Proceedings of the International Seminar on Mineral Processing Technology - 2006, Chennai, India. pp. 757 - 762.
Mechano-Chemical Activation and Bio-Leaching of Indian Ocean Nodules by A. Niger Chitrangada Das, K.D. Mehta, Rakesh Kumar, B.D. Pandey and S.P. Mehrotra MEF Division, National Metallurgical Laboratory, Jamshepur-831007, India Email:
[email protected] To improve the kinetics of bioleaching which is generally a slow process, Indian Ocean nodule was activated in attrition mill while recording zeta potential, particle size distribution and surface area. Activated material was bioleached by A. niger in the pH range 4.0 - 5.5. The mechano-chemical activation of mixed particles (≤ 75µm) in 10 min reduced 86% material to ≤ 10 µm with change in zeta potential from -18 to -34mV. Bioleaching of activated material was compared with that of the data without any pretreatment as well as chemical leaching under the same condition. More than 95% copper, nickel and cobalt each were leached out in 15 days from the nodules activated for 10 min at 5% (w/v) PD, 4.5 pH and 35 ºC temperature; bio-recovery being similar from 30 min of activation. In case of non-activated nodules, ≥ 89% metal recovery was achieved in 25 days under this condition. The mechano-chemical activation of sea nodules was thus found to influence kinetics of bioleaching process, besides wider pH range available for processing. INTRODUCTION Bioleaching of valuable metals from the deep sea nodules (Ehrlich 1963, Rossi & Ehrlich 1990, Ehrlich 1996, Bosecker 1997, Li et al. 2000, Feng et al. 2000, Zhang et al. 2001, Ehrlich 2001, Ehrlich 2002) has been investigated by several researchers. Some attempts were also made for biorecovery of metals from Indian Ocean Nodules (Sukla et al. 1995, Kumari & Natarajan 2001, Kumari & Natarajan 2002, Mehta et al. 2002, Mehta et al. 2003, Mukherjee et al. 2003, Mukherjee et al. 2004a and Mukherjee et al. 2004b). Recent bioleaching studies from the sea nodules (Mehta et al. 2002, Mehta et al. 2003) were carried out by using Acidithiobacillus ferrooxidans (Tf) and microbial isolate from the nodules (Kumari & Natarajan 2001, Kumari & Natarajan 2002, Mukherjee et al. 2003, Mukherjee et al. 2004a and Mukherjee et al. 2004b). In general, bioleaching of Indian Ocean nodules with microbes is a slow process with metal recovery taking days to months. This problem may be addressed by involving an input energy in the form of ultrasonics, microwave or mechanochemical activation (MA). The application of ultrasonics (Sukla et al. 1995) as pretreatment of A. niger for bioleaching of laterite nickel has resulted in improved nickel extraction. Use of mechanochemical activation would be worth exploring to improve the process of metal bio-recovery. MA comprises of those structural and physicochemical changes which are induced in solids by deformation, disintegration and/ dispersion due to mechanical energy or which are consequences of such action (Thacova 1989, Bernhardt 2000, Butyagin 2000, Steinik & Thacova 2000, Boldyrev & Thacova 2000). This may cause change in surface charge characteristics and introduce defects in the lattice - meaning deviation from the ideal structure (Steinik & Thacova 2000). The creation of defects often leads to storage of energy in the solids and changing the structural as well as thermodynamic state (Bernhardt 2000). The change may be in terms of atomic shift from lattice structure, bond length and angle and in some cases the excitation of electron subsystems (Boldyrev & Thacova 2000). Role of mechanochemical activation of sea nodules for improving the kinetics/extent of metal extraction has been investigated in the present study using Aspergillus niger. 757
Mechano-Chemical Activation and Bio-Leaching of Indian Ocean Nodules by A.Niger
MATERIALS AND METHODS Aspergillus niger (MTCC 281) collected from IMTECH, Chandigarh was revived at 35°C using Czapek Dox medium. The subcultured A. niger in liquid Czapek Dox medium was subjected to grow on 5% (w/v) sea nodules. In this process - adaptation, the fungi became tolerant to substrate. The four times adapted strain over nodules was used for the experiments. Sea nodules were obtained from NIO, Goa. Phases identified by XRD in the nodules were todorokite, birnesite, and lithiophorite as major Mn (IV) constituents while iron phases being goethite, maghemite and ferrihydrite. Copper, nickel and cobalt were a part of manganese oxide and iron phases. The sea nodule sample was crushed and ground to less than 300μm size. A representative sample obtained by coning and quartering, was analysed by AAS and the composition found as 0.89% Cu, 0.96% Ni, 0.12% Co, 18.31% Mn and 6.4% Fe. The activation of the sample was accomplished in a high energy attrition mill (PE 075, Netzsch, Germany) under the following conditions: 500ml volume, 2 kg SS balls of 2 mm dia (86% of volume filled up), 150 g nodules sample (≤75µm size), 250 ml water, 25 °C temperature and 5 – 30 min. of activation at 1000rpm. Particle size distribution and specific surface area was determined by laser particle size analyser (Mastersizer, Malven, UK). The zeta potential of the particles was measured by zeta meter (model 501 PENKEM Inc, USA). Bioleaching experiments were carried out in conical flasks of 250 ml in an orbital motion incubator shaker at the desired temperature. Adapted fungal culture was inoculated in the Czapek Dox medium (Sucrose-30g/L, NaNO3-3g/L, K2HPO4- 1g/L, MgSO4-0.50g/L, KCl-0.5g/L and FeSO4-0.01g/L) in presence of sea nodules. Experiments were run to determine the influence of variables such as pH, particle size of nodules, etc. Samples were collected at specific intervals and analysed by AAS for metal recovery. Redox potential against saturated calomel electrode (SCE) and pH were noted and maintained at alternate day. To determine the amount of metals adsorbed in the fungal biomass, the leach residue consisting of exhausted ore and the biomass was thoroughly washed with dilute sulphuric acid (pH: 1) and then centrifuged (10, 000 rpm). The leach residue after washing was taken for metal analysis. RESULTS AND DISCUSSION The mechano-chemically activated nodules were characterized for particle size distribution [18], zeta potential, surface area etc. Trend in particle size reduction (in terms of d50 = median diameter) and increase in specific surface area (SSA) with time of activation are plotted in Fig. 1. It clearly shows typical stages achieved during mechano-chemical activation in relation to milling. Initially in 5 minutes of milling, the particles pass through Rittinger stage where excessive breakage of particles occurs and SSA increases proportionately to the energy input. In the next stage, between 5- 20 minutes, limited breakage continues but the proportional increase in SSA is lost due to weak interactions between particles. Here the input energy is used to activate the material through plastic deformation, defects, transformation etc. Beyond 20 minutes some breakage occurs with the increase in SSA. Bioleaching was performed with the nodules activated for 5, 10 and 30 minutes. In Fig. 2a and 2b particle size distribution due to milling/activation has been shown. Fig. 2 a shows that all particles are of < 38.5 µm size in 10 minutes of activation, whereas in 20 minutes, activated particles are of < 28.72 µm and of < 11.92 µm in 30 min. activation. The sea nodules ground (for 45 min.) in planetary mill show that about 95% of the particles are below 42.45 µm. Fig. 2b shows that most of the activated particles lie in the range 0.5 – 10 µm. Very few of them are of 20 – 30 µm size and only 0- 4% of them are ≥ 30 µm. Lower particle size and higher SSA offer more reactive area for microbial and chemical dissolution. 758
Proceedings of the International Seminar on Mineral Processing Technology 20
38.5 42.45
80
2.5
10
2
8
1.5
6
SSA, m2/g
12
Volume under, %
3
14
1
4
Nonactivated activated: 10 min activated: 20 min activated: 30 min
60 40 20
a
0.5
2 0
0
0 0
5
10 15 20 25 Time of activation, min
0
30
45
30
40
50
60
60 Zeta potential, - mV
35
20
Fig. 2a: Particle Size Distribution - Cummulative Volume (%)
Nonactivated activated: 10 min activated: 20 min activated: 30 min
40
10
Particle size, µm
Fig. 1: Size Reduction and Surface Area during Activation of Sea Nodules
30 A m o u nt, %
11.9
100
3.5
surface area
16
Particle dia (d50 ), µm
4
Particle size
18
25 20 15 10 5
50 40 30 20 10 0
0 0
10
20
30
40 50 Particle size, µm
60
70
0
80
10
20
30
Time of activation, min
Fig. 2b: Particle Size Distribution During Milling of Sea Nodules
Fig. 3: Change in Zeta Potential with Time of Activation at Ph 7 in Aqueous Medium
Surface charge characteristics of particles in terms of zeta potential (ZP) are expressed in Fig 3. ZP dropped gradually from – 25 mV in case of non-activated sea nodules to -34mV in 10 min and -47 in 15 min of activation. However, ZP did not change much in 5 min. of activation. Increase in ZP with time of activation indicates the accumulation of the similar charge on the surface and higher electrophoretic mobility of the activated particles in the leaching medium. The activated particles thus gains so less weight that gravitational force becomes low and particles remain dispersed in bulk medium offering more contact for the chemical leaching / micro-organism. In the bioleaching of activated nodules for 10 min. with A. niger, more than 95% Cu, Ni and Co were recovered in 15 days (Table 1) which was achieved with non-activated sample in 25 days. The optimum pH was 4.5 in both the cases but in case of activated sea nodules for 10 minutes even leaching at 5 pH resulted in good metal recovery. Thus a faster kinetics of the process has been achieved along with a satisfactory recovery even at higher pH thus providing a broader pH range i.e. 4 to5 for biodissolution. The milling/activation for 5 minutes did not have much impact on metal biodissolution. Here, the size of non-activated particles ranged form 5- 75 µm whereas it was 2 – 38.5µm for the 10 min activated particles. The improved kinetics of biodissolution could be the results of finer particle 759
Mechano-Chemical Activation and Bio-Leaching of Indian Ocean Nodules by A.Niger Table 1: Metal Recovery from Sea Nodules* by A. Niger at 35 ºc, 5% PD While varying pH and Activation Time
Time of activation (min) 0
pH
Metal recovery (%) in 15 days Control leaching Cu Ni Co Mn 3.3 8.8 13 0 2 9 4 0.8 11.6 15.3 11.6 17.5 10.7 9.8 5.9 7.1 40 42 37 25 30 46 28 31.2 23 58 21 35 67 59.5 42.9 7.7
4 4.5 4.5 5 4 4.5 5 4.5
5 10 30
Fe 4.6 0.4 5 0.5 0.2 1 2 1.4
Bioleaching(with acid wash) Cu Ni Co Mn Fe 61 55 73 75 5.9 63 62 36 57 6.1 78 64 50 63 7.0 74 73 41 58 7.2 Recovery more than 95 % Cu, Ni, Co
Recovery more than 97 % Cu, Ni, and 94% Co * Bio-recovery in 25 days at 4.5 pH without activation: 89.2% Cu, 93.5% Ni, 93% Co & 79% Mn. 322
322
Recovery, %
:2
R e c o v e r y ,%
Cu Ni Co
82 62 42
:2 82 Cu
62
Ni
42
Co
2
2 7
32
37
42
7
32
37
Days
Days
(A) Activated Control
(B) Activated Bioleaching
Cu Ni
82
Co
62 42 2 32
37
42
Co 71
98 77
60.7 44
40 26.6
26
20
5.6 0
Days
88
60
0 7
92
Ni
80 Recovery, %
Recovery,%
Cu
100
322 :2
42
5
10
15
20
25
Days
(C) Non-Activated Control
(D) Non-Activated Bioleaching
Fig. 4 (A-D): Comparison of Bioleaching using Activated and Non-Activated (Ball Milled) Sea Nodules of ≤ 38.5 µm Particles, at 4.5 pH, 35oC Temperature and 5% PD [Recovery of Metals after Acid Wash]
size available due to the milling operations (10 min). The next experiment was carried out for the bioleaching of activated (attrition milling) and non-activated sea nodule (from ball milling) particles both of ≤ 38.5µm. These results are presented in Fig 4 (a- d). It may be seen that the final recovery of the metals was almost similar in 20 days of leaching, but copper bio-recovery after acid wash 760
Proceedings of the International Seminar on Mineral Processing Technology
increased from 49.8% on day 5 to 98% on day 10 and nickel recovery also reached to 98% on day 15, this kind of rise was not observed in case of non-activated nodules. Kinetics of cobalt recovery also improved with mechano-chemical activation. As such improvement in metal recovery was 7 – 10% in control experiments for activated nodules over non-activated material. At 4.5 pH and 35oC the variation of pH prior to adjustment and corresponding redox potential during bioleaching of activated nodules (for 10 min) were recorded. In 15 days, pH and Eh became almost stable at 3.3 and 380 mV respectively indicating that the bio-leaching reached to a saturation level. The XRD phase identification of leach residue after bioleaching of nodules without activation at pH 4 and pH 4.5 is shown in Table 2. Apart from the manganese phases such as birnesite, lithiphorite and silica, formation of hydronium jarosite at pH 4 and iron- hydroxide at pH 4.5 as major phases was an interesting feature. The SEM of residue at pH 4.5 confirmed the formation of Fe(OH)3 which covered the surface. Besides some amount of MnO, γ Mn2O3, braunite, maghemite were also formed as minor phases in leach residue at pH 4 and goethite was formed in that of 4.5 pH. Formation of phases comprising of mixed and lower oxidation states of manganese and iron clearly indicates microbial attack of host lattice and release of metals entrapped in the lattice. In case of mechano-chemically activated nodules similar phases were found, as identified in the sea nodules. Table 2: XRD Phase Identification of Sea Nodules Before and After Bioleaching at 35 ºc in 25 Days in Case of Non-Activated Nodules
Sample Sea nodules pH 4 Residue after bioleaching
pH 4.5
Mineral phase Major: Todorokite, birnesite, lithiophorite, silica Minor: Maghemite, goethite, alumina Major: Birnesite, lithiophorite, silica, hydronium jarosite, Minor: MnO, γ Mn2O3, braunite, maghemite, alumina Major: Silica, birnesite, lithiphorite and Fe(OH)3 Minor: goethite, alumina
Bioleaching with A. niger appears to follow an indirect mechanism releasing some acids (oxalic/ citric) which in turn converts Fe (III) to Fe (II) and Mn (IV) to Mn (II). The reactions (1&2) of oxalic acid released by A. niger are shown below. The valuable metals viz., Cu, Ni & Co associated with the two lattices viz., manganese oxide and goethite are thus released and get dissolved at lower pH besides even forming soluble metal complexes. Some of the metals are in turn adsorbed on fungal cell wall and easily desorbed again by acid wash (AW) of the biomass. MnO2+ HCOOC—COOH + 2H+ → Mn2+ + 2CO2 + 2 H2O (1) (2) 2 Fe-O-OH + (COOH)2 + 4 H+ → 2 Fe2+ + 2 CO2 + 4 H2O Activation of nodules unlocks the host lattice facilitated by shear stress/defects induced by milling thus improving the kinetics of bioleaching. CONCLUSIONS 1. Mechano-chemical activation of Indian Ocean nodules is accompanied by reduction in particle size and accumulation of surface charges. In 10 min. of milling, ≈86% particles are of ≤ 10µm size whereas the same size is obtained almost quantitatively (99%) in 30 min of milling. The zeta potential varies from -18mV to -21mV in 5 min of milling of the material which is -34mV in 10 min of activation and becomes constant (-48mV) beyond 15 min of activation. Beyond 5 min of milling, the shear stress and structural disintegrations/ defects might be developed in the particles. 2. Activation of nodules improves the bioleaching kinetics with A. niger and provides larger pH range (4-5 pH) for metal recovery. Above 95% Cu, Ni, Co and Mn are recovered within 15 days of bioleaching at 35oC and 5% PD with 10 min. activated particles as compared to 25 days time required for the non-activated material. 761
Mechano-Chemical Activation and Bio-Leaching of Indian Ocean Nodules by A.Niger
3. Improved metal recovery in activated material of similar size range (≤38.5µm) is obtained than that from ball milling. XRD phase identification and SEM of the leach samples show the formation of iron hydroxide/jarosite covering the particles. The bio-leaching with A. niger involves indirect leaching mechanism by the participation of secreted organic acids, with maximum Eh being ≈ 380mV in 15 days. REFERENCES [1] Bernhardt, C., 2000, Particle size analysis – Problems and possibilities in fine and ultrafine range, J. Mat. Synth. Process, 8(3-4), 213- 221. [2] Boldyrev, V. V. and Thacova, K., 2000, Mechanochemistry of solids: past, present and prospects, J. Mat. Synth. Process, 8(3-4), 197- 203. [3] Bosecker, K., 1997, Bioleaching: metal solubilisation by microorganisms. FEMS Microbial. Rev., 20, 591-604 [4] Butyagin. P., 2000, Mechano-chemical synthesis: mechanical and chemical factors, J. Mat. Synth. Process, 8(3-4), 205- 211. [5] Ehrlich, H.L., 1963, Appl. Microbiol., 16, 197–202 [6] Ehrlich, H.L., 1996, In: Geomicrobiology, Chapter 15,.Marcel Dekker Inc., New York, 406–416 [7] Ehrlich, H.L. 2001, Microbial transformations of minerals, 43-60, In H.Huekelekian and N.C.Dondero[ed.], Principles and applications in aquatic microbiology, John Wiley and sons, Inc., New York. [8] Ehrlich, H. L., 2002, "How microbes mobilize metals in ores: A view of current understandings and proposals for further research." Minerals & Metallurgical Processing, 19, 220-224. [9] Kumari, A, Natarajan, K.A., 2001, Electro bioleaching of polymetallic ocean nodules, Hydrometallurgy, 62(2), 125-134. [10] Kumari, A, Natarajan, K.A., 2002, Development of a clean bio-electrochemical process for leaching of ocean manganese nodules, Minerals Engineering, 15, 103–106 [11] Li H. ,Feng Y., Shi H., Ou Y. F. , Zhang W., 2000,Bioleaching valuable metals from multimetallic nodules in the deep sea bed;. J Univ Sc and Techno. Beijing 22(6), 489-492 [12] Li,H, Feng,Y, 2000,Bio-leaching metals from multimetallic nodules in deep-sea bed, Non Ferrous Metals(China), 52(4), 74-76 [13] Mehta, K.D., Pandey, B.D., Mankhand, T.R., 2002, Biochemical recovery of valuable metals from Indian Ocean Nodules in presence of pyrite and sulphur, Trans. Indian Inst. Met., 55, (3), 71-80 [14] Mehta, K.D., Pandey, B.D., Mankhand, T.R., 2003, Studies on kinetics of biodissolution of metals from Indian Ocean nodules, Mineral Engg., 16, 523-527. [15] Mukherjee A, Raichur A.M, Modak J.M, Natarajan K.A., 2003, Solubilisation of cobalt from ocean nodules at neutral pH-a novel bioprocess., J. Ind Microbiol Biotechnol., (10), 606-12. [16] Mukherjee A, Raichur A.M, Modak J.M, Natarajan K.A., 2004, Exploring process options to enhance metal dissolution in bioleaching of Indian Ocean Nodules, J Chemical Techno. Biotechnol, 79(5), 512-517. [17] Mukherjee A, Raichur A.M, Modak J., Natarajan K.A., 2004, Bioprocessing of polymetallic Indian Ocean nodules using a marine isolate, Hydrometallurgy, 73, 205–213. [18] Rossi, G. and Ehrlich, H. L., 1990, Other bioleaching processes, 1990, 149-170. In Ehrlich, H. L. and Brierley, C. L. (ed.), Microbial mineral leaching. McGraw-Hill Inc., New York. [19] Sukla, L.B., Swamy, K.M., Narayana, K.L., Kar, R.N., and Panchanadikar, V.V., 1995, Bioleaching of Sukinda Laterite using ultrasonics, Hydrometallurgy, 37, 387-391 [20] Steinik and Thacova, K., 2000, Mechanochemistry of solids – Real structure and reactivity, J. Mat. Synth. Process, 8(3-4), 121- 132. [21] Thacova, K., 1989, Mechanical activation of minerals, Elsevier Publishers, Amsterdam. Zhang, Y., Liu, Q., Sun, C., 2001, Miner. Eng. 14, 525– 537 [22]
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