The Direct Leaching of Nickel Sulfide Flotation Concentrates – A Historic and State-of-the-Art Review Part III: Laboratory Investigations into Atmospheric Leach Processes

Figures & data

Table 1. Summary of laboratory investigations carried out on ammoniacal leaching of nickel sulfide concentrates at ambient pressure.

Reference	Nickel sulfide mineralogy	Nickel grade (wt% Ni)	Concentrate feed particle size	Mode of leaching	Leaching conditions
Aaltonen et al. (1980)	Pentlandite, mackinawite^a	5.4%	86.5% under 74 µm	Stirred tank leaching	2 M NH3, 0.2 M (NH4)2SO4, 50°C 1 atm O2 pressure, up to 2 days leaching time, solids conc. 10 g/100 mL
Welham et al. (2008)	Pentlandite, violarite, and pyrrhotite	14.6%	Not stated	Not stated	Leaching with 40 g/L (NH4)2CO3 +20 g/L NH3 at ambient temperature & pressure. Concentrate also cured with NaClO prior to leaching.
Muzawazi and Petersen (2015)	Pentlandite	3.17%	P97 45 µm, coated onto 5–10 mm granite particles for column leaching	Column leaching and stirred tank leaching	Stirred tank leaching − 25 - 60°C 0.5–4 M NH4OH, 0.5–4 M (NH4)2CO3, 120 mL/min air flow, up to 5 days leaching time Column leaching − 25 - 40°C 0.5 – 4 M NH4OH, 0.25–4 M (NH4)2CO3, 80 mL/min air flow, up to 42 days leaching time

^aMackinawite - (Fe, Ni)S_0.9.

Table 2. Summary of laboratory investigations carried out on sulfuric acid leaching of nickel sulfide concentrates at atmospheric pressure.

Reference	Nickel sulfide mineralogy	Nickel grade (wt% Ni)	Concentrate feed particle size	Leaching conditions
Corrans and Scholtz (1976)	Pentlandite	30.6%	−74 + 44 µm	30 & 80°C 0.01 & 0.25 M Fe(III), 2 × 10^−4 & 2 M H+ (as sulfuric acid), solids conc. 100 g/L, 0 & 400 rev/min, PO2 1% & 100%
Aaltonen et al. (1980)	Pentlandite and mackinawite	5.4%	86.5% under 74 µm	pH 2, 3.5 & 5, 25 – 95°C up to 5 days leaching time, 21% O2 (air) and 100% O2 as oxidant
Kuzeci, Li, and Kammel (1989)	Pentlandite	6.3%	Not specified, concentrate reground in a Netzsch mill using 2 mm steel grinding media	20 g/L H2SO4, 22–23 g/L Fe^3+, 60–95°C solids conc. 20 g/L
Bredenhann and Van Vuuren (1999)	Millerite	50.2%	Not specified	60–90°C 5–45 g/L NaNO3, pH 0 sulfuric acid solution, 500 rev/min, up to 20 hours leaching time, solids conc. not specified
Lu and Lawson (1998), Lu, Jeffrey, and Lawson (2000)	Pentlandite	18.5%	P80 20 µm	60 – 96°C sulfuric acid solution (pH < 0.8), 0–2 M NaCl, 0 & 0.28 M Fe(III), solids conc. 40 g/L, 10 hour leaching time, 1 atm O2 pressure

Table 3. Summary of laboratory investigations carried out on chloride leaching of nickel sulfide concentrates at ambient pressure.

Reference	Nickel sulfide mineralogy	Nickel grade (wt% Ni)	Concentrate feed particle size	Mode of leaching	Leaching conditions
Ghali and Girard (1978)	Concentrate(s) A & B – pentlandite, awaruite, millerite & heazlewoodite Concentrate C – pentlandite Matte – heazlewoodite, metallic Ni	Concentrate A −20.1% Concentrate B−11.0% Concentrate C −5.14% Matte − 74.0%	Concentrate(s) A & B – P75 250 µm Concentrate C – P100 37 µm Matte – P99 250 µm	Batch stirred tank leaching, ambient pressure	1–5.7 M FeCl3, 80°C 100 rev/min, solids conc. 320 g/L, up to 66 hours leaching time
Ferron, Williamson, and Zunkel (1996)	Concentrate #1 & #2 - Pentlandite	Concentrate #1–3.58% Concentrate #2–4.00%	56 to 90% −37 µm	Batch stirred tank leaching, ambient pressure	95°C 7.5 h leaching time, 73–146 g/L Fe(III), 151–289 g/L Cl-, 10% w/v pulp density, impeller tip speed of 100 or 170 cm/s ORP controlled experiments − 95°C 7.5 h leaching time, 10% w/v pulp density 300–525 mV vs SCE via addition of either 300 g/L Fe(III) (as chloride) or Cl2 gas
Fang (1997a)	Pentlandite	7.74%	Not specified	Batch stirred tank leaching, ambient pressure	60 - 99°C 10–35 g/L Cu(II), 80–250 g/L NaCl, up to 12 h leaching time, 21% & 100% O2, 600 rev/min, pulp density not specified
Honey, Muir, and Hunt (1997)	Pentlandite	14.5%	P80 80 µm	Stirred tank leaching, ambient pressure	Leaching at 75, 110 & 115°C (reflux) over a 2-h period in 3 M chloride lixiviant. Oxygen-chlorine used as oxidant with cupric chloride as a catalyst (Cu conc. not specified)
Harris et al. (2004)	Pentlandite	18.65%	Not specified	Ambient pressure	2 or 4 N HCl plus MgCl2, up to 400 g/L total Cl-, 5% w/v solids, 95°C 4 h leaching time, ORP of 170–510 mV vs SHE, NaClO3, NaOCl, Cl2 and O2 used as oxidants, stirring rate not specified
Malkhuuz (2006)	Concentrate #1 – pentlandite Concentrate #2 – pentlandite, millerite	Concentrate #1(low MgO) −13.5% Ni,8.76% MgO Concentrate #2(high MgO) −25.75% Ni,17.4% MgO	Not specified	Batch stirred tank leaching, ambient pressure	60 or 100°C 2 molal MgCl2, 2–8 molal HCl, up to 24 h leaching time, pulp density not specified, 0.5 molal of either CuCl2 or FeCl3 added in some tests
Kshumaneva et al. (2009)	Pentlandite	39.4%	−50 + 20 µm	Batch stirred tank leaching, ambient pressure	0–4 M HCl, 0–4 M FeCl3, 0–4 M CuCl2, 40 - 98°C up to 300 min leaching time, solid:liquid ratio of 1:50

Table 4. Summary of laboratory investigations carried out on nitric acid leaching of nickel-bearing sulfide concentrates at ambient pressure.

Reference	Nickel sulfide mineralogy	Nickel grade (wt% Ni)	Concentrate feed particle size	Mode of leaching	Leaching conditions
Ouellet, Torma, and Bolduc (1975)	Ore & concentrate -pentlandite	Ore − 1.83% Concentrate − 5.14%	P100 32 µm	Ambient pressure leaching	50 - 95°C 0–7.5 M HNO3, 0–0.95 M H2SO4, 10–45% pulp density, up to 120 min leaching time
Shukla, Mukherjee, and Gupta (1978)	Pentlandite, millerite	6%	P100 149 µm	Ambient pressure leaching	40 - 100°C 10% pulp density, up to 10-hours leaching time, agitation rate of 400 rpm, 10–16% HNO3 Roast-leach – concentrate roasting at 450 - 700°C calcine leached in 15% HNO3 at 100°C for 4 hours

Table 5. Summary of laboratory and pilot plant investigations carried out since 2008 on bioleaching of nickel sulfide concentrates using various microorganisms.

Reference	Nickel sulfide mineralogy	Nickel grade (wt% Ni)	Concentrate feed particle size	Microorganisms	Mode of leaching	Leaching conditions
Neale et al. (2009)	Pentlandite, trace gersdorffite	5.24%	D90 varied between 10 & 35 µm	Thermophiles	Continuous stirred tank leaching	70°C 10% w/v solids, pH 1.1–1.3, 6-day residence time, Eh 600 mV vs Ag/AgCl
Cruz et al. (2010)	Pentlandite	5.9%	P80 47 µm	Mesophiles & moderate thermophiles	Shaker flasks	34°C (mesophiles), 50°C (thermophiles), 5% w/v solids, pH 1.2–2.4, 0–10 g/L Fe(II), up to 25 days leaching time
Gericke and Govender (2011)	Pentlandite, trace gersdorffite	5.6%	D90 varied between 10 & 40 µm	Moderate thermophiles & thermophiles	Batch & continuous stirred tank leaching	45°C (moderate thermophiles), 65 – 75°C (thermophiles), 3–6 days residence time, 10% w/v solids, pH 1.25–1.7, Eh 430–580 mV vs Ag/AgCl (thermophiles), 420–670 mV vs Ag/AgCl (moderate thermophiles)
Wakeman, Honkavirta, and Puhakka (2011)	Pentlandite, gersdorffite, niccolite	Concentrate #1–10.5% Concentrate #2–14.3%	Not specified	Mesophiles	Shaker flasks & continuous stirred tank leaching	6 – 27°C 2, 5 & 10% w/v solids, up to 56 days leaching time, pH 3
Mwase, Petersen, and Eksteen (2012)	Pentlandite	3.4%	83% passing 38 µm coated onto granite pebbles	Thermophiles	Column	65 – 80°C 10 g/L H2SO4, 2 g/L Fe, 88 days leaching time, lixiviant flow rate of 1000 mL/day, aeration rate of 130 mL/min
Norris (2017)	Concentrate #1 – Pentlandite, violarite Concentrate #2 & #3 – pentlandite	Concentrate #1–10.5% Concentrate #2–8.8% Concentrate #3–7.6%	Concentrate #1 – D80 75 µm Concentrate #2 – D80 88 µm Concentrate #3 – D80 9 µm	Moderate thermophiles & thermophiles	Continuous stirred tank leaching	Moderate thermophiles − 49°C pH 2.5 (concentrate #1), pH 1 (concentrate #2, #3), 5% w/v solids Thermophiles − 77°C pH 1.3, 5% w/v solids
Sun et al. (2020)	Pentlandite	27.4%	P100 74 µm	Mesophiles	Chemical leaching – shaker flasks Bioleaching – batch stirred tank leaching	Chemical leaching: pH 1, 33°C 3% w/v solids, 0–9 g/L Fe^3+ Bioleaching: pH 2–3, 33°C 2% w/v solids

Table 6. Summary of laboratory investigations carried out to date on mechanochemical treatment of nickel sulfide concentrates prior to atmospheric leaching using a range of lixiviant systems.

Reference	Nickel sulfide mineralogy	Nickel grade (wt% Ni)	Milling equipment	Milling conditions	Leaching media	Leaching conditions
Kulebakin (1977)	Pentlandite	25%	Planetary mill, 500 g of beads (wet milling), 1200 g (dry milling)	Wet milling − 25 g concentrate, 125 mL water, 7 min milling time Dry milling − 3g	Thiobacillus Ferrooxidans in 9K nutrient medium^a + 9 g/L Fe(III)	Ambient pressure, 8 hours, solids conc. 20 g/L, temperature not specified
Maurice and Hawk (1999)	Pentlandite	8.10–11.76% (depends on size fraction)	Shaker mill, 4.8 mm stainless steel beads, 30% filling factor	5:1 charge ratio^b, 1–30 min, dry conditions	1 M FeCl3 +1 M NaCl +0.25 M HCl	70 - 90°C 60–150 min, solids conc. 10 g/L, ambient pressure
Baláž et al. (1998, 2000)	Pentlandite	23.19%	Attrition mill, 2000 g of 2 mm beads, 86% fill factor	100g concentrate, 200 mL water, 15–60 min milling time at 25°C	Water, 0.25 M Fe2(SO4)3 +0.25 M H2SO4	45 - 90°C 120 min, solids conc. 4 g/L, ambient pressure

^aAqueous sulfuric acid solution containing dissolved salts [(NH₄)₂SO₄, KCl, K₂HPO₄, MgSO₄·7 H₂O, Ca(NO₃)₂, FeSO₄.7 H₂O].

^bMass of grinding media to mass of concentrate.

Table 7. Summary of research carried out to date on pyrometallurgical pre-treatments of nickel concentrates to render them more amenable to subsequent hydrometallurgical processing.

Reference	Nickel sulfide mineralogy	Nickel grade (wt% Ni)	Additive	Roasting conditions	Leaching conditions
Caron-type processes & oxidation roasting
Forward, Kudryk, and Samis (1948)	Not specified	Concentrate − 16.7% Middling − 2.86% Matte − 55.6%	Oxidizing roast stage – air Reduction roast stage – H2	Oxidizing roast − 760 to 815.6°C Reduction roast − 350 to 600°C	8% NH3 +8% (NH4)2CO3, 21.1–37.8°C 5% pulp density, 2 hour leaching time
Queneau et al. (1949)	Pyrrhotite, pentlandite	<1%	Oxidizing roast stage – air Reduction roast stage – CO + CO2 + H2 + H2O	Oxidizing roast − 704.4 to 1148.9°C Reduction roast − 537.8 to 926.7°C	6–10% NH3 +3–7% CO2, leach temperature, pulp density & time not specified
Leo and Georg (1954)	Not specified	5.6%	None	Not specified	Calcine leached in aqueous ammonia with aeration, however specific conditions not provided
Zhu et al. (2012)	Pentlandite, vaesite, violarite	6.20%	None	350–910°C	2 M HCl, 70 - 100°C 5 hour leaching time, L:S ratio varied up to 200:1
Reduction roasting
Dyson and Scott (1976)	Pentlandite, violarite, millerite	12.4–31.1%	None	650–850°C under a stream of CH4 gas for 1 hour	5 N HCl or 5 N H2SO4 at 100°C for up to 4 hours, solids conc. 250 g/L
Filmer and Balestra (1981)	Pentlandite	7.5%	None	850°C under a stream of H2 gas for various unspecified times	3–10 N HCl at 60°C for up to 4 hours, solids conc. 1.1 or 1.4%, 450 rpm agitation speed
Chloridizing roasting
Kershner and Hoertel (1961)	Siegenite in both concentrates	Cu concentrate – 0.7–0.9% Fe concentrate – 2–3%	NaCl	450–600°C 2 or 3 hour period	Calcine leached in water acidified to pH 0–1.5 (using HCl)
Smith and Iwasaki (1976, 1985)	Pentlandite	2.02%	Cl2	1^st stage – S2Cl2 conversion @ 300°C 2^nd stage – chlorination @ 100 - 300°C 3^rd stage – ferrous chloride decomposition (oxidation) @ 300 - 500°C	Distilled water for 10 min at a pulp density of 20% w/v; temperature of leach not specified
Mukherjee et al. (1985)	Pentlandite, millerite, violarite, bravoite^a	8%	NaCl	280–450°C up to 8 hours	Acidified water at pH 2
Imideev et al. (2014)	Pentlandite	6.88%	NaCl	300–500°C up to 3 hours	Distilled water at 90°C for 1.5 hours, S:L ratio 1:7
Xu et al. (2017)	Pentlandite	9.37%	NH4Cl	200–325°C up to 5 hours, N2 atmosphere	Distilled water at 90°C for 1 hour, solids conc. 200 g/L
Aleksandrov et al. (2019a, 2019b)	Pentlandite	5.78%	NaCl	300–500°C up to 3 hours	Distilled water at 90°C for 1.5 hours, S:L ratio 1:7
Li et al. (2020)	Pentlandite	9.35%	NH4Cl	1^st stage − 250°C 2 hours 2^nd stage − 650°C 1 hour	Distilled water at 80°C for 1 hour, solids conc. 50 g/L
Sulfation roasting
Fletcher and Shelef (1963, 1964)	Pentlandite	7.92%	Alkali metal sulfates (Li, Na, K, Rb, Cs)	680°C under a 90/10 air/SO2 mixture, no residence time stated	Calcine leached in boiling water
Fletcher and Hester (1964)	Pentlandite	4.69%	Na2SO4	670–690°C under air, 6-hour residence time	Calcine leached in 50 g/L H2SO4 at 60% solids and 80°C for up to 6 hours
Weir et al. (1983)	Ni & Co-bearing pyrite concentrates	-	Na2SO4	500–800°C under air, no residence time stated	Calcine is repulped in sulfate solution and then oxygen pressure leached at 100 - 180°C and 50–1500 kPa O2 overpressure
Rao, Natarajan, and Padmanabhan (2001)	Pentlandite & other unspecified sulfides	7%	Li, Na & K sulfate	500–650°C 4 to 6 hour holding time	Calcine water-leached twice at 60°C for 30 min at 30–40% solids
Yu, Utigard, and Barati (2014a)	Pentlandite	17.9%	None	650–775°C under air for up to 13 minutes	Water leach at 90°C for 30 min, solids conc. 4 g/L
Yu, Utigard, and Barati (2014b)	Pentlandite	17.9%	Na2SO4	660–740°C under a 95/5 air/SO2 mixture for up to 350 min	Water leach at 90°C for 30 min, solids conc. 4 g/L
Cui et al. (2018)	Pentlandite	5.7%	Mixture of (NH4)2SO4 & Na2SO4	300–550°C for up to 4 hours under a 80/20 N2/O2 mixture	Water leach at 95°C for 2 hours, S:L ratio not specified
Li et al. (2018)	Pentlandite	9.7%	Na2SO4	400–800°C up to 180 min holding time	Water leach at 80°C for 2 hours, S:L ratio 1:20
Li et al. (2019)	Pentlandite	8.93%	(NH4)2SO4	300–750°C up to 180 min holding time	Water leach at 80°C for 30 min, S:L ratio 1:4

^aNickel-rich variety of pyrite [(Fe, Ni, Co)S₂.

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