In�uence of Calcium Chloride Addition on Coal-Based Reduction Roasting of Low-Nickel Garnierite Ore

Jingcheng Dong1,2, Yonggang Wei1,2,*, Chao Lu1,2, Shiwei Zhou1,2, Bo Li1,2, Zhiguang Ding1,2, Chengyan Wang3 and Baozhong Ma4

1State Key Laboratory of Complex Nonferrous Metal Resources Clean Utilization, Kunming University of Science and Technology, Kunming 650093, China2Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China3School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, China4Beijing General Research Institute of Mining and Metallurgy, Beijing 100160, China

This work investigates the in�uence of calcium chloride addition on coal-based reduction roasting low-nickel garnierite ore, and which is most evident in nickel enrichment and ferronickel particles aggregation. The results demonstrate that a concentrate with 11.83% nickel, cor-responding to a nickel recovery of 97.38%, was obtained when the ore was reduced at 1150°C for 40 min in the presence of 12 mass% CaCl2·2H2O, followed by magnetic separation at 250 mT. Compared with the ore reduced without calcium chloride, the nickel enrichment ra-tio of the concentrate was increased from 3 to 14 by the addition of 12 mass% CaCl2·2H2O. Duing to the vaporization of the nickel chloride formed and the emergence of a new reactive surface, the addition of calcium chloride makes NiO in the garnierite easier to be reduced. The X-ray diffraction and scanning electron microscopy and energy dispersive spectrometry (SEM-EDS) studies show that metallic nickel was mainly enriched into a kamacite phase, and the presence of CaCl2·2H2O signi�cantly accelerated the aggregation and growth of ferronickel particles, attributing to the vaporization and precipitation of nickel chloride on carbon surface together with ferrou chloride. [doi:10.2320/matertrans.M2017086]

(Received March 13, 2017; Accepted May 29, 2017; Published July 7, 2017)

Keywords:　 reduction roasting, magnetic separation, nickel, calcium chloride

1.　 Introduction

Nickel laterite is an important nickel resource, compris-ing ~70% of the world’s total land-based nickel resources. However, it only accounts for 40% of the world’s nickel pro-duction1). In recent years, with the rapid rise in demand for nickel products and the diminution of high-grade nickel sul-�de ores, there has been increased research focus on pro-cessing nickel laterite ore to obtain nickel.

Laterite deposits can be divided into two primary layers based on their chemical and physical characteristics: limo-nite and garnierite. Limonite occurs in the upper layer and usually consists of goethite ((Fe,Ni)OOH), haematite (Fe2O3) or magnetite (Fe3O4). In all of these, the nickel is in a solid solution with the iron oxides, with its content averag-ing 0.8–1.5%2). The deeper garnierite layer is rich in magne-sium silicates, and here, nickel is found in the form of hy-drated magnesium-nickel silicate [(Mg,Fe,Ni)3Si2O5(OH)4], which has a lower nickel content and higher silica and mag-nesia contents3). Due to the poor crystallinity and �ne grain-size of nickel laterites, they are not amenable to processing by physical methods. To solve this problem, pyrometallurgi-cal, hydrometallurgical, hydro-pyrometallurgical and other emerging production methods have been applied to extract nickel from laterite ores. The traditional pyrometallurgical and hydrometallurgical extraction technologies mainly in-clude the rotary kiln-electric furnace (RKEF) process, re-duction roasting-ammonia leaching (Caron process), atmo-spheric leaching (AL) and high-pressure acid leaching (HPAL)4–7). Pyrometallurgical production is suitable for treating garnierite ore with a low iron content and high garn-

ierite content, while hydrometallurgical production is appli-cable for processing limonite ore, which has a high iron con-tent and low garnierite content. However, these traditional treatment processes also have some disadvantages, such as high energy consumption, huge capital cost overruns and a high residual acid concentration8–10). Typically, the hydro- pyrometallurgical process of reduction roasting-magnetic separation has been proposed as an easy, low-energy-con-sumption and environmentally friendly process, especially when it is used to treat low-grade nickel (<1%) laterite ore11).

Recently, many researchers have focused on the reduction roasting of laterite ore with different reductants, such as car-bon, hydrogen, carbon monoxide and even gas mixtures, fol-lowed by magnetic separation. However, the nickel content in the concentrate obtained with all of these methods is low-er than 4%12–15). To further improve the recovery and grade of nickel, additives such as chlorides, sulfates and calcium oxide are used to enhance the enrichment ratio of Ni16–18). In particular, chlorides such as NaCl and MgCl2 are ef�cient additives in terms of both the grade and recovery of Ni. In a study by Liu et al.19), the addition of magnesium chloride in-creased the nickel grade from 0.87% to 5.25%, and the re-covery of nickel reached 91.5%. Zhou et al.20) studied the chloridization and reduction of nickel laterite in the presence of sodium chloride, followed by magnetic separation to en-rich the ferronickel concentrate. The results indicated that sodium chloride has a signi�cant effect on the growth of fer-ronickel particles. A Ni grade of 7.09% and a corresponding recovery of up to 98.31% were obtained by reduction roast-ing at 1200°C for 20 min in the presence of 10% sodium chloride. However, a previous study suggested that the hy-drolysis temperature of calcium chloride was lower than that * Corresponding author, E-mail: weiygcp@aliyun.com

Materials Transactions, Vol. 58, No. 8 (2017) pp. 1161 to 1168 ©2017 The Japan Institute of Metals and Materials

of sodium chloride21). The hydrolysis of NaCl and CaCl2 and the standard Gibbs free energies of the reactions are: 2NaCl(s) +  SiO2(s) +  H2O(g) =  Na2SiO3(s) +  2HCl(g) ΔGθ =  216.328  −  0.09T kJ/mol; CaCl2(s)  +  SiO2(s)  +  H2O(g)  =  CaSiO3(s) +  2HCl(g) ΔGθ =  114.454 −  0.098T kJ/mol. The standard Gibbs free energies above indicate that the hydroly-sis of NaCl cannot occur at temperature below 2130°C, and the hydrolysis of CaCl2 is likely to occur when the tempera-ture is over 984°C. Meanwhile, due to a lower vapor pres-sure of calcium chloride compared to sodium chloride, the less calcium chloride is volatilized at high temperature, and thus calcium chloride appears to be a more effective chlorid-izing agent than NaCl to release HCl gas22). Therefore, in this study, coal-based reduction of low-nickel garnierite ore was conducted with the addition of CaCl2·2H2O followed by magnetic separation. The effects of the reduction tempera-ture, reduction duration, and dosages of reductant and CaCl2·2H2O on the reduction roasting process were deter-mined. The phase transformation corresponding to various CaCl2·2H2O dosages and reduction temperatures, and the ef-fects of the reduction temperature and CaCl2·2H2O on the aggregation and growth of ferronickel particles were investi-gated.

2.　 Experimental

2.1　 MaterialsThe low-grade nickel laterite ore used in this study was

collected from Yunnan Province, China. The chemical com-position of the nickel laterite ore was determined by chemi-cal analysis, as shown in Table 1. The distribution of nickel in the laterite ore was obtained using the chemical phase analysis method, as shown in Table 2. It was found that 84.2% of nickel is associated with silicates. This agrees well with the X-ray diffraction pattern shown in Fig. 1, which demonstrates that the predominant minerals are quartz [SiO2], lizardite [Mg3Si2O5(OH)4] and maghemite [γ-Fe2O3]. The industrial analysis of the reductant, anthra-cite, is given in Table 3. The ore and anthracite were ground using an XZM-100 laboratory vibratory mill to 98% passing 74 μm. The CaCl2·2H2O used in the study was of chemical grade.

2.2　 Experimental procedures2.2.1　 Sample preparation

Laterite ores were dried and then crushed to 100% pass-ing 0.25 mm, and particles larger than 0.25 mm were ground

to the required size using a vibration grinding machine.2.2.2　 Reduction roasting and magnetic separation

Twenty grams of the crushed laterite sample was thor-oughly mixed with the CaCl2·2H2O (the amount of CaCl2·2H2O added varied from 4 mass% to 20 mass%) and the reductant (the amount of anthracite varied from 4 mass% to 12 mass%) using a laboratory rotary mixing drum. The mixed ore was then placed into a corundum crucible (10 cm in length, 30 cm in width and 20 cm in height), which was placed in the constant-temperature zone of the tube furnace. The crucible was heated to the required temperature at a constant rate of 10°C/min and was allowed to react for a constant time. When the roasting test was completed, the sample was slid into the cool zone of the furnace using a ni-trogen atmosphere to avoid oxidation of the sample. Subse-quently, it was removed and ground with a small amount of water for a certain time by the above-mentioned vibratory mill to 98% below 70 μm and separated by a Laboratory Da-vis tube magnetic separator (Model: DTCXG-ZN50) at a magnetic �eld intensity of 250 mT. The magnetic product obtained is here referred to as the ferronickel concentrate.

The concentrate was dried for chemical analysis. The total contents of Fe and Ni in each concentration were determined through chemical analysis. The recoveries of nickel and iron were calculated using the following equation:

RNi (Fe) =mconcentration × t1

mraw ore × t2%; RNi (Fe) is the nickel (iron)

recovery rate, t1 is the content of elemental nickel (iron) in the concentrate, and t2 is the content of elemental nickel (iron) in the raw ore.

2.3　 XRD and SEM-EDS analysesThe phase transformation was identi�ed by X-ray diffrac-

tion (Rigaku XRD) (XRD) using a Cu-Kα radiation source (35 kV, 20 mA) to obtain data at a scanning rate of 8 (°)/min over the angular range of 10° to 90°. A HITACHI-S3400N scanning electron microscope (SEM) with a BSE resolution of 4.0 nm (30 kV) and an energy dispersive spectrometer

Table 1　Chemical analysis of the laterite ore sample.

Component Fetotal Ni Co MgO SiO2 Al2O3 CaO S Mn

Content mass% 9.67 0.82 0.033 31.49 37.37 1.89 0.033 0.01 0.083

Table 2　The distribution of nickel in garnierite.

Phase Sulfate Oxide Sul�de Silicate Total

Mass fraction of Ni/% 0.01 0.09 0.03 0.69 0.82

Distribution of Ni/% 1.20 11.0 3.60 84.20 100

Fig. 1　XRD patterns of garnierite ore.

Table 3　Industrial analysis of the reductant.

Properties Fixed carbon Volatile matter Ash Moisture

Content (mass%) 76.43 7.78 15.29 1.02

1162 J. Dong, et al.

(EDS) with EDAX were used to detect the microstructure of the roasted ore.

3.　 Results and Discussion

3.1　 Selective reduction and magnetic separation of lat-erite ore

3.1.1　 Effect of reduction temperature on nickel grade and recovery

The results for reduction roasting-magnetic separation of laterite ores at various temperatures for 40 min in the pres-ence of 12 mass% CaCl2·2H2O and 8 mass% anthracite are shown in Fig. 2. As seen from Fig. 2, when the reduction temperature was increased from 1100 to 1150°C, the nickel grade decreased from 22.08% to 11.83% and the recovery of nickel increased from 83.47% to 97.38% and reached the maximum at 1150°C. When reduction roasting is conducted at a relatively low temperature (1100°C), it limits the hydro-lysis of calcium chloride to generate hydrogen chloride. The limited amount of hydrogen chloride further leads to sup-pressed production and reduction of metal chlorides. More-over, the reduction of NiO is occurs prior to that of ma-ghemite at low temperatures, therefore, a small amount of maghemite is reduced to the metallic state, which results in a low recovery and high grade of nickel23,24). A further in-crease in the reducing temperature to 1300°C contributes to a decrease of the nickel content to 4.01% and a slight drop in the nickel recovery. There is an obvious increase in the re-covery of iron throughout the reduction roasting process, reaching 82.59% at 1300°C. The �rst reduced metallic phase of Ni acts as a catalyst and promotes the rate of reduction of maghemite, which increases the iron recovery25). With the signi�cant improvement in iron recovery, the nickel content in the concentrate is decreased from 11.83% to 4.01%. Based on these results, the optimal reduction temperature is determined to be 1150°C.

In the XRD patterns of the roasted ores reduced at differ-ent temperatures (Fig. 3), the appearance and stability of dif-fraction peak intensity of CaSiO3 indicates that the hydroly-sis of CaCl2 to generate CaSiO3 and HCl is occurred. When the reduction temperature is increased from 1100°C to 1150°C, the kamacite diffraction peak intensity increases and reaches maximum at 1150°C, this phenomena can be at-

tributed to the increasing reduction temperature, promoting the hydrolysis of CaCl2 and that further accelerating the chloridization of NiO and maghemite, which indirect in-creased the kamacite diffraction peak intensity. Thereafter, the diffraction peak intensity of kamacite decreases slightly with the reduction temperature increased to 1300°C. Accord-ing to the analyses above, the optimal reduction temperature is 1150°C, which is consistent with the former analysis re-sults.3.1.2　 Effect of reduction duration on nickel grade and

recoveryA series of reduction tests were performed for various du-

rations to determine the effect of the reduction time on the nickel concentrate. The results are shown in Fig. 4. As the duration is increased up to 40 min, the grade and recovery of nickel increase steadily and reach maximum values of 11.83% and 97.38%, respectively. If the reduction time is prolonged further to 80 min, the change in the recovery range is smaller than 3%, and the nickel grade decreases gradually from 11.83% to 6.58%. These results indicate that 40 min is the time required for the NiO to be chloridized and reduced. The formation and reduction of nickel chloride and the standard Gibbs free energies of the reactions can be ex-pressed as:

NiO(s) + 2HCI(g) = NiCl2(s) + H2O(g)

∆Gθ = −113.400 + 0.111T kJ/mol (1)

Fig. 2　The effect of the reduction temperature on reduction roasting of garnierite ore (12 mass% CaCl2·2H2O, 8 mass% anthracite, reduction for 40 min).

Fig. 3　X-ray diffraction patterns of the roasted ores reduced at different temperatures for 40 min with 12 mass% CaCl2·2H2O.

Fig. 4　Effect of reduction duration on reduction roasting of garnierite ore. (12 mass% CaCl2·2H2O, 8 mass% anthracite, reduction at 1150°C).

1163In�uence of Calcium Chloride Addition on Coal-Based Reduction Roasting of Low-Nickel Garnierite Ore

C(s) + H2O(g) = CO(g) + H2(g)

∆Gθ = 134.542 − 0.142T kJ/mol (2)

NiCl2(s) + H2(g) = Ni(s) + 2HCl(g)

∆Gθ = 107.285 − 0.149T kJ/mol (3)

NiCl2(s) + C(s) + H2O(g) = CO(g) + Ni(s) + 2HCl(g)

∆Gθ = 241.826 − 0.291T kJ/mol (4)

When the temperature is below 748°C, ΔGθ(2) <  0, which

means nickel chloride can form at temperature below 748°C, and the formed NiCl2 can be reduced by reaction (2)–(4) at temperature above 560°C. The slight decrease of nickel re-covery can be attributed to the rate of chloridization, which dependents on the countercurrent diffusion velocity of HC1 to the surface of NiO and partial pressure of HCl. After sev-eral minutes of reaction, the lower pressure of hydrochloride results in decreased HCl diffusion through the reactant. This is not conducive to the chloridizing process26). As the dura-tion is increased further, the reducing atmosphere is weak-ened, and a part of nickel is lost due to the volatilization of unreduced nickel chloride20,22). When the reduction time is more than 40 min, the chloridization of iron continues to in-crease as the reducing time is prolonged due to the higher iron content in ores. Finally, a magnetic concentrate with a higher iron recovery and a lower nickel grade is obtained27). Based on the energy savings and nickel recovery, a reduction time of 40 min is recommended for obtaining the optimal nickel content of 11.83% and nickel recovery of 97.38% in the �nal concentrate.3.1.3　 Effect of reductant dosage on nickel grade and re-

coveryFigure 5 presents the magnetic separation results of the

reduction of laterite at 1150°C as a function of the reductant dosage in the range of 6 mass%–14 mass%. When the re-ductant dosage is increased from 6 mass% to 8 mass%, the nickel content decreases from 17.24% to 11.83%, whereas the nickel recovery increases from 72.53% to 97.38%. This increase in nickel recovery indicates that 8 mass% reductant is suf�cient to produce the reducing gas, hydrogen, which reduces the NiO and NiCl2 to metallic nickel. A further in-crease in the reductant dosage to 12 mass% results in an ob-vious decrease in the nickel content and a decrease in the nickel recovery. This may be because the increased reducing

atmosphere results in decreased metallization of nickel, as the nickel re-oxidizes and goes into solution with the wustite phase28). To re-reduce the nickel, the reduction potential must be increased even further. Thus, when the anthracite dosage reaches 14 mass%, a more reducing atmosphere is obtained, again resulting in the increase of nickel recovery. Moreover, the nickel grade decreases with increasing reduc-tant dosage, accompanied by a signi�cant increase in the re-covery of iron from 16.48% to 68.79%. As the reductant dosage is increased, the higher reducing atmosphere causes the maghemite to be excessively reduced to Fe instead of FeO29). The increased iron recovery decreases the nickel grade in the concentrate from magnetic separation. Consid-ering these factors, 8 mass% anthracite is chosen as the opti-mal reductant dosage.3.1.4　 Effect of CaCl2·2H2O dosage on nickel grade and

recoveryThe effect of the CaCl2·2H2O dosage on the nickel grade

and recovery was studied by reduction roasting-magnetic separation experiments at CaCl2·2H2O dosages in the range of 4 mass%–20 mass%. The experiments were conducted in the presence of 8 mass% anthracite at a temperature of 1150°C and a magnetic �eld intensity of 250 mT for 40 min. The results in Fig. 6 show that the CaCl2·2H2O dosage ex-erts an obvious in�uence on the grade and recovery of nick-el. As the CaCl2·2H2O dosage is increased from 4 mass% to 12 mass%, the nickel grade increases from 7.07% to 11.83%, and the recovery also increases from 80.62% to 97.38%. These increases could be explained by the fact that the increased CaCl2·2H2O dosage produces more HCl, to chlorinate NiO in ores. As the CaCl2·2H2O dosage is further increased from 12 mass% to 20 mass%, the Ni recovery de-creases rapidly while the Ni grade increases gradually. This phenomenon is attributed to the metal chlorides can dissolve in water and lose later in wet magnetic separation30); more-over, some of the metal chlorides are lost by evaporation at a high temperature20). Considering the recovery and grade of nickel, an CaCl2·2H2O dosage of 12 mass% is deemed opti-mal.

The XRD patterns of laterite ores reduced at 1150°C for 40 min with various CaCl2·2H2O contents is shown in Fig. 7, in which the diffraction peak intensities of kamacite in Fig. 7(c) is stronger than that in Fig. 7(a), Fig. 7(b),

Fig. 5　Effect of reductant dosage on reduction roasting of garnierite ore. (12 mass% CaCl2·2H2O, reduction at 1150°C for 40 min).

Fig. 6　Effect of CaCl2·2H2O dosage on reduction roasting of garnierite ore. (8 mass% anthracite, reduction at 1150°C for 40 min).

1164 J. Dong, et al.

Fig. 7(d) and Fig. 7(e). This result demonstrates that when the CaCl2·2H2O increases to 12 mass%, the more calcium chloride is hydrolyzed to HCl, resulting in more NiCl2 formed and reduced to nickel subsequently; when CaCl2·2H2O is increased to 20 mass%, the decrease of ka-macite diffraction peak intensities due to apart of unreduced NiCl2 dissolve in water and lose later in wet magnetic sepa-ration30).

3.2　 SEM-EDS analysis of the roasted oresFigure 8 presents SEM images of the ores roasted at vari-

ous temperatures for 40 min in the presence of calcium chlo-ride. Figure 9 shows the SEM-EDS analysis of the laterite ore reduced at the optimal conditions. The EDS results demonstrate that the bright white and charcoal grey sub-stances in Fig. 9 are kamacite and forsterite, respectively. As seen from the SEM images (Fig. 8 (a)), small and scattered ferronickel grains with particle sizes <5 μm are embedded in the forsterite phase. As a result, the alloy particles cannot be

Fig. 7　XRD patterns of laterite ores reduced at 1150°C for 40 min with various CaCl2·2H2O contents.

Fig. 8　SEM images of laterite ore reduced at different temperature for 40 min in the presence of 12 mass% calcium chloride. (a) 1100°C, (b) 1150°C, (c) 1200°C, (d) 1250°C, (e) 1300°C.

1165In�uence of Calcium Chloride Addition on Coal-Based Reduction Roasting of Low-Nickel Garnierite Ore

recovered by magnetic separation, thus yielding a low nickel recovery. This may be because the nickel is embedded in a silicate matrix and is dif�cult to reduce at this temperature. Additionally, the CaCl2·2H2O is insuf�ciently hydrolyzed at this temperature, leading to inadequate chloridization of NiO16). When the reduction temperature is increased to 1150°C, the morphology of Fe-Ni grains changes such that the small particles become concentrated at the boundary of forsterite and are aggregated into long strip-grains. As the temperature is increased further to 1300°C, the SEM images (Fig. 8(c), Fig. 8(d) and Fig. 8(e)) clearly demonstrate the trend of migration and aggregation of metallic grains, fol-lowed by precipitation of the long strip grains on larger par-ticles; the average size of ferronickel particles is approxi-mately 10 μm. One of the reasons for this is that HCl initial-ly reacts with the NiO and maghemite to form a thin layer of metal chlorides. Then, the chlorides evaporate and precipi-tate on the carbon particles of the coal surface, are reduced to metal and, �nally, aggregate27,31). Another reason is that the high temperature facilitates mass transfer, especially that of iron and nickel ions, leading to the increase in the size of ferronickel particles32). However, the experimental results show that the nickel grade does not increase with the size of alloy particles. Under the same magnetic �eld (250 mT), larger ferronickel particles are more likely to be separated from the gangue by downstream magnetic separation. As a result, the ef�ciency of recovery of the magnetic concentrate is increased directly, leading to the indirect drop of the nick-el grade.

Figure 10(a) and Fig. 10(b) present SEM images of later-ite ore reduced under the optimal conditions (Table 4), in the

absence and presence of 12 mass% calcium chloride, respec-tively. The mineral phase mostly consists of forsterite, and a few kamacite grains of small size are observed scattered and embedded in the forsterite, as shown in Fig. 10(a). Nickel and iron are not reduced effectively and cannot be enriched by magnetic separation, which results in poor recovery of nickel, as shown in Table 5. This result contradicts that of the reduced ore with added CaCl2·2H2O, wherein the num-ber of kamacite particles increased several times and showed a trend towards aggregation and growth. This comparison suggests that calcium chloride greatly promotes the forma-tion of ferronickel grains and the recovery of nickel. When the calcium chloride is added to the reduction roasting, NiO can be chlorinated by HCl to produce NiCl2, and nickel chloride is vaporized and reduced on the carbon surface. Owing to the vaporization of the nickel chloride and the sub-sequent appearance of a new reactive surface, NiO can be reduced easily in the presence of the CaCl2·2H2O, and that improves the nickel recovery and ferronickel aggregation.

4.　 Conclusions

(1) The in�uence of coal-based reduction roasting and mag-netic separation of low-nickel garnierite ore was investi-gated in the presence of calcium chloride. The results in-dicate that a nickel concentrate with a nickel content of 11.83% and a nickel recovery of 97.38% can be ob-tained when the low-nickel garnierite ore is reduced at 1150°C for 40 min in the presence of 12 mass% calcium chloride.

(2) The addition of calcium chloride has a signi�cant pro-

Fig. 9　SEM-EDS analysis of laterite ore reduced at 1150°C for 40 min with 12 mass% calcium chloride. (a) Backscattered electron image and (b) EDS spectrum of spot 1 in image (a), (c) EDS spectrum of spot 2 in image (a).

1166 J. Dong, et al.

motive effect on nickel recovery. The enrichment ratio is increased from 3 to 14 in the presence of CaCl2·2H2O. Within a certain range, an increased calcium chloride dosage improves the nickel recovery by increasing the production of hydrogen chloride, which further chlorid-izes the NiO and increases the nickel grade. NiO is more readily reduced in the presence of calcium chloride due to the vaporization of the nickel chloride formed and the emergence of a new reactive surface.

(3) In the reduced ore, nickel is mainly concentrated in the kamacite phase, the aggregation and growth of this phase improves in the presence of calcium chloride ow-ing to vaporization of nickel chloride and precipitation, together with ferrous chloride, on carbon particles.

Acknowledgements

Financial support for this study was provided by the Na-tional Natural Science Foundation of China (Project Nos. U1302274 and 51304091), the Candidate Talents Training Fund of Yunnan Province (2012HB009), and the Scienti�c and Technological Leading Talent Projects in Yunnan Prov-ince (No. 2015HA019).

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Fig. 10　SEM analysis of laterite ore reduced at 1150°C for 40 min in the absence and presence of 12 mass% calcium chloride. (a) in the absence of calci-um chloride, (b) in the presence of calcium chloride.

Table 4　The optimal condition of reduction roasting of low-nickel garnierite.

Fixed parametersOptimal parameters

Reduction temperature(°C)

Reduction duration(min)

Reductant dosage(mass%)

Calcium chloride dosage(mass%)

Magnetic �eld intensity250 mT

1150 40 8 12

Table 5　Contrast test results on the enrichment of metal values.

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Ni enrichment ratio

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1167In�uence of Calcium Chloride Addition on Coal-Based Reduction Roasting of Low-Nickel Garnierite Ore

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