nickel often presents as ultrafine inclusions in a number of mineral phases. The CSIRO researchers (Elliot et al., 2009; Watling et al., 2011) have examined the composition of 50 nickel laterite ore samples and noted an extreme variability in both their elemental and mineralogical characteristics. Because of the low nickel concentration and variable distribution in these phases, effective upgrading by physical separation processes would be challenging. In addition, laterite ores often contain phyllosilicate minerals such as talc, serpentine and smectite. Therefore, a good knowledge of phyllosilicates is helpful to understand the mineralogy of such laterite ores. Recent papers on the classification of phyllosilicate minerals and their effect in mineral processing are
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available (Ndlovu et al., 2013; Ndlovu et al., 2014). Researchers have tried to improve nickel laterite flotation recovery by using a number of feed preparation techniques. A summary of the nickel grades obtained using flotation reported in the literature is presented in Table 1. It can be seen that only minor nickel upgrades have been reported. Quast et al. (2015a) have concluded that the complex mineralogy of nickel laterite ores makes it difficult to achieve any significant nickel upgrading by physical techniques, including flotation. They achieved 40% increase in the nickel content (from 1.0% to 1.4%) at a nickel recovery of 43% (Quast et al., 2015c). However, flotation is the most widely used separation technique in mineral processing. It will be beneficial both economically and technically if we could increase the nickel grade of laterite ores using flotation prior to hydro or pyro metallurgy processes. A recent comprehensive review on topics influencing nickel laterite flotation has shown that further investigations in the flotation of laterite ores are undoubtedly warranted (Farrokhpay and Filippov, 2016). David (2008) has highlighted that the lack of success in upgrading nickel in laterites via flotation is due to the absence of a specific nickel rich phase in laterite ores. In fact, nickel is present in a number of soft minerals which can easily report to the slimes during milling. Since flotation relies on selective adsorption of collectors on the surfaces of specific minerals, the low percentage of nickel and its fine-grained distribution can compromise the recovery of a high grade concentrate. This work aims to instigate upgrading the nickel content in laterite
Corresponding author at: Université de Lorraine, GeoRessources Laboratory, 2 rue du Doyen Marcel Roubault, 54518 Vandœuvre-lès-Nancy, France. E-mail address: [email protected] (S. Farrokhpay).
https://doi.org/10.1016/j.mineng.2018.02.021 Received 26 December 2017; Received in revised form 21 February 2018; Accepted 22 February 2018 0892-6875/ © 2018 Elsevier Ltd. All rights reserved.
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Fig. 1. World nickel consumption (after Mackey, 2011).
Table 1 Various attempt of upgrading nickel in laterite ores by flotation (modified from Farrokhpay and Filippov, 2016). Ore source
Conditions
Ni head grade
Ore type
Best Ni grade (%)
@ Ni Rec (%)
Brazil New Caledonia
Synthesized 2,3 octanedione dioxim as collector Micro-flotation of 53–74 μm fraction using a variety of reagents. Best selectivity by using cetyl trimethyl ammonium bromide (CTAB) or sodium NaOl Anionic collectors plus sodium silicate Sodium lauryl methylamino acetic acid and sodium salt of modified carboxylic acid A number of feed preparation techniques before flotation
1.2%
Saprolite Saprolite
63 –
0.6% 0.5% 1.0%
Lemonite Lemonite Lemonite
1.4 No or minor change 1.6 1.0 1.4
India India Australia
ore using flotation. After careful characterisation, the laterite samples were treated with different collectors, and at different flotation conditions. The results will be discussed in conjunction with the ores mineralogy.
60 70–80 43
USA), which is a commercial sample of hydroxamate (HDMA), were used as collectors. Methyl isobutyl carbinol (MIBC) was used as frother. The pH was adjusted using NaOH and/or HCl diluted solutions when needed. 600 g sample of laterite ore was mixed with tap water and placed in a 2 L cell attached to a rotor-stator type MINEMET laboratory flotation machine. Flotation tests were conducted at various pH values using different collectors. Conditioning time was 3 min and aeration rate was 4 L/min. Flotation time varied between 5 and 15 min. In addition to chemical assays, selected flotation products were analysed using XRD and infrared spectroscopy. All tests were done in triplicate, and the average experimental error was ± 5%. Diffuse reflectance (DRIFT) spectra were recorded with a 2 cm−1 spectral resolution using a Fourier-transform infrared spectrometer (BRUKER IFS 55) equipped with a large-band mercury cadmium telluride (MCT) detector cooled at 77 °K and associated with a diffuse reflectance attachment (Harrick Corporation). Sample preparation involves mixing 50 mg of sample with 320 mg of KBr. The infrared spectrum of each sample was scanned 200 times. The total amount of carbon was determined by heating the samples in an O2 atomosphere at 1150 °C, and then the formed CO2 was measured with an IR-detector. The amount of organic carbon was measured by heating the sample in HCl. The difference between the total amount of C and the amount of organic carbon is the amount of inorganic C (present as carbonate).
2. Material and experimental methods Nickel laterite ores with different mineralogies from South East Asia were used in this study. The ores were representative of different laterite zones of a particular mine with different feed grades. The ore samples will be named as L (i.e. limonite), S (i.e. saprolite), and I (i.e. intermediate) to identify their geological origin. The QEMSCAN (Fig. 2a) data as well as XRD spectra (Fig. 2b) showed that the “S” laterite sample is composed of serpentine, goethite, siderite, spinel, quartz, olivine and clays (nontronite, saponite), and nickel is mainly carried by serpentine, goethite and clays. The “L” and “I” laterite samples contain mainly spinel, goethite and quartz, with less amount of serpentine, olivine, and clays. Nickel is mainly carried by goethite in the I and L laterite samples. The size fraction of −300 µm was examined due to the ore supplier interest. This size fraction corresponds to a P80 of about 140 µm which is appropriate for flotation tests. The nickel head grade of samples L, I and S (at the −300 µm size fraction) was found to be 1.2%, 1.1%, and 3.0%, respectively. Nickel was found, more or less, at the same grade in all size fractions in these laterite ore samples. This is different from the result of a previous study of a laterite ore from an Australian deposit where nickel content increased with decreasing particle size (Quast et al., 2015b). The assays of the laterite samples is provided in Table 2 (measured by XRD). Sodium oleate (NaOl), dodecylamine (DDA) and Aero 6493 (Cytec, 101
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Quartz Olivine 0
20
40
60
80
100
Serpentine Pyroxene-Amphibole Feldspar Clay Minerals Goethite
0
20
40
60
80
100
Hematite/Magnetite Siderite Spinel(CrFeMgAlV) Asbolane
0
20
40
60
80
100
MnO - (OH)
Fig. 2a. QEMSCAN results of the (top) S, (middle) I and (bottom) L laterite samples. The coloured boxes correspond to the various minerals present in these samples obtained from the database (as shown in the right side).
3. Results and discussion
3.2. Flotation results
3.1. Infrared analysis of ore samples
For the limonite sample (ore L), no upgrade in the nickel content was found after flotation using different collectors at different conditions. This is not surprising as similar results have been previously reported for laterite ores with similar mineralogy (see Table 1). However, for the saprolite sample (ore S) the flotation results are promising, especially with the hydroxamate collector (HDMA), as the nickel content was upgraded to various levels (see Table 3). Table 3 also shows the nickel upgrading after flotation of the intermediate sample ore I. The best flotation result was for the S ore sample where nickel upgraded from 3.0% up to 4.2% (i.e. by 40%) at around 70% when HDMA was used. This is considerably better than nickel flotation grade and recovery data reported in the literature for this type of ores (i.e. saprolite) (Table 1). Based on these data, the best condition to upgrade nickel in the current study was obtained by using the HDMA collector at pH 10. On the other hand, NaOl and DDA (results not shown) produced nickel concentrates with a lower grade and recovery compared to HDMA. While Table 3 shows the changes in the Ni grade data, it should be mentioned that the grade of the other elements in the ores remained more or less similar after flotation (data not provided; only grade of iron slightly decreased from 18.7% to 17.1%). To better understand the flotation results, the concentrates and tailings obtained for the two best flotation results for the ore S (using NaOl at pH 4.5 and HDMA at pH 10.0) were analysed using XRD (Fig. 4). The concentrate and tailing of the flotation experiment with NaOl show relatively similar diffractograms, which makes it difficult to compare which minerals are floating. However, when hydroxamate was used as collector, the XRD results show that more serpentine (peaks at 7.29°), but less quartz (peaks at 3.34°) or siderite (peaks at 2.78° and 1.73°) are present in the flotation concentrate. Furthermore, goethite is observed in both flotation products (peaks at 4.56°). While it is often suggested that HDMA acts as a chelating agent for iron, the result of the current study shows the opposite where siderite (i.e. iron carbonate) being not floated. According to Miller et al. (2002), metal hydroxamate has a lower stability with Fe(II) compared to Fe(III) ions. Since siderite consists of Fe(II), this might explain the lower selectivity for siderite compared to serpentine (as the latter contains both Fe(II) and Fe(III) due to the replacement of Mg with Fe in the serpentine). Furthermore, Agrawal et al. (2001) showed that hydroxamate has a better stability with Ni2+ compared to Fe2+. However, to prove this hypothesis, further study of the adsorption of hydroxamic acid onto serpentine and iron carbonate is needed.
The infrared spectra of the ore samples in Fig. 3 show some similarities, as expected from their comparable mineral composition. In the higher wavenumber region a sharp peak at 3683, 3695 and 3685 cm−1 is present for the S, I and L samples, respectively, together with less defined peaks at 3571, 3619 and 3645 cm−1. All these peaks are characteristic of stretching vibrations of outer hydroxyl groups coordinated to metal ions such as magnesium or aluminium (Farmer and Russell, 1966; Mellini et al., 2002; Foresti et al., 2009; Liu et al., 2010). The very broad peak between 3500 and 3100 cm−1 is attributed to the water adsorbed on the minerals (Prost and Chaussidon, 1969; Sposito et al., 1983). The peak at 2509–2507 cm−1 is only observed in the S and I samples, and it is attributed to the combination IR bands of CO3 vibrations associated with for example Zn, Ca and Mg (Foresti et al., 2009; Chukanov, 2014). In the intermediate wavenumber region, a series of peaks are present: at around 1975 cm−1, 1863 cm−1 and 1805–1791 cm−1 combination bands of CO3 vibrations (Farmer, 1975; Okazaki, 1983; Ren et al., 2014; Van Olphen and Fripiat, 1979); at 1653–31 cm−1 due to OH or CO3 vibrations (Motlagh et al., 2011); and at 1443–39 cm−1 due to ν3CO3 (Dubrawski and Channon, 1989). These peaks have variable intensities in the samples; but the only difference is the absence of the 1443–39 cm−1 peak in the L sample. In the lower wavenumber region, a strong and broad peak is observed at around 1000 cm−1 for the L and S samples. The spectrum of sample I shows the presence of smaller peaks at 1106, 1032, 903 cm−1 which are also present in the spectra of the L and S samples and identified as shoulders in the 1000 cm−1 broad peak. These peaks and those at 802–798 and 646–21 cm−1 are all attributed to the Si-O vibrations (Lippincott et al., 1958; Hlavay et al., 1977; Hofmeister and Bowey, 2006; Foresti et al., 2009). Peaks at 868–7 and 739 cm−1 for samples S and I are attributed to the CO3 vibrations (Dubrawski and Channon, 1989; Regnier et al., 1994). The infrared results have confirmed the presence of magnesium and aluminium silicate and carbonate minerals in these ore samples; however, the carbonate component in the L sample is either absent or very low (compared to the other two samples). The carbonate peaks observed for the saprolite sample in the current study were absent in other saprolite ores from the same region which the authors have studied previously (Farrokhpay and Filippov, 2017), indicating the presence of metal carbonates (probably, siderite FeCO3) in the current sample as suggested by the QEMSCAN and XRD analyses. 102
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Fig. 2b. XRD results of the (top) S, (middle) I and (bottom) L laterite samples. The coloured vertical lines correspond to XRD patterns of various elements obtained from the XRD database.
saprolite ore sample when floated with HDMA. The XRD diffractograms of S ore sample (Fig. 2b) were compared with those of the flotation concentrates when NaOl and HDMA were used as collector (Fig. 4). It was noticed that several peaks are missing (or are largely reduced) in the flotation concentrate when HDMA was used (compared to the S ore sample). These peaks are at 4.24, 3.59, 3.33, 1.81 2.34, 2.12, 1.96° (related to quartz) and at 2.78 and 1.73°
Moreover, carbon analysis indicated the presence of 1.3%, 0.3% and 1.8% of inorganic carbon in the S ore feed, and flotation concentrate and tail products, respectively when HDMA was used as collector. If the carbon only originates from carbonate, these numbers correspond to about 12%, 3% and 18% siderite in the feed, flotation concentrate and tail samples, respectively. These data confirm the XRD results with the presence of a much higher amount of siderite in the flotation tail for the 103
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Table 2 The assays of major elements in laterite samples (% as measured by XRD).
Ni Si Al Fe Mn Mg Cr Co
Table 3 A summary of the flotation results for the saprolite and intermediate ores (sample S and I, respectively) (The Ni grades for sample S and I are 3.0% and 1.1%, respectively).
I
S
L
1.1 10.8 3.0 18.4 0.2 5.2 2.5 0.2
3.0 9.5 0.5 18.4 0.5 2.5 0.5 0.1
1.2 5.2 1.6 43.3 0.5 1.5 1.5 –
Ore
pH
Collector
Dosage (g/t)
Ni Rec (%)
Ni grade (%)
Ni upgrade (%)
S S S S S
4.5 4.5 10 10 10
NaOl NaOl HDMA HDMA HDMA
500 1000 500 1000 1500
39 17 44 60 70
3.4 3.5 4.2 4.1 4.2
16 17 40 40 40
I I I
4.5 9 10
NaOl NaOl HDMA
500 500 500
40 65 72
1.2 1.2 1.3
10 10 20
Fig. 3. DRIFT spectra of the (top) S, (middle) I and (bottom) L laterite samples.
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Fig. 4. XRD results of the flotation products of S ore sample: a and b, concentrate and tail respectively, when NaOl used as collector; c and d, concentrate and tail respectively, when HDMA was used as collector.
Fig. 5. Infrared spectra of the flotation products of the S sample floated with (top) NaOl (black: concentrate, red: tail) at pH 4.5 or (bottom) HDMA (blue: concentrate, green: tail) at pH 10.0. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
affinity, and provided strong flotation performances, for minerals containing trivalent transition metals such as Fe(III) in hematite and goethite (Han et al. 1973; Quast, 2000) because it can form an octahedral complex with them compared to a less stable square planar structure with divalent transition metals such as Cu(II) and Pt(II) (Codd, 2008). It should be also mentioned that the flotation test with HDMA was conducted at pH 10.0, and it has been reported that siderite is stable in aqueous solutions between pH 7 to 11 (Ignatow, 1975) These results have clearly shown that in the flotation of the S ore sample, HDMA is selective against siderite as this mineral was mainly found in the tailing. Since nickel is not present in siderite, this results in an increase in nickel grade after flotation, as discussed.
(related to siderite) (ICDD, 1992). Infrared spectroscopy analysis of the concentrate and tail products after flotation of the S sample using NaOl or HDMA collector was also conducted to confirm the above observations. The infrared spectra of these products (Fig. 5) look similar to the spectrum of the feed in Fig. 3, expect for the disappearance of the carbonate peaks (at 2503, 1801, 1441, 866 and 739 cm−1) in the concentrate when hydroxamate was used as collector, or their slight decrease in intensity when oleate was used. This indicates that hydroxamate is a very selective collector against the carbonate minerals present in this ore sample at pH 10.0, which could explain the increase in Ni grade after flotation of ore S, using this collector (Table 3). QEMSCAN data showed the absence of nickel in the siderite phase. If siderite is the main carbonate mineral in sample S, its low flotation can be explained by its low affinity to the hydroxamate collector because iron in siderite is mainly in Fe(II) state (Miller et al., 2002). Hydroxamate has previously shown a strong
4. Conclusions In this study, upgrading nickel by flotation in three laterite ore 105
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samples, limonite, saprolite and intermediate, from different geology zones, was investigated. It was possible to upgrade the nickel grade in the saprolite sample by about 40% at more about 70% recovery using a hydroxamate collector at pH 10. These grade and recovery results are considerably higher than the values previously reported in the literature for saprolite ores, and they were attributed to the flotation of the nickel-bearing minerals of serpentine and goethite with hydroxamate collector and the rejection of iron carbonate (siderite) present in this ore sample. The nickel content was slightly upgraded for the intermediate ore sample. However, no upgrading in nickel content was observed for the limonite ore. The findings of this project will help to unlock a substantial volume of nickel in laterite resources with significant economic value.
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Acknowledgements The financial support from Labex “Ressources 21” (Strategic Metals in the 21st Century) is gratefully acknowledged (Investissements d’Avenir-grant agreement no. ANR-11-LABX-0030). Frima Dhani is acknowledged for his contribution during his Master project (EMerald Erasmus Mundus Master in Georesources Engineering). The authors gratefully acknowledge the valuable discussion with Professor Jacques Yvon for XRD analysis. D. Fornasiero acknowledges the financial support provided by the Région Lorraine (FEDER) and EU’s Emerald program. References Agrawal, Y.K., Menon, S.K., Parekh, P.C., 2001. Mixed-ligand stability constants of divalent metal ions with glycine and hydroxamic acids. Indian J. Chem.– Sect. A Inorg. Phys. Theor. Anal. Chem. 40 (12), 1313–1318. Chukanov, N.V., 2014. Infrared Spectra of Mineral Species: Extended Library, vol I Springer. Codd, R., 2008. Traversing the coordination chemistry and chemical biology of hydroxamic acids. Coord. Chem. Rev. 252, 1387–1408. David, D. 2008, Beneficiation of nickel laterites for HPAL processing, in: Proceedings of the Metallurgical Plant Design and Operating Strategies (MetPlant), AusIMM, pp. 223–232. Dubrawski, J.V., Channon, A.L., 1989. Examination of the siderite-magnesite mineral series by Fourier transform infrared spectroscopy. Am. Mineral. 74, 187–190. Elliot, A., Fletcher, H., Li, J., Watling, H., Robinson, D.J. 2009, Heap leaching of nickel laterites-a challenge and an opportunity, in: Conference of Metallurgists, Sudbury. Farmer, V.C., Russell, J.D., 1966, Infrared absorption spectrometry in clay studies, in: Clays & Clay Minerals Conference Proceeding, pp. 121–142. Farrokhpay, S., Filippov, L., 2017. Aggregation of nickel laterite ore particles using polyacrylamide homo and copolymers with different charge densities. Powder Technol. 318, 206–213. Farrokhpay, S., Filippov, L., 2016. Challenges in processing nickel laterite ores by flotation. Int. J. Miner. Process. 151, 59–67. Foresti, E., Fornero, E., Lesci, I.G., Rinaudo, C., Zuccheri, T., Roveri, N., 2009. Asbestos health hazard: a spectroscopic study of synthetic geoinspired Fe-doped chrysotile. J. Hazard. Mater. 167, 1070–1079. Han, K.N., Healy, T.W., Fuerstenau, D.W., 1973. The mechanism of adsorption of fatty acids and other surfactants at the oxide-water interface. J. Colloid Interface Sci. 44 (3), 407–414.
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