- Email: [email protected]
Induced crystallization of goethite precipitate from nickel sulfate solution by limonite seeding
HYDROM-04534; No of Pages 5 Hydrometallurgy xxx (2017) xxx–xxx
Contents lists available at ScienceDirect
Hydrometallurgy journal homepage: www.elsevier.com/locate/hydromet
Technical note
Induced crystallization of goethite precipitate from nickel sulfate solution by limonite seeding Haisheng Han, Wei Sun ⁎, Yuehua Hu, Tong Yue ⁎, Li Wang, Runqing Liu, Zhiyong Gao, Pan Chen School of Minerals Processing and Bioengineering, Central South University, Changsha 410083, China
a r t i c l e
i n f o
Article history: Received 19 March 2016 Received in revised form 24 January 2017 Accepted 1 March 2017 Available online xxxx Keywords: Nickel adsorption Goethite process Iron removal Limonite seeds Induced crystallization
a b s t r a c t The goethite process has gained renewed attention due to the generation of environmentally acceptable sludge in hydrometallurgical processing of nickel. Goethite precipitation at low pH (2.1 to 2.5) contributes to minimizing the loss of nickel, but results in iron precipitates with poor filterability. In this paper, crystallization induced by natural limonite seeds was used to improve the filterability of iron precipitates. The X-ray Diffraction, Scanning Electron Microscopy and Laser Particle Size Analysis show that limonite seeds could induce the growth of goethite crystals and reduce the generation of amorphous iron phases at low pH. The limonite particles of size range − 74 + 37 μm were the most suitable for inducing goethite crystallization. A smaller specific surface area of goethite particles by limonite seeding and hot acid washing contributed to a decrease in the adsorption on to the precipitates. © 2017 Published by Elsevier B.V.
1. Introduction Iron removal from leach liquors is a common but complicated process. For almost 50 years, four kinds of hydrolysis–precipitation methods have been developed and widely used for solution purification, namely the Jarosite Process (Dutrizac and Jambor, 2000), the Hematite Process (Ismael and Carvalho, 2003), the Goethite Process (Davey and Scott, 1976) and the Para-goethite Process (Claassen et al., 2002). Each technique has associated strengths and weaknesses, however, today many hydrometallurgical enterprises increasingly focus on efficiency, energy saving and environmental protection during the production process. The goethite process has gained further attention, because of the advantages of lower energy consumption relative to the Hematite Process, resulting in production of an eco-friendly precipitate compared to the Jarosite Process, and better filtering ability compared to the Para-goethite Process. The Goethite Process is used for iron removal in zinc hydrometallurgical process (Davey and Scott, 1976; Pradel et al., 1993). The research activities on the removal of iron from leach liquors using goethite precipitation have been conducted on developing hydrometallurgical process for nickel sulfide or nickel laterite (Allan et al., 1973; Chang et al., 2010). However, there are two practical problems associated with the goethite process, such as the poor filterability of precipitates and the loss of nickel and cobalt. Recent studies have shown that carefully regulation of certain parameters, such as controlling pH at a lower level, could minimize the loss of nickel (Chang et al., 2010). Nickel loss and filterability ⁎ Corresponding authors. E-mail addresses: [email protected] (W. Sun), [email protected] (T. Yue).
issues for para-goethite precipitation studies also led to the same conclusion as reported by previous researchers (Wang et al., 2011; Wang et al., 2013). The residues of goethite were found to consist of amorphous iron phases, 6-line ferrihydrite, poorly crystalline goethite, solid solution jarosite phases, and silica at a low pH value or low temperature. These colloidal and microgranular particles result in poor filterability of the residues (Claassen and Sandenbergh, 2007; Loan et al., 2006). Two parallel mechanisms of Fe(II) oxidation (homogeneous and heterogeneous) have been reported in the literature (Tabakova et al., 1992; Andreeva et al., 1994): (i) the crystal α-FeOOH is formed as a result of “oriented crystal growth” and recrystallization of polymer particles of supersmall size, and (ii) the oxidation process in heterogeneous phase also contributes to the formation of the crystal phase with bettershaped and larger particles. However, many amorphous phases were produced inevitably during the hydrolysis and precipitation of Fe(III) (Dousma and De Bruyn, 1976, 1979). Long reaction time of several days was essential to produce the precipitate that resembles to goethite or hematite. There are many studies concerning the thermodynamics and kinetics of the goethite process. This process can be divided into four stages: (a) hydrolysis to monomers and dimers; (b) the reversible stage involving rapid growth to small polymers; (c) formation of slowly reacting large polymers; and (d) precipitation of a solid phase. This explains why many amorphous iron phases are produced during the goethite process at low pH or low temperature and so to change this process, an effective means to reduce the energy barrier must be developed. In hydrothermal crystallization, seeds induced crystallization was widely adopted to produce pharmaceutical and nano-materials (Kamimura et al., 2012; Murphy et al., 2011; Ran et al., 2013;
http://dx.doi.org/10.1016/j.hydromet.2017.03.001 0304-386X/© 2017 Published by Elsevier B.V.
Please cite this article as: Han, H., et al., Induced crystallization of goethite precipitate from nickel sulfate solution by limonite seeding, Hydrometallurgy (2017), http://dx.doi.org/10.1016/j.hydromet.2017.03.001
2
H. Han et al. / Hydrometallurgy xxx (2017) xxx–xxx
Fig. 1. A photograph of the experimental apparatus used for iron removal from nickel sulfate leach liquor by goethite precipitation process.
Wu et al., 2008). The addition of seeds effectively controls the crystal size and improves the precipitation conditions. With suitable seeds, crystals can precipitate from solution at lower supersaturation, low pH and at low temperature. This leads to partial or entire secondary nucleation which replaces primary nucleation so the energy barrier is significantly reduced. In this study, seeds induced crystallization was used to improve the poor filterability of goethite precipitates at low pH value. By comparing the crystal structure of goethite with various natural iron ores, natural limonite was selected as crystal seed.
2. Experimental Nickel-containing mother liquor for iron removal was obtained from the 4th Nickel Smelter of Jinchuan Group Ltd. in Gansu province, China. The nickel smelter adopted the pressure oxidative leaching process. The natural limonite specimen used for seeds preparation was supplied by Robe River Iron Associates (Western Australia, Australia). The mother liquor was analyzed using ICP-AES. Sodium hydroxide (6 mol/L) and hydrogen peroxide solutions (6%) were used as the neutralizer and oxidizing agent for iron(II), respectively. The experiments for iron removal from the mother liquor using the goethite process were carried out using a 50 L water-heated reaction vessel (Fig. 1). Mother liquor (30 L) and some limonite seeds were added into the reaction vessel at 85 °C and stirred at 800 rpm. The oxidizing agent was pumped at a constant rate to keep low levels of ferric iron (b1 g/L) in the reactor and the neutralizer was pumped at a fixed rate to control the pH within the range of 2.1–2.5. The duration of iron removal was 45 min. After the reaction was completed, 1 L of slurry was filtered to examine the filterability of the precipitates by a suction filter (0.04 MPa in vacuum, and the diameter of the filter plate was 10 cm). The filter cake was washed with hot acid liquor and dried at 80 ± 5 °C for 2–3 h. After drying, the samples were divided into several portions for a series of analyses. All of the experimental results show the average data of three or more repeated tests. Hot acid washing
Table 1 Composition of nickel sulfate leach liquor. Analyte
Fe(II) Fe(III) Ni
Content (g/L) 6.54
0.09
Cu
experiments of the residues were conducted in a 100 mL vessel with magnetic stirring. Residue samples of 20 g and 40 mL hot acid liquor (pH ranging from 2.0 to 3.0, temperature 55 ± 1 °C) were used in each experiment and the duration was 10 min. The residues of the experiments were filtered and the filter cakes were washed with water and dried at 80 ± 5 °C for 2–3 h. The pH measurements were recorded on-line using a pH meter with temperature compensation (Starter3100, Ohaus, NJ, USA). The ICP-AES and X-ray fluorescence (XRF) spectroscopy were used for elemental assays needed for mass balance. The XRD analysis was carried out to characterize the crystalline phase of iron precipitates. The particle size of the iron precipitates was measured using a laser particle size analyzer (LPSA, Mastersizer 3000, Malvern, England). The sample was sonicated 10 min prior to the particle size measurements. A microgram of goethite precipitates was captured using a double beam scanning electron microscope (FEI Helios Nanolab 600i, Portland, OR, USA). The limonite was milled and sieved to several fractions (− 850 + 150 μm, − 150 + 74 μm, − 74 + 37 μm and − 37 μm) serving as the seeds of goethite precipitates. 3. Results and discussion 3.1. Assays and characterization As shown in Table 1, the nickel sulfate leach liquor contained a 6.54 g/L of ferrous ion in addition to a variety of analytes such as Cd, As, Pb, Cu, Ni and Mn which accounted for the complication of the nickel-rich solution. The entire element component and XRD pattern of the limonite specimen are shown in Table 2 and Fig. 2 respectively. 3.2. Effect of limonite seed dosage The effect of the dosage of limonite seeds on goethite precipitation is presented in Table 3. It shows that the residual concentration of iron
Table 2 The X-ray fluorescence analysis of limonite specimen. Co
S
Na
Pb
Si
As
108 0.39 1.38 70.20 10.60 0.11 0.06 0.07
Element
Fe
Al
Si
Ca
Mn
Zn
Mg
Cl
F
S
Content % (w/w) 59.64 2.59 3.83 0.22 0.01 0.02 0.01 0.20 0.11 0.12
Please cite this article as: Han, H., et al., Induced crystallization of goethite precipitate from nickel sulfate solution by limonite seeding, Hydrometallurgy (2017), http://dx.doi.org/10.1016/j.hydromet.2017.03.001
H. Han et al. / Hydrometallurgy xxx (2017) xxx–xxx
3
Fig. 2. XRD pattern of limonite specimen from Robe River Iron Associates.
ions was significantly reduced by the addition of limonite seeds and the iron content of the goethite precipitate improved significantly. When the dosage of seeds was 2 g/L, the filtration time of goethite precipitate was only 25% of the time recorded without the addition of limonite seeds. In addition, the iron grade of goethite precipitates was up to 53% and the nickel grade was decreased from 2.41% to 1.22%. According to the results shown in Table 3, the limonite seeds remarkably contributed to the iron removal, indicating that adding limonite seeds maybe an effective means to improve the performance of the goethite process.
1). At the same time, some ferrous ions were oxidized to ferric ions forming para-goethite (formulas 2 and 3). In the goethite precipitation without any seeds, the probability of goethite crystal precipitating is equal at any area of the liquor. Thus, the nucleation process of goethite crystals has to be homogeneous. When a mass of limonite particles exist in the mother liquor and the concentration of ferric ion is lower than 1 g/L, the nucleation process of goethite crystals maybe heterogeneous. Limonite particles served as the crystal seeds for goethite precipitation due to the similar properties. Goethite precipitated on the surface of the seeds or aggregated with limonite seeds.
3.3. Effect of induced crystallization
2Fe2þ þ H2 O2 þ 2H2 O→2FeOOH þ 4Hþ
ð1Þ
Hydrogen peroxide was slowly injected into the nickel sulfate leaching solution, and ferrous ions were oxidized to goethite (formula
2Fe2þ þ H2 O2 þ 2Hþ ¼ 2Fe3þ þ 2H2 O
ð2Þ
Fe3þ þ H2 O þ OH− →FeðOHÞ3 =ferrihydrite=schwertmannite
ð3Þ
Table 3 Characteristics of goethite precipitation with different doses of limonite seeds. Dosage of limonite seeds (g/L)
The residual concentration of iron ion (mg/L)
Approximate Iron grade of goethite filtration precipitates/% time/min
Nickel grade of goethite precipitates/%
0 1 2 5
76.88 0.66 0.53 0.48
40 15 10 10
2.41 1.86 1.22 1.12
42.31 51.79 53.46 54.21
Fig. 3 shows the effect of limonite seeds on the particle size of iron precipitate and indicates that the limonite seeds significantly contributed to the growth of the goethite crystals. The particle sizes of the precipitate (Fig. 3-3) with limonite seeds are distributed in a range from 7 to 60 μm, which is around 10 times of the size of the precipitate (Fig. 32) without limonite seeds. In addition, the precipitates with limonite
Test conditions: pH 2.1–2.5, 85 °C, 45 min.
Fig. 3. The particle size distribution of limonite seeds (1), precipitate without seeds (2), and precipitate with limonite seeds (3). (Dosage of limonite seeds was 2 g/L, pH 2.1–2.5, and temperature 85 °C).
Fig. 4. XRD pattern of pure goethite precipitates and goethite precipitates with limonite seeds at pH 2.1–2.5. (Dosage of limonite seeds was 2 g/L, pH 2.1–2.5, and temperature 85 °C).
Please cite this article as: Han, H., et al., Induced crystallization of goethite precipitate from nickel sulfate solution by limonite seeding, Hydrometallurgy (2017), http://dx.doi.org/10.1016/j.hydromet.2017.03.001
4
H. Han et al. / Hydrometallurgy xxx (2017) xxx–xxx
Fig. 5. The SEM images of limonite seeds (−37 μm) (a) and goethite precipitate with limonite seeds (2 g/L) (b).
seeds have much fewer particles smaller than 1.0 μm than the limonite seeds. Fig. 4 shows the XRD pattern of the precipitates obtained with or without limonite seeding. There is a significant proportion of amorphous phase along with some goethite in the precipitates, which may contain ferrihydrite (Fe2O3·2FeOOH·xH2O)/schwertmannite (Fe8O8(OH)8 − 2x(SO4)x) (Schwertmann et al., 1995; Schwertmann and Cornell, 2007) type of compounds. The Fe analysis (42.3%) in the precipitate without seed indicates that most of the solid in the precipitate is due to para-goethite type of compounds even though the small XRD peaks corresponds to some goethite present in a less crystalline goethite phase. However, adding limonite seeds could significantly enhance the crystallinity of precipitates. Thus the addition of limonite seeds before precipitation would induce the growth of goethite crystals and reduce the generation of amorphous iron phases, causing improvement of filtration performance. Fig. 5 shows SEM images of limonite seeds (a) and the goethite precipitate with limonite seeds (b). The natural limonite particles have flat surfaces and angular edges, whilst the surfaces of the goethite precipitate with limonite seeds are jagged and scaly. The limonite particles are covered with goethite crystal indicating that they can serve as the core of goethite crystal precipitating from mother liquor. The crystal size distribution (CSD) has a direct influence to the particle size distribution of final product. When the crystal seeds distribute an appropriate and narrow size range, the product will have satisfactory size or morphology (Wang et al., 2014; Yan et al., 2015). Fig. 6 shows the particle size distributions of the iron precipitates with four different size ranges of limonite seeds, indicating that the limonite particles with size
ranging between 74 μm and 37 μm were the most suitable for inducing growth of goethite crystals at a larger size.
3.4. Nickel loss and hot acid washing The loss of nickel(II) during the iron removal process by precipitation is an issue. In the iron removal process by precipitation, the nickel(II) retained by the solids is included into the mineral lattices, adsorbed onto the mineral surfaces, or precipitated out of the solution onto the solid surface (Beukes et al., 2000). Fig. 7 shows the effects of the size range of limonite seeds on the specific surface area and the nickel grade of iron precipitates. The nickel grade in iron precipitate, which represents the nickel loss due to the fact that the lost nickel is mainly absorbed on the surface of the iron particle at lower pH (2.1–2.5) (Yue et al., 2016). The addition of limonite seeds with size ranging between 74 μm and 37 μm, having the smallest specific surface area of ~0.8 m2/g is therefore conducive to decreasing the loss of nickel in goethite precipitation resulting an iron precipitate with a nickel grade of b1%. It was expected that lost nickel could be further reduced by washing iron precipitates but the results were not satisfactory with acid washing liquor at room temperature. The hot washing liquor (50–60 °C) was used to wash iron precipitates, and contributed to a decreased nickel loss as shown in Fig. 8. After washing iron precipitates, the nickel grade showed a downward trend with decreasing pH value of the washing liquor. Nickel grade in the iron precipitate was 1.8% after hot
Fig. 6. The particle size distribution of iron precipitate with limonite seeds. −850 + 150 μm (1), −150 + 74 μm (2), −74 + 37 μm (3) and −37 μm (4).
Please cite this article as: Han, H., et al., Induced crystallization of goethite precipitate from nickel sulfate solution by limonite seeding, Hydrometallurgy (2017), http://dx.doi.org/10.1016/j.hydromet.2017.03.001
H. Han et al. / Hydrometallurgy xxx (2017) xxx–xxx
5
References
Fig. 7. The specific surface area and the nickel grade of iron precipitates with limonite seeds in different size ranges (2 g/L limonite seeds, pH 2.1–2.5, 85 °C).
washing at high pH value between 2.5 and 3.0 compared to 0.6% at a pH value between 2.3 and 2.5. 4. Conclusions The goethite process at a lower pH minimizes the loss of nickel during the precipitation of iron from clarified nickel(II) leach liquors, but generates precipitates of poor filterability. To solve the filtration problem, limonite seeds were applied to induce crystallization and improve the goethite precipitation. The current study showed that the particle size of goethite precipitates was significantly increased by the addition of limonite seeds, especially in the size range of −74 + 37 μm. Nickel loss and iron removal were also shown to be significantly improved by addition of limonite seeds. Acknowledgement This study was supported by the Program of Introducing Talents of Discipline to Universities (111 Project) of China (Grant No.: B14034), Collaborative Innovation Center for Clean and Efficient Utilization of Strategic Metal Mineral Resources, and innovation Driven Plan of Central South University (No. 2015CX005).
Allan, R., Haigh, C., Hamdorf, J., 1973. Method of Removing Dissolved Ferric Iron From Iron-bearing Solutions (Google Patents). Beukes, J., Giesekke, E., Elliott, W., 2000. Nickel retention by goethite and hematite. Miner. Eng. 13 (14), 1573–1579. Chang, Y., Zhai, X., Li, B., Fu, Y., 2010. Removal of iron from acidic leach liquor of lateritic nickel ore by goethite precipitate. Hydrometallurgy 101 (1), 84–87. Claassen, J.O., Meyer, E.H.O., Rennie, J., Sandenbergh, R.F., 2002. Iron precipitation from zinc-rich solutions: defining the Zincor Process. Hydrometallurgy 67 (1–3), 87–108. Claassen, J.O., Sandenbergh, R.F., 2007. Influence of temperature and pH on the quality of metastable iron phases produced in zinc-rich solutions. Hydrometallurgy 86 (3–4), 178–190. Andreeva, D., Mitov, I., Tabakova, T., Andreev, A., 1994. Formation of goethite by oxidation hydrolysis of Fe(II) sulphate. J. Mater. Sci. Mater. Electron. 5, 168–172. Davey, P., Scott, T., 1976. Removal of iron from leach liquors by the “goethite” process. Hydrometallurgy 2 (1), 25–33. Dousma, J., De Bruyn, P.L., 1976. Hydrolysis-precipitation studies of iron solutions. I. Model for hydrolysis and precipitation from Fe (III) nitrate solutions. J. Colloid Interface Sci. 56 (3), 527–539. Dousma, J., de Bruyn, P.L., 1979. Hydrolysis—precipitation studies of iron solutions: III. Application of growth models to the formation of colloidal αFeOOH from acid solutions. J. Colloid Interface Sci. 72 (2), 314–320. Dutrizac, J.E., Jambor, J.L., 2000. Jarosites and their application in hydrometallurgy. Rev. Mineral. Geochem. 40 (1), 405–452. Ismael, M.R.C., Carvalho, J.M.R., 2003. Iron recovery from sulphate leach liquors in zinc hydrometallurgy. Miner. Eng. 16 (1), 31–39. Kamimura, Y., et al., 2012. OSDA-free synthesis of MTW-type zeolite from sodium aluminosilicate gels with zeolite beta seeds. Microporous Mesoporous Mater. 163, 282–290. Loan, M., Newman, O.M.G., Cooper, R.M.G., Farrow, J.B., Parkinson, G.M., 2006. Defining the Paragoethite process for iron removal in zinc hydrometallurgy. Hydrometallurgy 81 (2), 104–129. Murphy, C.J., et al., 2011. Gold nanorod crystal growth: from seed-mediated synthesis to nanoscale sculpting. Curr. Opin. Colloid Interface Sci. 16 (2), 128–134. Pradel, J., Castillo, S., Traverse, J.P., Grezes-Besset, R., Darcy, M., 1993. Ferric hydroxide oxide from the goethite process: characterization and potential use. Ind. Eng. Chem. Res. 32 (9), 1801–1804. Ran, Z., Sun, Y., Chang, B., Ren, Q., Yang, W., 2013. Silica composite nanoparticles containing fluorescent solid core and mesoporous shell with different thickness as drug carrier. J. Colloid Interface Sci. 410, 94–101. Schwertmann, U., Bigham, J.M., Murad, E., 1995. The first occurrence of schwertmannite in a natural stream environment. Eur. J. Mineral. 7 (3), 547–552. Schwertmann, U., Cornell, R.M., 2007. Ferrihydrite. Wiley-VCH Verlag GmbH, pp. 103–112. Tabakova, T., Andreeva, D., Andreev, A., Vladov, C.H., Mitov, I., 1992. Mechanism of the oxidative hydrolysis of Fe(II) sulphate. J. Mater. Sci. Mater. Electron. 3, 201–205. Wang, K., Li, J., McDonald, R.G. and Browner, R.E., 2011. The effect of iron precipitation upon nickel losses from synthetic atmospheric nickel laterite leach solutions: statistical analysis and modelling. Hydrometallurgy, 109(1–2): 140–152. Wang, K., Li, J., McDonald, R.G., Browner, R.E., 2013. Characterisation of iron-rich precipitates from synthetic atmospheric nickel laterite leach solutions. Miner. Eng. 40, 1–11. Wang, L., et al., 2014. Seed-assisted synthesis of high silica ZSM-35 through interface-induced growth over MCM-49 seeds. Microporous Mesoporous Mater. 196, 89–96. Wu, Y., Ren, X., Lu, Y., Wang, J., 2008. Crystallization and morphology of zeolite MCM-22 influenced by various conditions in the static hydrothermal synthesis. Microporous Mesoporous Mater. 112 (1–3), 138–146. Yan, H., Ma, N., Zhan, Z., Wang, Z., 2015. Fabrication of zeolite NaA membranes on hollow fibers using nano-sized seeds exfoliated from mesoporous zeolite crystals. Microporous Mesoporous Mater. 215, 244–248. Yue, T., et al., 2016. Low-pH mediated goethite precipitation and nickel loss in nickel hydrometallurgy. Hydrometallurgy 165, 238–243.
Fig. 8. The change of nickel grade by washing iron precipitates with different pH value hot washing liquor of 50–60 °C (particle size of limonite seeds: −74 + 37 μm, and the starting Ni analysis: 2.57%).
Please cite this article as: Han, H., et al., Induced crystallization of goethite precipitate from nickel sulfate solution by limonite seeding, Hydrometallurgy (2017), http://dx.doi.org/10.1016/j.hydromet.2017.03.001
Contents lists available at ScienceDirect
Hydrometallurgy journal homepage: www.elsevier.com/locate/hydromet
Technical note
Induced crystallization of goethite precipitate from nickel sulfate solution by limonite seeding Haisheng Han, Wei Sun ⁎, Yuehua Hu, Tong Yue ⁎, Li Wang, Runqing Liu, Zhiyong Gao, Pan Chen School of Minerals Processing and Bioengineering, Central South University, Changsha 410083, China
a r t i c l e
i n f o
Article history: Received 19 March 2016 Received in revised form 24 January 2017 Accepted 1 March 2017 Available online xxxx Keywords: Nickel adsorption Goethite process Iron removal Limonite seeds Induced crystallization
a b s t r a c t The goethite process has gained renewed attention due to the generation of environmentally acceptable sludge in hydrometallurgical processing of nickel. Goethite precipitation at low pH (2.1 to 2.5) contributes to minimizing the loss of nickel, but results in iron precipitates with poor filterability. In this paper, crystallization induced by natural limonite seeds was used to improve the filterability of iron precipitates. The X-ray Diffraction, Scanning Electron Microscopy and Laser Particle Size Analysis show that limonite seeds could induce the growth of goethite crystals and reduce the generation of amorphous iron phases at low pH. The limonite particles of size range − 74 + 37 μm were the most suitable for inducing goethite crystallization. A smaller specific surface area of goethite particles by limonite seeding and hot acid washing contributed to a decrease in the adsorption on to the precipitates. © 2017 Published by Elsevier B.V.
1. Introduction Iron removal from leach liquors is a common but complicated process. For almost 50 years, four kinds of hydrolysis–precipitation methods have been developed and widely used for solution purification, namely the Jarosite Process (Dutrizac and Jambor, 2000), the Hematite Process (Ismael and Carvalho, 2003), the Goethite Process (Davey and Scott, 1976) and the Para-goethite Process (Claassen et al., 2002). Each technique has associated strengths and weaknesses, however, today many hydrometallurgical enterprises increasingly focus on efficiency, energy saving and environmental protection during the production process. The goethite process has gained further attention, because of the advantages of lower energy consumption relative to the Hematite Process, resulting in production of an eco-friendly precipitate compared to the Jarosite Process, and better filtering ability compared to the Para-goethite Process. The Goethite Process is used for iron removal in zinc hydrometallurgical process (Davey and Scott, 1976; Pradel et al., 1993). The research activities on the removal of iron from leach liquors using goethite precipitation have been conducted on developing hydrometallurgical process for nickel sulfide or nickel laterite (Allan et al., 1973; Chang et al., 2010). However, there are two practical problems associated with the goethite process, such as the poor filterability of precipitates and the loss of nickel and cobalt. Recent studies have shown that carefully regulation of certain parameters, such as controlling pH at a lower level, could minimize the loss of nickel (Chang et al., 2010). Nickel loss and filterability ⁎ Corresponding authors. E-mail addresses: [email protected] (W. Sun), [email protected] (T. Yue).
issues for para-goethite precipitation studies also led to the same conclusion as reported by previous researchers (Wang et al., 2011; Wang et al., 2013). The residues of goethite were found to consist of amorphous iron phases, 6-line ferrihydrite, poorly crystalline goethite, solid solution jarosite phases, and silica at a low pH value or low temperature. These colloidal and microgranular particles result in poor filterability of the residues (Claassen and Sandenbergh, 2007; Loan et al., 2006). Two parallel mechanisms of Fe(II) oxidation (homogeneous and heterogeneous) have been reported in the literature (Tabakova et al., 1992; Andreeva et al., 1994): (i) the crystal α-FeOOH is formed as a result of “oriented crystal growth” and recrystallization of polymer particles of supersmall size, and (ii) the oxidation process in heterogeneous phase also contributes to the formation of the crystal phase with bettershaped and larger particles. However, many amorphous phases were produced inevitably during the hydrolysis and precipitation of Fe(III) (Dousma and De Bruyn, 1976, 1979). Long reaction time of several days was essential to produce the precipitate that resembles to goethite or hematite. There are many studies concerning the thermodynamics and kinetics of the goethite process. This process can be divided into four stages: (a) hydrolysis to monomers and dimers; (b) the reversible stage involving rapid growth to small polymers; (c) formation of slowly reacting large polymers; and (d) precipitation of a solid phase. This explains why many amorphous iron phases are produced during the goethite process at low pH or low temperature and so to change this process, an effective means to reduce the energy barrier must be developed. In hydrothermal crystallization, seeds induced crystallization was widely adopted to produce pharmaceutical and nano-materials (Kamimura et al., 2012; Murphy et al., 2011; Ran et al., 2013;
http://dx.doi.org/10.1016/j.hydromet.2017.03.001 0304-386X/© 2017 Published by Elsevier B.V.
Please cite this article as: Han, H., et al., Induced crystallization of goethite precipitate from nickel sulfate solution by limonite seeding, Hydrometallurgy (2017), http://dx.doi.org/10.1016/j.hydromet.2017.03.001
2
H. Han et al. / Hydrometallurgy xxx (2017) xxx–xxx
Fig. 1. A photograph of the experimental apparatus used for iron removal from nickel sulfate leach liquor by goethite precipitation process.
Wu et al., 2008). The addition of seeds effectively controls the crystal size and improves the precipitation conditions. With suitable seeds, crystals can precipitate from solution at lower supersaturation, low pH and at low temperature. This leads to partial or entire secondary nucleation which replaces primary nucleation so the energy barrier is significantly reduced. In this study, seeds induced crystallization was used to improve the poor filterability of goethite precipitates at low pH value. By comparing the crystal structure of goethite with various natural iron ores, natural limonite was selected as crystal seed.
2. Experimental Nickel-containing mother liquor for iron removal was obtained from the 4th Nickel Smelter of Jinchuan Group Ltd. in Gansu province, China. The nickel smelter adopted the pressure oxidative leaching process. The natural limonite specimen used for seeds preparation was supplied by Robe River Iron Associates (Western Australia, Australia). The mother liquor was analyzed using ICP-AES. Sodium hydroxide (6 mol/L) and hydrogen peroxide solutions (6%) were used as the neutralizer and oxidizing agent for iron(II), respectively. The experiments for iron removal from the mother liquor using the goethite process were carried out using a 50 L water-heated reaction vessel (Fig. 1). Mother liquor (30 L) and some limonite seeds were added into the reaction vessel at 85 °C and stirred at 800 rpm. The oxidizing agent was pumped at a constant rate to keep low levels of ferric iron (b1 g/L) in the reactor and the neutralizer was pumped at a fixed rate to control the pH within the range of 2.1–2.5. The duration of iron removal was 45 min. After the reaction was completed, 1 L of slurry was filtered to examine the filterability of the precipitates by a suction filter (0.04 MPa in vacuum, and the diameter of the filter plate was 10 cm). The filter cake was washed with hot acid liquor and dried at 80 ± 5 °C for 2–3 h. After drying, the samples were divided into several portions for a series of analyses. All of the experimental results show the average data of three or more repeated tests. Hot acid washing
Table 1 Composition of nickel sulfate leach liquor. Analyte
Fe(II) Fe(III) Ni
Content (g/L) 6.54
0.09
Cu
experiments of the residues were conducted in a 100 mL vessel with magnetic stirring. Residue samples of 20 g and 40 mL hot acid liquor (pH ranging from 2.0 to 3.0, temperature 55 ± 1 °C) were used in each experiment and the duration was 10 min. The residues of the experiments were filtered and the filter cakes were washed with water and dried at 80 ± 5 °C for 2–3 h. The pH measurements were recorded on-line using a pH meter with temperature compensation (Starter3100, Ohaus, NJ, USA). The ICP-AES and X-ray fluorescence (XRF) spectroscopy were used for elemental assays needed for mass balance. The XRD analysis was carried out to characterize the crystalline phase of iron precipitates. The particle size of the iron precipitates was measured using a laser particle size analyzer (LPSA, Mastersizer 3000, Malvern, England). The sample was sonicated 10 min prior to the particle size measurements. A microgram of goethite precipitates was captured using a double beam scanning electron microscope (FEI Helios Nanolab 600i, Portland, OR, USA). The limonite was milled and sieved to several fractions (− 850 + 150 μm, − 150 + 74 μm, − 74 + 37 μm and − 37 μm) serving as the seeds of goethite precipitates. 3. Results and discussion 3.1. Assays and characterization As shown in Table 1, the nickel sulfate leach liquor contained a 6.54 g/L of ferrous ion in addition to a variety of analytes such as Cd, As, Pb, Cu, Ni and Mn which accounted for the complication of the nickel-rich solution. The entire element component and XRD pattern of the limonite specimen are shown in Table 2 and Fig. 2 respectively. 3.2. Effect of limonite seed dosage The effect of the dosage of limonite seeds on goethite precipitation is presented in Table 3. It shows that the residual concentration of iron
Table 2 The X-ray fluorescence analysis of limonite specimen. Co
S
Na
Pb
Si
As
108 0.39 1.38 70.20 10.60 0.11 0.06 0.07
Element
Fe
Al
Si
Ca
Mn
Zn
Mg
Cl
F
S
Content % (w/w) 59.64 2.59 3.83 0.22 0.01 0.02 0.01 0.20 0.11 0.12
Please cite this article as: Han, H., et al., Induced crystallization of goethite precipitate from nickel sulfate solution by limonite seeding, Hydrometallurgy (2017), http://dx.doi.org/10.1016/j.hydromet.2017.03.001
H. Han et al. / Hydrometallurgy xxx (2017) xxx–xxx
3
Fig. 2. XRD pattern of limonite specimen from Robe River Iron Associates.
ions was significantly reduced by the addition of limonite seeds and the iron content of the goethite precipitate improved significantly. When the dosage of seeds was 2 g/L, the filtration time of goethite precipitate was only 25% of the time recorded without the addition of limonite seeds. In addition, the iron grade of goethite precipitates was up to 53% and the nickel grade was decreased from 2.41% to 1.22%. According to the results shown in Table 3, the limonite seeds remarkably contributed to the iron removal, indicating that adding limonite seeds maybe an effective means to improve the performance of the goethite process.
1). At the same time, some ferrous ions were oxidized to ferric ions forming para-goethite (formulas 2 and 3). In the goethite precipitation without any seeds, the probability of goethite crystal precipitating is equal at any area of the liquor. Thus, the nucleation process of goethite crystals has to be homogeneous. When a mass of limonite particles exist in the mother liquor and the concentration of ferric ion is lower than 1 g/L, the nucleation process of goethite crystals maybe heterogeneous. Limonite particles served as the crystal seeds for goethite precipitation due to the similar properties. Goethite precipitated on the surface of the seeds or aggregated with limonite seeds.
3.3. Effect of induced crystallization
2Fe2þ þ H2 O2 þ 2H2 O→2FeOOH þ 4Hþ
ð1Þ
Hydrogen peroxide was slowly injected into the nickel sulfate leaching solution, and ferrous ions were oxidized to goethite (formula
2Fe2þ þ H2 O2 þ 2Hþ ¼ 2Fe3þ þ 2H2 O
ð2Þ
Fe3þ þ H2 O þ OH− →FeðOHÞ3 =ferrihydrite=schwertmannite
ð3Þ
Table 3 Characteristics of goethite precipitation with different doses of limonite seeds. Dosage of limonite seeds (g/L)
The residual concentration of iron ion (mg/L)
Approximate Iron grade of goethite filtration precipitates/% time/min
Nickel grade of goethite precipitates/%
0 1 2 5
76.88 0.66 0.53 0.48
40 15 10 10
2.41 1.86 1.22 1.12
42.31 51.79 53.46 54.21
Fig. 3 shows the effect of limonite seeds on the particle size of iron precipitate and indicates that the limonite seeds significantly contributed to the growth of the goethite crystals. The particle sizes of the precipitate (Fig. 3-3) with limonite seeds are distributed in a range from 7 to 60 μm, which is around 10 times of the size of the precipitate (Fig. 32) without limonite seeds. In addition, the precipitates with limonite
Test conditions: pH 2.1–2.5, 85 °C, 45 min.
Fig. 3. The particle size distribution of limonite seeds (1), precipitate without seeds (2), and precipitate with limonite seeds (3). (Dosage of limonite seeds was 2 g/L, pH 2.1–2.5, and temperature 85 °C).
Fig. 4. XRD pattern of pure goethite precipitates and goethite precipitates with limonite seeds at pH 2.1–2.5. (Dosage of limonite seeds was 2 g/L, pH 2.1–2.5, and temperature 85 °C).
Please cite this article as: Han, H., et al., Induced crystallization of goethite precipitate from nickel sulfate solution by limonite seeding, Hydrometallurgy (2017), http://dx.doi.org/10.1016/j.hydromet.2017.03.001
4
H. Han et al. / Hydrometallurgy xxx (2017) xxx–xxx
Fig. 5. The SEM images of limonite seeds (−37 μm) (a) and goethite precipitate with limonite seeds (2 g/L) (b).
seeds have much fewer particles smaller than 1.0 μm than the limonite seeds. Fig. 4 shows the XRD pattern of the precipitates obtained with or without limonite seeding. There is a significant proportion of amorphous phase along with some goethite in the precipitates, which may contain ferrihydrite (Fe2O3·2FeOOH·xH2O)/schwertmannite (Fe8O8(OH)8 − 2x(SO4)x) (Schwertmann et al., 1995; Schwertmann and Cornell, 2007) type of compounds. The Fe analysis (42.3%) in the precipitate without seed indicates that most of the solid in the precipitate is due to para-goethite type of compounds even though the small XRD peaks corresponds to some goethite present in a less crystalline goethite phase. However, adding limonite seeds could significantly enhance the crystallinity of precipitates. Thus the addition of limonite seeds before precipitation would induce the growth of goethite crystals and reduce the generation of amorphous iron phases, causing improvement of filtration performance. Fig. 5 shows SEM images of limonite seeds (a) and the goethite precipitate with limonite seeds (b). The natural limonite particles have flat surfaces and angular edges, whilst the surfaces of the goethite precipitate with limonite seeds are jagged and scaly. The limonite particles are covered with goethite crystal indicating that they can serve as the core of goethite crystal precipitating from mother liquor. The crystal size distribution (CSD) has a direct influence to the particle size distribution of final product. When the crystal seeds distribute an appropriate and narrow size range, the product will have satisfactory size or morphology (Wang et al., 2014; Yan et al., 2015). Fig. 6 shows the particle size distributions of the iron precipitates with four different size ranges of limonite seeds, indicating that the limonite particles with size
ranging between 74 μm and 37 μm were the most suitable for inducing growth of goethite crystals at a larger size.
3.4. Nickel loss and hot acid washing The loss of nickel(II) during the iron removal process by precipitation is an issue. In the iron removal process by precipitation, the nickel(II) retained by the solids is included into the mineral lattices, adsorbed onto the mineral surfaces, or precipitated out of the solution onto the solid surface (Beukes et al., 2000). Fig. 7 shows the effects of the size range of limonite seeds on the specific surface area and the nickel grade of iron precipitates. The nickel grade in iron precipitate, which represents the nickel loss due to the fact that the lost nickel is mainly absorbed on the surface of the iron particle at lower pH (2.1–2.5) (Yue et al., 2016). The addition of limonite seeds with size ranging between 74 μm and 37 μm, having the smallest specific surface area of ~0.8 m2/g is therefore conducive to decreasing the loss of nickel in goethite precipitation resulting an iron precipitate with a nickel grade of b1%. It was expected that lost nickel could be further reduced by washing iron precipitates but the results were not satisfactory with acid washing liquor at room temperature. The hot washing liquor (50–60 °C) was used to wash iron precipitates, and contributed to a decreased nickel loss as shown in Fig. 8. After washing iron precipitates, the nickel grade showed a downward trend with decreasing pH value of the washing liquor. Nickel grade in the iron precipitate was 1.8% after hot
Fig. 6. The particle size distribution of iron precipitate with limonite seeds. −850 + 150 μm (1), −150 + 74 μm (2), −74 + 37 μm (3) and −37 μm (4).
Please cite this article as: Han, H., et al., Induced crystallization of goethite precipitate from nickel sulfate solution by limonite seeding, Hydrometallurgy (2017), http://dx.doi.org/10.1016/j.hydromet.2017.03.001
H. Han et al. / Hydrometallurgy xxx (2017) xxx–xxx
5
References
Fig. 7. The specific surface area and the nickel grade of iron precipitates with limonite seeds in different size ranges (2 g/L limonite seeds, pH 2.1–2.5, 85 °C).
washing at high pH value between 2.5 and 3.0 compared to 0.6% at a pH value between 2.3 and 2.5. 4. Conclusions The goethite process at a lower pH minimizes the loss of nickel during the precipitation of iron from clarified nickel(II) leach liquors, but generates precipitates of poor filterability. To solve the filtration problem, limonite seeds were applied to induce crystallization and improve the goethite precipitation. The current study showed that the particle size of goethite precipitates was significantly increased by the addition of limonite seeds, especially in the size range of −74 + 37 μm. Nickel loss and iron removal were also shown to be significantly improved by addition of limonite seeds. Acknowledgement This study was supported by the Program of Introducing Talents of Discipline to Universities (111 Project) of China (Grant No.: B14034), Collaborative Innovation Center for Clean and Efficient Utilization of Strategic Metal Mineral Resources, and innovation Driven Plan of Central South University (No. 2015CX005).
Allan, R., Haigh, C., Hamdorf, J., 1973. Method of Removing Dissolved Ferric Iron From Iron-bearing Solutions (Google Patents). Beukes, J., Giesekke, E., Elliott, W., 2000. Nickel retention by goethite and hematite. Miner. Eng. 13 (14), 1573–1579. Chang, Y., Zhai, X., Li, B., Fu, Y., 2010. Removal of iron from acidic leach liquor of lateritic nickel ore by goethite precipitate. Hydrometallurgy 101 (1), 84–87. Claassen, J.O., Meyer, E.H.O., Rennie, J., Sandenbergh, R.F., 2002. Iron precipitation from zinc-rich solutions: defining the Zincor Process. Hydrometallurgy 67 (1–3), 87–108. Claassen, J.O., Sandenbergh, R.F., 2007. Influence of temperature and pH on the quality of metastable iron phases produced in zinc-rich solutions. Hydrometallurgy 86 (3–4), 178–190. Andreeva, D., Mitov, I., Tabakova, T., Andreev, A., 1994. Formation of goethite by oxidation hydrolysis of Fe(II) sulphate. J. Mater. Sci. Mater. Electron. 5, 168–172. Davey, P., Scott, T., 1976. Removal of iron from leach liquors by the “goethite” process. Hydrometallurgy 2 (1), 25–33. Dousma, J., De Bruyn, P.L., 1976. Hydrolysis-precipitation studies of iron solutions. I. Model for hydrolysis and precipitation from Fe (III) nitrate solutions. J. Colloid Interface Sci. 56 (3), 527–539. Dousma, J., de Bruyn, P.L., 1979. Hydrolysis—precipitation studies of iron solutions: III. Application of growth models to the formation of colloidal αFeOOH from acid solutions. J. Colloid Interface Sci. 72 (2), 314–320. Dutrizac, J.E., Jambor, J.L., 2000. Jarosites and their application in hydrometallurgy. Rev. Mineral. Geochem. 40 (1), 405–452. Ismael, M.R.C., Carvalho, J.M.R., 2003. Iron recovery from sulphate leach liquors in zinc hydrometallurgy. Miner. Eng. 16 (1), 31–39. Kamimura, Y., et al., 2012. OSDA-free synthesis of MTW-type zeolite from sodium aluminosilicate gels with zeolite beta seeds. Microporous Mesoporous Mater. 163, 282–290. Loan, M., Newman, O.M.G., Cooper, R.M.G., Farrow, J.B., Parkinson, G.M., 2006. Defining the Paragoethite process for iron removal in zinc hydrometallurgy. Hydrometallurgy 81 (2), 104–129. Murphy, C.J., et al., 2011. Gold nanorod crystal growth: from seed-mediated synthesis to nanoscale sculpting. Curr. Opin. Colloid Interface Sci. 16 (2), 128–134. Pradel, J., Castillo, S., Traverse, J.P., Grezes-Besset, R., Darcy, M., 1993. Ferric hydroxide oxide from the goethite process: characterization and potential use. Ind. Eng. Chem. Res. 32 (9), 1801–1804. Ran, Z., Sun, Y., Chang, B., Ren, Q., Yang, W., 2013. Silica composite nanoparticles containing fluorescent solid core and mesoporous shell with different thickness as drug carrier. J. Colloid Interface Sci. 410, 94–101. Schwertmann, U., Bigham, J.M., Murad, E., 1995. The first occurrence of schwertmannite in a natural stream environment. Eur. J. Mineral. 7 (3), 547–552. Schwertmann, U., Cornell, R.M., 2007. Ferrihydrite. Wiley-VCH Verlag GmbH, pp. 103–112. Tabakova, T., Andreeva, D., Andreev, A., Vladov, C.H., Mitov, I., 1992. Mechanism of the oxidative hydrolysis of Fe(II) sulphate. J. Mater. Sci. Mater. Electron. 3, 201–205. Wang, K., Li, J., McDonald, R.G. and Browner, R.E., 2011. The effect of iron precipitation upon nickel losses from synthetic atmospheric nickel laterite leach solutions: statistical analysis and modelling. Hydrometallurgy, 109(1–2): 140–152. Wang, K., Li, J., McDonald, R.G., Browner, R.E., 2013. Characterisation of iron-rich precipitates from synthetic atmospheric nickel laterite leach solutions. Miner. Eng. 40, 1–11. Wang, L., et al., 2014. Seed-assisted synthesis of high silica ZSM-35 through interface-induced growth over MCM-49 seeds. Microporous Mesoporous Mater. 196, 89–96. Wu, Y., Ren, X., Lu, Y., Wang, J., 2008. Crystallization and morphology of zeolite MCM-22 influenced by various conditions in the static hydrothermal synthesis. Microporous Mesoporous Mater. 112 (1–3), 138–146. Yan, H., Ma, N., Zhan, Z., Wang, Z., 2015. Fabrication of zeolite NaA membranes on hollow fibers using nano-sized seeds exfoliated from mesoporous zeolite crystals. Microporous Mesoporous Mater. 215, 244–248. Yue, T., et al., 2016. Low-pH mediated goethite precipitation and nickel loss in nickel hydrometallurgy. Hydrometallurgy 165, 238–243.
Fig. 8. The change of nickel grade by washing iron precipitates with different pH value hot washing liquor of 50–60 °C (particle size of limonite seeds: −74 + 37 μm, and the starting Ni analysis: 2.57%).
Please cite this article as: Han, H., et al., Induced crystallization of goethite precipitate from nickel sulfate solution by limonite seeding, Hydrometallurgy (2017), http://dx.doi.org/10.1016/j.hydromet.2017.03.001