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Based on key intermediates, two indirect leach mechanisms need to be differentiated: the thiosulfate and the polysulfide mechanism, both of which will be described in …
Direct and indirect mechanisms are involved in sulfur based leaching process by bacteria leading to the formation of metal sulfides and its dissolution (Fig. 4). In direct leaching process, bacteria directly contact and react with metal sulfide and oxidize it to soluble metal sulfates like NiS, ZnS, CuS, etc.
There are two pathways involved in bacterial leaching: direct and indirect. In direct leaching, the electron transfer occurs from metallic sulfide to the cell attached to the mineral surface. In contrast, indirect leaching is enhanced by an oxidizing metallic agent, typically the Fe 3+ ions derived from the oxidation of Fe 2+ ions, a byproduct ...
Indirect Bacterial Leaching (Non- contact leaching) In Indirect bacterial leaching, no direct contact between the microorganisms and the mineral occurs. Here, the strong oxidizing agents produced by bacteria, such as ferric ions and sulfuric acids
Cosmochim. Acta 56 (1992) 3133–3156. [29] A. Schippers, W. Sand, Bacterial leaching of metal sulfides proceeds by two indirect mechanisms via thiosulfate or via polysulfides and sulfur, Appl. Environ. Microbiol. 65 (1999) 319–321. [30] A. Schippers, P.G. Jozsa, W. Sand, Sulfur chemistry in bacterial leaching of pyrite, Appl. Environ.
ions. The depositions passivated the chalcopyrite leaching process. The crystallized jarosite in the bacteria EPS layer belonged to bacteria–mineral contact leaching system, while that in the sulfur
Direct and indirect mechanisms are involved in sulfur based leaching process by bacteria leading to the formation of metal sulfides and its dissolution (Fig. 4). In direct leaching process, bacteria directly contact and react with metal sulfide and oxidize it …
In indirect bacterial leaching microbes are not in direct contact with minerals but leaching agents are produced by microorganisms which oxidize them. (i) Slope Leaching. About 10,000 tonnes …
The thin-layer leaching process originally conceived and developed for leaching oxide ores has been successfully adapted to bacterial leaching of mixed and secondary sulphide ores.
Bacterial Leaching of Metal Sulfides Proceeds by Two Indirect Mechanisms via Thiosulfate or via Polysulfides and Sulfur AXEL SCHIPPERS* AND WOLFGANG SAND Abteilung Mikrobiologie, Institut fu¨r Allgemeine Botanik, Universita¨t Hamburg, D-22609 Hamburg, Germany Received 20 July 1998/Accepted 22 October 1998 The acid-insoluble metal sulfides ...
Bacteria have evolved multiple strategies for gaining chemical energy from sulfides of different electronic and crystalline structure. Besides indirect leaching, contact leaching as …
There are two major mechanisms of bacterial leaching. One involves the ferric-ferrous cycle (indirect mechanism), whereas the other involves physical contact of the organism with the …
In the bioleaching of metal sulfides using sulfur-oxidizing and iron-oxidizing bacteria, the indirect mechanism is the most recognized mechanism (25). In the direct mechanism, the bacteria contribute to generating the oxidizing agent, ferric iron. ... The difference was that the pH during the leaching process was maintained at 1.20 using 5 mol ...
Schippers A, Sand W. Bacterial leaching of metal sulfides proceeds by two indirect mechanisms via thiosulfate or via polysulfides and sulfur. Appl Environ Microbiol. 1999;65:319–321. doi: …
The microbial leaching process was evaluated for the treatment of synthetic sediments contaminated with cadmium and nickel sulfides to compare metal solubilization in sediment inoculated with Acidithiobacillus ferrooxidans -inoculated sediments to that in sterile control sediment, indicating that indirect non-contact leaching by the products of microbial …
This is an indirect leaching process since the microbial attack is not on uranium ore directly but on the Iron oxidant. Ferric sulphate and sulfuric acid can be produced by T.ferrooxidans from the …
is further confirmed by the leaching of synthetic sulphides free of iron, where only the direct attack of the bacteria can lead to leaching: CuS (covellite) + 202 ~ CuSO4, ZnS (sphalerite) + 20 z ~ ZnSO 4. Bacterial Leaching Techniques The two major techniques used in leaching are percolation and agitation leaching.
The mechanism of bacterial leaching of sulfides has interested researchers for a long time [1], [2].While many parameters affecting the leaching process have been known as empirical factors, a more profound understanding of the heterogeneous mechanism of sulfide degradation has only gradually emerged as a consequence of advances in semiconductor …
2. Mechanisms of bioleaching. The two majorly known mechanism in bacterial leaching are direct mechanism (involves physical contact of the organism with the insoluble sulphide) or hypothesized enzymatic reaction taking place between an attached cell and the underlying mineral surface which is independent of indirect mechanisms and it is where …
The disulfides pyrite (FeS 2), molybdenite (MoS 2), and tungstenite (WS 2) are degraded via the main intermediate thiosulfate.Exclusively iron(III) ions are the oxidizing agents for the dissolution. Thiosulfate is, consequently, degraded in a cyclic process to sulfate, with elemental sulfur being a side product. This explains, why only iron(II) ion-oxidizing bacteria are …
The application of a bioleaching process using native bacteria capable of removing contaminating elements is a viable option. The objective of this research was to maximize the removal of ...
The acid-insoluble metal sulfides FeS 2, MoS2, and WS2 are chemically attacked by iron(III) hexahydrate ions, generating thiosulfate, which is oxidized to sulfuric acid, explaining leaching of metal sulfide by Thiobacillus thiooxidans. ABSTRACT The acid-insoluble metal sulfides FeS2, MoS2, and WS2 are chemically attacked by iron(III) hexahydrate ions, …
is further confirmed by the leaching of synthetic sulphides free of iron, where only the direct attack of the bacteria can lead to leaching: CuS (covellite) + 202 --.CuS04, ZnS (sphalerite) + 20z -+ ZnS04 • Bacterial Leaching Techniques The two major techniques used in leaching are percolation and agitation leaching.
The oxidation products in the case of FeS 2 and MoS 2 consisted of up to 90% sulfate and about 1 to 2% polythionates. Because the valence bands of FeS 2 and MoS 2 are derived only from the metal orbitals, the valence bands do not contribute to the chemical bond between the metal and the sulfur moiety in the crystal (2, 25).Consequently, these metal …
Bacterial assisted leaching processes are based on the ability of certain microorganisms to solubilize/or expose the metals contained in the ores and concentrates by direct oxidation, or through ...
The present review describes the historical development and mechanisms of bioleaching, which has shown commercial application of the process and, concurrently, details pertaining to the key microorganisms involved in these processes have been described. The present review describes the historical development and mechanisms of bioleaching. Recent …
In process scheme 1, indirect bioleaching (IBL), the ore bed porosity is assumed to be completely filled with the leaching solution and leaching of copper sulfides occurred just with the 3 g/L of ferric contained in the incoming leaching solution produced in an external bioreactor (Pakostova et al., 2017; Biomore, 2018).
Non-contact leaching is basically exerted by planktonic bacteria, which oxidize iron (II) ions in solution. The resulting iron (III) ions (somehow) come into contact with a …
To keep enough iron in solution the chemical oxidation of metal sulfides must occur in an acid environment below pH 5.0. The ferrous iron arising in this reaction can be reoxidized to ferric iron by T. ferrooxidans or L. ferrooxidans and as such can take part in the oxidation process again. In indirect leaching the bacteria do not need to be in contact with the mineral surface.
The Leaching Process. Bacteria perform the key reaction of regenerating the major ore oxidizer which in most cases is ferric iron as well as further ore oxidation. The reaction is performed at the bacterial cell membrane. In the process, free electrons are generated and used for the reduction of oxygen to water which produces energy in the ...
