Sundramurthy et al. Appl Biol Chem (2020) 63:44 https://doi.org/10.1186/s13765-020-00528-8 ARTICLE Open Access Bioleaching of Zn from sphalerite using Leptospirillum ferriphilum isolate: efect of temperature and kinetic aspects Venkatesa Prabhu Sundramurthy1* , Baskar Rajoo2, Natesan Rajendran Srinivasan1 and Rajan Kavitha3 Abstract Biological methods for leaching of nonferrous and noble metals from its sulfde ores are widely applied at industrial enterprises of diferent countries. This process is based on the use of the oxidative activity of acidophilic microorgan- isms. Since all bio systems are quite sensitive to the temperature, bacterial leaching process also signifcantly efects. In the present study, the impact of temperature on bacterial leaching of Zn from its sulphide ore, sphalerite, was investigated using ore adapted iron oxidizing bacteria. The bacteria were isolated from mine drainage samples and subjected to gene sequencing. The acquired nucleotide sequence revealed that the isolate was Leptospirillum ferriphi- lum. The nucleotide sequence of L. ferriphilum isolate was submitted to National Center for Biotechnology Informa- tion (NCBI) and accession number KF743135 was assigned. Using the isolate, the Zn leaching data were collected in the 298–318 K temperature range. The results showed that leaching of Zn increases with temperature until optimum temperature of 313 K and achieves highest leaching efciency of 96.96% within 20 days. Since bioleaching of minerals have become increasingly applied in diferent mining industries, there is immense important to analyze mechanisti- cally-based kinetics for the design, optimization, operation, and control of biochemical processes. The kinetic study showed that the rate of Zn leaching was maximized at the optimum temperature. Further, the leaching data were analyzed using shrinking core model which revealed that the rate of leaching was inhibited by difusion through product layer. Reaction kinetics is also to be contrasted with thermodynamics. Using Arrhenius law of thermodynam- 1 ics, it was found that activation energy for Zn bioleaching reaction was 39.557 kJ mol− . Such investigations will be necessitated for designing and implanting the ideal bioleaching system for metal bio-mining industries. Keywords: Activation energy, Bioleaching, Sphalerite, Leptospirillum ferriphilum, Rate kinetics shrinking core model, Zn Introduction annually worldwide, and the demand of Zn has expanded Zn is the fourth most broadly used metal in the world altogether since 2005 [1]. Zn is separated from sphaler- after iron, aluminum, and copper. Inferable from its ite (ZnS), which is one of the most signifcant Zn-bearing solid anticorrosive properties and its ability to bond well sulfde mineral resources [2]. Tese days, approximately with other diferent metals, it has a wide range of uses in 90% of the world’s all out Zn is produced by customary applications, such as galvanizing and nonstructural cast- techniques such as roast–leach–electrowinning and pres- ings, and used as a major component of batteries and sure hydrometallurgy from sphalerite [3, 4]. Extracting alloys. More than 11 million tons of Zn is manufactured Zn using traditional methods is difcult and expensive because sphalerite is generally associated with other min- *Correspondence: [email protected] erals, such as pyrite and galena [5, 6]. Bacterial-assisted 1 Department of Chemical Engineering, Addis Ababa Science leaching (bioleaching) has been proven to be ecofriendly and Technology University, Addis Ababa, Ethiopia and the most cost-efective option to the traditional pro- Full list of author information is available at the end of the article cedures without making use of sulfur dioxide that follows © The Author(s) 2020. 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Appl Biol Chem (2020) 63:44 Page 2 of 13 as by-product in traditional methods and causes envi- (3), in which all iron-oxidizing bacteria (IOB), for exam- ronmental issues [7–9]. Bioleaching can be applied for ple, A. ferrooxidans, Acidimicrobium ferrooxidans, A. extracting Zn from sphalerite. Haghshenas et al. [10] albertensis, Alicyclobacillus tolerans, Leptospirillum fer- have studied experimentation on sphalerite bioleaching rooxidans, and Leptospirillum ferriphilum, are used for by A. ferrooxidans. Te highest extraction of Zn from cartelization [13]. IOB are capable of re-oxidizing ferrous sphalerite by bioleaching was obtained at particle size, ions to ferric ions during bioleaching [20, 21]. Regener- pulp density and temperature of 38–150 μm, 4% wt/ ated ferric ions can be reused to oxidize sphalerite [22]. vol and 33 °C, respectively. Ghassa et al. [11] have car- Sphalerite usually occurs in association with pyrite ried out an investigation on high grade Zn–Pb bearing (FeS2). Te pyritic phase present with sphalerite can be ore using mixed moderate thermophilic microorgan- used as the energy source by IOB, as described in Eq. (4), isms. Te results showed that the highest zinc recovery, which enhances Zn leaching and provides a necessary 98.5%, was obtained during 25 days with pulp density 50 acidic environment for bacterial growth [23]. (g/L). A. ferrooxidans, isolated from native province of SOB MS + 2O −→ MSO lead–zinc tailing, was used to leach Zn from sphalerite by 2 4 (1) Lei et al. [12]. During 25 days of leaching, they observed 2+ + IOB 3+ 70% of highest leaching at optimized pH value 2. Tree 2Fe + 2H + 0.5O2−→ 2Fe + H2O (2) diferent types of zinc sulphides, marmatite, sphalerite and ZnS (synthetically prepared), were studied for com- ZnS + 2Fe3+ → Zn2+ + S◦ + 2Fe2+ parative bioleaching of Zn using A. ferrooxidans and a (3) moderately thermoacidophilic iron-oxidizing bacterium IOB 2+ 2− + FeS2 + (7/2)O2 + H2O −→ Fe + 2SO + 2H by Shi et al. [13]. Tey observed that the bioleaching of 4 marmatite concentrate was advantageous over that of the (4) sphalerite and synthetic ZnS which clears that Zn extrac- Several studies reported that A. ferrooxidans is con- tion could be infuenced by mineral properties. A polym- sidered as prime important IOB. Even though it grows etallic (Cu, Zn, Pb, Fe, Ag, and Au) sulphide concentrate well with higher Fe 2+ concentrations, the members of the was subjected to bioleaching studies by Vesna et al. [14]. genus Leptospirillum attain good attention as an alter- Tey have used a mixed culture of A. ferrooxidans, A. native to A. ferrooxidans. Because Leptospirillum mem- thiooxidans, and Leptospirillum ferrooxidans. Te study bers tolerate higher cultivation temperature, lower pH, showed that Zn had a highest leaching efciency of 89% higher redox potential of the medium, and higher toler- which revealed the signifcant afnity of Zn on biologi- ance on of ferric ion concentration compared to A. fer- cal leaching. A Bioleaching study on lead–zinc tailing rooxidans [24, 25]. Tese properties make them potential dam’s sample was carried out by Mehrabani et al. [15] candidates in bio-hydrometallurgical handling of sulfde with respect to examine Zn extraction using a mixed minerals using IOB. Under genus Leptospirillum, two culture of mesophile bacteria and mixed culture of mod- most normal spices correspond to L. ferriphilum and erate thermophile bacteria. Tey observed that the mod- L. ferrooxidans. Low value of pH can be tolerated by L. erate thermophile bacteria showed signifcantly higher ferriphilum; they are more extremophile and can with- leaching efciency than that of the mesophile microbe stand higher cultivation temperature [26]. Henceforth, it which indicated the impact of temperature on the Zn was picked as the biological agent for this study. Tough bioleaching. bioleaching process has been used for several decades, Zinc sulphide ores can be treated by bioleaching there are several issues still continuing [27]. One of the through direct or indirect mechanism [16]. In the direct signifcant issues of the bioleaching process is still lower bioleaching mechanism, Zn is extracted by direct oxi- rate of leaching, which consumes high residence time dation of insoluble zinc sulfde to soluble zinc sulfate, compared to the traditional processes and hinders suc- which is catalyzed by sulfur-oxidizing bacteria (SOB) cess. In addition, diferent key factors, such as, types of such as Acidithiobacillus ferrooxidans and Acidithiobacil- metal concentrates quantity and nature of metal, nutri- lus thiooxidans, as shown in Eq. (1). Indirect bioleaching ents availability during bioleaching, oxygen supply, pH, principally pursues an iron-based mechanism in which temperature, solid-ratio, and shear rate during agita- ferric ions are produced from bio-oxidation of ferrous tion, control microbial growth [28]. Although the bacte- ions, which go about as an oxidizing agent to facilitate Zn rial population, leaching efectiveness, and leaching rate dissolution from its sulfde mineral [17–19]. Accordingly, appear closely related to the bioleaching conditions based bioleaching of sphalerite can be depicted by Eqs. (2) and on the above-mentioned factors, this work is limited to Sundramurthy et al. Appl Biol Chem (2020) 63:44 Page 3 of 13 study the efect of temperature on bioleaching of Zn from mineral composition of raw sample was conducted using sphalerite by L. ferriphilum isolate. Since bioleaching of X-ray difraction (XRD) strategy. Te XRD pattern is minerals have become increasingly applied bio-hydro- shown in Fig.