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Micellar mediated selective leaching of manganese nodule in high temperature sulfuric acid medium
HYDROM-04242; No of Pages 7 Hydrometallurgy xxx (2015) xxx–xxx
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Micellar mediated selective leaching of manganese nodule in high temperature sulfuric acid medium R. Barik, K. Sanjay, B.K. Mishra, M. Mohapatra ⁎ CSIR-Institute of Minerals & Materials Technology, Bhubaneswar, Odisha, 751013, India
a r t i c l e
i n f o
Article history: Received 15 June 2015 Received in revised form 8 December 2015 Accepted 12 December 2015 Available online xxxx Keywords: Anganese nodules CTAB surfactant Acid leaching Leached residue FESEM
a b s t r a c t The present study evaluates the possibility of selective leaching of manganese from complex, manganese and iron oxy-hydroxide based sea bed nodule utilising micelles in high temperature acid dissolution process. Application of surfactants during acid leaching of manganese nodules are described based on results from leaching studies. The factors that affected the sulfuric acid leaching of the manganese nodules in the presence of various surfactants were investigated. The effect of anionic (SDS-Sodium Dodecyl Sulphate), cationic (CTAB-Cetyl Trimethyl Ammonium Bromide) and nonionic (Triton-X 100) surfactant on the various metals extraction with respect to sulfuric acid concentration, temperature, type of surfactants and surfactant concentration is reported. Among them, CTAB showed highest improvement in the recovery of Cu, Ni, Co, Zn and Mn. Iron, aluminium, and silica were removed effectively through the present approach of high temperature sulfuric acid leaching route assisted by surfactant. Increasing the temperature of the medium has significant impact in the selective leaching of Mn, Cu, Ni and Co. The optimum conditions established for maximum metal extraction are: pulp density 10%, time 2 h, temperature 160 °C, sulfuric acid 5.0% (v/v) and at critical micellar concentration of CTAB. Under these conditions, recovery of Mn was 99% along with the (˃99%) recovery of Cu, Co, and Ni. The leached residues were analysed and their phase and morphologies were included herein. The present process may find application of separation of manganese from iron and aluminium at high temperature during various hydrometallurgical treatment of manganese based ores. © 2015 Elsevier B.V. All rights reserved.
1. Introduction A number of surfactants are extensively used in mining, petroleum, industrial, agriculture, food, cosmetics, and pharmaceutical (Li and Fang, 2002) processes due to reduction of the surface or interface tension. Surfactants are also beneficial as dispersants to increase extraction rates during leaching of metals and non-metals (Owusu et al., 1995; Karavasteva, 2001; Fan et al., 2004; Tan et al., 2004; Tan et al., 2014; Zhuo et al., 2009; Mohammad et al., 2012; Okoliegbe and Agarry, 2012; Samanta et al., 2013). It has been established from the published literature that surfactants are beneficial during extraction of uranium from low permeable sandstone uranium deposits and sulphur containing ores. Recently, addition of the surfactant during wet grinding of roast-reduced polymetallic sea nodule pellets was found to be beneficial in improving recovery of cobalt from polymetallic sea nodules in NH3–(NH4)2CO3 leaching process (Mishra et al., 2011). Nodules are good alternative resources of Mn, other important transition metals (Meylan, 1968; Bezrukov and Andrushchenko, 1972; Mukhopadhayay et al., 2003) and some rare earth elements (Heina et al., 2013; Mohwinkel et al., 2014; Randhawa et al., 2015). The metals such as ⁎ Corresponding author. E-mail address: [email protected] (M. Mohapatra).
Cu, Ni, Co and Mn are present in the form of oxides or hydroxides (Acharya et al., 1999; Ghosh et al., 2008). Voluminous work has been reported for recovery and processing of nodules by various metallurgical routes (Sen, 1999; Randhawa et al., 2015). Extraction of metal values from low and medium grade ores is also attracting the industries such as steel, nonferrous metallurgy, dry cells or batteries and chemical industries (Hariprasad et al., 2007; Xue et al., 2014; Jiang et al., 2004). The extraction of manganese from these resources should be carried out under reducing conditions as manganese dioxide ores are quite stable in acidic medium. Researchers have studied different routes for the recovery of Mn containing ores via roasting process (Sharma, 1992; Sahoo and Rao, 1989), reductive acid leaching using various reducing agents (Hariprasad et al., 2007; Xue et al., 2014; Cheng et al., 2009; Abbruzzese, 1987; Das et al., 1982, 2012; Ismail et al., 2004; Sahoo et al., 2001; Tang et al., 2014) in aqueous methanol-sulfuric acid medium (Momade and Momade, 1999) and also in sulfuric acid medium (Su et al., 2008; Tian et al., 2010). Efficacy of the extraction of metal values depends on the reducing atmosphere, leaching temperatures and acid concentrations (See Table 1). Thus continuous research is going on to develop suitable flowsheets for improving the leaching efficiencies of the valuable metal values along with the rejection of iron. In the present work, we have attempted to find one such solution for the recovery of metal values from sea bed nodules in absence of reductant
http://dx.doi.org/10.1016/j.hydromet.2015.12.005 0304-386X/© 2015 Elsevier B.V. All rights reserved.
Please cite this article as: Barik, R., et al., Micellar mediated selective leaching of manganese nodule in high temperature sulfuric acid medium, Hydrometallurgy (2015), http://dx.doi.org/10.1016/j.hydromet.2015.12.005
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Table 1 % extraction of metal values from manganese nodule leaching under various conditions. Material
Reducing agent
Temperature
Result
Reference
Ground nodule + H2SO4
Hydroxyl benzene
Ambient
Zhang et al. (2001)
H2SO4 + sea nodule Sulphuric acid solution H2SO4 + sea nodule MnO2 and H2SO4 conc. Manganese oxide ore +
Sawdust Oxalic acid Cane molasses Glucose Methanol
90 °C ∼85 °C 90 °C 90 °C 150 and 170 °C
Mn, Cu, Ni and Co increased to 97%, 95%, 94% and 98%, respectively with 90% of Fe – 98.4% Mn 97.0% for Mn, whereas 21.5% for Al and 32.4% for Fe – 98% Mn
Sawdust (C6H10O5)n or Lactose (C12H22O11)n FeSO4 NH3 NH2 H2SO4 (hydrazine sulphate) Oxygen pressure to 100 psig
70 °C
92.5% Mn recovery
Ismail et al. (2004)
90 °C 110 °C
99% of manganese recovery 96.9% Mn, 85.25% Cu, 92.58% Ni and 76.5% Co extraction Recovery of Mn,Ni,Co
Das et al. (1982) Hariprasad et al. (2013)
Oxygen partial pressure at 0.55
150 °C
MPa FeSO4–H2SO4–H2O SO2 –H2SO4 — (NH4)2 SO)4
Extraction of copper, nickel, cobalt and manganese were 77, 99.8, 88 and 99.8% respectively
90 °C 263 K
90% of Ni, Cu and Mn extracted 88.5% Cu, 99.8% Ni, 91.8% Co, 97.8% Zn, 99.6% Mn with iron extraction of 2.48% 94.80% Cu, 94.0% Ni and 80.8% Co
H2SO4 H2SO4 + MnO2 MnO2 + H2SO4 Sea based manganese ores + H2SO4 Sea based manganese ores + H2SO4 Sea based manganese ores + H2SO4 Manganese nodules Manganese nodules Roasted Sea nodules + surfactant
NH3–(NH4)2CO3
200 °C
at room temperature (~25 °C)
using various surfactants. Mishra et al. (Mishra et al., 2011) has showed that using anionic surfactant in ammoniacal process of nodules, the recovery of cobalt can be improved. However no work has been reported so far on the role of surfactants during the acid leaching of nodules. In the present study, cationic, anionic and neutral surfactants are used in sulfuric acid medium for the recovery of manganese and other metals due to their interaction with solute through electrostatic force or hydrogen bond interaction, or by the self-organization process. The present work is thus an attempt to leach Cu, Ni, Co, and Mn while maximizing the rejection of iron to the residue. Surfactant media may offer a cleaner alternative to more traditional methods. 2. Materials & methods Manganese nodules collected from the Central Indian Ocean Basin by CSIR-NIO, Goa, were air-dried and ground. The nodule samples were crushed, ground and sieved to obtain 100% -150 mesh B.S.S fraction (b100 μm). Cetyltrimethylammonium bromide (C19H42BrN) and sulfuric acid from Merck, India were used without further purification. Double distilled water was used in all the experiments. Electrokinetic measurements of manganese nodule particles, both in the presence and absence of surfactants, were performed under room temperature in a particle size analyser (Microtrac–Zetatrac). The pH of the suspensions was adjusted with the addition of 0.01 M HCl or NaOH. Leaching experiments were carried out in 2 L Parr autoclave (Model 4542) made of 316 stainless steel. The reactor has provisions for gas inlet/outlet, sampling and internal cooling. For mixing, two six bladed turbine impellers with downward thrust were attached to the shaft. Temperature was controlled through a PID controller with digital read-out for temperature, pressure and agitation speed. Initially, the required amount of concentrated H2SO4 was mixed with the weighed amount of surfactant and mixed thoroughly, followed by addition of manganese nodule. The whole mass was then transferred to the reactor under required temperature and time period. After 2 h, the slurry was cooled, filtered and the filtrate was analysed for metal ions using atomic adsorption spectrophotometer (Perkin Elmer AA 200). Experiments were carried out in triplicate in order to estimate the error. The average values of percent extraction of metal values of three experiments were considered for graphical representation. The crystal structures of the Mn nodule and leach residues were studied by X-ray diffraction (XRD) using an automated XRD Phillips Powder Diffractometer, Japan
Hariprasad et al. (2007) Sahoo et al. (2001)) Su et al. (2008) Furlani et al. (2006) Momade et al. (1999)
Han and Fuerstenau (1975) Anand et al. (1988) Vu et al. (2005) Acharya et al. (1999) Mishra et al. (2011)
(Model PAN ANALYTICAL PW 1830) in the range of 5–80° (2θ) at a scanning rate of 2°/min with Copper target. Morphology were identified with Supra 55; Zeiss (Germany Make) with a resolution of 1.0 nm at 30 kV and equipped with 20 mm2 Oxford EDS detector. 3. Results and discussion 3.1. Digestion studies (elemental analysis) and XRD analysis of the manganese nodules Required amount of sieved manganese nodules were digested using combination of various acids such as H2SO4, HCl, HNO3 and HClO4. The filtrates were used for elemental analysis of Mn, Cu, Ni, Co, Zn, Mo and Al and the acid insoluble residues mostly contain silica. The average content of valuable metals in the nodules were estimated to be 18.88% Mn, 0.98% Cu, 5.28% Fe, 1.17% Ni, 0.09% Co, 0.078% Zn, 1.78% Al, 0.056% Mo along with 22.5% acid insoluble residue. The different crystalline phases of the sample have been identified from the XRD patterns in Fig. 1. The peak locations and their corresponding relative intensities for the phases were cited from the Joint Committee on Powder Diffraction Standards (JCPDS) database. The peaks located at two-theta values of 8.97, 12.29, 18.11, 27.96 and 36.69° corresponded to the planes of the todorokite phase (ICDD00-012-0183) and the peaks located at twotheta values of 20.84, 26.69, 50.27, 55.14° corresponded to the planes of the quartz phase (01-087-2096) respectively. The mineralogy of Mn nodules had also been reported earlier as todorokite and subordinate δ-MnO2 (Nayak et al., 2011). The other minor cationic species such as copper, cobalt, nickel and rare earth metals were disseminated in the oxide matrix through sorption process. Thus, the phases of nodule were described by many authors as hydrous oxide of Mn and Fe. 3.2. Sulfuric acid leaching studies of manganese nodules 3.2.1. Effect of the nature of surfactant on the metal extraction To study the effect of nature of surfactant on the metal extraction values, cationic, anionic, and non-ionic surfactants like CTAB, SDS, Triton X-100 and Tween-80 were used under similar two experimental conditions. Amount of the surfactants were added to the acidic leaching reagent as per their critical micelle concentration (CMC) values. CMC values for CTAB, Triton X-100, SDS and Tween-80 were found to be 0.92, 0.24, 8.2 and 0.012 mM under room temperature respectively. In
Please cite this article as: Barik, R., et al., Micellar mediated selective leaching of manganese nodule in high temperature sulfuric acid medium, Hydrometallurgy (2015), http://dx.doi.org/10.1016/j.hydromet.2015.12.005
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Fig. 1. XRD pattern of grounded manganese nodule.
the first set, all the leaching experiments were carried out for 2 h, with 2.5% H2SO4 and 10% pulp density (PD), at 120 °C in autoclave without any sampling or further disturbance. From the Fig. 2a, it was clearly observed that in the presence of cationic surfactant CTAB, the percentage extraction of Mn, Cu, Ni and Co was slightly more in comparison with the other surfactants with minimum extraction of iron. This might be due to different association and adsorption of the surfactant molecules onto ore surface, which was found to be responsible for the enhancement or inhibition of extraction of the metal ion and was directly related to aggregate to form micelles. Due to the strong electrostatic force or hydrogen bond interaction, CTAB emerged as important surfactant. To clarify the effect of nature of surfactant on extraction of metal values more distinctly, the second set of experiments were carried out for 2 h, with 5% H2SO4, and 10% pulp density (PD) at 160 °C. The percentage extraction of metal values is given in Fig. 2b. The influence of concentration of surfactants became more apparent when the concentration of acid and temperature were high. Complete recovery of Mn, Cu and Ni along with ~ 94% of Co was achieved in the presence of CTAB. Here, the extraction of iron was only ~6%. Since Mn-nodule consists of phases of manganese and iron oxides, CTAB surfactant might preferably adsorb on iron oxide phase and inhibits its dissolution. Previously, it was also reported that CTAB could act as inhibitor of corrosion of steel (Khamis et al., 1997). The formation of ion pair between positive head group of CTAB micelles and reactive species of sulfuric acid and MnO2 phase might be responsible for the catalytic role of CTAB during the leaching process. With a view to find out the selective recovery of Mn and other non-ferrous metals with respect to iron, further experimental parameters were varied in the presence of only CTAB surfactant. 3.2.2. Effect of concentration of CTAB The effect of concentration of CTAB was studied using half value of CMC, CMC and double value of CMC values of CTAB, while keeping other conditions as 2 h, 5% H2SO4, and 10% pulp density (PD) at 160 °C. The results are presented in Fig. 3. A gradual decrease in the iron dissolution was observed with the increasing concentration of CTAB. In all the cases, silica in leached solution is found to be nil. However, extraction of other metal ions was higher in the presence of CMC concentration value of CTAB as evident from Fig. 3. CMC was a key parameter for the optimization for use of surfactant in various fields. In dilute solutions, amphiphilic molecules of surfactant remain as individual species with ideal physical and chemical properties. As the concentration increases more than CMC value, these properties deviate gradually from
Fig. 2. a. % extraction of metal ions under experimental conditions of leaching: time, 2 h, 2.5% H2SO4, 10% pulp density(PD), temp. 120 °C and CMC concentration of surfactants. b. % extraction of metal ions under the experimental conditions of leaching: time, 2 h, 5% H2SO4, 10% pulp density(PD), temp. 160 °C CMC concentration of surfactants.
ideal performance and aggregation of monomers into micelles occurs which might alter the mechanism of dissolution of the metal values, thus resulting to comparatively lower extraction. To know the role of
Fig. 3. % extraction of metal ions under experimental conditions: time, 2 h, 5% H2SO4, 10% pulp density(PD), temp. 160 °C.
Please cite this article as: Barik, R., et al., Micellar mediated selective leaching of manganese nodule in high temperature sulfuric acid medium, Hydrometallurgy (2015), http://dx.doi.org/10.1016/j.hydromet.2015.12.005
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Fig. 4. Electrokinetic measurements, expressed as zeta-potential of the manganese nodule in the presence of CTAB as a function of solution pH.
CTAB on the surface properties of Mn nodules, electro-kinetic measurement was carried out by immersing it in CTAB solution and the results shown in Fig. 4. The magnitude of the surface charges depends on the acidic or basic strength of the surface functional groups and on pH of the solution. The PZC (point of zero charge) for manganese nodules was found to be initially 3.74, but when CTAB (half CMC value) was added, this value was shifted to 4.37 indicating a weak chemisorption or perhaps, a combination of physical and chemical adsorption. Interaction of ionic surfactants with solid surface generally depends on the concentration of the surfactant, and the surface characteristics of the solid. Below the CMC, the addition of surfactant to an aqueous solution enhances the number of charge carriers that causes increase in conductivity. Beyond the CMC value, addition of surfactant increases the micelle concentration, while keeping the monomer concentration approximately constant (at the CMC level). The surfactant wets the surface of the nodules thereby reducing the fluid film thickness around the ore particle. The permeability thus increases and facilitates the mass
Fig. 6. % extraction of metal ions under experimental conditions: time, 2 h, CMC concentration of CTAB, 10% pulp density (PD) and temp. 160 °C.
transfer through the electrostatic interactions. The overall mechanism of dissolution of metal ion could be predicted as shown in Fig. 5. At a higher concentration of CMC, micelle diffuses more slowly through the solution than monomer due to their large size and hence was less efficient charge carrier which caused slowdown of surface leaching.
3.2.3. Effect of H2SO4 concentration The effect of H2SO4 concentration on percent metal extraction of the Mn nodules sample is presented in Fig. 6. The Mn, Cu and Ni extraction efficiency has increased remarkably from 1.1, 2.4 and 9.98% respectively to 99.99% with the increase in acid concentration from nil to 5% whereas, extraction of cobalt increased from 5% to ~ 94%. In an earlier study (Mishra et al., 2011), cobalt extraction was achieved up to 80.8% at optimum condition of leaching of roasted nodules in the presence of anionic surfactant. However, extraction of iron varied marginally from 4 to 6.69%. Further increase in acid concentration did not have any effect.
Fig. 5. Possible mechanism of the sulphuric acid leaching of manganese nodule in the presence of CTAB.
Please cite this article as: Barik, R., et al., Micellar mediated selective leaching of manganese nodule in high temperature sulfuric acid medium, Hydrometallurgy (2015), http://dx.doi.org/10.1016/j.hydromet.2015.12.005
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Fig. 7. % extraction of metal ions under experimental conditions: time, 2 h, CMC concentration of CTAB, 10% pulp density (PD) and 5% H2SO4.
3.2.4. Effect of temperature Fig. 7 illustrates the effect of the leaching temperature on the leaching efficiency of metal values at different temperatures. The other leaching conditions remained constant in the tests — 10% PD, 5% acid, 2 h and CTAB surfactant as per CMC value. Temperature also exerted a profound effect on the leaching efficiency. As shown in Fig. 7, manganese dissolution increased from 23.3 to 99.99% by increasing temperature from 100 to 160 °C. Therefore, a higher temperature was preferred for complete dissolution of manganese. A similar trend was observed for Cu, Ni and Co, whereas iron dissolution decreased from 81 to 6.69%. On comparing the results of the extraction of metal values with acid variation and temperature variation, temperature had more prominent effect on enhancing the percent extraction of metals other than iron, while iron extraction was drastically decreased at higher temperature. According to several earlier reports, separation of Fe from other nonferrous metals during acid leaching of manganese nodule was a difficult task but with this above condition feasibility of separation of iron during leaching time was possible. 3.3. Residue analysis From the above studies, it was observed that under experimental conditions of leaching at 10% PD, 2 h, 160 °C with CMC value of CTAB
surfactant, the recovery of Mn was 99% along with all other metal values with almost similar percentage except for iron. The colour of the leached residue (LR) was observed as yellowish-brown colour contrast to precursor which was black in colour. As mentioned in earlier Section 3.2.1 and Fig .2b, under similar conditions without CTAB, the percentage extraction of Mn observed was only about 60%. The residues obtained in the above two conditions were further characterized to find out any difference in their phase and morphologies. Residue contained only iron, silica and alumina which were confirmed from chemical analysis. XRD and SEM were employed to examine the phase forms of LR. XRD patterns of the residue obtained under above condition were compared with the XRD pattern of the residue obtained without CTAB, keeping other condition of leaching as same as earlier. The XRD patterns as shown in Fig. 8, were matched with mixed crystalline phases of aluminium silicate, iron–aluminium silicate hydroxide and iron oxide phases for the earlier residue whereas the XRD pattern of the sample obtained without CTAB showed iron silicate and manganese ferrite phases. While Mishra et al. (Mishra et al., 2011) reported in their process, the precipitated iron material as Fe-cake showed broad and diffuse peaks in the XRD patterns corresponding ferrihydrite [Fe5O7(OH)4H2O], and [Mn7O135H2O] phases. To see the morphologies of the leach residues, FESEM of the original Mn-nodule, leached residues obtained in the above two conditions were shown in Fig. 9. It was seen that both colour
Fig. 8. XRD pattern of manganese nodule leached residues (left) matched with various phases (right).
Please cite this article as: Barik, R., et al., Micellar mediated selective leaching of manganese nodule in high temperature sulfuric acid medium, Hydrometallurgy (2015), http://dx.doi.org/10.1016/j.hydromet.2015.12.005
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Fig. 9. FESEM images of manganese nodule and their leached residues (insets are shown their respective visual appearance).
and morphologies of the LR samples were different, fibrous type nanoranged particles were observed with CTAB surfactants. All the above observations implied this process could be a novel process of separation of iron, aluminium and silica in one step leaching process from other metal values as their dissolution during leaching was suppressed in the presence of CTAB at higher temperature, which simplifies the process reducing the load on iron removal steps. Thus the proposed modified leaching method in the current work may find a way to develop novel hydrometallurgical recovery process of manganese nodules for Cu, Ni, Co and Mn. However, for complete flowsheet development, in addition to the above leaching process experimental studies for other expected downstream processes such as removal of partially leached iron, bulk sulphide precipitation of Cu, Ni and Co values, recovery of manganese carbonate from the solution, dissolution of bulk sulphide followed by solvent extraction and electro-winning of Cu, Ni and Co or EMD/CMD from the Mn containing solution after bulk sulphide precipitation will be required to test the commercial viability of the treatment of manganese ores.
4. Conclusions The dissolution of manganese nodule in sulfuric acid solution was studied both in the presence and in the absence of the various surfactants. It showed that the surfactant could be effectively used to enhance leaching of Cu, Ni, Co and Mn from manganese nodules. Particularly, cationic surfactant CTAB played an important role for the recovery of metal values along with rejection of iron. Under the optimum conditions 99% Mn could be recovered along with other metal values Cu, Co, Ni. Higher temperature was preferred for complete dissolution of manganese with minimisation of iron dissolution (about 6.69%). The XRD pattern of the residue obtained from the leaching study using CTAB matched with mixed phase of aluminium silicate, iron–aluminium silicate hydroxide and iron oxide phases, whereas the sample obtained without CTAB showed iron silicate and manganese ferrite phases. These findings highlight that surfactant assisted leaching is a suitable method for enhancing extraction of Mn, Cu, Ni and Co metal ions while rejecting iron into the residue from polymetallic manganese nodules.
Acknowledgements Authors are thankful to the Director, CSIR-IMMT for permitting to present and publish the work in IC-LGO, Dr. I. N. Bhattacharya, Head, H&EM Department and Dr. M.K. Ghosh, Sr. Pr. Scientist for their thoughtful help. Authors gratefully acknowledge the funding and support from the projects CSC-0101(MULTIFUN) and GAP-001 (Seabed minerals extractive metallurgy laboratory activity by Ministry of Earth Sciences, New Delhi). One of the authors, Rasmita Barik, expresses her gratitude to DST-INSPIRE division, New Delhi, India for providing financial support as a senior research fellowship to carry out the research work at CSIR-IMMT, Bhubaneswar, Odisha, India.
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Please cite this article as: Barik, R., et al., Micellar mediated selective leaching of manganese nodule in high temperature sulfuric acid medium, Hydrometallurgy (2015), http://dx.doi.org/10.1016/j.hydromet.2015.12.005
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Micellar mediated selective leaching of manganese nodule in high temperature sulfuric acid medium R. Barik, K. Sanjay, B.K. Mishra, M. Mohapatra ⁎ CSIR-Institute of Minerals & Materials Technology, Bhubaneswar, Odisha, 751013, India
a r t i c l e
i n f o
Article history: Received 15 June 2015 Received in revised form 8 December 2015 Accepted 12 December 2015 Available online xxxx Keywords: Anganese nodules CTAB surfactant Acid leaching Leached residue FESEM
a b s t r a c t The present study evaluates the possibility of selective leaching of manganese from complex, manganese and iron oxy-hydroxide based sea bed nodule utilising micelles in high temperature acid dissolution process. Application of surfactants during acid leaching of manganese nodules are described based on results from leaching studies. The factors that affected the sulfuric acid leaching of the manganese nodules in the presence of various surfactants were investigated. The effect of anionic (SDS-Sodium Dodecyl Sulphate), cationic (CTAB-Cetyl Trimethyl Ammonium Bromide) and nonionic (Triton-X 100) surfactant on the various metals extraction with respect to sulfuric acid concentration, temperature, type of surfactants and surfactant concentration is reported. Among them, CTAB showed highest improvement in the recovery of Cu, Ni, Co, Zn and Mn. Iron, aluminium, and silica were removed effectively through the present approach of high temperature sulfuric acid leaching route assisted by surfactant. Increasing the temperature of the medium has significant impact in the selective leaching of Mn, Cu, Ni and Co. The optimum conditions established for maximum metal extraction are: pulp density 10%, time 2 h, temperature 160 °C, sulfuric acid 5.0% (v/v) and at critical micellar concentration of CTAB. Under these conditions, recovery of Mn was 99% along with the (˃99%) recovery of Cu, Co, and Ni. The leached residues were analysed and their phase and morphologies were included herein. The present process may find application of separation of manganese from iron and aluminium at high temperature during various hydrometallurgical treatment of manganese based ores. © 2015 Elsevier B.V. All rights reserved.
1. Introduction A number of surfactants are extensively used in mining, petroleum, industrial, agriculture, food, cosmetics, and pharmaceutical (Li and Fang, 2002) processes due to reduction of the surface or interface tension. Surfactants are also beneficial as dispersants to increase extraction rates during leaching of metals and non-metals (Owusu et al., 1995; Karavasteva, 2001; Fan et al., 2004; Tan et al., 2004; Tan et al., 2014; Zhuo et al., 2009; Mohammad et al., 2012; Okoliegbe and Agarry, 2012; Samanta et al., 2013). It has been established from the published literature that surfactants are beneficial during extraction of uranium from low permeable sandstone uranium deposits and sulphur containing ores. Recently, addition of the surfactant during wet grinding of roast-reduced polymetallic sea nodule pellets was found to be beneficial in improving recovery of cobalt from polymetallic sea nodules in NH3–(NH4)2CO3 leaching process (Mishra et al., 2011). Nodules are good alternative resources of Mn, other important transition metals (Meylan, 1968; Bezrukov and Andrushchenko, 1972; Mukhopadhayay et al., 2003) and some rare earth elements (Heina et al., 2013; Mohwinkel et al., 2014; Randhawa et al., 2015). The metals such as ⁎ Corresponding author. E-mail address: [email protected] (M. Mohapatra).
Cu, Ni, Co and Mn are present in the form of oxides or hydroxides (Acharya et al., 1999; Ghosh et al., 2008). Voluminous work has been reported for recovery and processing of nodules by various metallurgical routes (Sen, 1999; Randhawa et al., 2015). Extraction of metal values from low and medium grade ores is also attracting the industries such as steel, nonferrous metallurgy, dry cells or batteries and chemical industries (Hariprasad et al., 2007; Xue et al., 2014; Jiang et al., 2004). The extraction of manganese from these resources should be carried out under reducing conditions as manganese dioxide ores are quite stable in acidic medium. Researchers have studied different routes for the recovery of Mn containing ores via roasting process (Sharma, 1992; Sahoo and Rao, 1989), reductive acid leaching using various reducing agents (Hariprasad et al., 2007; Xue et al., 2014; Cheng et al., 2009; Abbruzzese, 1987; Das et al., 1982, 2012; Ismail et al., 2004; Sahoo et al., 2001; Tang et al., 2014) in aqueous methanol-sulfuric acid medium (Momade and Momade, 1999) and also in sulfuric acid medium (Su et al., 2008; Tian et al., 2010). Efficacy of the extraction of metal values depends on the reducing atmosphere, leaching temperatures and acid concentrations (See Table 1). Thus continuous research is going on to develop suitable flowsheets for improving the leaching efficiencies of the valuable metal values along with the rejection of iron. In the present work, we have attempted to find one such solution for the recovery of metal values from sea bed nodules in absence of reductant
http://dx.doi.org/10.1016/j.hydromet.2015.12.005 0304-386X/© 2015 Elsevier B.V. All rights reserved.
Please cite this article as: Barik, R., et al., Micellar mediated selective leaching of manganese nodule in high temperature sulfuric acid medium, Hydrometallurgy (2015), http://dx.doi.org/10.1016/j.hydromet.2015.12.005
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Table 1 % extraction of metal values from manganese nodule leaching under various conditions. Material
Reducing agent
Temperature
Result
Reference
Ground nodule + H2SO4
Hydroxyl benzene
Ambient
Zhang et al. (2001)
H2SO4 + sea nodule Sulphuric acid solution H2SO4 + sea nodule MnO2 and H2SO4 conc. Manganese oxide ore +
Sawdust Oxalic acid Cane molasses Glucose Methanol
90 °C ∼85 °C 90 °C 90 °C 150 and 170 °C
Mn, Cu, Ni and Co increased to 97%, 95%, 94% and 98%, respectively with 90% of Fe – 98.4% Mn 97.0% for Mn, whereas 21.5% for Al and 32.4% for Fe – 98% Mn
Sawdust (C6H10O5)n or Lactose (C12H22O11)n FeSO4 NH3 NH2 H2SO4 (hydrazine sulphate) Oxygen pressure to 100 psig
70 °C
92.5% Mn recovery
Ismail et al. (2004)
90 °C 110 °C
99% of manganese recovery 96.9% Mn, 85.25% Cu, 92.58% Ni and 76.5% Co extraction Recovery of Mn,Ni,Co
Das et al. (1982) Hariprasad et al. (2013)
Oxygen partial pressure at 0.55
150 °C
MPa FeSO4–H2SO4–H2O SO2 –H2SO4 — (NH4)2 SO)4
Extraction of copper, nickel, cobalt and manganese were 77, 99.8, 88 and 99.8% respectively
90 °C 263 K
90% of Ni, Cu and Mn extracted 88.5% Cu, 99.8% Ni, 91.8% Co, 97.8% Zn, 99.6% Mn with iron extraction of 2.48% 94.80% Cu, 94.0% Ni and 80.8% Co
H2SO4 H2SO4 + MnO2 MnO2 + H2SO4 Sea based manganese ores + H2SO4 Sea based manganese ores + H2SO4 Sea based manganese ores + H2SO4 Manganese nodules Manganese nodules Roasted Sea nodules + surfactant
NH3–(NH4)2CO3
200 °C
at room temperature (~25 °C)
using various surfactants. Mishra et al. (Mishra et al., 2011) has showed that using anionic surfactant in ammoniacal process of nodules, the recovery of cobalt can be improved. However no work has been reported so far on the role of surfactants during the acid leaching of nodules. In the present study, cationic, anionic and neutral surfactants are used in sulfuric acid medium for the recovery of manganese and other metals due to their interaction with solute through electrostatic force or hydrogen bond interaction, or by the self-organization process. The present work is thus an attempt to leach Cu, Ni, Co, and Mn while maximizing the rejection of iron to the residue. Surfactant media may offer a cleaner alternative to more traditional methods. 2. Materials & methods Manganese nodules collected from the Central Indian Ocean Basin by CSIR-NIO, Goa, were air-dried and ground. The nodule samples were crushed, ground and sieved to obtain 100% -150 mesh B.S.S fraction (b100 μm). Cetyltrimethylammonium bromide (C19H42BrN) and sulfuric acid from Merck, India were used without further purification. Double distilled water was used in all the experiments. Electrokinetic measurements of manganese nodule particles, both in the presence and absence of surfactants, were performed under room temperature in a particle size analyser (Microtrac–Zetatrac). The pH of the suspensions was adjusted with the addition of 0.01 M HCl or NaOH. Leaching experiments were carried out in 2 L Parr autoclave (Model 4542) made of 316 stainless steel. The reactor has provisions for gas inlet/outlet, sampling and internal cooling. For mixing, two six bladed turbine impellers with downward thrust were attached to the shaft. Temperature was controlled through a PID controller with digital read-out for temperature, pressure and agitation speed. Initially, the required amount of concentrated H2SO4 was mixed with the weighed amount of surfactant and mixed thoroughly, followed by addition of manganese nodule. The whole mass was then transferred to the reactor under required temperature and time period. After 2 h, the slurry was cooled, filtered and the filtrate was analysed for metal ions using atomic adsorption spectrophotometer (Perkin Elmer AA 200). Experiments were carried out in triplicate in order to estimate the error. The average values of percent extraction of metal values of three experiments were considered for graphical representation. The crystal structures of the Mn nodule and leach residues were studied by X-ray diffraction (XRD) using an automated XRD Phillips Powder Diffractometer, Japan
Hariprasad et al. (2007) Sahoo et al. (2001)) Su et al. (2008) Furlani et al. (2006) Momade et al. (1999)
Han and Fuerstenau (1975) Anand et al. (1988) Vu et al. (2005) Acharya et al. (1999) Mishra et al. (2011)
(Model PAN ANALYTICAL PW 1830) in the range of 5–80° (2θ) at a scanning rate of 2°/min with Copper target. Morphology were identified with Supra 55; Zeiss (Germany Make) with a resolution of 1.0 nm at 30 kV and equipped with 20 mm2 Oxford EDS detector. 3. Results and discussion 3.1. Digestion studies (elemental analysis) and XRD analysis of the manganese nodules Required amount of sieved manganese nodules were digested using combination of various acids such as H2SO4, HCl, HNO3 and HClO4. The filtrates were used for elemental analysis of Mn, Cu, Ni, Co, Zn, Mo and Al and the acid insoluble residues mostly contain silica. The average content of valuable metals in the nodules were estimated to be 18.88% Mn, 0.98% Cu, 5.28% Fe, 1.17% Ni, 0.09% Co, 0.078% Zn, 1.78% Al, 0.056% Mo along with 22.5% acid insoluble residue. The different crystalline phases of the sample have been identified from the XRD patterns in Fig. 1. The peak locations and their corresponding relative intensities for the phases were cited from the Joint Committee on Powder Diffraction Standards (JCPDS) database. The peaks located at two-theta values of 8.97, 12.29, 18.11, 27.96 and 36.69° corresponded to the planes of the todorokite phase (ICDD00-012-0183) and the peaks located at twotheta values of 20.84, 26.69, 50.27, 55.14° corresponded to the planes of the quartz phase (01-087-2096) respectively. The mineralogy of Mn nodules had also been reported earlier as todorokite and subordinate δ-MnO2 (Nayak et al., 2011). The other minor cationic species such as copper, cobalt, nickel and rare earth metals were disseminated in the oxide matrix through sorption process. Thus, the phases of nodule were described by many authors as hydrous oxide of Mn and Fe. 3.2. Sulfuric acid leaching studies of manganese nodules 3.2.1. Effect of the nature of surfactant on the metal extraction To study the effect of nature of surfactant on the metal extraction values, cationic, anionic, and non-ionic surfactants like CTAB, SDS, Triton X-100 and Tween-80 were used under similar two experimental conditions. Amount of the surfactants were added to the acidic leaching reagent as per their critical micelle concentration (CMC) values. CMC values for CTAB, Triton X-100, SDS and Tween-80 were found to be 0.92, 0.24, 8.2 and 0.012 mM under room temperature respectively. In
Please cite this article as: Barik, R., et al., Micellar mediated selective leaching of manganese nodule in high temperature sulfuric acid medium, Hydrometallurgy (2015), http://dx.doi.org/10.1016/j.hydromet.2015.12.005
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Fig. 1. XRD pattern of grounded manganese nodule.
the first set, all the leaching experiments were carried out for 2 h, with 2.5% H2SO4 and 10% pulp density (PD), at 120 °C in autoclave without any sampling or further disturbance. From the Fig. 2a, it was clearly observed that in the presence of cationic surfactant CTAB, the percentage extraction of Mn, Cu, Ni and Co was slightly more in comparison with the other surfactants with minimum extraction of iron. This might be due to different association and adsorption of the surfactant molecules onto ore surface, which was found to be responsible for the enhancement or inhibition of extraction of the metal ion and was directly related to aggregate to form micelles. Due to the strong electrostatic force or hydrogen bond interaction, CTAB emerged as important surfactant. To clarify the effect of nature of surfactant on extraction of metal values more distinctly, the second set of experiments were carried out for 2 h, with 5% H2SO4, and 10% pulp density (PD) at 160 °C. The percentage extraction of metal values is given in Fig. 2b. The influence of concentration of surfactants became more apparent when the concentration of acid and temperature were high. Complete recovery of Mn, Cu and Ni along with ~ 94% of Co was achieved in the presence of CTAB. Here, the extraction of iron was only ~6%. Since Mn-nodule consists of phases of manganese and iron oxides, CTAB surfactant might preferably adsorb on iron oxide phase and inhibits its dissolution. Previously, it was also reported that CTAB could act as inhibitor of corrosion of steel (Khamis et al., 1997). The formation of ion pair between positive head group of CTAB micelles and reactive species of sulfuric acid and MnO2 phase might be responsible for the catalytic role of CTAB during the leaching process. With a view to find out the selective recovery of Mn and other non-ferrous metals with respect to iron, further experimental parameters were varied in the presence of only CTAB surfactant. 3.2.2. Effect of concentration of CTAB The effect of concentration of CTAB was studied using half value of CMC, CMC and double value of CMC values of CTAB, while keeping other conditions as 2 h, 5% H2SO4, and 10% pulp density (PD) at 160 °C. The results are presented in Fig. 3. A gradual decrease in the iron dissolution was observed with the increasing concentration of CTAB. In all the cases, silica in leached solution is found to be nil. However, extraction of other metal ions was higher in the presence of CMC concentration value of CTAB as evident from Fig. 3. CMC was a key parameter for the optimization for use of surfactant in various fields. In dilute solutions, amphiphilic molecules of surfactant remain as individual species with ideal physical and chemical properties. As the concentration increases more than CMC value, these properties deviate gradually from
Fig. 2. a. % extraction of metal ions under experimental conditions of leaching: time, 2 h, 2.5% H2SO4, 10% pulp density(PD), temp. 120 °C and CMC concentration of surfactants. b. % extraction of metal ions under the experimental conditions of leaching: time, 2 h, 5% H2SO4, 10% pulp density(PD), temp. 160 °C CMC concentration of surfactants.
ideal performance and aggregation of monomers into micelles occurs which might alter the mechanism of dissolution of the metal values, thus resulting to comparatively lower extraction. To know the role of
Fig. 3. % extraction of metal ions under experimental conditions: time, 2 h, 5% H2SO4, 10% pulp density(PD), temp. 160 °C.
Please cite this article as: Barik, R., et al., Micellar mediated selective leaching of manganese nodule in high temperature sulfuric acid medium, Hydrometallurgy (2015), http://dx.doi.org/10.1016/j.hydromet.2015.12.005
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Fig. 4. Electrokinetic measurements, expressed as zeta-potential of the manganese nodule in the presence of CTAB as a function of solution pH.
CTAB on the surface properties of Mn nodules, electro-kinetic measurement was carried out by immersing it in CTAB solution and the results shown in Fig. 4. The magnitude of the surface charges depends on the acidic or basic strength of the surface functional groups and on pH of the solution. The PZC (point of zero charge) for manganese nodules was found to be initially 3.74, but when CTAB (half CMC value) was added, this value was shifted to 4.37 indicating a weak chemisorption or perhaps, a combination of physical and chemical adsorption. Interaction of ionic surfactants with solid surface generally depends on the concentration of the surfactant, and the surface characteristics of the solid. Below the CMC, the addition of surfactant to an aqueous solution enhances the number of charge carriers that causes increase in conductivity. Beyond the CMC value, addition of surfactant increases the micelle concentration, while keeping the monomer concentration approximately constant (at the CMC level). The surfactant wets the surface of the nodules thereby reducing the fluid film thickness around the ore particle. The permeability thus increases and facilitates the mass
Fig. 6. % extraction of metal ions under experimental conditions: time, 2 h, CMC concentration of CTAB, 10% pulp density (PD) and temp. 160 °C.
transfer through the electrostatic interactions. The overall mechanism of dissolution of metal ion could be predicted as shown in Fig. 5. At a higher concentration of CMC, micelle diffuses more slowly through the solution than monomer due to their large size and hence was less efficient charge carrier which caused slowdown of surface leaching.
3.2.3. Effect of H2SO4 concentration The effect of H2SO4 concentration on percent metal extraction of the Mn nodules sample is presented in Fig. 6. The Mn, Cu and Ni extraction efficiency has increased remarkably from 1.1, 2.4 and 9.98% respectively to 99.99% with the increase in acid concentration from nil to 5% whereas, extraction of cobalt increased from 5% to ~ 94%. In an earlier study (Mishra et al., 2011), cobalt extraction was achieved up to 80.8% at optimum condition of leaching of roasted nodules in the presence of anionic surfactant. However, extraction of iron varied marginally from 4 to 6.69%. Further increase in acid concentration did not have any effect.
Fig. 5. Possible mechanism of the sulphuric acid leaching of manganese nodule in the presence of CTAB.
Please cite this article as: Barik, R., et al., Micellar mediated selective leaching of manganese nodule in high temperature sulfuric acid medium, Hydrometallurgy (2015), http://dx.doi.org/10.1016/j.hydromet.2015.12.005
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Fig. 7. % extraction of metal ions under experimental conditions: time, 2 h, CMC concentration of CTAB, 10% pulp density (PD) and 5% H2SO4.
3.2.4. Effect of temperature Fig. 7 illustrates the effect of the leaching temperature on the leaching efficiency of metal values at different temperatures. The other leaching conditions remained constant in the tests — 10% PD, 5% acid, 2 h and CTAB surfactant as per CMC value. Temperature also exerted a profound effect on the leaching efficiency. As shown in Fig. 7, manganese dissolution increased from 23.3 to 99.99% by increasing temperature from 100 to 160 °C. Therefore, a higher temperature was preferred for complete dissolution of manganese. A similar trend was observed for Cu, Ni and Co, whereas iron dissolution decreased from 81 to 6.69%. On comparing the results of the extraction of metal values with acid variation and temperature variation, temperature had more prominent effect on enhancing the percent extraction of metals other than iron, while iron extraction was drastically decreased at higher temperature. According to several earlier reports, separation of Fe from other nonferrous metals during acid leaching of manganese nodule was a difficult task but with this above condition feasibility of separation of iron during leaching time was possible. 3.3. Residue analysis From the above studies, it was observed that under experimental conditions of leaching at 10% PD, 2 h, 160 °C with CMC value of CTAB
surfactant, the recovery of Mn was 99% along with all other metal values with almost similar percentage except for iron. The colour of the leached residue (LR) was observed as yellowish-brown colour contrast to precursor which was black in colour. As mentioned in earlier Section 3.2.1 and Fig .2b, under similar conditions without CTAB, the percentage extraction of Mn observed was only about 60%. The residues obtained in the above two conditions were further characterized to find out any difference in their phase and morphologies. Residue contained only iron, silica and alumina which were confirmed from chemical analysis. XRD and SEM were employed to examine the phase forms of LR. XRD patterns of the residue obtained under above condition were compared with the XRD pattern of the residue obtained without CTAB, keeping other condition of leaching as same as earlier. The XRD patterns as shown in Fig. 8, were matched with mixed crystalline phases of aluminium silicate, iron–aluminium silicate hydroxide and iron oxide phases for the earlier residue whereas the XRD pattern of the sample obtained without CTAB showed iron silicate and manganese ferrite phases. While Mishra et al. (Mishra et al., 2011) reported in their process, the precipitated iron material as Fe-cake showed broad and diffuse peaks in the XRD patterns corresponding ferrihydrite [Fe5O7(OH)4H2O], and [Mn7O135H2O] phases. To see the morphologies of the leach residues, FESEM of the original Mn-nodule, leached residues obtained in the above two conditions were shown in Fig. 9. It was seen that both colour
Fig. 8. XRD pattern of manganese nodule leached residues (left) matched with various phases (right).
Please cite this article as: Barik, R., et al., Micellar mediated selective leaching of manganese nodule in high temperature sulfuric acid medium, Hydrometallurgy (2015), http://dx.doi.org/10.1016/j.hydromet.2015.12.005
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Fig. 9. FESEM images of manganese nodule and their leached residues (insets are shown their respective visual appearance).
and morphologies of the LR samples were different, fibrous type nanoranged particles were observed with CTAB surfactants. All the above observations implied this process could be a novel process of separation of iron, aluminium and silica in one step leaching process from other metal values as their dissolution during leaching was suppressed in the presence of CTAB at higher temperature, which simplifies the process reducing the load on iron removal steps. Thus the proposed modified leaching method in the current work may find a way to develop novel hydrometallurgical recovery process of manganese nodules for Cu, Ni, Co and Mn. However, for complete flowsheet development, in addition to the above leaching process experimental studies for other expected downstream processes such as removal of partially leached iron, bulk sulphide precipitation of Cu, Ni and Co values, recovery of manganese carbonate from the solution, dissolution of bulk sulphide followed by solvent extraction and electro-winning of Cu, Ni and Co or EMD/CMD from the Mn containing solution after bulk sulphide precipitation will be required to test the commercial viability of the treatment of manganese ores.
4. Conclusions The dissolution of manganese nodule in sulfuric acid solution was studied both in the presence and in the absence of the various surfactants. It showed that the surfactant could be effectively used to enhance leaching of Cu, Ni, Co and Mn from manganese nodules. Particularly, cationic surfactant CTAB played an important role for the recovery of metal values along with rejection of iron. Under the optimum conditions 99% Mn could be recovered along with other metal values Cu, Co, Ni. Higher temperature was preferred for complete dissolution of manganese with minimisation of iron dissolution (about 6.69%). The XRD pattern of the residue obtained from the leaching study using CTAB matched with mixed phase of aluminium silicate, iron–aluminium silicate hydroxide and iron oxide phases, whereas the sample obtained without CTAB showed iron silicate and manganese ferrite phases. These findings highlight that surfactant assisted leaching is a suitable method for enhancing extraction of Mn, Cu, Ni and Co metal ions while rejecting iron into the residue from polymetallic manganese nodules.
Acknowledgements Authors are thankful to the Director, CSIR-IMMT for permitting to present and publish the work in IC-LGO, Dr. I. N. Bhattacharya, Head, H&EM Department and Dr. M.K. Ghosh, Sr. Pr. Scientist for their thoughtful help. Authors gratefully acknowledge the funding and support from the projects CSC-0101(MULTIFUN) and GAP-001 (Seabed minerals extractive metallurgy laboratory activity by Ministry of Earth Sciences, New Delhi). One of the authors, Rasmita Barik, expresses her gratitude to DST-INSPIRE division, New Delhi, India for providing financial support as a senior research fellowship to carry out the research work at CSIR-IMMT, Bhubaneswar, Odisha, India.
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Please cite this article as: Barik, R., et al., Micellar mediated selective leaching of manganese nodule in high temperature sulfuric acid medium, Hydrometallurgy (2015), http://dx.doi.org/10.1016/j.hydromet.2015.12.005