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Beneficiation of iron ore slime using Aspergillus niger and Bacillus circulans
Bioresource Technology 97 (2006) 1876–1879
Beneficiation of iron ore slime using Aspergillus niger and Bacillus circulans N. Pradhan *, B. Das, C.S. Gahan, R.N. Kar, L.B. Sukla Regional Research Laboratory, CSIR, Bhubaneshwar 751 013, India Received 17 December 2004; received in revised form 8 August 2005; accepted 26 August 2005 Available online 13 March 2006
Abstract Studies were carried out on the removal of alumina from iron ore slime containing (%) Fe2O3 75.7, Al2O3 9.95, SiO2 6.1, Fe (total) 52.94 with the help of Bacillus circulans and Aspergillus niger. B. circulans and A. niger showed 39% and 38% alumina removal after six and 15 days of in situ leaching at 10% pulp density, respectively. Culture filtrate leaching with A. niger removed 20% alumina at 2% pulp density with 13 day old culture filtrate. B. circulans was more efficient than A. niger for selective removal of alumina. In case of A. niger in situ leaching rather than culture filtrate leaching was found to be more effective. 2005 Elsevier Ltd. All rights reserved. Keywords: Iron ore slime; Aspergillus niger, Bacillus circulans; Bio-beneficiation; Alumina removal
1. Introduction Reserves of high-grade ores are diminishing all over the world at an alarming rate as a result of rapid increase in demands for metals. The recovery of mineral value from the low-grade ores using present technology is prohibitively expensive due to high energy and capital costs. Presently available physico-chemical methods are not environment friendly. Bio-beneficiation is considered as eco-friendly, promising and revolutionary solutions to these problems and is gaining more importance due to depletion of highgrade ores and enforcement of strict anti-pollution laws. Iron ore slimes containing around 48–62% Fe are generated from the iron ore washing plants and are disposed into tailing ponds without any further utility. The slimes are not suitable in iron and steel making due to the extremely finer size and presence of higher amount of gangue constituents. Several beneficiation techniques have been tried from time * Corresponding author. Tel.: +91 674 2584091 94x528; fax: +91 674 2581636. E-mail addresses: [email protected], nilotpala_pradhan@ yahoo.co.in (N. Pradhan).
0960-8524/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2005.08.010
to time to reduce the gangue constituents so that the beneficiated products could be effectively used for iron and steel making (Das et al., 1992; Pradip, 1994; Prakash et al., 1999). Gangue minerals present in iron ores comprise both metallic and non-metallic components. Usually, siliceous gangue consists of larger proportion of alumina in the form of clay and laterite along with varying amounts of undesirable constituents such as phosphorous, sulphur, titanium, copper and arsenic. Many microorganisms have been reported to solubilise different alumino-silicate compounds found in nature. In silicates, silicon is usually surrounded by four oxygen atoms in tetrahedral fashion (Kretz, 1972) whereas aluminium in aluminosilicates is coordinated with oxygen in tetrahedral or octahedral fashion, depending upon the mineral (Tan, 1986). In minerals, these units are arranged in bi- or tri-layers separated by water layers of variable thickness into which other polar molecules, including some organic molecules can enter. This type of structure makes them susceptible for weathering by microorganisms. Si–O bonds of silloxanes linkages (Si–O–Si) in silicates and aluminosilicates are very strong, whereas Al–O bonds are somewhat weaker. Thus Si–O bonds are relatively resistant to acid hydrolysis (Karavaiko
N. Pradhan et al. / Bioresource Technology 97 (2006) 1876–1879
et al., 1985), unlike Al–O bonds. Some bacteria and fungi are known to solubilise silica and silicates. They accomplish this by forming chelators, acids or bases, which react with silicates and exo-polysaccharides, which react with silica and silicates. Although the use of different microorganisms in ore leaching is well-established, use of microorganism to reduce alumina and silica from ore has been attempted in very few investigations (Natarajan and Deo, 2000). This paper describes the bio-beneficiation of iron ore slimes using Aspergillus niger and Bacillus circulans.
1877
tively. Different sets were incubated for different period of 5, 10, 15 days, after which the solid residues were separated and analyzed as above. For culture filtrate leaching, A. niger grown in mineral salt medium for different time durations was used. To the culture filtrates of different period, iron ore slime at a rate of 2% pulp density was added and boiled for three hours with occasional replacement of volume by water. After boiling, the solid residue was separated by sedimentation and filtration, dried and analyzed for Al and Fe. 3. Results and discussion
2. Methods 3.1. Chemical and size analysis of iron ore slimes 2.1. Sample Iron ore slime sample was obtained from Bolani iron ore washing plant, Orissa, India. Around one ton of the tailing sample from the washing plant was mixed thoroughly and representative sample was drawn for the experiments. The sample was analyzed by wet chemical and instrumental techniques (Vogel, 1978). The size analysis of the sample was done in wet conditions with standard sieves. All size fractions were collected separately, dried in a hot air oven (105 C) and analyzed by standard methods (Vogel, 1978).
Complete chemical analysis of Bolani iron ore slime revealed that the sample on an average contained (%) Fe2O3 75.7, Al2O3 9.95, SiO2 6.1, LOI 8.7, Fe (total) 52.94. As alumina concentration in the sample was quite high, it could not be used in iron and steel making. Besides this, the ratio of SiO2:Al2O3 was also very high contradicting to blast furnace chemistry. The size analysis of the iron ore slimes down to 20 lm size is shown in Table 1. The result indicated that the sample was very fine in nature with 76.7% of the material of below 20 lm size.
2.2. Microorganisms
3.2. Beneficiation experiments
B. circulans MTCC 879 and A. niger MTCC 282 were used for the bio-beneficiation of iron ore slime. Strains were maintained on nutrient agar and potato dextrose agar slants, respectively. Bromfield medium was used for beneficiation studies by B. circulans, which contained (g/L) sucrose 20, yeast extract 1, K2HPO4 0.25, NH4SO4 0.25, MgSO4 0.75, sodium bisphosphate 0.30, pH 6.8 ± 0.2. Medium used for growth and beneficiation studies by A. niger was mineral salt medium containing (g/L) Sucrose 10, K2HPO4 1, NH4NO3 3, MgSO4 0.5, pH 6.8 ± 0.2.
Both Aspergillus sp. and Bacillus sp. are known to be involved in the leaching and beneficiation processes of silicate ores and minerals (Karavaiko et al., 1980; Avakyan et al., 1986). The solubilizing action by microorganisms may involve the cleavage of Si–O–Si or Al–O framework bonds, or the removal of cations from the crystal lattice of silicate causing the subsequent collapse of silicate lattice structure. In situ leaching with A. niger varied with incubation time and 5, 10 and 15 days incubation resulted in 10%, 27% and 38% removal of alumina, respectively (Table 2). Final pH of the medium was 2.1, 1.75 and 1.32 after 5, 10 and 15 days, respectively. About 2% and 25% iron was also leached out along with the alumina in 10 and 15 days of leaching, respectively. Removal of alumina was maximum with 15 days incubation but simultaneous dissolution of Fe was also substantially high.
2.3. Beneficiation process In situ leaching experiments with B. circulans were carried out in 100 ml of Bromfield medium in 250 ml Erlenmeyer flask under sterile conditions at a pulp density, temperature and agitation speed of 10%, 35 C and 150 rpm, respectively. Inoculation was done with 10% inoculum (v/v) containing 1 · 108 cfu/ml of B. circulans and incubation time was six days. At the end of experiments, solid residue was separated by filtration through medium fast filter paper, dried in hot air oven and analyzed for Al and Fe. With A. niger, in situ leaching was done in 100 ml of mineral salt medium under sterile conditions. Iron ore slime sample was added at 10% pulp density (w/v). Inoculation was done with 10% inoculum (v/v) containing 1 · 106 spores/ml of A. niger spores. Incubation temperature and agitation speed were 35 C and 150 rpm, respec-
Table 1 Size analysis and distribution of Al2O3 and Fe in different size fractions Size (lm) +212 212 + 150 150 + 105 105 + 75 75 + 45 45 + 30 30 + 20 20 Head
Weight (%) 0.6 0.4 3.2 5.7 9.1 2.7 1.6 76.7 100
Fe (%)
Al2O3 (%)
54.45 58.64 59.76 62.55 62.00 62.55 64.50 50.27
4.97 2.87 1.95 2.66 2.50 2.98 3.19 4.73
52.98
9.95
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N. Pradhan et al. / Bioresource Technology 97 (2006) 1876–1879
Table 2 In situ leaching with A. niger and B. circulans Microorganism
Duration (days/pH)
Al2O3 (%)
Fe (%)
Al2O3 removed (%)
Fe removed (%)
Original sample A. niger A. niger A. niger B. circulans
– 5/2.10 10/1.75 15/1.32 6/4.03
9.56 8.63 7.01 5.93 5.80
53.62 53.12 52.49 40.21 51.74
– 10 27 38 39
– 0.93 2.10 25.0 3.50
Table 3 Culture filtrate leaching with A. niger pH of culture filtrate
Culture age (days)
Strength of acid (Moles)
Fe (T) (%)
Al2O3 (%)
Al2O3 removed (%)
1.35 2.10 3.02
13 6 2
0.18 0.07 0.03
53.00 51.76 52.44
7.64 8.10 8.78
20 15 8
For culture filtrate leaching A. niger grown in mineral salt medium of initial pH of 6.8 was used, which after 2, 6 and 13 days growth resulted in pH around 3, 2 and 1, respectively. Beneficiation studies with A. niger using culture filtrate of different pH showed that pH 1 was more suitable with 20% removal of alumina (Table 3). At pH 2 and 3, the removal of alumina was 15% and 8%, respectively. Some amount of iron was also leached out along with alumina but was below 4%. Higher leaching of alumina at lower pH could be due to higher acidity and more metabolites of the culture filtrate (Table 3). Alumina removal was better in case of in situ leaching compared to culture filtrate leaching. During metabolism, microorganisms convert glucose or other carbohydrates into variety of products, including organic acids. Bio-leaching processes are mediated due to the chemical attack by the extracted organic acids on the ores. Acids usually have dual effect of increasing metal dissolution by lowering the pH and increasing the load of soluble metals by complexing/chelating into soluble organo-metallic complexes (Burgstaller and Schinner, 1993). Microbially produced ligands of divalent cations have been shown to cause dissolution of calcium containing silicates. These ligands include 2-ketogluconic acid (Duff et al., 1963), gluconic acid (Kim et al., 1997; Fenice et al., 2000; Vandevivere et al., 1994), citric (Pandey et al., 2000), oxalic, humic acid (Bennett et al., 1988) etc. A wide variety of microorganisms have been reported to produce acidic metabolites, which are responsible in solubilisation of alumino-silicates (Karavaiko et al., 1979). Dissolution of spodumene (LiAlSi2O6) has been reported by many microorganisms including A. niger (Karavaiko et al., 1980; Avakyan et al., 1986) by production of acid. Alkaline conditions have been reported to be very conducive to mobilize silicon, from silicates, aluminosilicates or even quartz (Karavaiko et al., 1985; Kutuzova, 1969). But in our case we find that alumina removal by A. niger was associated with increase in acidity of the medium due to production of acidic metabolites. In situ leaching with B. circulans resulted in 39% removal of alumina with simultaneous removal of only
3.5% iron in six days (Table 2). Drop in pH was from 6.8 to 4.03, which was not significant when compared to A. niger. Bacillus sp. is known to produce extra-cellular polysaccharides (Shih et al., 2001) and other metabolites, which may be playing a role in alumina solubilisation from iron ore slime. Extra-cellular polysaccharides have been reported to be involved in silicon release (Avakyan et al., 1986). Such polysaccharides, of bacterial or fungal origin, are able to react with silioxanes to form organic silioxane. Bacillus mucilaginosus (Malinovskaya et al., 1990) was effective in solubilising Si in addition to Li and Al by reaction of its extra-cellular polysaccharides with the silicate of spodumene. In case of B. circulans, drop in pH was less when compared to A. niger but solubilization of Al to significant extent even at pH 4.03 indicated the role of extracellular polysaccharides. Culture filtrate leaching and in situ leaching with these cultures indicated that it was possible to remove the silica and alumina from iron ore slime with the help of microorganisms. Simultaneous dissolution of Fe was less with B. circulans as compared to A. niger which was desirable. 4. Conclusions Bolani iron ore slime containing 53% Fe, 9.56% Al2O3 and 6.14% SiO2 was subjected to bio-beneficiation studies. In situ leaching by A. niger removed about 38% of alumina in 15 days, while B. circulans could removed 39% of alumina after six days at 10% pulp density. Culture filtrate leaching with A. niger removed 20% alumina with 13 day culture filtrate at 2% pulp density. With B. circulans simultaneous dissolution of Fe was also less. Thus, B. circulans proved to be more effective than the A. niger in removal of alumina from the iron ore slime. Acknowledgements Authors are grateful to Dr. R.P. Das, Director, Regional Research Laboratory, Bhubaneshwar for his kind permission to publish this paper.
N. Pradhan et al. / Bioresource Technology 97 (2006) 1876–1879
References Avakyan, Z.A., Pivovarora, T.A., Karavaiko, G.I., 1986. Properties of a new species, Bacillus mucilaginosus. Mikrobiologiya 55, 369– 374. Bennett, P.C., Melcer, M.E., Sigel, D.I., Hassett, J.P., 1988. The dissolution of quartz in dilute aqueous solutions of organic acids at 25 C. Geochimica Cosmochimica Acta 52, 1521–1530. Burgstaller, W., Schinner, E., 1993. In: Torma, A.E., Wey, J.E., Askshmanan, V.L. (Eds.), Metal Leaching with Fungi in Biohydrometallurgical Techniques. The Mineral, Metal and Materials Society, Warrendale, PA, pp. 325–333. Das, B., Prakash, S., Mohapatra, B.K., Bhaumik, S.K., Narsimhan, K.S., 1992. Beneficiation of iron ore slimes using hydrocyclone. Minerals and Metallurgical Processing 4, 101–103. Duff, R.B., Webley, D.M., Scott, R.O., 1963. Solubilization of minerals by 2-ketogluconic acid producing bacteria. Soil Science 95, 105– 114. Fenice, M., Selbman, L., Federici, F., Vassilev, N., 2000. Application of encapsulated Penicillium variable in solubilization of rock phosphate. Bioresource Technology 73, 157–162. Karavaiko, G.I., Avakyan, Z.A., Krutsko, V.S., Zhdanov, A.V., Piskunov, V.P., 1979. Microbiological investigations on a spodumene deposit. Mikrobiologiya 48, 383–398. Karavaiko, G.I., Belkanova, N.P., Eroshchev-Shak, V.A., Avakyan, Z.A., 1985. Role of microorganisms and some physicochemical factors of the medium in quartz destruction. Mikrobiologiya 53, 795–800. Karavaiko, G.I., Krutsko, V.S., MelÕnikova, E.O., Avakyan, Z.A., Ostroushko, Yu.I., 1980. Role of microorganisms in spodumene degradation. Mikrobiologiya 49, 402–406. Kim, K.Y., Jordan, D., Krishnan, H.B., 1997. Rahnella aquatilis, a bacterium isolated from soybean rhizosphere, can solubilize hydroxyapatite. FEMS Microbiology Letters 153, 273–277.
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Kretz, R., 1972. Silicon: elements and geochemistry. In: Fairbridge, R.W. (Ed.), The Encyclopedia of Geochemistry and Environmental Sciences, Encyclopedia of earth sciences series, vol. IVA. Van Norstrand Reinhold, New York, pp. 1091–1092. Kutuzova, R.S., 1969. Release of silica from minerals as result of microbiological activity. Mickrobiologiya 38, 596–602. Malinovskaya, I.M., Kosenko, L.V., Vostelko, S.K., Podgorskii, V.S., 1990. Role of Bacillus mucilaginosus polysaccharide in degradation of silicate minerals. Mikobiologiya 59, 49–55. Natarajan, K., Deo, N., 2000. Role of bacterial interaction and bioreagents in iron ore floatation. International Journal of Mineral Processing 62, 143–157. Pandey, A., Soccol, C.R., Nigam, P., Soccol, V.T., Vandenberghe, L.P.S., Mohan, R., 2000. Biotechnological potential of agro-industrial residues II: Cassava bagasse. Bioresource Technology 74, 81–87. Pradip, P., 1994. Beneficiation of alumina rich Indian iron ore slimes. Metal Material and Processes 6, 170–194. Prakash, S., Das, B., Mohanty, J.K., Venugopal, R., 1999. Recovery of iron minerals from quartz and corundum mixture by selective coating. International Journal of Mineral Processing 57, 87–103. Shih, I.L., Van, Y.T., Yeh, L.C., Lin, H.G., Chang, Y.N., 2001. Production of a biopolymer flocculant from Bacillus licheniformis and its flocculation properties. Bioresource Technology 78, 267–272. Tan, K.H., 1986. Degradation of soil minerals by organic acids. In: Haung P.M., Schnitzer, M. (Eds.), Interaction of soil minerals with natural organics and microbes. SSSA Special publication Number 17. Soil Science Society of America Madison, WI, pp. 1–27. Vandevivere, P., Welch, S.A., Ullman, W.J., Kirchman, D.L., 1994. Enhanced dissolution of silicate minerals by bacteria at near neutral pH. Microbial Ecology 27, 241–251. Vogel, A.I., 1978. Textbook of Quantitative Inorganic Analysis Including Elementary Instrumental Analysis. ELBS and Longman publications, London.
Beneficiation of iron ore slime using Aspergillus niger and Bacillus circulans N. Pradhan *, B. Das, C.S. Gahan, R.N. Kar, L.B. Sukla Regional Research Laboratory, CSIR, Bhubaneshwar 751 013, India Received 17 December 2004; received in revised form 8 August 2005; accepted 26 August 2005 Available online 13 March 2006
Abstract Studies were carried out on the removal of alumina from iron ore slime containing (%) Fe2O3 75.7, Al2O3 9.95, SiO2 6.1, Fe (total) 52.94 with the help of Bacillus circulans and Aspergillus niger. B. circulans and A. niger showed 39% and 38% alumina removal after six and 15 days of in situ leaching at 10% pulp density, respectively. Culture filtrate leaching with A. niger removed 20% alumina at 2% pulp density with 13 day old culture filtrate. B. circulans was more efficient than A. niger for selective removal of alumina. In case of A. niger in situ leaching rather than culture filtrate leaching was found to be more effective. 2005 Elsevier Ltd. All rights reserved. Keywords: Iron ore slime; Aspergillus niger, Bacillus circulans; Bio-beneficiation; Alumina removal
1. Introduction Reserves of high-grade ores are diminishing all over the world at an alarming rate as a result of rapid increase in demands for metals. The recovery of mineral value from the low-grade ores using present technology is prohibitively expensive due to high energy and capital costs. Presently available physico-chemical methods are not environment friendly. Bio-beneficiation is considered as eco-friendly, promising and revolutionary solutions to these problems and is gaining more importance due to depletion of highgrade ores and enforcement of strict anti-pollution laws. Iron ore slimes containing around 48–62% Fe are generated from the iron ore washing plants and are disposed into tailing ponds without any further utility. The slimes are not suitable in iron and steel making due to the extremely finer size and presence of higher amount of gangue constituents. Several beneficiation techniques have been tried from time * Corresponding author. Tel.: +91 674 2584091 94x528; fax: +91 674 2581636. E-mail addresses: [email protected], nilotpala_pradhan@ yahoo.co.in (N. Pradhan).
0960-8524/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2005.08.010
to time to reduce the gangue constituents so that the beneficiated products could be effectively used for iron and steel making (Das et al., 1992; Pradip, 1994; Prakash et al., 1999). Gangue minerals present in iron ores comprise both metallic and non-metallic components. Usually, siliceous gangue consists of larger proportion of alumina in the form of clay and laterite along with varying amounts of undesirable constituents such as phosphorous, sulphur, titanium, copper and arsenic. Many microorganisms have been reported to solubilise different alumino-silicate compounds found in nature. In silicates, silicon is usually surrounded by four oxygen atoms in tetrahedral fashion (Kretz, 1972) whereas aluminium in aluminosilicates is coordinated with oxygen in tetrahedral or octahedral fashion, depending upon the mineral (Tan, 1986). In minerals, these units are arranged in bi- or tri-layers separated by water layers of variable thickness into which other polar molecules, including some organic molecules can enter. This type of structure makes them susceptible for weathering by microorganisms. Si–O bonds of silloxanes linkages (Si–O–Si) in silicates and aluminosilicates are very strong, whereas Al–O bonds are somewhat weaker. Thus Si–O bonds are relatively resistant to acid hydrolysis (Karavaiko
N. Pradhan et al. / Bioresource Technology 97 (2006) 1876–1879
et al., 1985), unlike Al–O bonds. Some bacteria and fungi are known to solubilise silica and silicates. They accomplish this by forming chelators, acids or bases, which react with silicates and exo-polysaccharides, which react with silica and silicates. Although the use of different microorganisms in ore leaching is well-established, use of microorganism to reduce alumina and silica from ore has been attempted in very few investigations (Natarajan and Deo, 2000). This paper describes the bio-beneficiation of iron ore slimes using Aspergillus niger and Bacillus circulans.
1877
tively. Different sets were incubated for different period of 5, 10, 15 days, after which the solid residues were separated and analyzed as above. For culture filtrate leaching, A. niger grown in mineral salt medium for different time durations was used. To the culture filtrates of different period, iron ore slime at a rate of 2% pulp density was added and boiled for three hours with occasional replacement of volume by water. After boiling, the solid residue was separated by sedimentation and filtration, dried and analyzed for Al and Fe. 3. Results and discussion
2. Methods 3.1. Chemical and size analysis of iron ore slimes 2.1. Sample Iron ore slime sample was obtained from Bolani iron ore washing plant, Orissa, India. Around one ton of the tailing sample from the washing plant was mixed thoroughly and representative sample was drawn for the experiments. The sample was analyzed by wet chemical and instrumental techniques (Vogel, 1978). The size analysis of the sample was done in wet conditions with standard sieves. All size fractions were collected separately, dried in a hot air oven (105 C) and analyzed by standard methods (Vogel, 1978).
Complete chemical analysis of Bolani iron ore slime revealed that the sample on an average contained (%) Fe2O3 75.7, Al2O3 9.95, SiO2 6.1, LOI 8.7, Fe (total) 52.94. As alumina concentration in the sample was quite high, it could not be used in iron and steel making. Besides this, the ratio of SiO2:Al2O3 was also very high contradicting to blast furnace chemistry. The size analysis of the iron ore slimes down to 20 lm size is shown in Table 1. The result indicated that the sample was very fine in nature with 76.7% of the material of below 20 lm size.
2.2. Microorganisms
3.2. Beneficiation experiments
B. circulans MTCC 879 and A. niger MTCC 282 were used for the bio-beneficiation of iron ore slime. Strains were maintained on nutrient agar and potato dextrose agar slants, respectively. Bromfield medium was used for beneficiation studies by B. circulans, which contained (g/L) sucrose 20, yeast extract 1, K2HPO4 0.25, NH4SO4 0.25, MgSO4 0.75, sodium bisphosphate 0.30, pH 6.8 ± 0.2. Medium used for growth and beneficiation studies by A. niger was mineral salt medium containing (g/L) Sucrose 10, K2HPO4 1, NH4NO3 3, MgSO4 0.5, pH 6.8 ± 0.2.
Both Aspergillus sp. and Bacillus sp. are known to be involved in the leaching and beneficiation processes of silicate ores and minerals (Karavaiko et al., 1980; Avakyan et al., 1986). The solubilizing action by microorganisms may involve the cleavage of Si–O–Si or Al–O framework bonds, or the removal of cations from the crystal lattice of silicate causing the subsequent collapse of silicate lattice structure. In situ leaching with A. niger varied with incubation time and 5, 10 and 15 days incubation resulted in 10%, 27% and 38% removal of alumina, respectively (Table 2). Final pH of the medium was 2.1, 1.75 and 1.32 after 5, 10 and 15 days, respectively. About 2% and 25% iron was also leached out along with the alumina in 10 and 15 days of leaching, respectively. Removal of alumina was maximum with 15 days incubation but simultaneous dissolution of Fe was also substantially high.
2.3. Beneficiation process In situ leaching experiments with B. circulans were carried out in 100 ml of Bromfield medium in 250 ml Erlenmeyer flask under sterile conditions at a pulp density, temperature and agitation speed of 10%, 35 C and 150 rpm, respectively. Inoculation was done with 10% inoculum (v/v) containing 1 · 108 cfu/ml of B. circulans and incubation time was six days. At the end of experiments, solid residue was separated by filtration through medium fast filter paper, dried in hot air oven and analyzed for Al and Fe. With A. niger, in situ leaching was done in 100 ml of mineral salt medium under sterile conditions. Iron ore slime sample was added at 10% pulp density (w/v). Inoculation was done with 10% inoculum (v/v) containing 1 · 106 spores/ml of A. niger spores. Incubation temperature and agitation speed were 35 C and 150 rpm, respec-
Table 1 Size analysis and distribution of Al2O3 and Fe in different size fractions Size (lm) +212 212 + 150 150 + 105 105 + 75 75 + 45 45 + 30 30 + 20 20 Head
Weight (%) 0.6 0.4 3.2 5.7 9.1 2.7 1.6 76.7 100
Fe (%)
Al2O3 (%)
54.45 58.64 59.76 62.55 62.00 62.55 64.50 50.27
4.97 2.87 1.95 2.66 2.50 2.98 3.19 4.73
52.98
9.95
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N. Pradhan et al. / Bioresource Technology 97 (2006) 1876–1879
Table 2 In situ leaching with A. niger and B. circulans Microorganism
Duration (days/pH)
Al2O3 (%)
Fe (%)
Al2O3 removed (%)
Fe removed (%)
Original sample A. niger A. niger A. niger B. circulans
– 5/2.10 10/1.75 15/1.32 6/4.03
9.56 8.63 7.01 5.93 5.80
53.62 53.12 52.49 40.21 51.74
– 10 27 38 39
– 0.93 2.10 25.0 3.50
Table 3 Culture filtrate leaching with A. niger pH of culture filtrate
Culture age (days)
Strength of acid (Moles)
Fe (T) (%)
Al2O3 (%)
Al2O3 removed (%)
1.35 2.10 3.02
13 6 2
0.18 0.07 0.03
53.00 51.76 52.44
7.64 8.10 8.78
20 15 8
For culture filtrate leaching A. niger grown in mineral salt medium of initial pH of 6.8 was used, which after 2, 6 and 13 days growth resulted in pH around 3, 2 and 1, respectively. Beneficiation studies with A. niger using culture filtrate of different pH showed that pH 1 was more suitable with 20% removal of alumina (Table 3). At pH 2 and 3, the removal of alumina was 15% and 8%, respectively. Some amount of iron was also leached out along with alumina but was below 4%. Higher leaching of alumina at lower pH could be due to higher acidity and more metabolites of the culture filtrate (Table 3). Alumina removal was better in case of in situ leaching compared to culture filtrate leaching. During metabolism, microorganisms convert glucose or other carbohydrates into variety of products, including organic acids. Bio-leaching processes are mediated due to the chemical attack by the extracted organic acids on the ores. Acids usually have dual effect of increasing metal dissolution by lowering the pH and increasing the load of soluble metals by complexing/chelating into soluble organo-metallic complexes (Burgstaller and Schinner, 1993). Microbially produced ligands of divalent cations have been shown to cause dissolution of calcium containing silicates. These ligands include 2-ketogluconic acid (Duff et al., 1963), gluconic acid (Kim et al., 1997; Fenice et al., 2000; Vandevivere et al., 1994), citric (Pandey et al., 2000), oxalic, humic acid (Bennett et al., 1988) etc. A wide variety of microorganisms have been reported to produce acidic metabolites, which are responsible in solubilisation of alumino-silicates (Karavaiko et al., 1979). Dissolution of spodumene (LiAlSi2O6) has been reported by many microorganisms including A. niger (Karavaiko et al., 1980; Avakyan et al., 1986) by production of acid. Alkaline conditions have been reported to be very conducive to mobilize silicon, from silicates, aluminosilicates or even quartz (Karavaiko et al., 1985; Kutuzova, 1969). But in our case we find that alumina removal by A. niger was associated with increase in acidity of the medium due to production of acidic metabolites. In situ leaching with B. circulans resulted in 39% removal of alumina with simultaneous removal of only
3.5% iron in six days (Table 2). Drop in pH was from 6.8 to 4.03, which was not significant when compared to A. niger. Bacillus sp. is known to produce extra-cellular polysaccharides (Shih et al., 2001) and other metabolites, which may be playing a role in alumina solubilisation from iron ore slime. Extra-cellular polysaccharides have been reported to be involved in silicon release (Avakyan et al., 1986). Such polysaccharides, of bacterial or fungal origin, are able to react with silioxanes to form organic silioxane. Bacillus mucilaginosus (Malinovskaya et al., 1990) was effective in solubilising Si in addition to Li and Al by reaction of its extra-cellular polysaccharides with the silicate of spodumene. In case of B. circulans, drop in pH was less when compared to A. niger but solubilization of Al to significant extent even at pH 4.03 indicated the role of extracellular polysaccharides. Culture filtrate leaching and in situ leaching with these cultures indicated that it was possible to remove the silica and alumina from iron ore slime with the help of microorganisms. Simultaneous dissolution of Fe was less with B. circulans as compared to A. niger which was desirable. 4. Conclusions Bolani iron ore slime containing 53% Fe, 9.56% Al2O3 and 6.14% SiO2 was subjected to bio-beneficiation studies. In situ leaching by A. niger removed about 38% of alumina in 15 days, while B. circulans could removed 39% of alumina after six days at 10% pulp density. Culture filtrate leaching with A. niger removed 20% alumina with 13 day culture filtrate at 2% pulp density. With B. circulans simultaneous dissolution of Fe was also less. Thus, B. circulans proved to be more effective than the A. niger in removal of alumina from the iron ore slime. Acknowledgements Authors are grateful to Dr. R.P. Das, Director, Regional Research Laboratory, Bhubaneshwar for his kind permission to publish this paper.
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