Bio-oxidation behavior of pyrite, marcasite, pyrrhotite, and arsenopyrite by sulfur- and iron-oxidizing acidophiles

https://doi.org/10.1016/j.biteb.2021.100699Get rights and content

Highlights

  • Bio-oxidation of pyrite, marcasite, pyrrhotite and arsenopyrite was studied.

  • Sulfide minerals show different bio-oxidation behavior in different conditions.

  • Marcasite has a high potential in producing acid mine drainage compared to pyrrhotite.

  • Sulfur and jarosite formed passivation layers during bio-oxidation process.

Abstract

The oxidation of sulfide minerals is of central importance due to the acid mine drainage (AMD) production. The bio-oxidation of pyrrhotite, pyrite, marcasite, and arsenopyrite was carried out with mesophilic bacteria (Acidithiobacillus ferrooxidans, A. thiooxidans, and Leptospirillum ferrooxidans) at 34 °C for 30 days. Bio-oxidation tests showed that marcasite has a high potential in producing AMD compared to pyrrhotite. Arsenopyrite has different behavior in the presence and the absence of additives (i.e., FeSO4·7H2O and sulfur). While the absence of additives increased the nickel and zinc dissolution, their presence increased the total iron dissolution. Sulfur and jarosite were observed on the surfaces of pyrrhotite and arsenopyrite. With the formation of these passivation layers, the continuous iron extraction is effectively suppressed. This study is helpful to comparatively evaluate the AMD production of sulfide minerals in an oxidizing environment and to study the effects of passivation layers on their biooxidation in different conditions.

Introduction

Acid mine drainage (AMD) is recognized to be a notorious problem in mining industry that can contaminate surface and underground water due to the metal sulfides oxidation responsible for the high dissolution of sulfates, heavy metals, and protons (Zolfaghari et al., 2020). Sulfide minerals are known to contain a broad range of heavy metals such as iron, copper, nickel, lead, and zinc that adversely damage the environment (Xing et al., 2020). Iron sulfides are among the minerals frequently used for metal extraction and generally presented in various types of rock such as igneous, sedimentary, and metamorphic ones (Hawkins, 2014). Pyrite is the most common form of iron sulfide that showed a higher reactivity than orthorhombic marcasite and (hexagonal and monoclinic) pyrrhotite (Fe1xS where x = 0–0.125) (Sun et al., 2011). Marcasite (FeS2) and pyrite are polymorph and are found in many reserves; however, their structure and morphology differ from each other (Kitchaev and Ceder, 2016). Generally, the oxidation chemistry of sulfide minerals is quite complex, and a simple study of pyrite oxidation is unlikely to provide a sufficient understanding of the reaction mechanism. On the other hand, pyrrhotite is an important mineral waste in many mining environments and usually found along with valuable minerals and huge sulfide reserves (Brierley and Brierley, 2013). Moreover, iron sulfide can be also present in different matrices such as pentlandite ((Fe, Ni)9S8), chalcopyrite (CuFeS2), and arsenopyrite (FeAsS) (Hawkins, 2014; Watling et al., 2009).

While the global demand of metals is escalating through population growth, urbanization, and industrialization, excessive mining extraction has caused high-grade ore deposits depletion. Several approaches have been widely and extensively used to extract low-grade reserves through pyrometallurgy flotation or leaching with strong inorganic acids, etc. (Rötzer and Schmidt, 2018). All of these methods are generally energy-consuming and show drastic environmental and economic problems. Per consequent, looking for efficient methods with less environmental impacts to recover low-grade metals such as bacterial leaching is promising (Brar et al., 2020). Bioleaching is usually used to convert insoluble metals into a soluble form and the extracted metal is found within the aqueous solution. Mineral bio-oxidation refers to the microbial decomposition of a mineral matrix that blocks or locks the precious metal; such as gold or silver to make them more accessible for chemical extraction (Kutschke et al., 2015). Occasionally, some conventional techniques fail to recover precious metals that are not dissolved during the biological process. In this regard, looking for an environmentally friendly replacement to improve metal/solid separation is highly required (Brar et al., 2020; Liu et al., 2008; Nordstrom et al., 2015). Sulfur-oxidizing microorganisms (SOMs) and iron-oxidizing microorganisms (IOMs) such as mesophilic bacteria (Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, and Leptospirillum ferrooxidans) are known to play principal roles in bioleaching approaches especially for the removal of the elemental sulfur accumulated on the mineral surface and the production of ferric ions for the dissolution of sulfide minerals (Liu et al., 2017). Bio-oxidation aims to convert heavily soluble metal sulfides via bio-chemical oxidation reactions into water-soluble metal sulfates. Occasionally, due to formation of passivation layers on the mineral surfaces, secondary minerals such as jarosite and amorphous ferric arsenate/scorodite decrease the extraction efficiency (Wang et al., 2016).

Ni et al. (2014) bioleached pyrrhotite using Sulfobacillus thermosulfidooxidans and found that pH has a significant effect on bacterial activity and precipitation of ferric ions. Besides, Zhang et al. (2008) have examined the pyrite oxidation under various conditions in the presence of A. ferrooxidans and L. ferriphilum, and have observed that high redox potential and high initial pH values are beneficial for leaching; however, due to the jarosite formation, pyrite leaching is hindered. In the same context, Fomchenko and Muravyov (2014) showed that the solubilization of ferrous ions and the electron flow from mineral surface to the solution increased as a result of bio-oxidation of the sulfides and trivalent arsenic in the presence of ferric ions.

To the best of authors knowledge, the effect of bacteria on the leaching and oxidation of various iron sulfide minerals and AMD production have not been reported in previous works. Generally, bacteria act as catalysts in the oxidation reactions and impact the process kinetics. The investigation of these catalysts that play a significant role in the bio-oxidation of sulfide minerals is crucial to decipher the oxidation mechanisms and products of biological oxidation. Therefore, a better understanding of the reactivity and oxidation of pyrite, marcasite, pyrrhotite, and arsenopyrite is needed to prevent the production of acid mine drainage (AMD) from iron sulfides in mine waste but also to improve mineral processing and recovery. In this regard, the aim of this work is to present a comparative experimental study on the bio-oxidation of iron bearing sulfide minerals. The variation of pH, redox potential and concentration of iron (ferrous ions, ferric ions and total iron) in different conditions was compared along four iron bearing sulfide minerals by using mixed cultures of mesophilic bacteria. Particularly, the recovery of nickel from pyrrhotite and zinc from marcasite was further investigated. These experiments were analyzed and reported to show the effect of bacteria on the dissolution of iron and other elements entrapped in minerals and their potential of AMD generation. X-ray diffraction (XRD) and scanning electron microscopy (SEM) methods were also used to study the changes of different samples and solid residues of minerals in different components after bio-oxidation and to improve our understanding the mechanism of bio-oxidation of different sulfide minerals at the molecular level.

Section snippets

Sample preparation and characterization studies

Four samples of iron bearing sulfide minerals including pyrrhotite, pyrite, marcasite and arsenopyrite were used in these experiments. All of these minerals were obtained from Mineralogy laboratory of School of Mining Engineering, University of Tehran, Iran. For bio-oxidation experiments, the samples were ground with a roller crusher and grinded with a ball mill in dry conditions to achieve a suitable size fraction less than 150 μm. Since mineral surface may be oxidized during grinding and air

Adaptation test

The variation of pH, ORP, and microbial population of adaptation tests is shown in Fig. 1. While the pH of pyrrhotite initially increases due to the presence of illite, montmorillonite, and other impurities, right after, it decreases as a result of bacterial activity. It can be noted that the high concentration of arsenic is the main cause of slow increase of ORP in arsenopyrite unlike the three other minerals (Fig. 1b). Bacterial counts rapidly increase that means these bacteria can be easily

Conclusions

This study provides a better understanding on the effect of mesophilic bacteria on AMD generation during the oxidation of pyrrhotite, pyrite, marcasite and arsenopyrite. During the bio-oxidation of arsenopyrite, an increase of iron dissolution was observed and notable concentrations of iron were released due to the oxidation of pyrite and marcasite demonstrating an environmental potential hazard. Besides, the precipitates formed during the bio-oxidation of arsenopyrite and pyrrhotite in the

CRediT authorship contribution statement

Ali Yadollahi: Methodology, Formal analysis, Investigation, Writing – original draft. Hadi Abdollahi: Methodology, Formal analysis, Investigation, Resources, Writing – original draft. Faramarz Dolati Ardejani: Methodology, Investigation, Writing – review & editing. Mirsaleh Mirmohammadi: Methodology, Formal analysis, Writing – review & editing. Sara Magdouli: Methodology, Investigation, Writing – review & editing, Supervision.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

We would like to thank Mr. A. Rezaei insightful discussions and contributions to my research and acknowledge the Mineral Processing and X-ray laboratory, School of Mining, College of Engineering, University of Tehran for kind participation and collaborations made throughout the present study.

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