Bioleaching

Last updated May 03, 2024

Bioleaching is the extraction or liberation of metals from their ores through the use of living organisms. Bioleaching is one of several applications within biohydrometallurgy and several methods are used to treat ores or concentrates containing copper, zinc, lead, arsenic, antimony, nickel, molybdenum, gold, silver, and cobalt.

Process

Bioleaching can involve numerous ferrous iron and sulfur oxidizing bacteria, including Acidithiobacillus ferrooxidans (formerly known as Thiobacillus ferrooxidans) and Acidithiobacillus thiooxidans (formerly known as Thiobacillus thiooxidans). As a general principle, in one proposed method of bacterial leaching known as Indirect Leaching, Fe³⁺ ions are used to oxidize the ore. This step is entirely independent of microbes. The role of the bacteria is further oxidation of the ore, but also the regeneration of the chemical oxidant Fe³⁺ from Fe²⁺. For example, bacteria catalyse the breakdown of the mineral pyrite (FeS₂) by oxidising the sulfur and metal (in this case ferrous iron, (Fe²⁺)) using oxygen. This yields soluble products that can be further purified and refined to yield the desired metal.^{[ citation needed ]}

Pyrite leaching (FeS₂): In the first step, disulfide is spontaneously oxidized to thiosulfate by ferric ion (Fe³⁺), which in turn is reduced to give ferrous ion (Fe²⁺):

(1)

\mathrm {FeS_{2}+6\ Fe^{\,3+}+3\ H_{2}O\longrightarrow 7\ Fe^{\,2+}+S_{2}O_{3}^{\,2-}+6\ H^{+}}

spontaneous

The ferrous ion is then oxidized by bacteria using oxygen:

(2)

\mathrm {4\ Fe^{\,2+}+\ O_{2}+4\ H^{+}\longrightarrow 4\ Fe^{\,3+}+2\ H_{2}O}

(iron oxidizers)

Thiosulfate is also oxidized by bacteria to give sulfate:

(3)

\mathrm {S_{2}O_{3}^{\,2-}+2\ O_{2}+H_{2}O\longrightarrow 2\ SO_{4}^{\,2-}+2\ H^{+}}

(sulfur oxidizers)

The ferric ion produced in reaction (2) oxidized more sulfide as in reaction (1), closing the cycle and given the net reaction:

(4)

\mathrm {2\ FeS_{2}+7\ O_{2}+2\ H_{2}O\longrightarrow 2\ Fe^{\,2+}+4\ SO_{4}^{\,2-}+4\ H^{+}}

The net products of the reaction are soluble ferrous sulfate and sulfuric acid.^{[ citation needed ]}

The microbial oxidation process occurs at the cell membrane of the bacteria. The electrons pass into the cells and are used in biochemical processes to produce energy for the bacteria while reducing oxygen to water. The critical reaction is the oxidation of sulfide by ferric iron. The main role of the bacterial step is the regeneration of this reactant.^{[ citation needed ]}

The process for copper is very similar, but the efficiency and kinetics depend on the copper mineralogy. The most efficient minerals are supergene minerals such as chalcocite, Cu₂S and covellite, CuS. The main copper mineral chalcopyrite (CuFeS₂) is not leached very efficiently, which is why the dominant copper-producing technology remains flotation, followed by smelting and refining. The leaching of CuFeS₂ follows the two stages of being dissolved and then further oxidised, with Cu²⁺ ions being left in solution.^{[ citation needed ]}

Chalcopyrite leaching:

(1)

\mathrm {CuFeS_{2}+4\ Fe^{\,3+}\longrightarrow Cu^{\,2+}+5\ Fe^{\,2+}+2\ S_{0}}

spontaneous

(2)

\mathrm {4\ Fe^{\,2+}+O_{2}+4\ H^{+}\longrightarrow 4\ Fe^{\,3+}+2\ H_{2}O}

(iron oxidizers)

(3)

\mathrm {2\ S^{0}+3\ O_{2}+2\ H_{2}O\longrightarrow 2\ SO_{4}^{\,2-}+4\ H^{+}}

(sulfur oxidizers)

net reaction:

(4)

\mathrm {CuFeS_{2}+4\ O_{2}\longrightarrow Cu^{\,2+}+Fe^{\,2+}+2\ SO_{4}^{\,2-}}

In general, sulfides are first oxidized to elemental sulfur, whereas disulfides are oxidized to give thiosulfate, and the processes above can be applied to other sulfidic ores. Bioleaching of non-sulfidic ores such as pitchblende also uses ferric iron as an oxidant (e.g., UO₂ + 2 Fe³⁺ ==> UO₂²⁺ + 2 Fe²⁺). In this case, the sole purpose of the bacterial step is the regeneration of Fe³⁺. Sulfidic iron ores can be added to speed up the process and provide a source of iron. Bioleaching of non-sulfidic ores by layering of waste sulfides and elemental sulfur, colonized by Acidithiobacillus spp., has been accomplished, which provides a strategy for accelerated leaching of materials that do not contain sulfide minerals.^[1]

Further processing

The dissolved copper (Cu²⁺) ions are removed from the solution by ligand exchange solvent extraction, which leaves other ions in the solution. The copper is removed by bonding to a ligand, which is a large molecule consisting of a number of smaller groups, each possessing a lone electron pair. The ligand-copper complex is extracted from the solution using an organic solvent such as kerosene:

Cu²⁺_(aq) + 2LH(organic) → CuL₂(organic) + 2H⁺_(aq)

The ligand donates electrons to the copper, producing a complex - a central metal atom (copper) bonded to the ligand. Because this complex has no charge, it is no longer attracted to polar water molecules and dissolves in the kerosene, which is then easily separated from the solution. Because the initial reaction is reversible, it is determined by pH. Adding concentrated acid reverses the equation, and the copper ions go back into an aqueous solution.^{[ citation needed ]}

Then the copper is passed through an electro-winning process to increase its purity: An electric current is passed through the resulting solution of copper ions. Because copper ions have a 2+ charge, they are attracted to the negative cathodes and collect there.^{[ citation needed ]}

The copper can also be concentrated and separated by displacing the copper with Fe from scrap iron:

Cu²⁺_(aq) + Fe_(s)→ Cu_(s) + Fe²⁺_(aq)

The electrons lost by the iron are taken up by the copper. Copper is the oxidising agent (it accepts electrons), and iron is the reducing agent (it loses electrons).^{[ citation needed ]}

Traces of precious metals such as gold may be left in the original solution. Treating the mixture with sodium cyanide in the presence of free oxygen dissolves the gold.^[2] The gold is removed from the solution by adsorbing (taking it up on the surface) to charcoal.^[3]

With fungi

Several species of fungi can be used for bioleaching. Fungi can be grown on many different substrates, such as electronic scrap, catalytic converters, and fly ash from municipal waste incineration. Experiments have shown that two fungal strains (Aspergillus niger, Penicillium simplicissimum) were able to mobilize Cu and Sn by 65%, and Al, Ni, Pb, and Zn by more than 95%. Aspergillus niger can produce some organic acids such as citric acid. This form of leaching does not rely on microbial oxidation of metal but rather uses microbial metabolism as source of acids that directly dissolve the metal.^[4]

Feasibility

Economic feasibility

Bioleaching is in general simpler and, therefore, cheaper to operate and maintain than traditional processes, since fewer specialists are needed to operate complex chemical plants. And low concentrations are not a problem for bacteria because they simply ignore the waste that surrounds the metals, attaining extraction yields of over 90% in some cases. These microorganisms actually gain energy by breaking down minerals into their constituent elements.^[5] The company simply collects the ions out of the solution after the bacteria have finished.

Bioleaching can be used to extract metals from low concentration ores such as gold that are too poor for other technologies. It can be used to partially replace the extensive crushing and grinding that translates to prohibitive cost and energy consumption in a conventional process. Because the lower cost of bacterial leaching outweighs the time it takes to extract the metal.^{[ citation needed ]}

High concentration ores, such as copper, are more economical to smelt rather bioleach due to the slow speed of the bacterial leaching process compared to smelting. The slow speed of bioleaching introduces a significant delay in cash flow for new mines. Nonetheless, at the largest copper mine of the world, Escondida in Chile the process seems to be favorable.^[6]

Economically it is also very expensive and many companies once started can not keep up with the demand and end up in debt.^{[ citation needed ]}

In space

The experimental unit of the experiment

S. desiccabilis is a microorganisms that showed high efficacy

In 2020 scientists showed, with an experiment with different gravity environments on the ISS, that microorganisms could be employed to mine useful elements from basaltic rocks via bioleaching in space.^[7]^[8]

Environmental impact

The process is more environmentally friendly than traditional extraction methods.^[9] For the company this can translate into profit, since the necessary limiting of sulfur dioxide emissions during smelting is expensive. Less landscape damage occurs, since the bacteria involved grow naturally, and the mine and surrounding area can be left relatively untouched. As the bacteria breed in the conditions of the mine, they are easily cultivated and recycled.^[10]

Toxic chemicals are sometimes produced in the process. Sulfuric acid and H⁺ ions that have been formed can leak into the ground and surface water turning it acidic, causing environmental damage. Heavy ions such as iron, zinc, and arsenic leak during acid mine drainage. When the pH of this solution rises, as a result of dilution by fresh water, these ions precipitate, forming "Yellow Boy" pollution.^[11] For these reasons, a setup of bioleaching must be carefully planned, since the process can lead to a biosafety failure. Unlike other methods, once started, bioheap leaching cannot be quickly stopped, because leaching would still continue with rainwater and natural bacteria. Projects like Finnish Talvivaara proved to be environmentally and economically disastrous.^[12]^[13]

Related Research Articles

Sulfuric acid or sulphuric acid, known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen, and hydrogen, with the molecular formula H₂SO₄. It is a colorless, odorless, and viscous liquid that is miscible with water.

The mineral pyrite ( PY-ryte), or iron pyrite, also known as fool's gold, is an iron sulfide with the chemical formula FeS₂ (iron (II) disulfide). Pyrite is the most abundant sulfide mineral.

Redox is a type of chemical reaction in which the oxidation states of a reactant change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a decrease in the oxidation state.

<span class="mw-page-title-main">Ferrous</span> The element iron in its +2 oxidation state

In chemistry, iron(II) refers to the element iron in its +2 oxidation state. The adjective ferrous or the prefix ferro- is often used to specify such compounds, as in ferrous chloride for iron(II) chloride (FeCl₂). The adjective ferric is used instead for iron(III) salts, containing the cation Fe³⁺. The word ferrous is derived from the Latin word ferrum, meaning "iron".

Extractive metallurgy is a branch of metallurgical engineering wherein process and methods of extraction of metals from their natural mineral deposits are studied. The field is a materials science, covering all aspects of the types of ore, washing, concentration, separation, chemical processes and extraction of pure metal and their alloying to suit various applications, sometimes for direct use as a finished product, but more often in a form that requires further working to achieve the given properties to suit the applications.

<span class="mw-page-title-main">Chalcopyrite</span> Copper iron sulfide mineral

Chalcopyrite ( KAL-kə-PY-ryte, -⁠koh-) is a copper iron sulfide mineral and the most abundant copper ore mineral. It has the chemical formula CuFeS₂ and crystallizes in the tetragonal system. It has a brassy to golden yellow color and a hardness of 3.5 to 4 on the Mohs scale. Its streak is diagnostic as green-tinged black.

Sulfide (British English also sulphide) is an inorganic anion of sulfur with the chemical formula S²⁻ or a compound containing one or more S²⁻ ions. Solutions of sulfide salts are corrosive. Sulfide also refers to large families of inorganic and organic compounds, e.g. lead sulfide and dimethyl sulfide. Hydrogen sulfide (H₂S) and bisulfide (SH⁻) are the conjugate acids of sulfide.

Acid mine drainage, acid and metalliferous drainage (AMD), or acid rock drainage (ARD) is the outflow of acidic water from metal mines and coal mines.

Copper extraction refers to the methods used to obtain copper from its ores. The conversion of copper ores consists of a series of physical, chemical and electrochemical processes. Methods have evolved and vary with country depending on the ore source, local environmental regulations, and other factors.

The pedosphere is the outermost layer of the Earth that is composed of soil and subject to soil formation processes. It exists at the interface of the lithosphere, atmosphere, hydrosphere and biosphere. The pedosphere is the skin of the Earth and only develops when there is a dynamic interaction between the atmosphere, biosphere, lithosphere and the hydrosphere. The pedosphere is the foundation of terrestrial life on Earth.

Classical qualitative inorganic analysis is a method of analytical chemistry which seeks to find the elemental composition of inorganic compounds. It is mainly focused on detecting ions in an aqueous solution, therefore materials in other forms may need to be brought to this state before using standard methods. The solution is then treated with various reagents to test for reactions characteristic of certain ions, which may cause color change, precipitation and other visible changes.

Pitting corrosion, or pitting, is a form of extremely localized corrosion that leads to the random creation of small holes in metal. The driving power for pitting corrosion is the depassivation of a small area, which becomes anodic while an unknown but potentially vast area becomes cathodic, leading to very localized galvanic corrosion. The corrosion penetrates the mass of the metal, with a limited diffusion of ions.

Iron–sulfur proteins are proteins characterized by the presence of iron–sulfur clusters containing sulfide-linked di-, tri-, and tetrairon centers in variable oxidation states. Iron–sulfur clusters are found in a variety of metalloproteins, such as the ferredoxins, as well as NADH dehydrogenase, hydrogenases, coenzyme Q – cytochrome c reductase, succinate – coenzyme Q reductase and nitrogenase. Iron–sulfur clusters are best known for their role in the oxidation-reduction reactions of electron transport in mitochondria and chloroplasts. Both Complex I and Complex II of oxidative phosphorylation have multiple Fe–S clusters. They have many other functions including catalysis as illustrated by aconitase, generation of radicals as illustrated by SAM-dependent enzymes, and as sulfur donors in the biosynthesis of lipoic acid and biotin. Additionally, some Fe–S proteins regulate gene expression. Fe–S proteins are vulnerable to attack by biogenic nitric oxide, forming dinitrosyl iron complexes. In most Fe–S proteins, the terminal ligands on Fe are thiolate, but exceptions exist.

Ferroplasma is a genus of Archaea that belong to the family Ferroplasmaceae. Members of the Ferroplasma are typically acidophillic, pleomorphic, irregularly shaped cocci.

In ore deposit geology, supergene processes or enrichment are those that occur relatively near the surface as opposed to deep hypogene processes. Supergene processes include the predominance of meteoric water circulation (i.e. water derived from precipitation) with concomitant oxidation and chemical weathering. The descending meteoric waters oxidize the primary (hypogene) sulfide ore minerals and redistribute the metallic ore elements. Supergene enrichment occurs at the base of the oxidized portion of an ore deposit. Metals that have been leached from the oxidized ore are carried downward by percolating groundwater, and react with hypogene sulfides at the supergene-hypogene boundary. The reaction produces secondary sulfides with metal contents higher than those of the primary ore. This is particularly noted in copper ore deposits where the copper sulfide minerals chalcocite (Cu₂S), covellite (CuS), digenite (Cu₁₈S₁₀), and djurleite (Cu₃₁S₁₆) are deposited by the descending surface waters.

In geology, a redox buffer is an assemblage of minerals or compounds that constrains oxygen fugacity as a function of temperature. Knowledge of the redox conditions (or equivalently, oxygen fugacities) at which a rock forms and evolves can be important for interpreting the rock history. Iron, sulfur, and manganese are three of the relatively abundant elements in the Earth's crust that occur in more than one oxidation state. For instance, iron, the fourth most abundant element in the crust, exists as native iron, ferrous iron (Fe²⁺), and ferric iron (Fe³⁺). The redox state of a rock affects the relative proportions of the oxidation states of these elements and hence may determine both the minerals present and their compositions. If a rock contains pure minerals that constitute a redox buffer, then the oxygen fugacity of equilibration is defined by one of the curves in the accompanying fugacity-temperature diagram.

Biomining refers to any process that uses living organisms to extract metals from ores and other solid materials. Typically these processes involve prokaryotes, however fungi and plants may also be used. Biomining is one of several applications within biohydrometallurgy with applications in ore refinement, precious metal recovery, and bioremediation. The largest application currently being used is the treatment of mining waste containing iron, copper, zinc, and gold allowing for salvation of any discarded minerals. It may also be useful in maximizing the yields of increasingly low grade ore deposits. Biomining has been proposed as a relatively environmentally friendly alternative and/or supplementation to traditional mining. Current methods of biomining are modified leach mining processes. These aptly named bioleaching processes most commonly includes the inoculation of extracted rock with bacteria and acidic solution, with the leachate salvaged and processed for the metals of value. Biomining has many applications outside of metal recovery, most notably is bioremediation which has already been used to clean up coastlines after oil spills. There are also many promising future applications, like space biomining, fungal bioleaching and biomining with hybrid biomaterials.

Arthurite is a mineral composed of divalent copper and iron ions in combination with trivalent arsenate, phosphate and sulfate ions with hydrogen and oxygen. Initially discovered by Sir Arthur Russell in 1954 at Hingston Down Consols mine in Calstock, Cornwall, England, arthurite is formed as a resultant mineral in the oxidation region of some copper deposits by the variation of enargite or arsenopyrite. The chemical formula of Arthurite is CuFe₂³⁺(AsO₄,PO₄,SO₄)₂(O,OH)₂·4H₂O.

Cementation is a type of precipitation, a heterogeneous process in which ions are reduced to zero valence at a solid metallic interface. The process is often used to refine leach solutions.

Sulfolobus metallicus is a coccoid shaped thermophilic archaeon. It is a strict chemolithoautotroph gaining energy by oxidation of sulphur and sulphidic ores into sulfuric acid. Its type strain is Kra 23. It has many uses that take advantage of its ability to grow on metal media under acidic and hot environments.

References

↑ Power, Ian M.; Dipple, Gregory M.; Southam, Gordon (2010). "Bioleaching of Ultramafic Tailings by Acidithiobacillusspp. For CO2Sequestration". Environmental Science & Technology. 44 (1): 456–462. Bibcode:2010EnST...44..456P. doi:10.1021/es900986n. PMID 19950896.
↑ Natarajan, K.A. (2018). "Experimental and Research Methods in Metals Biotechnology". Biotechnology of Metals. pp. 433–468. doi:10.1016/B978-0-12-804022-5.00014-1. ISBN 978-0-12-804022-5.
↑ "Use in Mining | International Cyanide Management Code (ICMI) For The Manufacture, Transport and Use of Cyanide In The Production of Gold(ICMI)". www.cyanidecode.org. Archived from the original on 2012-02-29. Retrieved 2021-02-03.
↑ Dusengemungu, Leonce; Kasali, George; Gwanama, Cousins; Mubemba, Benjamin (27 June 2021). "Overview of fungal bioleaching of metals". Environmental Advances. 5 (2021). Elsevier Ltd.: 100083. doi: 10.1016/j.envadv.2021.100083 . ISSN 2666-7657.
↑ "Enterprise Europe Network". een.ec.europa.eu. Retrieved 2020-08-28.
↑ "Bioleaching: The worldwide copper mining is slowly turning green | CAR ENGINE AND SPORT". topgear-autoguide.com. Retrieved 2022-05-06.
↑ Crane, Leah. "Asteroid-munching microbes could mine materials from space rocks". New Scientist. Retrieved 9 December 2020.
↑ Cockell, Charles S.; Santomartino, Rosa; Finster, Kai; Waajen, Annemiek C.; Eades, Lorna J.; Moeller, Ralf; Rettberg, Petra; Fuchs, Felix M.; Van Houdt, Rob; Leys, Natalie; Coninx, Ilse; Hatton, Jason; Parmitano, Luca; Krause, Jutta; Koehler, Andrea; Caplin, Nicol; Zuijderduijn, Lobke; Mariani, Alessandro; Pellari, Stefano S.; Carubia, Fabrizio; Luciani, Giacomo; Balsamo, Michele; Zolesi, Valfredo; Nicholson, Natasha; Loudon, Claire-Marie; Doswald-Winkler, Jeannine; Herová, Magdalena; Rattenbacher, Bernd; Wadsworth, Jennifer; Craig Everroad, R.; Demets, René (10 November 2020). "Space station biomining experiment demonstrates rare earth element extraction in microgravity and Mars gravity". Nature Communications. 11 (1): 5523. Bibcode:2020NatCo..11.5523C. doi:10.1038/s41467-020-19276-w. ISSN 2041-1723. PMC 7656455 . PMID 33173035. Available under CC BY 4.0.
↑ Putra, Nicky Rahmana; Yustisia, Yustisia; Heryanto, R. Bambang; Asmaliyah, Asmaliyah; Miswarti, Miswarti; Rizkiyah, Dwila Nur; Yunus, Mohd Azizi Che; Irianto, Irianto; Qomariyah, Lailatul; Rohman, Gus Ali Nur (2023-10-01). "Advancements and challenges in green extraction techniques for Indonesian natural products: A review". South African Journal of Chemical Engineering. 46: 88–98. doi: 10.1016/j.sajce.2023.08.002 . ISSN 1026-9185.
↑ "Mission 2015: Bioleaching". web.mit.edu. Retrieved 2024-01-21.
↑ Dr. R.C. Dubey (1993). A textbook of biotechnology : for university and college students in India and abroad. New Delhi. p. 442. ISBN 978-81-219-2608-9. OCLC 974386114.{{cite book}}: CS1 maint: location missing publisher (link)
↑ "Four charged in Talvivaara toxic leak case". Yle. 22 September 2014.
↑ Sairinen, Rauno; Tiainen, Heidi; Mononen, Tuija (July 2017). "Talvivaara mine and water pollution: An analysis of mining conflict in Finland". The Extractive Industries and Society. 4 (3): 640–651. doi:10.1016/j.exis.2017.05.001. S2CID 134427827 . Retrieved 4 August 2022.