Indirect bioleaching of Co and Ni from iron rich laterite ore, using metabolic carboxylic acids generated by P. putida, P. koreensis, P. bilaji and A. niger
Graphical abstract
Introduction
Complex mineralogy and limited application of existing technologies have caused difficulties in processing of nickel-bearing laterites. Extraction of cobalt and nickel from laterites in commercial scale is energy-consuming and associated with high operating costs (Valix et al., 2009; Behera et al., 2011; Behera et al., 2012). Therefore, economic and environmentally friendly replacement technologies need to be developed (Valix et al., 2009). In general, the most important reactions that occur for nickel ions in laterite dissolution are proton absorption, reduction and complexation/chelation. In proton absorption, protons produced by organic acids have a significant effect on dissolution of the mineral, the reduction reaction accelerates release of nickel, and the organic acid complexing with metal ions in the solution decreases activity of the metal, therefore the apparent solubility of the mineral accordingly increases (Simate et al., 2010).
A number of advantages have been mentioned for biological leaching of low grade ores over the traditional techniques of leaching including its relative simplicity, lower operational costs and energy consumption, as well as its environmentally friendly process (Li et al., 2010; Simate et al., 2010; Li et al., 2014; Ahmadi et al., 2015; Mahmoud et al., 2017). Bioleaching is the utilization of microorganisms and their metabolic products to dissolve metals from low-grade reserves (Sahu et al., 2011). The application of microorganisms depends on their capability to produce hydroxycarboxylic acids (gluconic, citric, pyruvic, tartaric and lactic acids) and other metabolites that are produced within the cultivation medium which depends on microorganism resistance to heavy metals (Simate et al., 2010; Behera et al., 2011). However, until now, bioleaching of non‑sulfuric minerals has not been developed on a commercial scale (Gadd, 2010; Urík et al., 2015; Jafari et al., 2018).
In recent years, extraction of metals from laterite ores has been studied using organic acid metabolites generated by microorganisms (Li et al., 2010; Behera et al., 2011). Although metal leaching using organic acids is considered as an effective method for selective extraction of specific metals from laterite ores, problems such as the long time required for leaching and low metal yield should be resolved prior to industrialization. The most effective organic acid for the Ni extraction from laterite ores of serpentine type is citric acid however, because of the low reactivity of citric acid with goethite, this acid is not efficient to dissolve nickel from laterite ore of the limonite type. However, this method is not suitable for nickel extraction since nickel is surrounded by goethite in limonite laterite ore (Li et al., 2010). Autotrophic and heterotrophic microorganisms have the ability to dissolve nickel from laterite ore (Sahu et al., 2011). It seems that chemoorganotrophic bioleaching of oxide ores have a high ability for processing of low-grade laterite ore and therefore their bioleaching process needs to be optimized (Chaerun et al., 2017). The use of heterotrophic microorganisms to leach non-sulfide minerals is very common (Sahu et al., 2011; Mubarok et al., 2013). Among heterotrophic bacteria, Pseudomonas species are effective in leaching the non-sulfide minerals. Since, non-sulfide ores have no energy sources for the use of microorganisms, when a carbon source exists to provide microorganism energy and growth, these ores can be dissolved through heterotrophic bacteria and fungi. Organisms use the carbon source and produce organic acids and compounds with at least two hydrophilic reactive groups (for instance, phenol derivatives) in the cultivation medium, called metabolic products. Secondary metabolites generated by heterotrophic organisms that use organic carbon to generate energy, react with mineral surfaces. In addition to formation of several organic acids such as citric acid, acetic acid, α-ketoglutaric acid and oxalic acid, these metabolites also have proteins, amino acids and exopolysaccharides, which can dissolve metals through different mechanisms (Sahu et al., 2011). Organic acids play an important role in the overall process of dissolution because they provide both the protons and anions to form metal complexes (Behera et al., 2011; Sahu et al., 2011). Laterite oxides can react with heterotrophic fungi and Acidithiobacilli acidophilic species. Acidophilic bacteria produce sulfuric acid and fungi produce organic acids, which both assist dissolution of metals (Jang and Valix, 2017). Fungal metabolism converts sucrose or other carbohydrates into diverse products including organic acids, which leads to decreasing the pH. Accumulation of organic acids by the microorganisms decreases the pH (Behera et al., 2011). In many investigations, two species of Aspergillus and Penicillium fungi have been used for bioleaching of laterites (Bosecker, 1986; Bosecker, 1989; Franz et al., 1991; Bosecker, 1997; Coto et al., 2001; Valix et al., 2001a; Valix et al., 2001b; Valix et al., 2001c; Coto et al., 2003; Coto et al., 2005; Behera et al., 2012). These two species are the most effective organisms for dissolution of laterites (Mubarok et al., 2013; Valix et al., 2001a). Aspergillus foetidus and Aspergillus niger are species of Aspergillus which are commonly used for extraction of nickel and cobalt from laterite ore (Mubarok et al., 2013). The dissolution behavior and kinetics of nickel-bearing laterite are influenced by different parameters such as pulp density, temperature, particle size, and acidity of the leaching solution (Petrus et al., 2018). Available studies in the literature related to the laterite bioleaching are summarized in Table 1.
Based on the results of previous investigations, the most efficient leaching agent was citric acid, while oxalic acid had the least efficacy on leaching of nickel laterites. Parameters affecting the bioleaching process include ultrasonic waves, salinity of the culture medium and type of the growth medium of the microorganism, pulp density, pH, particle size, species type, temperature, solid percentage, etc. Optimization of these parameters can greatly increase the dissolution rate and the nickel and cobalt recoveries in nickel bearing laterites (Sukla and Panchanadikar, 1993; Tzeferis, 1994; Swamy et al., 1995; Le et al., 2006; Thangavelu et al., 2006; Mubarok et al., 2013; Pawlowska and Sadowski, 2017; Petrus et al., 2018).
Nickel is considered as an important and strategic metal however, despite its frequent applications, very few investigations have focused on its extraction process. Here, the available research have been carried out in the field of nickel ore leaching, while bioleaching of these ores is less well-studied.
In this study, for the first time, the biological dissolution mechanism of cobalt and nickel elements from iron-rich laterite ore was investigated using spent medium produced by four species include Pseudomonas koreensis, Pseudomonas putida, Aspergillus niger and Penicillium bilaji. The organic acids produced by the microorganisms were in contact with the laterite sample previously heated at 500 °C for 2 h. Leaching experiments were performed at different temperatures, and the data was used to determine the activation energy for the nickel and cobalt dissolutions. Finally, the kinetics of the biological dissolution process (type of kinetic model and activation energy) was assessed. Importantly, nickel bioleaching for the laterite sample studied in this research has not been investigated. This laterite sample has low magnesium and high Fe2O3. Consequently, due to the change in mineralogical composition, the bioleaching process would be different. Bioleaching is considered an environmentally friendly method (Mahmoud et al., 2017). Therefore, results of this study can help to achieve a more environmentaly friendly process for the nickel and cobalt extractions, and increase nickel grade to provide stainless steel and metal alloys benefiting from the high resistance and fracture toughness of nickel especially at high temperatures.
Section snippets
Sample and characterization studies
A representative sample of laterite from Kanshargh mine (located east of Sarbisheh in southern Khorasan province, Iran, with a proved reserve of 3,700,000 tons) was prepared. The laterite sample was rich in nickel and cobalt with high iron content. Elemental analysis showed that the average nickel, cobalt and iron contents in this sample were 1.74%, 0.14% and 40.83%, respectively. Results of the particle size analyzes based on wet method (using Particle Size Analyzer, Micro Tec Plus) indicated
Indirect bioleaching using spent media
Variation of the pH for each medium as a function of the cultivation time is presented in Fig. S1. The pH of the PDB medium with Aspergillus niger showed the highest decline, and reached close to 1, after 2 days. For other species, pH of the culture medium decreased to about 3, after 1 day. The highest amount of biomass was produced after 4 days of cultivation for bacterial species and 7 days for fungal species. After this time, the pH increased possibly due to lack of food in the medium which
Conclusion
For the first time, this research investigated on the indirect bioleaching of nickel and cobalt from iron-rich laterite ore type, using four different species of fungus and bacteria. Results of the HPLC analysis confirmed presence of citric acid (1.3–10.0 g/l), gluconic acid (4.5–14.4 g/l) and oxalic acid (0.07–1.05 g/l) in most of the samples, while none of the species produced lactic acid. Although, the concentration of the organic acids produced by microorganisms was very low, they had the
Author contributions
Hadi abdollahi conceived and designed the experiments; Marzieh Hosseini Nasab performed the experiments; Marzieh Hosseini Nasab, Hadi Abdollahi, Mohammad Noaparast and Mohammad Ali Amoozegar analyzed the data; Marzieh Hosseini Nasab and Hadi Abdollahi wrote the paper. Mohammad Noaparast is responsible for ensuring that the descriptions are accurate and agreed by all authors.
Declaration of Competing Interest
The authors claim that they have no conflict of interest.
Acknowledgments
The authors are thankful to Mr. Rezaei and Mr. Hosseini at University of Tehran for their valuable laboratory assistance and Mr. Mehdinejad from Kanshargh Company for providing the representative laterite sample.
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