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1 The SEM and EDS element mapping of Chinese nickel sulphide ore
(c) (d)
(e) (f)
(g) (h)
(a) J(talc) (b)
Fig. S1 SEM image(a) of samples and EDS element mapping((b)-(i)) and EDS result(j).
2 Methods
The experimental flowsheet is shown in Fig. S2. The experiment was based on the procedures of
roasting and leaching.
Fig. S2 Flow sheet for the two-stage roasting–leaching process
3 XRD patterns at different roasting time
Fig. S3 shows the XRD patterns of roasted clinkers obtained by roasting ores with sulfuric acid
for different times at an acid-to-ore ratio of 1.1:1 and a roasting temperature of 295°C. Table 1 shows
the mineralogical phases at different times.
(i) (j)
Inte
nsity
(Cou
nts)
10 20 30 40 50 60 70 80 9083-0080> Cu(SO4)(H2O) - Copper Sulfate Hydrate
81-0019> Szomolnokite, syn - Fe(SO4)(H2O)
76-0364> Mg(HSO4)2(H2O) - Magnesium Hydrogen Sulfate Hydrate
74-1329> Dw ornikite, syn - NiSO4(H2O)
73-1057> FeSO4 - Iron Sulfate
73-0147> Talc - Mg3(Si2O5)2(OH)2
72-1259> MgSO4 - Magnesium Sulfate
72-0544> Kieserite - MgSO4H2O
72-0090> Chalcocyanite - CuSO4
70-2091> Fe2(SO4)3 - Iron Sulfate
20-0790> Ni-Si-O!H2O - Nickel Silicate Hydrate
Theta(deg)
10min
20min
30min
40min
60min
90min
120min
150min
Fig. S3 XRD patterns at different roasting time at 295°C
Table S1 Phases identified in the XRD patterns at different roasting time at 295°C
10
min
20 min 30 min 40 min 60
min
90
min
120
min
150
min
talc[Mg3(Si2O5)(OH)2] √ √ √ √ √ √ √
ferrous sulfate(FeSO4) √ √ √ √ √
magnesium sulfate(MgSO4) √ √ √ √ √
copper sulfate(CuSO4) √ √ √ √ √
ferric sulfate[Fe2(SO4)3] √ √ √
szomolnokite[Fe(SO4)(H2O)] √ √ √ √
magnesium hydrogen sulfate
hydrate[Mg(HSO4)2(H2O)]
√ √ √
dwornikite[NiSO4(H2O)] √ √ √
copper sulfate
hydrate[CuSO4(H2O)]
√ √ √
nickel silicate
hydrate[NiSiO3(H2O)]
√
kieserite[MgSO4(H2O)] √ √
It can be seen from Fig. S3 and Table S1that the main phases in the specimen obtained at a
roasting time of 10 min are Fe(SO4)(H2O), Mg(HSO4)2(H2O), NiSO4(H2O) and CuSO4(H2O) and that
the diffraction peaks of talc are obscured by other diffraction peaks. Talc phases, NiSiO 3(H2O) and
MgSO4(H2O), appear in the specimen obtained with a roasting time of 20 min, indicating that part of
the Ni is hosted in silicate. Compared to a roasting time of 20 min, the NiSiO3(H2O) phase disappears
after roasting for 30 min. However, this may result from its low content and other strong diffraction
peaks may obscure its diffraction peaks. The main phases in the specimen roasted for 40 min are talc,
Fe(SO4)(H2O), FeSO4, MgSO4 and CuSO4. Roasting for 60 min, 90 min, 120 min and 150 min results
in the Fe(SO4)(H2O) disappearing while Fe2(SO4)3 appears. The diffraction peaks of NiSO4 cannot be
identified because they are hidden by the strong diffraction peaks of other phases.
3.2.2 DTA-TG analysis
Fig. S4 shows the DTA-TG curve obtained from heating a sulfuric acid and ore sample from 0 to
1000°C using a Diamond 6300 (PerkinElmer, America) thermal analysis instrument at a heating rate of
10°C/min.
Fig. S4 The diagram of DTA and TG for sulfuric acid and ore
It can be seen from the DTA curve that there are nine endothermic peaks, located at 111.68°C,
195.05°C, 234.91°C, 310.11°C, 531.46°C, 684.12°C, 740.01°C, 869.12°C and 940.95°C, and three
exothermic peaks, located at 169.48°C, 210.09°C and 259.72°C, respectively. The first endothermic
process, below 111.68°C, is the removal of free water, accompanied by a weight loss of 2.20%. In the
temperature range of 130.78°C to 321.51°C, there are three exothermic peaks corresponding to the
three endothermic peaks. In this stage, sulfuric acid begins to react with ores, releasing SO 2 (or SO3)
and steam. The initial react temperature is 130.78°C with a corresponding weight loss of 3.54%. The
reactions between sulfuric acid and the ore can be summarized as (1) to (21).
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
(9)
(10)
(11)
(12)
(13)
(14)
(15)
(16)
(17)
(18)
(19)
(20)
(21)
The reactions continue with increasing temperature until the sulfuric acid is exhausted. After that,
the metal sulfates begin to decompose into metal oxide and sulfur trioxide. In this process, four
endothermic peaks at 531.46°C, 684.12°C, 740.01°C and 869.12°C are produced. The last endothermic
peak at 940.95°C is mainly attributed to the decomposition of unreacted talc to release structural water.
The reactions can be expressed as Eqs. (22) to (29).
(22)
(23)
(24)
(25)
(26)
(27)
(28)
(29)
4 Thermodynamic analysis
Fig. S5 Free energy values for corresponding reactions in first stage roasting
Fig. S5 shows the Gibbs free energy values of Eqs. (1) to (21) that take place in the first stage of
roasting (using HSC Chemistry 6) from 0-500°C.
Fig. S6 Free energy values for the corresponding reactions in the second roasting stage
Fig. S6 shows the Gibbs free energy values of Eq. (22) to (29) in the second roasting stage
(using HSC Chemistry 6) from 0-1000°C. According to Fig. S6, it was expected that some metal
sulfates decompose at particular temperatures, although the actual decomposition will be dependent
upon the SO3 partial pressure. A suitable second stage roasting temperature was explored to promote
the decomposition of ferric sulfate, while ensuring that nickel sulfate and copper sulfate would be
thermodynamically stable. This could thermodynamically explain the extractions of different
components in the second stage roasting process.