Waste Valorization Process: Sulfur Removal and Hematite Recovery

Research Article pubs.acs.org/journal/ascecg

Waste Valorization Process: Sulfur Removal and Hematite Recovery from High Pressure Acid Leach Residue for Steelmaking Cheen Aik Ang,† Feixiong Zhang,† and Gisele Azimi*,†,‡ †

Department of Chemical Engineering and Applied Chemistry, Laboratory for Strategic Materials, 200 College Street, Toronto, Ontario M5S 3E5, Canada ‡ Department of Materials Science and Engineering, University of Toronto, 184 College Street, Toronto, Ontario M5S 3E4, Canada ABSTRACT: The current study put the emphasis on developing a novel and environmentally friendly waste valorization process to refine hematite from the residue of the high-pressure acid leaching (HPAL) of nickel laterite ore. The developed process consists of an alkaline leaching step utilizing sodium hydroxide to reduce the sulfur impurity content in the HPAL residue. This novel process is very efficient as it can be run at room temperature in a significantly short residence time (10 min). The refined HPAL residue has sulfur content below the accepted threshold by the steelmaking industry; hence, it can potentially be used as a raw material. The proposed waste valorization process has the double advantage of generating a commercially valuable product from otherwise a waste stream and simultaneously providing environmental benefits through reducing the amount of scrapped leach residue and costs associated with constructing and maintaining storage facilities. KEYWORDS: Waste valorization, Sulfur removal, Hematite recovery, HPAL residue, High pressure acid leaching, Alkaline leaching

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INTRODUCTION

phases ((X)(Al)3(SO4)2(OH)6 (X = Na, K, NH4, H3O)) depending on the leaching conditions.12,13 The leach slurry from the autoclave is sent to a countercurrent decantation (CCD) stage, where solid residue is separated from the liquor, which is sent to a neutralization stage to remove residual iron and aluminum and recover the soluble nickel and cobalt.14 The solid HPAL residue is stockpiled in tailing ponds and or disposal yards that take up valuable land. Because the HPAL residue contains a high concentration of hematite, it can potentially be used as feedstock for steelmaking. However, it also contains alunite with associated sulfur, which is a detrimental element in steelmaking. To valorize the HPAL residue and make it a valuable product, the sulfur concentration must be reduced to below 1 wt % through removing the alunite.15 Previously, a few studies have been conducted to refine hematite present in metallurgical residues. One study investigated the hydrothermal conversion of sodium jarosite (NaFe3(SO4)2(OH)6), the byproduct of the zinc industry, to hematite using sulfuric acid at 225 °C and showed that the process requires 100% hematite seed addition and the optimum operating conditions are low free acid concentration (less than 0.5 M), temperature of 200−210 °C, and 1 h residence time.16,17 Another study investigated the precipitation of

Conventional steelmaking relies on reducing iron ore containing iron oxides in the form of hematite (Fe2O3), magnetite (Fe3O4), and wüstite (FeO) in a blast furnace with coke to obtain crude steel, and refining the crude steel in a basic oxygen furnace to obtain steel with desired properties.1,2 Steel has many desirable properties and is a crucial construction material in many applications and technologies relied upon by modern society. The annual demand for steel has increased at a compound growth rate of 5% over the last 20 years, surpassing the growth rate of other materials.3 The 2016 global demand for steel has been reported to be 1501 Mt and it is expected to at least double by 2050.4,5 Because of the rapid demand growth, new approaches have been considered to find secondary resources for iron oxide.6−8 One such resource is the residue produced during highpressure acid leaching (HPAL) of laterite ore for nickel production.9 About 60% of nickel resources containing more than 1% nickel (total of 130 million tons) are laterite deposits that account for about 40−50% of world annual nickel production.10 Whittington and Muir have reviewed the chemistry of HPAL process.11 In this process, after the feed preparation stage, ore concentrate is fed into a titanium-clad autoclave, where it is mixed with sulfuric acid at 250−270 °C to extract nickel and cobalt together with iron, chromium, and aluminum. At such high temperature, the iron and aluminum go through hydrolysis and precipitate as hematite and alunite © 2017 American Chemical Society

Received: July 6, 2017 Revised: July 31, 2017 Published: August 7, 2017 8416

DOI: 10.1021/acssuschemeng.7b02245 ACS Sustainable Chem. Eng. 2017, 5, 8416−8423

Research Article

ACS Sustainable Chemistry & Engineering Table 1. Chemical Composition of the Original HPAL Residue Measured by ICP-OES

a

element

Fe

Ni

Cr

Al

Mg

Mn

Na

Ca

K

S

Sia

wt %

53.7

0.038

1.28

1.68

0.205

0.0610

0.0917

0.0935

0.00300

2.98

4.20

Si composition was obtained by X-ray fluorescence (XRF). reagent grade, 45.0% w/w) were purchased from VWR and diluted with deionized water to the desired concentrations for the leaching experiments. Anhydrous Na2CO3 (ACS reagent grade, Bioshop Inc., Canada) and anhydrous NaHCO3 (ACS reagent grade, SigmaAldrich), and Ca(OH)2 (Certified grade, Fisher Scientific) were dissolved in the desired volume of deionized water and used for the experiments. Experimental Process. All leaching experiments were conducted in a 500 mL glass reaction vessel. Most experiments were conducted at room temperature (25 °C), and for the ones at higher temperatures, heating was provided by a heating mantle. The system was able to maintain the temperature within an accuracy of ±1 °C. The agitation was set at 700 rpm. The leaching experiments were conducted using five leaching agents (NaOH, KOH, Ca(OH)2, Na2CO3, and NaHCO3) and the effect of leachant concentration, S/L ratio, temperature, and residence time were investigated to determine the best leachant and optimum operating conditions. A predetermined amount of the HPAL residue (based on the desired S/L ratio) was added to the alkaline solution. Sample solutions of 1 mL were withdrawn through a sampling tube using a syringe and filtrations were performed using 0.45 μm nylon syringe filters from VWR. These were diluted with 1.5 M HNO3 to a pH of less than 3 by making the volume up to 10 mL and stored in sealed plastic test tubes at room temperature. Samples were analyzed with ICP-OES to determine the concentration of all the elements. Initial leaching experiments were conducted for 30 min and the results indicated that the kinetics of the leaching process is fast and 10 min residence time is sufficient; hence the rest of experiments were conducted with 10 min residence time. After the reaction was complete, the leached solid residue was filtered using vacuum through grade 3 Whatman filter paper. The leached solid samples were dried in an oven at 50 °C for 24 h. These samples were analyzed using aqua regia digestion followed by ICP-OES and XRF to determine the concentration of sulfur and other elements remaining in the leached residue. Reproducibility tests (three independent experiments) showed that the experimentally measured data are accurate to within ±5%. Characterization. The composition of the original and leached HPAL residue was determined by aqua regia digestion followed by ICP-OES (PerkinElmer Optima 8000), except for that of silicon, which was measured by X-ray fluorescence (XRF; Bruker S2-Range), because Si does not dissolve in aqua regia. Three independent experiments were conducted to determine the average composition. The crystalline components of the original and leached HPAL residue were determined by X-ray diffraction (XRD; Philips PW1830 diffractometer). The composition of various phases in the original HPAL residue was determined by electron probe microanalyzer (JEOL JXA8230). The elemental distribution of the original and leached HPAL residue was determined by scanning electron microscopy energy dispersive spectroscopy (SEM-EDS; Hitachi SU8230). Particle size analysis of the original HPAL residue was performed using the light scattering technique with a particle size analyzer (Malvern Mastersizer S).

hematite from chloride media via atmospheric acid leaching and showed that regardless of temperature, a minimum amount of hematite seed is required, and presence of impurities (CaCl2 and NaCl) and higher initial HCl concentration decreases the product yield.18 One study investigated the kinetics of dissolution of alunite in KOH and determined that a temperature of 80 °C and 4 M concentration of KOH are optimum to completely dissolve alunite within a short period of time.19 There were also a few studies on the recovery of hematite from HPAL residue. One study investigated leaching with sodium hydroxide to reduce the sulfur content and showed that alkali concentration of at least 20 wt % (7.5 M) was required.15 The minimum residence time and temperature were reported to be 2 h and 60 °C, respectively. Under these conditions, a sulfur level of 0.9−1.3 wt % was achieved in the residue. This study poses a few disadvantages, mainly very high base concentration and long residence time. Two other studies investigated the addition of a neutralizing agent to leach slurry followed by solid−liquid separation.20,21 The neutralized residue was heated at 600−1400 °C to form hematite with a sulfur grade of 1.0 wt %. The main disadvantage of this process is very high operating temperature. A recent study investigated a two-step recovery process: (1) separating the leach residue into an overflow and an underflow with a wet cyclone; and (2) magnetic separation of the overflow into a strong magnetic substance and a weak magnetic substance.22 In this process, wet cycloning is essential; otherwise gypsum particles will clog the separator mesh. A strong magnetic field of the intensity of 5 to 20 [kGauss] is required. The main disadvantage of this process is its complexity. The current study focused on developing an innovative and cost-effective process for refining the HPAL residue obtained from Vale’s New Caledonia nickel plant. The refining process is based on the direct leaching of alunite from the HPAL residue using alkaline leachant to lower sulfur content to below 1 wt % and increase iron content to above 56 wt %. The process produces high purity hematite that can be used as a feedstock for steelmaking. It should be mentioned that the HPAL residue in this study originates from a tropical region where the weathering process provides the advantage of removing some of the sulfur present in the laterite ore. Preliminary cost analysis based on an average price of 125 USD/tonne for NaOH 50.0% w/w, indicates that the cost of processing 1 tonne of HPAL residue would be about 20 USD. Detailed design and economic cost analysis of the process is outside of the scope of this work and requires future investigations. The results and findings from this study provide insight for the further development of an efficient hematite recovery process from the HPAL residue with potential for large-scale implementation.

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RESULTS AND DISCUSSION Characterization Results. Table 1 presents the concentration of major elements in the residue. As can be seen, the concentration of sulfur is 2.98 wt %, which should be reduced to 1 wt % or below to make the residue a suitable feedstock for steelmaking. The mineral composition of original HPAL residue was obtained using electron probe microanalyzer (EPMA) (Figure

EXPERIMENTAL SECTION

Materials. HPAL residue was obtained from Vale’s nickel plant located near the Goro mine in the south of New Caledonia, near the township of Yaté, Prony Bay, in the South Province. The residue was filtered, washed three times with deionized water (0.055 μS, Millipore), and dried for 24 h in an oven at 50 °C. Sodium hydroxide (ACS reagent grade, 50.0% w/w) and potassium hydroxide (ACS 8417


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ACS Sustainable Chemistry & Engineering

Figure 1. Electron probe microanalyzer (EPMA) results (a) and X-ray diffraction (XRD) diffractogram (b) of the original HPAL residue.

Figure 2. SEM image of an original HPAL residue particle (a); elemental maps for iron (b), silicon (c), aluminum (d), sulfur (e), and sodium (f).

silicate (3.87%), an iron magnesium silicate (2.16%), and a sulfur-rich iron oxide (2.16%), and minor amount of other phases, as shown in Figure 1a.

1a) and X-ray diffraction (Figure 1b). The EPMA results indicate the presence of hematite (78.7%), natroalunite (NaAl3(SO4)2(OH)6) (9.42%), silica (2.74%), a magnesium 8418


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Figure 3. Particle size distribution of the original HPAL residue sample on a logarithmic scale (a), SEM image of agglomerated silica and hematite (b) and nanosize hematite particles.

The SEM-EDS analysis was performed to obtain the elemental distribution within the sample. Figure 2a presents the cross-sectional backscattered SEM image of an original HPAL residue particle, and Figure 2b−f presents the elemental maps of the particle. As can be seen, iron is the major element and is distributed throughout the particle. Aluminum, sulfur, and sodium occur in the same regions confirming the presence of natroalunite, which is finely disseminated throughout the particle. The SEM images indicate that the HPAL sample is an agglomeration of various phases and Si is not associated with hematite or natroalunite and that the natroalunite is rich in Al. Figure 3a presents the particle size distribution of the original HPAL residue sample. The average particle size is about 1.88 μm. The span (d90−d10) is 25.8 μm; the quartile ratio (d75/d25) is 7.3 μm, and the median diameter (d50) is 2.7 μm. The wide particle size distribution is due to having different types of particles, such as quartz that is larger in size and hematite that is smaller, as shown in SEM images of Figure 3b,c. The particle size distribution was not expected to affect the leaching process.

Figure 4. Content of the remaining sulfur in the leached HPAL residue at various S/L ratios using 1 M NaOH at 25 °C and 30 min residence time. Error bars represent the standard error of the mean for three replicates.

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LEACHING RESULTS Reaction Stoichiometry. The reaction of natroalunite with sodium hydroxide produces sodium aluminate (NaAlO2) and sodium sulfate:

requires smaller tankage. This result validates the theoretical investigations. Under these conditions, the concentration of sulfur is reduced to 0.989 wt %, which is equivalent to 67% reduction and is below the 1 wt % threshold for sulfur level in steelmaking. Optimum Residence Time and Operating Temperature. Figure 5a presents the concentration of sulfur in the leached solution at 25, 45, 65, and 80 °C when 1 M NaOH was used as the leaching agent with S/L of 1/2. As can be seen, the reaction is fast and a plateau is achieved after 10 min, which was selected as the optimum residence time for this process. The leaching efficiency increases by 9% at 80 °C (perhaps due to more complete reaction of alunite) compared with that at 25 °C; however, because running the process at 25 °C eliminates the need for heating the system and the gain in the leaching efficiency is below 10%, we selected 25 °C as the proposed operating temperature. For comparison, we performed leaching experiments using 1 M KOH at the same temperature with S/L of 1/2. As can be seen in Figure 5d, the reaction kinetics at 25 °C is significantly slower than that of NaOH. The final leaching efficiency for the case of KOH is 64%, which is 6% less than that of NaOH. A kinetic model is constructed to explain the difference in leaching efficiencies between NaOH and KOH. To develop the kinetic model for the leaching of sulfur from HPAL residue using NaOH and KOH, the concentration vs time curves were fitted by polynomials (as shown in Figure

NaAl3(SO4 )2 (OH)6(s) + 6NaOH → 3NaAlO2 + 2Na 2SO4 + 6H 2O

(1)

Using the natroalunite content of the HPAL residue, molarity (M), and volume of NaOH, we calculated the theoretical S/L ratio to be 0.70 MNaOH. Optimum S/L Ratio. In the first set of experiments, NaOH was selected as the leaching agent and the operating conditions were set at 25 °C and 30 min residence time. The effect of residence time, temperature, and other leaching agents were subsequently investigated and the results are described in the Reaction Stoichiometry section. For all experiments, a predetermined mass of the original HPAL residue was leached by the alkaline solution with a known concentration and the concentration of sulfur in the leached liquid and solid samples was measured. Figure 4 presents the content of the remaining sulfur in the leached HPAL residue at various S/L ratio when 1 M NaOH at 25 °C and 30 min was used. As can be seen, a plateau is achieved for S/L ≤ 1/2; therefore, a S/L ratio of 1/2 was selected as the optimum value, because a higher S/L ratio 8419


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Figure 5. (a) Concentration of sulfur as a function of time at various temperatures using 1 M NaOH, S/L = 1/2 as the leaching agent. (b) Plot of dc/ dt (i.e., reaction rate) as a function of log c, where the intercept is log k. (c) Arrhenius equation plot to determine the apparent activation energy (Ea) of the leaching reaction using 1 M NaOH, S/L = 1/2. (d) Concentration of sulfur as a function of time at various temperatures using 1 M KOH, S/L = 1/2 as the leaching agent. (e) Plot of dc/dt (i.e., reaction rate) as a function of log c. (f) Arrhenius equation plot for 1 M KOH, S/L = 1/2. Error bars represent the standard error of the mean for three replicates.

mol; whereas it is greater than 40 kJ/mol for a chemical reaction-controlled leaching.23 Therefore, based on the Ea value, the sulfur leaching process from HPAL residue is controlled by chemical reaction. These results are consistent with the results of a previous study using KOH as the leaching agent for the extraction of aluminum and sulfur from alunite, which showed the activation energy of 94.18 kJ/mol.19 Effect of Other Leaching Agent. The effect of leaching agents other than NaOH, i.e., NaHCO3, Na2CO3, KOH, and Ca(OH)2, was investigated. The use of KOH as the leaching agent for natural alunite (K0.63Na0.21(H3O)0.16Al3(SO4)2(OH)6) has previously been investigated, and it was shown that 4 M and 80 °C with S/L ratio of 1/200 are the best operating conditions.19 Figure 6 presents the concentration of sulfur in the leach solution for all the cases studied. In the first instance, the possibility of using Ca(OH)2, which is more cost-effective compared to other leachants, was investigated based on the following reaction:

5a,d), and using the equation, dc/dt (i.e., reaction rate) was calculated for each data point. Using the differential method and eqs 4 and 5, plot of log(dc/dt) vs log(c) resulted straight lines with the adjusted coefficient of determination (R2) more than 0.99, for which the intercept is log k, where k is the apparent reaction rate constant (Figure 5b,e).

dc = kc n dt

(4)

⎛ dc ⎞ log⎜ ⎟ = log k + n log(c) ⎝ dt ⎠

(5)

On the basis of the apparent reaction rate constant (k) from Figure 5b,e, the Arrhenius equation (eq 6) was employed to determine the activation energy of the reaction.

⎛ E ⎞ k = A exp⎜ − a ⎟ ⎝ RT ⎠

(6)

2NaAl3(SO4 )2 (OH)6(s) + 6Ca(OH)2

where A is the frequency factor, Ea is the apparent activation energy (J mol−1), R is the universal gas constant (8.314 J mol−1 K−1) and T (K) is absolute temperature. Plotting ln k as a function of 1/T resulted a straight line with R2 of 0.83 and 0.89, respectively (Figure 5c,f). Using the slope of the line, the apparent activation energy for leaching of sulfur from HPAL residue using 1 M NaOH and 1 M KOH was calculated to be 88.5 and 97.9 kJ/mol. It should be mentioned that the variations in the plots are due to the convolution of errors and that the mechanism does not change over the temperature range of interest. According to the literature, the apparent activation energy of the diffusion-controlled leaching is ∼20 kJ/

→ 3Ca(AlO2 )2 + Na 2SO4 + 3CaSO4 .2H 2O + 6H 2O (7)

Because the solubility of Ca(OH)2 in water is limited (0.02 mol/L at 25 °C),24 it was not possible to make a 1 M solution. On the basis of the reaction in eq 7, and using the same procedure described, the theoretical S/L ratio is 1/22, which means that this process requires a reactor 11 times larger than the case where NaOH is used, which is not desirable. To further investigate this case, the leaching experiments were conducted at 25 and 80 °C and leaching efficiencies of 9.7% 8420


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ICP-OES. Figure 7 presents the X-ray diffraction pattern of the leached and original HPAL residue. As can be seen the

Figure 6. Concentration of the extracted sulfur in the leached solution using Ca(OH)2 (0.02 M, S/L = 1/22, 25, and 80 °C), NaHCO3 (1 M, S/L = 1/2, 80 °C), Na2CO3 (1 M, S/L = 1/2, 65, 80 °C), KOH (1 M, S/L = 1/2, 80 °C), and NaOH (1 M, S/L = 1/2, 80 °C) as the leaching agent. Error bars represent the standard error of the mean for three replicates.

Figure 7. X-ray diffraction (XRD) diffractogram of the leached vs original HPAL residue.

natroalunite peaks are eliminated after leaching in 1 M NaOH, confirming that almost all of the natroalunite has been dissolved. Table 2 presents the elemental composition of original HPAL residue and leached residue. On the basis of measured data for sulfur and aluminum in the leach solution, 67% of sulfur and 64% of aluminum present in the original HPAL residue were leached out with NaOH. The remaining aluminum can be attributed to aluminum associated with hematite and chromite or aluminosilicate minerals remaining in the residue. Most of the remaining sulfur is associated with iron. The association of sulfur with iron is due to the entrapment of sulfate in the hematite structure when the hematite particle is formed, the hematite formed in sulfate based systems will have a certain amount of associate sulfur, typically in the range 0.5− 1%.21 Therefore, the remaining sulfur is scattered homogeneously throughout the residue. To investigate the fate of Si during the leaching process, we characterized the original and leached HPAL residue using XRF. The results showed 4.2 wt % Si for both cases, which means that this leaching process does not remove the Si content of the HPAL residue. Figure 8 presents the SEM-EDS elemental map of sulfur and aluminum for the leached and original HPAL residue.

and 17.3% were obtained after 2 h residence time, respectively. In the case of 1 M NaHCO3 and Na2CO3 with S/L of 1/2 at 80 °C for 2 h residence time leaching efficiencies of 29.8% and 41.4% were obtained, respectively. The leaching efficiencies of sulfur using KOH and NaOH with S/L of 1/2 at 80 °C for 1 h residence time under similar operating conditions was calculated at 64% and 67%, respectively. Figure 6 presents the concentration of the extracted sulfur in the leached solution using all five bases as the leaching agent. The reactions in eqs 8−10 illustrate the leaching process for NaHCO3, Na2CO3, and KOH leaching agents, respectively. NaAl3(SO4 )2 (OH)6(s) + 6NaHCO3 → 3NaAlO2 + 2Na 2SO4 + 6H 2CO3

(8)

NaAl3(SO4 )2 (OH)6(s) + 3Na 2CO3 → 3NaAlO2 + 2Na 2SO4 + 3H 2CO3

(9)

NaAl3(SO4 )2 (OH)6(s) + 6KOH → 3KAlO2 + 0.5Na 2SO4 + 1.5K 2SO4 + 6H 2O

(10)

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As can be seen in Figure 6, sulfur extraction is close to zero when Ca(OH)2 was used as the leaching agent. Furthermore, both Na2CO3 and NaHCO3 resulted in lower sulfur extraction compared with the NaOH and KOH cases. The extraction was almost the same when NaOH and KOH were used, with NaOH being the highest. On the basis of these observations and the fact that NaOH is more cost-effective than KOH, we propose to use that as the leaching agent. The reason behind having different leaching efficiencies for the five leaching agents studied could be due to different basic strength. We measured pH of each basic solution at 80 °C before the leaching process. Though the pH values of NaOH and KOH were between 13.5 and 13.8, the pH of Na2CO3 and NaHCO3 were at 11.0 and 8.3, respectively.

CONCLUSIONS In summary, a process relying on alkaline leaching was proposed to valorize the residue from the high-pressure acid leaching (HPAL) of nickel laterite ore. The characterization results indicated that the HPAL residue contains high concentration of hematite, a raw material for steelmaking. However, the sulfur content of the HPAL residue is above the threshold required by the steel industry and it must be lowered to convert the residue to a suitable feedstock. The proposed process is novel, efficient, and easy to implement at industrial settings in a sense that it runs at room temperature (25 °C) with large S/L ratio (1/2), and short residence time (10 min) for the current HPAL residue. Five leaching agents were investigated, and 1 M sodium hydroxide was selected as the most effective. Not only does the proposed process valorize an otherwise waste stream to produce a valuable product, but it also has environmental benefits because this can reduce the volume of HPAL residues generated.

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LEACHED HPAL RESIDUE CHARACTERIZATION RESULTS The leached HPAL residue was characterized by X-ray diffraction, SEM-EDS, and aqua regia digestion followed by 8421


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Table 2. Chemical Composition of the Original HPAL Residue and Leached HPAL Using 1 M NaOH at 25 °C for 10 min with S/L = 1/2 Measured by ICP-OES

a

element/wt %

Fe

Ni

Cr

Al

Mg

Mn

Na

Ca

K

S

Sia

before leaching after leaching

53.7 56.1

0.038 0.043

1.28 0.132

1.68 0.608

0.205 0.249

0.061 0.067

0.092 0.135

0.093 0.073

0.003 0.003

2.98 0.99

4.20 4.20

Si composition was measured by X-ray fluorescence (XRF).

Figure 8. SEM-EDS elemental maps of sulfur and aluminum in the original and leached HPAL residue.

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(5) Cullen, J. M.; Allwood, J. M.; Bambach, M. D. Mapping the global flow of steel: From steelmaking to end-use goods. Environ. Sci. Technol. 2012, 46 (24), 13048−13055. (6) Yi, Z.; Sun, H.; Wei, X.; Li, C. Iron ore tailings used for the preparation of cementitious material by compound thermal activation. Int. J. Miner., Metall. Mater. 2009, 16 (3), 355−358. (7) Das, S. K.; Kumar, S.; Ramachandrarao, P. Exploitation of iron ore tailing for the development of ceramic tiles. Waste Manage. 2000, 20 (8), 725−729. (8) Li, C.; Sun, H.; Yi, Z.; Li, L. Innovative methodology for comprehensive utilization of iron ore tailings. Part 2: The residues after iron recovery from iron ore tailings to prepare cementitious material. J. Hazard. Mater. 2010, 174 (1−3), 78−83. (9) McDonald, R. G.; Whittington, B. I. Atmospheric acid leaching of nickel laterites review: Part I. Sulphuric acid technologies. Hydrometallurgy 2008, 91 (1), 35−55. (10) U.S. Geological Survey. Mineral Commodity Summaries 2016; 2016, DOI: http://dx.doi.org/10.3133/70170140. (11) Whittington, B. I.; Muir, D. Pressure Acid Leaching of Nickel Laterites: A Review. Miner. Process. Extr. Metall. Rev. 2000, 21 (6), 527−599. (12) Chou, E. C.; Queneau, P. B.; Rickard, R. S. Sulfuric acid pressure leaching of nickeliferous limonites. Metall. Trans. B 1977, 8 (3), 547− 554. (13) Georgiou, D.; Papangelakis, V. G. Sulphuric acid pressure leaching of a limonitic laterite: chemistry and kinetics. Hydrometallurgy 1998, 49 (1−2), 23−46. (14) Nicol, M. J.; Zainol, Z. The development of a resin-in-pulp process for the recovery of nickel and cobalt from laterite leach slurries. Int. J. Miner. Process. 2003, 72 (1), 407−415. (15) Ozaki, Y.; Enomoto, M.; Shouji, H.; Higaki, T. Method for producing hematite for ironmaking. Patent US20150050201A1, 2015. (16) Dutrizac, J. E. Converting jarosite residues into compact hematite products. JOM 1990, 42 (1), 36−39. (17) Reynolds, G. A. The Jarosite Group of Compounds-Stability, Decomposition and Conversion. M.Sc. Thesis, University of Newcastle, Newcastle, NSW, 2007.

AUTHOR INFORMATION

Corresponding Author

*G. Azimi. E-mail: [email protected]. ORCID

Gisele Azimi: 0000-0002-0665-7199 Funding

This work was supported by Natural Sciences and Engineering Research Council of Canada (NSERC) [grant number 499792]; Ontario Centers of Excellence (OCE) and Vale Base Metals Technical Excellence Centre [grant number 499790]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors acknowledge Vale Base Metals for providing the HPAL samples and their technical support. We thank Dr. Indje Mihaylov for providing guidance throughout the project and reviewing the paper. We thank Jason Tam for his support with SEM-EDS analysis and George Kretschmann for his support with XRD characterization. We thank William Judge for his help with reviewing the materials.

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REFERENCES

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Waste Valorization Process: Sulfur Removal and Hematite Recovery

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