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Direct extraction of nickel and iron from laterite ores using the carbonyl process
Minerals Engineering xxx (2013) xxx–xxx
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Direct extraction of nickel and iron from laterite ores using the carbonyl process Dmitri S. Terekhov ⇑, Nanthakumar Victor Emmanuel CVMRÒ Corporation, 35 Kenhar Dr., Toronto, Ontario M9L 1M9, Canada
a r t i c l e
i n f o
Article history: Available online xxxx Keywords: Metal carbonyls Carbonylation Laterite ore Reduction Magnetic separation Nickel
a b s t r a c t The carbonyl method of refining nickel and iron was invented more than 100 years ago and has been used for refining of nickel commercially. CVMRÒ developed the process of direct extraction of nickel and iron from laterite ores as metal carbonyls which in turn produced pure nickel and iron metals. CVMRÒ’s carbonyl technology has been applied to several types of limonite and saprolite ores containing other metals such as copper, cobalt and PGE. The process consists of reducing the ore with hydrogen, extracting of iron and nickel in the form of volatile metal carbonyls, separating the metal carbonyls and producing high purity nickel and iron metals; and production of copper, cobalt and PGE concentrate by gravity or magnetic separation. Economic evaluation of this process shows significant increase in cash flow. The CVMRÒ process does not produce liquid waste and does not require tailing dumps. This makes CVMRÒ’s process attractive for projects in areas that are environmentally sensitive, or have a high level of rainfall. Ó 2013 Published by Elsevier Ltd.
1. Introduction Over the past 30 years laterite ores have become increasingly more important as a source of nickel metal (Dalvi et al., 2004). Several methods of nickel extraction from laterite ores have been piloted and some were put into full operation, including acid leach with sulphuric, nitric and hydrochloric acids, ammonia leach and the pyrometallurgical process (Superiadi, 2007). Meanwhile, the production of nickel pig iron in China and India has been supplementing some of the refined nickel in stainless steel production, in the past 15 years (Widmer, 2009). Some of the methods stated above have processing cost advantages over others due to the credits generated from cobalt, copper and other metals. These credits can, at times, create significant cash flow for a refining operation and could make a difference in the financial viability of a project. Nickel refining by the Mond (carbonyl) process was commercially applied more than 100 years ago. The first operation was commissioned in 1902 in Clydach, Wales, UK. In 1973 INCO commissioned its Canadian nickel carbonyl refinery in Sudbury, Ontario, Canada. Traditionally the carbonyl process was used only by one company (INCO now taken over by Vale). However, in 1983 Norilsk Nickel built a relatively small operation in ⇑ Corresponding author. Tel.: +1 416 7432746; fax: +1 416 7434193. E-mail address: [email protected] (D.S. Terekhov). URL: http://www.cvmr.ca (D.S. Terekhov).
Monchegorsk, Russia, to produce nickel powders. In 2007 CVMR Corporation built and commissioned its Carbonyl refining plant in Jilin China (China). The Jinchuan Group Co., Ltd., in China attempted to implement a carbonyl technology in 2006 which failed and its pilot plant was shut down several years later. Because of Vale’s (INCO’s) 100 years monopoly of the carbonyl method of nickel refining, seldom any process details were published or discussed in public. Nevertheless, despite all these measures, today, between 20% and 25% of nickel is refined by the Mond process (Crundwell et al., 2011). In July 1970 INCO proposed to a French consortium to use the carbonyl method (as one of 3 technologies) for refining of nickel in the Gorolaterite project in New Caledonia (with capacity to produce 45,000 ton/year nickel metal). So called ‘‘Carbonyl Refining Method for Laterite Ore’’ was developed by INCO up to the full scale pilot stage and included partial reduction of nickel and iron by CO/CO2 gas mixture and direct extraction of nickel from ore in the form of nickel carbonyl. The product of the refining was forecasted as ferronickel with Fe/Ni ratio of 1.4/1. The method was rejected by the French consortium, not for technical reasons (Dunbar and Wing, 1970). To date it has not been clarified by INCO or the French consortium why the proposal was rejected if it was technically acceptable. Subsequently, since that time, no significant progress was made in the development of a method for direct extraction of nickel from laterite ores. However, in 2006 CVMR started a thorough review of the process and its application for direct extraction of nickel from laterite ores.
0892-6875/$ - see front matter Ó 2013 Published by Elsevier Ltd. http://dx.doi.org/10.1016/j.mineng.2013.07.008
Please cite this article in press as: Terekhov, D.S., Emmanuel, N.V. Direct extraction of nickel and iron from laterite ores using the carbonyl process. Miner. Eng. (2013), http://dx.doi.org/10.1016/j.mineng.2013.07.008
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D.S. Terekhov, N.V. Emmanuel / Minerals Engineering xxx (2013) xxx–xxx
Table 1 AAS analysis of ore samples. Sample ID
Al (%)
Co (%)
Cu (%)
Fe (%)
Mg (%)
Mn (%)
Ni (%)
Limonite Limonite Limonite Saprolite
2.89 2.51
0.10 0.14 0.38 0.03
0.30 0.40
35.70 44.30 42.00 14.90
0.50 0.48
0.73 0.81 2.11 0.14
0.68 1.10 0.62 1.83
#1 #2 #3 #1
1.80
0.21
2. Experimental Limonite and saprolite ores from central Africa were analyzed by flame atomic absorption spectrometry (AAS) and X-ray fluorescence (XRF, NitonXLt). AAS analyses of ores are presented in Table 1. Process gases: argon (99.95%), carbon monoxide (99.5%), hydrogen (99.995%) were purchased from Praxair. Reduction and metal extraction from the ores were carried out in a high pressure TGA unit (Thermomax 500 supplied by Thermofisher) capable of testing 100 g of ore. The formed metal carbonyls were not collected. Mass balances of the experiments were calculated based on weight loss and AAS analysis of starting material and residue.
6.86
Si (%) 3.14 5.20 16.80
A sample of ore was placed in a quartz bucket suspended inside the TGA. TGA was closed and pressure tested. The instrument was purged with argon and the sample was heated to 650 °C at rate of 5 °C per minute. Hydrogen was introduced at 350 °C. After completion of reduction, the sample was cooled down to 180 °C and hydrogen was replaced with carbon monoxide. TGA was pressurized with carbon monoxide to 60 bar and formed carbonyls were removed by flow of reagent gas. The progress of extraction was monitored by weight lost of the sample. After completion of extraction TGA was depressurized, purged with argon and sample was cooled down to room temperature. The residual sample was analyzed by AAS. A medium scale pilot unit (5 kg scale) was used for reduction and metal extraction experiments. The schematic diagram of the
Fig. 1. Schematics of the pilot unit.
Table 2 Degree of reduction of metals with CO/CO2 gas mixture at 650 °C. Materials
Limonite
Temp (°C)
650 650 650 650 650
CO2:CO
1:1 1.5:1 2:1 5:1 H2
Alloy composition, %Ni:%Fe
24:76 56:44 70:30 91:9 2:98
Degree of reduction Ni (%)
Fe (%)
98.0 93.6 89.5 67.0 100.0
3.0 15.0 23.0 36.0 100.0
Please cite this article in press as: Terekhov, D.S., Emmanuel, N.V. Direct extraction of nickel and iron from laterite ores using the carbonyl process. Miner. Eng. (2013), http://dx.doi.org/10.1016/j.mineng.2013.07.008
D.S. Terekhov, N.V. Emmanuel / Minerals Engineering xxx (2013) xxx–xxx
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reduction was monitored by collecting released water. After the reduction was completed, the reactor was cooled down to 180 °C and connected to the extraction system. Pilot unit was pressure tested with argon and pressurized to 60 bar with carbon monoxide. Carbon monoxide was passed through reactor and exhausting gas mixture of formed metal carbonyls and carbon monoxide was cooled down to 10 °C to liquefy metal carbonyls. The metal carbonyls mixture was collected in carbonyl storage tanks, carbonyls were separated by distillation and decomposed to produce metal powders. During the extraction, carbon monoxide was added to the system to keep pressure at 60 bar. Progress of extraction was monitored by reactor and liquid carbonyl storage tanks weight cells. After reaction was completed, system was depressurized; reactor was isolated from the rest of the system, purged with argon and opened. Starting material, residue and products were analyzed by AAS.
3. General process description Fig. 2. Reduction of limonite ore using CO/CO2 mixture and H2.
pilot unit is presented in Fig. 1. The sample of ore was placed inside of the metal reactor and purged with argon. The reactor was heated up to 650 °C at rate of 5 °C per minute. At temperature of 350 °C argon was replaced with hydrogen. Preheated reagent gas was continuously introduced into reactor at 5 L per minute. Progress of
3.1. Drying of ore, calcining and reduction There are two major steps in refining of laterite ores by the carbonyl method: the first step consists of drying, calcining and reduction of the ore being used and the second consists of extracting the metals in the ore in the form of volatile carbonyls. Hydrogen, carbon monoxide and coal could be used for laterite ore reduction. The process is well investigated and widely used for
Fig. 3. Process flow diagram for limonite ore (samples #2).
Please cite this article in press as: Terekhov, D.S., Emmanuel, N.V. Direct extraction of nickel and iron from laterite ores using the carbonyl process. Miner. Eng. (2013), http://dx.doi.org/10.1016/j.mineng.2013.07.008
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Fig. 4. Process flow diagram for saprolite ore.
Table 3 TGA test, samples #1. Ni
Feed Residue Yield
Fe
Cu
g
g
%
g
%
g
%
60.0 14.2
0.402 0.03
0.67 0.23 92
28.1 2.3
46.9 16.4 92
0.2 0.2
0.37 1.27
production of DRI, pig iron and nickel pig iron (Sarangi and Sarangi, 2011). The initial approach in the 1970s was to minimize the reduction of Iron, and to use appropriate conditions for preferential nickel reduction (Curlook, 1972). Usage of CO/CO2 gas mixture (1:1.5) for reduction of Limonite ore can achieve selectivity in metallization
at temperatures close to 650 °C. CO2 was used for oxidation of Iron metal to minimize Iron reduction. At these conditions, close to 92% of nickel and only 4% of Iron can be reduced (Eqs. (1) and (2)). As a result, after extraction and carbonyl decomposition Ni/Fe alloy material is produced at the approximate ration of 1/1. Theoretical calculations for these reactions are presented in Table 2. In practice, the composition of extracted alloy is Ni/Fe 1/1.2.
NiO þ CO ¼ Ni þ CO2
ð1Þ
Fe2 O3 þ 3CO ¼ 2Fe þ 3CO2
ð2Þ
Using hydrogen at the same temperature will reduce nickel, almost completely, and approximately 95% of iron (Eqs. (3) and (4)). High concentration of water in H2 (H2/H2O ratio of 4/6) can be used for selective nickel reduction as well, but it has never been used commercially.
Table 4 Primary carbonylation pilot unit test results. Nickel
Iron
g Feed (g) Residue 1 (g)
5000 1490
Yield (%)
%
55.00 2.01 52.99
1.10 0.14
Nickel
96.3
Cobalt
Copper
g
%
g
%
g
%
2215 478.29 1736.71
44.3 32.1
6.75 6.54 0.21
0.14 0.44
20.00 19.97 0.03
0.40 1.34
Iron
78.4
Cobalt
3.09
Copper
0.17
Table 5 Magnetic separation test. Yield (%)
Nickel
Magnetic separation Efficiency
59.8%
Iron
76.7%
Cobalt
77.68%
Copper
72.84%
65
Please cite this article in press as: Terekhov, D.S., Emmanuel, N.V. Direct extraction of nickel and iron from laterite ores using the carbonyl process. Miner. Eng. (2013), http://dx.doi.org/10.1016/j.mineng.2013.07.008
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D.S. Terekhov, N.V. Emmanuel / Minerals Engineering xxx (2013) xxx–xxx Table 6 Secondary carbonylation. Nickel
Iron
g Mass balance Feed (Magnetic, g) Residue 2 (g) Extracted (g)
6.05 3.23
%
0.01 0.00 0.00
Yield (%)
0.13 0.14
Nickel
44.6
%
g
%
g
%
2.58 0.61 1.98
42.7 18.8
0.03 0.03 0.00
0.41 0.87
0.06 0.06 0.00
0.98 1.82
Iron
76.5
Typical time for reduction with CO/CO2 mixture is 20–30 min. Reduction with hydrogen is 60–90 min. Representative kinetics of limonite ore reduction are presented in Fig. 2.Increase in reduction temperature creates problems in the next step of the process as it creates particles with low surface area. Such particles are not suitable for the carbonyl process. For example, reduction of limonite, in our sample, at 750 °C reduced yield to 30% only. For this reason we, at CVMR, did not consider reduction of ore by coal.
0.63 ppm 1.13 ppm BDL 0.17 ppm 3.64 ppm 4.19 ppm 0.72 ppm 1.25 ppm
3.2. Metal extraction Metal extraction phase of the process consists of formation of volatile nickel and iron carbonyls at an elevated pressure and temperature (60 bar, 180 °C) (Eqs. (5) and (6)). Kinetics of extraction depend on physical form of reduced feed material, iron concentration and pressure. For example, when a partially reduced ore is used as feed material, the extraction time is between 4 h and 6 h. Extraction of Ni and Fe from completely reduced limonite will take between 24 h and 48 h.
6.35 ppm 4.84 ppm 0.98 ppm 1.07 ppm 15.4 ppm 10.3 ppm 2.22 ppm 1.82 ppm
NiO þ H2 ¼ Ni þ H2 O Fe2 O3 þ 3H2 ¼ 2Fe þ 3H2 O
Copper
g
Table 7 Concentrations of PGE, samples #2. Head sample Platinum Palladium Rhodium Gold Primary carbonylation residue Platinum Palladium Rhodium Gold Magnetic fraction Platinum Palladium Rhodium Gold Secondary carbonylation residue Platinum Palladium Rhodium Gold
Cobalt
Ni þ 4CO ¼ NiðCOÞ4
ð5Þ
Fe þ 5CO ¼ FeðCOÞ5
ð6Þ
Under these conditions (60 bar, 180 °C) both carbonyls are gaseous. In a TGA, at CVMR we passed CO over the feed material. The carbonyls thus formed were removed from the reaction chamber
ð3Þ ð4Þ
Table 8 Mass balance samples #3. Ni Total weight (g) Feed Residue
4.07 1.44
Fe
% 0.62 0.02
Yield
Co
Cr
Mn
g
%
g
%
g
%
g
%
g
0.03 0.00
42.00 16.06
1.71 0.23
0.38 1.22
0.02 0.02
2.24 8.68
0.09 0.12
2.11 7.39
0.09 0.11
98.9
86.5
Table 9 Extraction from saprolite sample. Nickel g Feed (g) Residue 1 (g)
4800 2860
Iron %
87.84 3.86
Yield (%)
1.83 0.14
Cobalt
Copper
g
%
g
%
g
%
715.20 213.93
14.9 7.5
1.56 0.73
0.03 0.03
10.27 10.27
0.21 0.36
95.6
70.1
Table 10 Composition of different grades of iron. Name
Fe%
C%
Si%
Mn%
P%
S%
Metallization (%)
Pig iron DRI Steel billets GB Q235 CVMR Fe product High purity Iron
95 92 99 99.9 99.9
3.5–4.5 2.5 0.14–0.22 0.1–0.2 0.003–0.015
0.3–3.0 4.5–5.0 0.12–0.30 <10 ppm 0.010
0.05–1.0
0.05–0.15 0.07 0.045 max <10 ppm 50–80 ppm
0.02–0.05 0.005 0.05 max 0.001 max 20–80 ppm
93 100 100 100
0.30–0.65 <10 ppm 0.030–0.100
Please cite this article in press as: Terekhov, D.S., Emmanuel, N.V. Direct extraction of nickel and iron from laterite ores using the carbonyl process. Miner. Eng. (2013), http://dx.doi.org/10.1016/j.mineng.2013.07.008
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D.S. Terekhov, N.V. Emmanuel / Minerals Engineering xxx (2013) xxx–xxx
into the thermal oxidizer.In our pilot unit, at CVMR, we passed carbon monoxide through a bubble bed reactor, and it reacted with metallic nickel and iron. The mixture of volatile carbonyls was then removed from the reactor by excess of CO. The gas mixture was passed through a heat exchanger and the carbonyls were condensed in storage tanks. CO was recycled back into the reactor. Carbonylation reaction was exothermic and it required heat to be removed from the carbonylation reactor. Iron and nickel carbonyls are separated by fractional distillation. Less volatile iron carbonyl (Tb.p.103 °C) is removed from the bottom of the distillation column, vaporized and directed into the decomposer to produce Iron powder. Gaseous nickel carbonyl (Tb.p. 43 °C) then exits from the top of the column and is used to produce nickel powder. Decomposition of metal carbonyls is carried out at temperatures between 175 and 240 °C. Decomposition reactions of nickel and iron carbonyls are presented in Eqs. (7) and (8).
NiðCOÞ4 ¼ Ni þ 4CO
ð7Þ
FeðCOÞ5 ¼ Fe þ 5CO
ð8Þ
Reduction with hydrogen at 650 °C (2 h) and extraction at 60 bar and 180 °C (48 h) resulted in 92% extraction of nickel and 92% extraction of iron. The mass balance is presented in Table 3. Sample #2 had higher concentration of Ni and Fe; and similar composition of Cu, Co and PGE. The initial tests were performed in a TGA. Pre-treatment, reduction and metal extraction resulted in 98.1% and 86.5% yield for Ni and Fe. The same treatment in the pilot unit yielded 96.3% and 78.4% extraction for Ni and Fe. The recovery rate for both metals was more than 99% (Table 4). The metallic residue was tested in Davis tube for magnetic separation of metals and oxides. Yields of metals after magnetic separation are presented in Table 5. Co and Cu recovery were quite high, but Ni recovery was moderate. This was due to low concentration of Ni in the concentrate. Secondary extraction of Fe and Ni afforded only 44.6% and 76.5% yields. Overall yields after primary metal extraction, magnetic separation and secondary metal extraction were 97.3% for Ni and 90.7% for Fe. The residue contained Co, Cu and PGE (platinum group of metals and Au). After Ni and Fe extraction, concentration of Cu increased from 0.2% to 1.8% (Table 6) and concentration of PGE rose from 2 ppm to 30 ppm (Table 7). The ore sample #3 contained 0.62% of Nickel, 42.0% of Fe, 0.38% of Co, 2.24% Cr and 2.11% Mn. Reduction and Fe/Ni extraction in the TGA resulted in a residue the contained 0.02% Ni and 16.06% Fe. These correspond to yields of 98.9% Ni and 86.5% Fe. Co and Mn were concentrated by this method in the residue to 1.22% Co and 7.39% Mn. Table 8 shows the mass balance calculations. Cobalt refining was not part the study, but metallic Co could easily be recovered using one of the leach processes or magnetic separation.
The residue after Ni and Fe extraction contains trace amounts of Ni, reduced Fe, Co, Cu, Platinum Group Elements (PGE) and mixture of oxides. Magnetic separation of the residue can recover close to 80% of Fe, Cu and Co, 60% of Ni. Gravity separation is considered in cases when an ore contains significant amounts of PGE. The concentrate is then redirected to a secondary carbonylation cycle to maximize recovery of Ni and to extract Cobalt. When high concentration of Cu is present, the residue can be treated with sulphur followed by flotation. A typical process flow diagram is presented in Figs. 3 and 4 for limonite and Saprolite ores (calculated for 1 million tons of ore per year). A cobalt recovery method was also developed at CVMR. In this process Cobalt forms solid cobalt carbonyl which could be converted to volatile cobalt nitrosyl carbonyl. The decomposition of cobalt nitrosyl carbonyl produces Co metal (Terekhov, 2002). Chemical reactions of the process are presented in Eqs. (9)–(11).
2Co þ 8CO ¼ Co2 ðCOÞ8
4.2. Extraction from saprolite ore The sample Saprolite ore used for this experiment was composed of elements presented in Table 1. This sample was poly metallic and contained significant amounts of Cu and high concentration of Mg. The tests were carried out in the TGA and in the CVMR pilot unit. The ore was pre-treated for silicates decomposition and reduced at 650 °C with hydrogen. Extraction of Ni and Fe was much faster, compared to limonite samples due to lower concentration of Fe. Extraction of Ni and Fe was completed in 18 h. Ni recovery was 95.6% and Fe extraction yield was 70.1% in the pilot unit. Additional work is planned to test magnetic separation of the residue and Cu recovery.
ð9Þ
Co2 ðCOÞ8 þ NO ¼ CoNoðCOÞ3 þ CO
ð10Þ
CoNoðCOÞ3 ¼ Co þ 3CO þ NO
ð11Þ
4. Results and discussion 4.1. Treatment of limonite ore
4.3. Financial considerations Composition of limonite ore is presented in Table 1. The polymetallic sample #1 had significant concentration of copper, cobalt and close to 2 g/ton of PGE (Pt, Pd and Au). Pre-treatment, reduction and metal extraction tests were performed in a TGA unit.
Addition of iron as a product of the refining process significantly increases cash flow of the operation. In addition to cash flow from produced iron, production of high purity metals further increase
Table 11 Comparison of chemical grade nickel and nickel produces by CVMR. Product
Carbon (%)
Sulphur (ppm)
Oxygen (%)
Nitrogen (ppm)
Iron (ppm)
Cobalt (ppm)
Other elements
Nickel
Chemical grade nickel CVMR’s nickel
<0.10 <0.10
<50 <50
<0.12 <0.12
<0.125 <0.125
<20 <20
<10 <10
<10 <10
Balance Balance
Table 12 Estimation of Ni and Fe product values. Sample ID
Ni (%)
Fe (%)
LME price per ton of Ni
LME price per ton of steel billets
Estimated yield Ni product (%)
Estimated yield Fe product (%)
Value per ton of ore Ni product
Value per ton of ore Fe product
Limonite Limonite Limonite Saprolite
0.68 1.10 0.62 1.83
35.70 44.30 42.00 14.90
$18,000.00 $18,000.00 $18,000.00 $18,000.00
$400.00 $400.00 $400.00 $400.00
92.00 97.30 98.90 95.60
92.00 90.70 86.50 70.10
$112.61 $192.65 $110.37 $314.91
$131.38 $160.72 $145.32 $41.78
#1 #2 #3 #1
Please cite this article in press as: Terekhov, D.S., Emmanuel, N.V. Direct extraction of nickel and iron from laterite ores using the carbonyl process. Miner. Eng. (2013), http://dx.doi.org/10.1016/j.mineng.2013.07.008
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cash flow. For example even if price of iron product was to be calculated as DRI or sponge iron, one could observe significant increases in the cash flow. Nevertheless, the purity of produced iron by the CVMR carbonyl process corresponds more to the high purity iron or LME steel billets (Table 10). High purity nickel from carbonyl process (Chemical grade nickel) is produced by Vale and sold above LME. A comparison of purity of chemical grade nickel and CVMR’s nickel produced directly from the ore is presented in Table 11. A simple calculation shows that iron product cash flow can be close or even equal to the cash flow from nickel metal sales. Based on today’s LME prices of Ni and steel billets, iron, produced from low grade laterite ore (samples #1 and #3), will have the same value as the nickel product. Addition of Co, Cu and PGE product lines will increase the cash flow 3 times. Table 12 represents a simple calculation for the value of Ni and Fe product lines per ton of ore. These calculations are not intended to be used for economic evaluation of a project, but to show the importance of iron product line for low grade polymetallic laterite ores.
H2 allows extraction of Fe together with Ni with rather high yields. Metal extraction parameters of 60 bar and 180 °C were used in all experiments. Optimization of reduction and extraction parameters was not included in this article. Magnetic separation of residue after extraction of Ni and Fe was presented as a single case. Secondary carbonylation of magnetic fraction increased PGE concentration from 2 ppm (ore) to 30 ppm (carbonylation residue after secondary carbonylation). Purity of Ni and Fe products were compared with chemical grade Ni, Steel billets and high purity iron and summarized in Tables 9 and 10. High purity of metal products could further increase cash flow of a project.
The authors gratefully acknowledge the assistance of several persons, all of whom are members or were members CVMR Corporation especially Professor Walter Curlook, Dr. OlujideB. Olurin, Dr Kamran M. Khozan and Mr. Colwyn van der Linder.
5. Conclusions
References
In this study, direct extraction of nickel and iron from laterite ores was investigated in a two step process using CVMR’s carbonyl technology. Iron turns out to be an important product of this process, increasing the cash flow and decreasing costs of disposal of the tailing. Application of the carbonyl process to low Ni grade laterite ores containing significant amount of Co, Cu and PGE makes recovery of these metals quite feasible. Considering experimental results given in Sections 4.1 and 4.2, an estimated value of Fe product was calculated close or equal to the value of Ni product and summarized in Table 11. Ore reduction with hydrogen gas (temperature of 650 °C) was compared with reduction by CO/CO2 gas mixture. Reduction by
Crundwell, F.K., Moats, M.S., Ramachandran, V., Robinson, T.G., Davenport, W.G., 2011. Extractive Metallurgy of Nickel, Cobalt and Platinum-Group Metals. Elsevier, The Netherlands, pp. 269–280. Curlook W., Bell J.A.E., 1972. Rotary kiln reduction of limonitic ores. US Patent 3,656,934. Dalvi, A.D., Bacon, W.G., Osborne, R.C., 2004. The past and future of nickel laterites. PDAC 2004 International Convention. Dunbar, M., Wing, D.J., 1970. New caledonia project outlined in inco’s report. INCO triangle, vol. 40, pp. 4. Sarangi, A., Sarangi, B., 2011. Sponge Iron Production in Rotary Kiln. PHI Learning Private Limited, India, pp. 37–62. Superiadi, A., 2007. Processing technology vs. nickel laterite ore characteristic. Pt Inco. Terekhov, D.S., 2002. Cobalt recovery process. US Patent 6,428,601. Widmer, M., 2009. Nickel pig iron in China. Presentation, Bank of America-Merrill Lynch.
Acknowledgements
Please cite this article in press as: Terekhov, D.S., Emmanuel, N.V. Direct extraction of nickel and iron from laterite ores using the carbonyl process. Miner. Eng. (2013), http://dx.doi.org/10.1016/j.mineng.2013.07.008
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Minerals Engineering journal homepage: www.elsevier.com/locate/mineng
Direct extraction of nickel and iron from laterite ores using the carbonyl process Dmitri S. Terekhov ⇑, Nanthakumar Victor Emmanuel CVMRÒ Corporation, 35 Kenhar Dr., Toronto, Ontario M9L 1M9, Canada
a r t i c l e
i n f o
Article history: Available online xxxx Keywords: Metal carbonyls Carbonylation Laterite ore Reduction Magnetic separation Nickel
a b s t r a c t The carbonyl method of refining nickel and iron was invented more than 100 years ago and has been used for refining of nickel commercially. CVMRÒ developed the process of direct extraction of nickel and iron from laterite ores as metal carbonyls which in turn produced pure nickel and iron metals. CVMRÒ’s carbonyl technology has been applied to several types of limonite and saprolite ores containing other metals such as copper, cobalt and PGE. The process consists of reducing the ore with hydrogen, extracting of iron and nickel in the form of volatile metal carbonyls, separating the metal carbonyls and producing high purity nickel and iron metals; and production of copper, cobalt and PGE concentrate by gravity or magnetic separation. Economic evaluation of this process shows significant increase in cash flow. The CVMRÒ process does not produce liquid waste and does not require tailing dumps. This makes CVMRÒ’s process attractive for projects in areas that are environmentally sensitive, or have a high level of rainfall. Ó 2013 Published by Elsevier Ltd.
1. Introduction Over the past 30 years laterite ores have become increasingly more important as a source of nickel metal (Dalvi et al., 2004). Several methods of nickel extraction from laterite ores have been piloted and some were put into full operation, including acid leach with sulphuric, nitric and hydrochloric acids, ammonia leach and the pyrometallurgical process (Superiadi, 2007). Meanwhile, the production of nickel pig iron in China and India has been supplementing some of the refined nickel in stainless steel production, in the past 15 years (Widmer, 2009). Some of the methods stated above have processing cost advantages over others due to the credits generated from cobalt, copper and other metals. These credits can, at times, create significant cash flow for a refining operation and could make a difference in the financial viability of a project. Nickel refining by the Mond (carbonyl) process was commercially applied more than 100 years ago. The first operation was commissioned in 1902 in Clydach, Wales, UK. In 1973 INCO commissioned its Canadian nickel carbonyl refinery in Sudbury, Ontario, Canada. Traditionally the carbonyl process was used only by one company (INCO now taken over by Vale). However, in 1983 Norilsk Nickel built a relatively small operation in ⇑ Corresponding author. Tel.: +1 416 7432746; fax: +1 416 7434193. E-mail address: [email protected] (D.S. Terekhov). URL: http://www.cvmr.ca (D.S. Terekhov).
Monchegorsk, Russia, to produce nickel powders. In 2007 CVMR Corporation built and commissioned its Carbonyl refining plant in Jilin China (China). The Jinchuan Group Co., Ltd., in China attempted to implement a carbonyl technology in 2006 which failed and its pilot plant was shut down several years later. Because of Vale’s (INCO’s) 100 years monopoly of the carbonyl method of nickel refining, seldom any process details were published or discussed in public. Nevertheless, despite all these measures, today, between 20% and 25% of nickel is refined by the Mond process (Crundwell et al., 2011). In July 1970 INCO proposed to a French consortium to use the carbonyl method (as one of 3 technologies) for refining of nickel in the Gorolaterite project in New Caledonia (with capacity to produce 45,000 ton/year nickel metal). So called ‘‘Carbonyl Refining Method for Laterite Ore’’ was developed by INCO up to the full scale pilot stage and included partial reduction of nickel and iron by CO/CO2 gas mixture and direct extraction of nickel from ore in the form of nickel carbonyl. The product of the refining was forecasted as ferronickel with Fe/Ni ratio of 1.4/1. The method was rejected by the French consortium, not for technical reasons (Dunbar and Wing, 1970). To date it has not been clarified by INCO or the French consortium why the proposal was rejected if it was technically acceptable. Subsequently, since that time, no significant progress was made in the development of a method for direct extraction of nickel from laterite ores. However, in 2006 CVMR started a thorough review of the process and its application for direct extraction of nickel from laterite ores.
0892-6875/$ - see front matter Ó 2013 Published by Elsevier Ltd. http://dx.doi.org/10.1016/j.mineng.2013.07.008
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Table 1 AAS analysis of ore samples. Sample ID
Al (%)
Co (%)
Cu (%)
Fe (%)
Mg (%)
Mn (%)
Ni (%)
Limonite Limonite Limonite Saprolite
2.89 2.51
0.10 0.14 0.38 0.03
0.30 0.40
35.70 44.30 42.00 14.90
0.50 0.48
0.73 0.81 2.11 0.14
0.68 1.10 0.62 1.83
#1 #2 #3 #1
1.80
0.21
2. Experimental Limonite and saprolite ores from central Africa were analyzed by flame atomic absorption spectrometry (AAS) and X-ray fluorescence (XRF, NitonXLt). AAS analyses of ores are presented in Table 1. Process gases: argon (99.95%), carbon monoxide (99.5%), hydrogen (99.995%) were purchased from Praxair. Reduction and metal extraction from the ores were carried out in a high pressure TGA unit (Thermomax 500 supplied by Thermofisher) capable of testing 100 g of ore. The formed metal carbonyls were not collected. Mass balances of the experiments were calculated based on weight loss and AAS analysis of starting material and residue.
6.86
Si (%) 3.14 5.20 16.80
A sample of ore was placed in a quartz bucket suspended inside the TGA. TGA was closed and pressure tested. The instrument was purged with argon and the sample was heated to 650 °C at rate of 5 °C per minute. Hydrogen was introduced at 350 °C. After completion of reduction, the sample was cooled down to 180 °C and hydrogen was replaced with carbon monoxide. TGA was pressurized with carbon monoxide to 60 bar and formed carbonyls were removed by flow of reagent gas. The progress of extraction was monitored by weight lost of the sample. After completion of extraction TGA was depressurized, purged with argon and sample was cooled down to room temperature. The residual sample was analyzed by AAS. A medium scale pilot unit (5 kg scale) was used for reduction and metal extraction experiments. The schematic diagram of the
Fig. 1. Schematics of the pilot unit.
Table 2 Degree of reduction of metals with CO/CO2 gas mixture at 650 °C. Materials
Limonite
Temp (°C)
650 650 650 650 650
CO2:CO
1:1 1.5:1 2:1 5:1 H2
Alloy composition, %Ni:%Fe
24:76 56:44 70:30 91:9 2:98
Degree of reduction Ni (%)
Fe (%)
98.0 93.6 89.5 67.0 100.0
3.0 15.0 23.0 36.0 100.0
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reduction was monitored by collecting released water. After the reduction was completed, the reactor was cooled down to 180 °C and connected to the extraction system. Pilot unit was pressure tested with argon and pressurized to 60 bar with carbon monoxide. Carbon monoxide was passed through reactor and exhausting gas mixture of formed metal carbonyls and carbon monoxide was cooled down to 10 °C to liquefy metal carbonyls. The metal carbonyls mixture was collected in carbonyl storage tanks, carbonyls were separated by distillation and decomposed to produce metal powders. During the extraction, carbon monoxide was added to the system to keep pressure at 60 bar. Progress of extraction was monitored by reactor and liquid carbonyl storage tanks weight cells. After reaction was completed, system was depressurized; reactor was isolated from the rest of the system, purged with argon and opened. Starting material, residue and products were analyzed by AAS.
3. General process description Fig. 2. Reduction of limonite ore using CO/CO2 mixture and H2.
pilot unit is presented in Fig. 1. The sample of ore was placed inside of the metal reactor and purged with argon. The reactor was heated up to 650 °C at rate of 5 °C per minute. At temperature of 350 °C argon was replaced with hydrogen. Preheated reagent gas was continuously introduced into reactor at 5 L per minute. Progress of
3.1. Drying of ore, calcining and reduction There are two major steps in refining of laterite ores by the carbonyl method: the first step consists of drying, calcining and reduction of the ore being used and the second consists of extracting the metals in the ore in the form of volatile carbonyls. Hydrogen, carbon monoxide and coal could be used for laterite ore reduction. The process is well investigated and widely used for
Fig. 3. Process flow diagram for limonite ore (samples #2).
Please cite this article in press as: Terekhov, D.S., Emmanuel, N.V. Direct extraction of nickel and iron from laterite ores using the carbonyl process. Miner. Eng. (2013), http://dx.doi.org/10.1016/j.mineng.2013.07.008
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Fig. 4. Process flow diagram for saprolite ore.
Table 3 TGA test, samples #1. Ni
Feed Residue Yield
Fe
Cu
g
g
%
g
%
g
%
60.0 14.2
0.402 0.03
0.67 0.23 92
28.1 2.3
46.9 16.4 92
0.2 0.2
0.37 1.27
production of DRI, pig iron and nickel pig iron (Sarangi and Sarangi, 2011). The initial approach in the 1970s was to minimize the reduction of Iron, and to use appropriate conditions for preferential nickel reduction (Curlook, 1972). Usage of CO/CO2 gas mixture (1:1.5) for reduction of Limonite ore can achieve selectivity in metallization
at temperatures close to 650 °C. CO2 was used for oxidation of Iron metal to minimize Iron reduction. At these conditions, close to 92% of nickel and only 4% of Iron can be reduced (Eqs. (1) and (2)). As a result, after extraction and carbonyl decomposition Ni/Fe alloy material is produced at the approximate ration of 1/1. Theoretical calculations for these reactions are presented in Table 2. In practice, the composition of extracted alloy is Ni/Fe 1/1.2.
NiO þ CO ¼ Ni þ CO2
ð1Þ
Fe2 O3 þ 3CO ¼ 2Fe þ 3CO2
ð2Þ
Using hydrogen at the same temperature will reduce nickel, almost completely, and approximately 95% of iron (Eqs. (3) and (4)). High concentration of water in H2 (H2/H2O ratio of 4/6) can be used for selective nickel reduction as well, but it has never been used commercially.
Table 4 Primary carbonylation pilot unit test results. Nickel
Iron
g Feed (g) Residue 1 (g)
5000 1490
Yield (%)
%
55.00 2.01 52.99
1.10 0.14
Nickel
96.3
Cobalt
Copper
g
%
g
%
g
%
2215 478.29 1736.71
44.3 32.1
6.75 6.54 0.21
0.14 0.44
20.00 19.97 0.03
0.40 1.34
Iron
78.4
Cobalt
3.09
Copper
0.17
Table 5 Magnetic separation test. Yield (%)
Nickel
Magnetic separation Efficiency
59.8%
Iron
76.7%
Cobalt
77.68%
Copper
72.84%
65
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D.S. Terekhov, N.V. Emmanuel / Minerals Engineering xxx (2013) xxx–xxx Table 6 Secondary carbonylation. Nickel
Iron
g Mass balance Feed (Magnetic, g) Residue 2 (g) Extracted (g)
6.05 3.23
%
0.01 0.00 0.00
Yield (%)
0.13 0.14
Nickel
44.6
%
g
%
g
%
2.58 0.61 1.98
42.7 18.8
0.03 0.03 0.00
0.41 0.87
0.06 0.06 0.00
0.98 1.82
Iron
76.5
Typical time for reduction with CO/CO2 mixture is 20–30 min. Reduction with hydrogen is 60–90 min. Representative kinetics of limonite ore reduction are presented in Fig. 2.Increase in reduction temperature creates problems in the next step of the process as it creates particles with low surface area. Such particles are not suitable for the carbonyl process. For example, reduction of limonite, in our sample, at 750 °C reduced yield to 30% only. For this reason we, at CVMR, did not consider reduction of ore by coal.
0.63 ppm 1.13 ppm BDL 0.17 ppm 3.64 ppm 4.19 ppm 0.72 ppm 1.25 ppm
3.2. Metal extraction Metal extraction phase of the process consists of formation of volatile nickel and iron carbonyls at an elevated pressure and temperature (60 bar, 180 °C) (Eqs. (5) and (6)). Kinetics of extraction depend on physical form of reduced feed material, iron concentration and pressure. For example, when a partially reduced ore is used as feed material, the extraction time is between 4 h and 6 h. Extraction of Ni and Fe from completely reduced limonite will take between 24 h and 48 h.
6.35 ppm 4.84 ppm 0.98 ppm 1.07 ppm 15.4 ppm 10.3 ppm 2.22 ppm 1.82 ppm
NiO þ H2 ¼ Ni þ H2 O Fe2 O3 þ 3H2 ¼ 2Fe þ 3H2 O
Copper
g
Table 7 Concentrations of PGE, samples #2. Head sample Platinum Palladium Rhodium Gold Primary carbonylation residue Platinum Palladium Rhodium Gold Magnetic fraction Platinum Palladium Rhodium Gold Secondary carbonylation residue Platinum Palladium Rhodium Gold
Cobalt
Ni þ 4CO ¼ NiðCOÞ4
ð5Þ
Fe þ 5CO ¼ FeðCOÞ5
ð6Þ
Under these conditions (60 bar, 180 °C) both carbonyls are gaseous. In a TGA, at CVMR we passed CO over the feed material. The carbonyls thus formed were removed from the reaction chamber
ð3Þ ð4Þ
Table 8 Mass balance samples #3. Ni Total weight (g) Feed Residue
4.07 1.44
Fe
% 0.62 0.02
Yield
Co
Cr
Mn
g
%
g
%
g
%
g
%
g
0.03 0.00
42.00 16.06
1.71 0.23
0.38 1.22
0.02 0.02
2.24 8.68
0.09 0.12
2.11 7.39
0.09 0.11
98.9
86.5
Table 9 Extraction from saprolite sample. Nickel g Feed (g) Residue 1 (g)
4800 2860
Iron %
87.84 3.86
Yield (%)
1.83 0.14
Cobalt
Copper
g
%
g
%
g
%
715.20 213.93
14.9 7.5
1.56 0.73
0.03 0.03
10.27 10.27
0.21 0.36
95.6
70.1
Table 10 Composition of different grades of iron. Name
Fe%
C%
Si%
Mn%
P%
S%
Metallization (%)
Pig iron DRI Steel billets GB Q235 CVMR Fe product High purity Iron
95 92 99 99.9 99.9
3.5–4.5 2.5 0.14–0.22 0.1–0.2 0.003–0.015
0.3–3.0 4.5–5.0 0.12–0.30 <10 ppm 0.010
0.05–1.0
0.05–0.15 0.07 0.045 max <10 ppm 50–80 ppm
0.02–0.05 0.005 0.05 max 0.001 max 20–80 ppm
93 100 100 100
0.30–0.65 <10 ppm 0.030–0.100
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into the thermal oxidizer.In our pilot unit, at CVMR, we passed carbon monoxide through a bubble bed reactor, and it reacted with metallic nickel and iron. The mixture of volatile carbonyls was then removed from the reactor by excess of CO. The gas mixture was passed through a heat exchanger and the carbonyls were condensed in storage tanks. CO was recycled back into the reactor. Carbonylation reaction was exothermic and it required heat to be removed from the carbonylation reactor. Iron and nickel carbonyls are separated by fractional distillation. Less volatile iron carbonyl (Tb.p.103 °C) is removed from the bottom of the distillation column, vaporized and directed into the decomposer to produce Iron powder. Gaseous nickel carbonyl (Tb.p. 43 °C) then exits from the top of the column and is used to produce nickel powder. Decomposition of metal carbonyls is carried out at temperatures between 175 and 240 °C. Decomposition reactions of nickel and iron carbonyls are presented in Eqs. (7) and (8).
NiðCOÞ4 ¼ Ni þ 4CO
ð7Þ
FeðCOÞ5 ¼ Fe þ 5CO
ð8Þ
Reduction with hydrogen at 650 °C (2 h) and extraction at 60 bar and 180 °C (48 h) resulted in 92% extraction of nickel and 92% extraction of iron. The mass balance is presented in Table 3. Sample #2 had higher concentration of Ni and Fe; and similar composition of Cu, Co and PGE. The initial tests were performed in a TGA. Pre-treatment, reduction and metal extraction resulted in 98.1% and 86.5% yield for Ni and Fe. The same treatment in the pilot unit yielded 96.3% and 78.4% extraction for Ni and Fe. The recovery rate for both metals was more than 99% (Table 4). The metallic residue was tested in Davis tube for magnetic separation of metals and oxides. Yields of metals after magnetic separation are presented in Table 5. Co and Cu recovery were quite high, but Ni recovery was moderate. This was due to low concentration of Ni in the concentrate. Secondary extraction of Fe and Ni afforded only 44.6% and 76.5% yields. Overall yields after primary metal extraction, magnetic separation and secondary metal extraction were 97.3% for Ni and 90.7% for Fe. The residue contained Co, Cu and PGE (platinum group of metals and Au). After Ni and Fe extraction, concentration of Cu increased from 0.2% to 1.8% (Table 6) and concentration of PGE rose from 2 ppm to 30 ppm (Table 7). The ore sample #3 contained 0.62% of Nickel, 42.0% of Fe, 0.38% of Co, 2.24% Cr and 2.11% Mn. Reduction and Fe/Ni extraction in the TGA resulted in a residue the contained 0.02% Ni and 16.06% Fe. These correspond to yields of 98.9% Ni and 86.5% Fe. Co and Mn were concentrated by this method in the residue to 1.22% Co and 7.39% Mn. Table 8 shows the mass balance calculations. Cobalt refining was not part the study, but metallic Co could easily be recovered using one of the leach processes or magnetic separation.
The residue after Ni and Fe extraction contains trace amounts of Ni, reduced Fe, Co, Cu, Platinum Group Elements (PGE) and mixture of oxides. Magnetic separation of the residue can recover close to 80% of Fe, Cu and Co, 60% of Ni. Gravity separation is considered in cases when an ore contains significant amounts of PGE. The concentrate is then redirected to a secondary carbonylation cycle to maximize recovery of Ni and to extract Cobalt. When high concentration of Cu is present, the residue can be treated with sulphur followed by flotation. A typical process flow diagram is presented in Figs. 3 and 4 for limonite and Saprolite ores (calculated for 1 million tons of ore per year). A cobalt recovery method was also developed at CVMR. In this process Cobalt forms solid cobalt carbonyl which could be converted to volatile cobalt nitrosyl carbonyl. The decomposition of cobalt nitrosyl carbonyl produces Co metal (Terekhov, 2002). Chemical reactions of the process are presented in Eqs. (9)–(11).
2Co þ 8CO ¼ Co2 ðCOÞ8
4.2. Extraction from saprolite ore The sample Saprolite ore used for this experiment was composed of elements presented in Table 1. This sample was poly metallic and contained significant amounts of Cu and high concentration of Mg. The tests were carried out in the TGA and in the CVMR pilot unit. The ore was pre-treated for silicates decomposition and reduced at 650 °C with hydrogen. Extraction of Ni and Fe was much faster, compared to limonite samples due to lower concentration of Fe. Extraction of Ni and Fe was completed in 18 h. Ni recovery was 95.6% and Fe extraction yield was 70.1% in the pilot unit. Additional work is planned to test magnetic separation of the residue and Cu recovery.
ð9Þ
Co2 ðCOÞ8 þ NO ¼ CoNoðCOÞ3 þ CO
ð10Þ
CoNoðCOÞ3 ¼ Co þ 3CO þ NO
ð11Þ
4. Results and discussion 4.1. Treatment of limonite ore
4.3. Financial considerations Composition of limonite ore is presented in Table 1. The polymetallic sample #1 had significant concentration of copper, cobalt and close to 2 g/ton of PGE (Pt, Pd and Au). Pre-treatment, reduction and metal extraction tests were performed in a TGA unit.
Addition of iron as a product of the refining process significantly increases cash flow of the operation. In addition to cash flow from produced iron, production of high purity metals further increase
Table 11 Comparison of chemical grade nickel and nickel produces by CVMR. Product
Carbon (%)
Sulphur (ppm)
Oxygen (%)
Nitrogen (ppm)
Iron (ppm)
Cobalt (ppm)
Other elements
Nickel
Chemical grade nickel CVMR’s nickel
<0.10 <0.10
<50 <50
<0.12 <0.12
<0.125 <0.125
<20 <20
<10 <10
<10 <10
Balance Balance
Table 12 Estimation of Ni and Fe product values. Sample ID
Ni (%)
Fe (%)
LME price per ton of Ni
LME price per ton of steel billets
Estimated yield Ni product (%)
Estimated yield Fe product (%)
Value per ton of ore Ni product
Value per ton of ore Fe product
Limonite Limonite Limonite Saprolite
0.68 1.10 0.62 1.83
35.70 44.30 42.00 14.90
$18,000.00 $18,000.00 $18,000.00 $18,000.00
$400.00 $400.00 $400.00 $400.00
92.00 97.30 98.90 95.60
92.00 90.70 86.50 70.10
$112.61 $192.65 $110.37 $314.91
$131.38 $160.72 $145.32 $41.78
#1 #2 #3 #1
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cash flow. For example even if price of iron product was to be calculated as DRI or sponge iron, one could observe significant increases in the cash flow. Nevertheless, the purity of produced iron by the CVMR carbonyl process corresponds more to the high purity iron or LME steel billets (Table 10). High purity nickel from carbonyl process (Chemical grade nickel) is produced by Vale and sold above LME. A comparison of purity of chemical grade nickel and CVMR’s nickel produced directly from the ore is presented in Table 11. A simple calculation shows that iron product cash flow can be close or even equal to the cash flow from nickel metal sales. Based on today’s LME prices of Ni and steel billets, iron, produced from low grade laterite ore (samples #1 and #3), will have the same value as the nickel product. Addition of Co, Cu and PGE product lines will increase the cash flow 3 times. Table 12 represents a simple calculation for the value of Ni and Fe product lines per ton of ore. These calculations are not intended to be used for economic evaluation of a project, but to show the importance of iron product line for low grade polymetallic laterite ores.
H2 allows extraction of Fe together with Ni with rather high yields. Metal extraction parameters of 60 bar and 180 °C were used in all experiments. Optimization of reduction and extraction parameters was not included in this article. Magnetic separation of residue after extraction of Ni and Fe was presented as a single case. Secondary carbonylation of magnetic fraction increased PGE concentration from 2 ppm (ore) to 30 ppm (carbonylation residue after secondary carbonylation). Purity of Ni and Fe products were compared with chemical grade Ni, Steel billets and high purity iron and summarized in Tables 9 and 10. High purity of metal products could further increase cash flow of a project.
The authors gratefully acknowledge the assistance of several persons, all of whom are members or were members CVMR Corporation especially Professor Walter Curlook, Dr. OlujideB. Olurin, Dr Kamran M. Khozan and Mr. Colwyn van der Linder.
5. Conclusions
References
In this study, direct extraction of nickel and iron from laterite ores was investigated in a two step process using CVMR’s carbonyl technology. Iron turns out to be an important product of this process, increasing the cash flow and decreasing costs of disposal of the tailing. Application of the carbonyl process to low Ni grade laterite ores containing significant amount of Co, Cu and PGE makes recovery of these metals quite feasible. Considering experimental results given in Sections 4.1 and 4.2, an estimated value of Fe product was calculated close or equal to the value of Ni product and summarized in Table 11. Ore reduction with hydrogen gas (temperature of 650 °C) was compared with reduction by CO/CO2 gas mixture. Reduction by
Crundwell, F.K., Moats, M.S., Ramachandran, V., Robinson, T.G., Davenport, W.G., 2011. Extractive Metallurgy of Nickel, Cobalt and Platinum-Group Metals. Elsevier, The Netherlands, pp. 269–280. Curlook W., Bell J.A.E., 1972. Rotary kiln reduction of limonitic ores. US Patent 3,656,934. Dalvi, A.D., Bacon, W.G., Osborne, R.C., 2004. The past and future of nickel laterites. PDAC 2004 International Convention. Dunbar, M., Wing, D.J., 1970. New caledonia project outlined in inco’s report. INCO triangle, vol. 40, pp. 4. Sarangi, A., Sarangi, B., 2011. Sponge Iron Production in Rotary Kiln. PHI Learning Private Limited, India, pp. 37–62. Superiadi, A., 2007. Processing technology vs. nickel laterite ore characteristic. Pt Inco. Terekhov, D.S., 2002. Cobalt recovery process. US Patent 6,428,601. Widmer, M., 2009. Nickel pig iron in China. Presentation, Bank of America-Merrill Lynch.
Acknowledgements
Please cite this article in press as: Terekhov, D.S., Emmanuel, N.V. Direct extraction of nickel and iron from laterite ores using the carbonyl process. Miner. Eng. (2013), http://dx.doi.org/10.1016/j.mineng.2013.07.008