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Yenpeng Ting - One of the best experts on this subject based on the ideXlab platform.
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alkaline Bioleaching of municipal solid waste incineration fly ash by autochthonous extremophiles
Chemosphere, 2016Co-Authors: Thulasya Ramanathan, Yenpeng TingAbstract:Abstract The increasing demand for energy and the generation of solid waste have caused an alarming rise in fly ash production globally. Since heavy metals continue to be in demand for the production of materials, resource recovery from the recycling of these wastes has the potential to delay the depletion of natural ores. The use of microorganisms for the leaching of metals, in a process called Bioleaching, is an eco-friendly and economical way to treat the metal-laden wastes. Bioleaching of fly ash is challenging due largely to the alkaline nature and toxic levels of heavy metals which are detrimental to microbial growth and Bioleaching activity. The present work reports the isolation of indigenous bacteria from a local fly ash landfill site and their Bioleaching performance. 38 autochthonous strains of bacteria were isolated from eight samples collected and plated on five different media. 18 of the isolates showed Bioleaching potential, with significant alkaline pH or fly ash tolerance. Genetic characterization of the strains revealed a dominance of Firmicutes, with Alkalibacterium sp. TRTYP6 showing highest fly ash tolerance of up to 20% w/v fly ash, and growth over a pH range 8–12.5. The organism selectively recovered about 52% Cu from the waste. To the best of our knowledge, this is the first time a study on Bioleaching with extreme alkaliphiles is reported.
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two step Bioleaching and spent medium leaching of gold from electronic scrap material using chromobacterium violaceum
Advanced Materials Research, 2013Co-Authors: Gayathri Natraja, Yenpeng TingAbstract:Rapid technological advancement and the relatively short life time of electronic goods have resulted in an alarming growth rate of electronic waste which often contains significant quantities of toxic and precious metals. Compared to conventional chemical recovery methods, Bioleaching has been shown to be an environmentally friendly process for metal extraction. In this work, gold Bioleaching from electronic scrap material (ESM) was examined using batch cultures of the bacterium Chromobacterium violaceum which produces cyanide as a secondary metabolite. Gold was bioleached via gold cyanide complexation. The ESM was pretreated using nitric acid to dissolve the base metals (mainly copper) in order to reduce competition for the cyanide ion from other metals present in ESM. ESM was added to the bacterial culture after it reached maximum cyanide production during early stationary phase. Spent medium Bioleaching using bacterial cell- free metabolites showed a higher gold recovery of 18%, compared to that of two-step Bioleaching of 11% at 0.5% w/v pulp density of ESM. Gold Bioleaching was further enhanced to 30% when the pH of the spent medium was increased to shift the equilibrium in favor of cyanide ions production. Spent medium Bioleaching of pretreated ESM yield a higher gold recovery compared to two-step Bioleaching at a pulp density of 0.5% w/v.
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metal extraction from municipal solid waste msw incinerator fly ash chemical leaching and fungal Bioleaching
Enzyme and Microbial Technology, 2006Co-Authors: Yenpeng TingAbstract:Abstract Fly ash from a municipal solid waste (MSW) incinerator in Singapore was physically and chemically characterized. The very fine amorphous ash particle was found to have a non-porous structure with a low specific surface area and a tendency to agglomerate. Chemical analysis indicated that a significant amount (2000–20,000 mg/kg) of toxic heavy metals, such as Al, Pb and Zn were present in the fly ash. Bioleaching using the fungus Aspergillus niger was carried out at different pulp densities of fly ash (1–8%, w/v), and results were compared with chemical leaching using various organic and inorganic acids. Although the fungus grew only in the presence of 1–2% (w/v) fly ash when it was incubated together with the fly ash (one-step Bioleaching), growth was observed even at 4% (w/v) fly ash when the ash was added after 2 days of fungal incubation (two-step Bioleaching). Both one-step and two-step Bioleaching experiments showed similar metal extraction yield for 1% (w/v) of fly ash pulp density (80–100% for Al, Mn and Zn; 60–70% for Cu and Pb, and about 30% for Fe). Optimum pulp density for Bioleaching was observed at 1% (w/v), and leaching efficiency decreased with increasing pulp density in fungal Bioleaching as well as in spent medium leaching. The main lixiviant in Bioleaching was shown to be gluconic acid, which was produced only in the presence of fly ash (in one-step and two-step Bioleaching). Compared with chemical leaching at 1% pulp density, the fungus was more efficient in the leaching of Mn and Zn, and showed similar extraction yield for Al. However, Cu extraction yield was lower in Bioleaching than chemical leaching. These results suggest that Bioleaching by A. niger may be an alternative or adjunct to conventional physicochemical treatment processes of MSW fly ash to remove hazardous heavy metals. Bioleaching mechanisms are also discussed.
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Bioleaching of spent fluid catalytic cracking catalyst using aspergillus niger
Journal of Biotechnology, 2005Co-Authors: Khin Moh Moh Aung, Yenpeng TingAbstract:The use of the fungus Aspergillus niger for the Bioleaching of heavy metals from spent catalyst was investigated, with fluid catalytic cracking (FCC) catalyst as a model. Bioleaching was examined in batch cultures with the spent catalysts at various pulp densities (1-12%). Chemical leaching was also performed using mineral acids (sulphuric and nitric acids) and organic acids (citric, oxalic and gluconic acids), as well as a mixture of organic acids at the same concentrations as that biogenically produced. It was shown that Bioleaching realised higher metal extraction than chemical leaching, with A. niger mobilizing Ni (9%), Fe (23%), Al (30%), V (36%) and Sb (64%) at 1% pulp density. Extraction efficiency generally decreased with increased pulp density. Compared with abiotic controls, Bioleaching gave rise to higher metal extractions than leaching using fresh medium and cell-free spent medium. pH decreased during Bioleaching, but remained relatively constant in both leaching using fresh medium and cell-free spent medium, thus indicating that the fungus played a role in effecting metal extraction from the spent catalyst.
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optimisation on Bioleaching of incinerator fly ash by aspergillus niger use of central composite design
Enzyme and Microbial Technology, 2004Co-Authors: Yenpeng TingAbstract:Previous work has shown that heavy metals may be bioleached from municipal solid waste (MSW) incinerator fly ash. The Bioleaching of heavy metals from the ash depends on physical, chemical and biological factors. Our research objective is to establish the factors that exert a greater impact on the Bioleaching process, and to determine the optimal Bioleaching conditions in order to achieve the maximum metal leaching efficiency for selected metals. Four factors were investigated: sucrose concentration, inoculum spore concentration, fly ash pulp density, and the time of addition of fly ash to the fungus Aspergillus niger. Using the central composite design (CCD), 31 batch Bioleaching tests were run under high and low values of these four factors. Empirical models obtained through second-order (Taylor series approximation) regression provided the optimal Bioleaching conditions. Results showed that sucrose concentration and pulp density were more important factors than spore concentration and the time of addition of the fly ash. The concentration of Al, Fe, Zn, citric acid, and gluconic acid attained in the leached liquor was 12.3, 12.3, 77.6 ppm, 51 and 281 mM, respectively.
Jun Wang - One of the best experts on this subject based on the ideXlab platform.
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sulfide mineral Bioleaching understanding of microbe chemistry assisted hydrometallurgy technology and acid mine drainage environment protection
Journal of Central South University, 2020Co-Authors: Rui Liao, Jun Wang, Maoxin Hong, Chunxiao Zhao, Hao Lin, Congren Yang, Yansheng Zhang, Jianping Xie, Wenqing Qin, Guanzhou QiuAbstract:Bioleaching is regarded as an essential technology to treat low grade minerals, with the distinctive superiorities of lower-cost and environment-friendly compared with traditional pyrometallurgy method. However, the Bioleaching efficiency is unsatisfactory owing to the passivation film formed on the minerals surface. It is of particular interest to know the dissolution and passivation mechanism of sulfide minerals in the presence of microorganism. Although Bioleaching can be useful in extracting metals, it is a double-edged sword. Metallurgical activities have caused serious environmental problems such as acid mine drainage (AMD). The understanding of some common sulfide minerals Bioleaching processes and protection of Amd environment is reviewed in this article.
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Intermediates Transformation of Bornite Bioleaching by Leptospirillum ferriphilum and Acidithiobacillus caldus
Minerals, 2019Co-Authors: Maoxin Hong, Xiaotao Huang, Rui Liao, Hongbo Zhao, Xingxing Wang, Guanzhou Qiu, Chaojun Fang, Jun WangAbstract:Bioleaching experiments, electrochemical tests, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were conducted to investigate the intermediates transformation of bornite by Leptospirillum ferriphilum and Acidithiobacillus caldus. The Bioleaching experimental results showed that the presence of L. ferriphilum and A. caldus significantly accelerated the bornite Bioleaching. In addition, the intermediate species of bornite Bioleaching with these two kinds of bacteria were similar. Electrochemical analysis indicated that the dissolution of bornite was an acid-consuming process. The results of XRD showed that intermediate species, namely covellite (CuS), mooihoekit (Cu9Fe9S16) and isocubanite (CuFe2S3), were formed during bornite Bioleaching, and a mass of elemental sulfur was formed in the late stage of Bioleaching. The Cu 2p photoelectron spectrum revealed that Cu was present in the form of Cu (I) during the bornite Bioleaching. Additionally, the S 2p3/2 photoelectron spectrum suggested that S2− and S22− were gradually converted to Sn2−/S0, and the formation of elemental sulfur hindered the further dissolution of the bornite.
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a strategy to accelerate the Bioleaching of chalcopyrite through the goethite process
Minerals & Metallurgical Processing, 2018Co-Authors: Xiaotao Huang, Rui Liao, Hongbo Zhao, Yansheng Zhang, Jun WangAbstract:Theoretically, controlling redox potential to a relatively low value and inhibiting jarosite formation on the chalcopyrite surface would be an effective strategy to accelerate the Bioleaching of chalcopyrite. In this work, using limonite as seed crystals, the effects of the goethite precipitation process on the Bioleaching of chalcopyrite were studied for the first time. The Bioleaching results showed that the addition of limonite controlled the redox potential in an appropriate range and promoted chalcopyrite dissolution through the removal of ferric (Fe3+) ions. X-ray diffraction and scanning electron microscope analyses indicate that limonite significantly induced the goethite precipitation process and inhibited the production of jarosite. We conclude that promoting the goethite precipitation process with limonite is an effective strategy in accelerating the Bioleaching process of chalcopyrite.
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synergetic effect of pyrite on strengthening bornite Bioleaching by leptospirillum ferriphilum
Hydrometallurgy, 2018Co-Authors: Xingxing Wang, Maoxing Hong, Caoming Huang, Xiaotao Huang, Rui Liao, Hongbo Zhao, Hong Peng, Jun WangAbstract:Abstract Bioleaching experiments and electrochemical measurements were conducted to investigate the effect of pyrite on bornite Bioleaching by Leptospirillum ferriphilum. Bioleaching experiments results showed that the addition of pyrite increased the redox potential to 360 mV vs. an Ag/AgCl electrode in the initial period of Bioleaching process. The presence of pyrite significantly increased the copper extraction efficiency to 95.9% while the extraction value was only 19% without pyrite addition after 20 days. Furthermore, the addition of pyrite also decreased the consumption of acid during Bioleaching of bornite. Especially, the total acid consumption was only 0.002 mmol at a pyrite to bornite ratio of 5:1 while the value was 2.842 mmol without pyrite addition. The results of electrochemical experiments identified that a galvanic effect existed between bornite and pyrite, and bornite was more prone to oxidation sand reduction. Tafel plot and galvanic corrosion tests indicated that the addition of pyrite accelerated the dissolution of bornite. Furthermore, the dissolution of bornite with pyrite additon was not inhibited by the formation of element sulfur and jarosite that may lead to passivation of chalcopyrite Bioleaching. Based on all the observations, a mechanism model on how pyrite accelerated bornite dissolution is proposed.
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stepwise Bioleaching of cu zn mixed ores with comprehensive utilization of silver bearing solid waste through a new technique process
Hydrometallurgy, 2017Co-Authors: Hongbo Zhao, Jun Wang, Lang Tao, Wenqing Qin, Xiaowen GanAbstract:Abstract In this work, a new technique process for processing Cu-Zn mixed ores containing chalcopyrite and marmatite was proposed to avoid the complex Cu-Zn flotation and extraction separation processes, as well as for the comprehensive utilization of abandoned silver-containing zinc leaching residue (ZLR). In the first step, stepwise Bioleaching of Cu-Zn mixed ores in the presence of mixed moderately thermophilic microorganisms and Fe 3 + was conducted for recovering Zn from marmatite. Copper was then efficiently extracted from the copper-containing Bioleaching residues through catalytic Bioleaching by using ZLR as catalyst. The final Bioleaching residues were subsequently leached by thiourea for recovering Ag efficiently. The provided technique process accomplished the stepwise dissolution of Cu-Zn mixed ores and the comprehensive utilization of silver-bearing ZLR. The intermediate species, the electrochemical dissolution process and the electrochemical interactions between chalcopyrite and marmatite were also discussed to interpret the detailed mechanisms of stepwise Bioleaching.
Hongbo Zhao - One of the best experts on this subject based on the ideXlab platform.
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the dissolution and passivation mechanism of chalcopyrite in Bioleaching an overview
Minerals Engineering, 2019Co-Authors: Hongbo Zhao, Yisheng Zhang, Xian Zhang, Lu Qian, Menglin SunAbstract:Abstract Chalcopyrite (CuFeS2) is the most abundant copper-containing resource in the earth and is also widely distributed in solid wastes and secondary resources. Biohydrometallurgy (Bioleaching) is considered as a promising minerals processing and extractive metallurgy technology because of its environmental and economic advantages over the conventional beneficiation-pyrometallurgy process, and the Bioleaching of chalcopyrite is always a challenge because chalcopyrite can be easily passivated in Bioleaching. Hence, it is important to understand the dissolution process and passivation mechanism of chalcopyrite in Bioleaching. In this paper, the dissolution process and passivation mechanism of chalcopyrite Bioleaching have been summarized and discussed according to previous publications. The reported possible passivating species are mainly S-containing species consisting of polysulfide (Sn2−), elemental sulfur (S0) and insoluble sulfate (SO42−). The effects of physicochemical properties of chalcopyrite and multiple factors on the dissolution and passivation mechanism of chalcopyrite Bioleaching have been summarized. We particularly discussed the role of redox potential in chalcopyrite Bioleaching and its controlling techniques.
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Intermediates Transformation of Bornite Bioleaching by Leptospirillum ferriphilum and Acidithiobacillus caldus
Minerals, 2019Co-Authors: Maoxin Hong, Xiaotao Huang, Rui Liao, Hongbo Zhao, Xingxing Wang, Guanzhou Qiu, Chaojun Fang, Jun WangAbstract:Bioleaching experiments, electrochemical tests, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were conducted to investigate the intermediates transformation of bornite by Leptospirillum ferriphilum and Acidithiobacillus caldus. The Bioleaching experimental results showed that the presence of L. ferriphilum and A. caldus significantly accelerated the bornite Bioleaching. In addition, the intermediate species of bornite Bioleaching with these two kinds of bacteria were similar. Electrochemical analysis indicated that the dissolution of bornite was an acid-consuming process. The results of XRD showed that intermediate species, namely covellite (CuS), mooihoekit (Cu9Fe9S16) and isocubanite (CuFe2S3), were formed during bornite Bioleaching, and a mass of elemental sulfur was formed in the late stage of Bioleaching. The Cu 2p photoelectron spectrum revealed that Cu was present in the form of Cu (I) during the bornite Bioleaching. Additionally, the S 2p3/2 photoelectron spectrum suggested that S2− and S22− were gradually converted to Sn2−/S0, and the formation of elemental sulfur hindered the further dissolution of the bornite.
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a strategy to accelerate the Bioleaching of chalcopyrite through the goethite process
Minerals & Metallurgical Processing, 2018Co-Authors: Xiaotao Huang, Rui Liao, Hongbo Zhao, Yansheng Zhang, Jun WangAbstract:Theoretically, controlling redox potential to a relatively low value and inhibiting jarosite formation on the chalcopyrite surface would be an effective strategy to accelerate the Bioleaching of chalcopyrite. In this work, using limonite as seed crystals, the effects of the goethite precipitation process on the Bioleaching of chalcopyrite were studied for the first time. The Bioleaching results showed that the addition of limonite controlled the redox potential in an appropriate range and promoted chalcopyrite dissolution through the removal of ferric (Fe3+) ions. X-ray diffraction and scanning electron microscope analyses indicate that limonite significantly induced the goethite precipitation process and inhibited the production of jarosite. We conclude that promoting the goethite precipitation process with limonite is an effective strategy in accelerating the Bioleaching process of chalcopyrite.
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synergetic effect of pyrite on strengthening bornite Bioleaching by leptospirillum ferriphilum
Hydrometallurgy, 2018Co-Authors: Xingxing Wang, Maoxing Hong, Caoming Huang, Xiaotao Huang, Rui Liao, Hongbo Zhao, Hong Peng, Jun WangAbstract:Abstract Bioleaching experiments and electrochemical measurements were conducted to investigate the effect of pyrite on bornite Bioleaching by Leptospirillum ferriphilum. Bioleaching experiments results showed that the addition of pyrite increased the redox potential to 360 mV vs. an Ag/AgCl electrode in the initial period of Bioleaching process. The presence of pyrite significantly increased the copper extraction efficiency to 95.9% while the extraction value was only 19% without pyrite addition after 20 days. Furthermore, the addition of pyrite also decreased the consumption of acid during Bioleaching of bornite. Especially, the total acid consumption was only 0.002 mmol at a pyrite to bornite ratio of 5:1 while the value was 2.842 mmol without pyrite addition. The results of electrochemical experiments identified that a galvanic effect existed between bornite and pyrite, and bornite was more prone to oxidation sand reduction. Tafel plot and galvanic corrosion tests indicated that the addition of pyrite accelerated the dissolution of bornite. Furthermore, the dissolution of bornite with pyrite additon was not inhibited by the formation of element sulfur and jarosite that may lead to passivation of chalcopyrite Bioleaching. Based on all the observations, a mechanism model on how pyrite accelerated bornite dissolution is proposed.
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stepwise Bioleaching of cu zn mixed ores with comprehensive utilization of silver bearing solid waste through a new technique process
Hydrometallurgy, 2017Co-Authors: Hongbo Zhao, Jun Wang, Lang Tao, Wenqing Qin, Xiaowen GanAbstract:Abstract In this work, a new technique process for processing Cu-Zn mixed ores containing chalcopyrite and marmatite was proposed to avoid the complex Cu-Zn flotation and extraction separation processes, as well as for the comprehensive utilization of abandoned silver-containing zinc leaching residue (ZLR). In the first step, stepwise Bioleaching of Cu-Zn mixed ores in the presence of mixed moderately thermophilic microorganisms and Fe 3 + was conducted for recovering Zn from marmatite. Copper was then efficiently extracted from the copper-containing Bioleaching residues through catalytic Bioleaching by using ZLR as catalyst. The final Bioleaching residues were subsequently leached by thiourea for recovering Ag efficiently. The provided technique process accomplished the stepwise dissolution of Cu-Zn mixed ores and the comprehensive utilization of silver-bearing ZLR. The intermediate species, the electrochemical dissolution process and the electrochemical interactions between chalcopyrite and marmatite were also discussed to interpret the detailed mechanisms of stepwise Bioleaching.
Bulent Sari - One of the best experts on this subject based on the ideXlab platform.
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comparative evaluation of microbial and chemical leaching processes for heavy metal removal from dewatered metal plating sludge
Journal of Hazardous Materials, 2010Co-Authors: Belgin Bayat, Bulent SariAbstract:Abstract The purpose of the study described in this paper was to evaluate the application of Bioleaching technique involving Acidithiobacillus ferrooxidans to recover heavy metals (Zn, Cu, Ni, Pb, Cd and Cr) in dewatered metal plating sludge (with no sulfide or sulfate compounds). The effect of some conditional parameters (i.e. pH, oxidation–reduction potential (ORP), sulfate production) and operational parameters (i.e. pulp density of the sludge and agitation time) were investigated in a 3 l completely mixed batch (CMB) reactor. The metal recovery yields in Bioleaching were also compared with chemical leaching of the sludge waste using commercial inorganic acids (sulfuric acids and ferric chloride). The leaching of heavy metals increased with decreasing of pH and increasing of ORP and sulfate production during the Bioleaching experiment. Optimum pulp density for Bioleaching was observed at 2% (w/v), and leaching efficiency decreased with increasing pulp density in Bioleaching experiments. Maximum metal solubilization (97% of Zn, 96% of Cu, 93% of Ni, 84% of Pb, 67% of Cd and 34% of Cr) was achieved at pH 2, solids contents of 2% (w/v), and a reaction temperature of 25 ± 2 °C during the Bioleaching process. The maximum removal efficiencies of 72% and 79% Zn, 70% and 75% Cu, 69% and 73% Ni, 57% and 70% Pb, 55% and 65% Cd, and 11% and 22% Cr were also attained with the chemical leaching using sulfuric acids and ferric chloride, respectively, at pH 2, solids contents of 2% (w/v), and a reaction temperature of 25 ± 2 °C during the acid leaching processes. The rates of metal leaching for Bioleaching and chemical leaching are well described by a kinetic equation related to time. Although Bioleaching generally requires a longer period of operation compared to chemical leaching, it achieves higher removal efficiency for heavy metals. The efficiency of leaching processes can be arranged in descending order as follows: Bioleaching > ferric chloride leaching > sulfuric acid leaching. These results suggest that Bioleaching may be an alternative or adjunct to conventional physicochemical treatment of dewatered metal plating sludge for the removal hazardous heavy metals.
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Bioleaching of dewatered metal plating sludge by acidithiobacillus ferrooxidans using shake flask and completely mixed batch reactor
African Journal of Biotechnology, 2010Co-Authors: Belgin Bayat, Bulent SariAbstract:The objective of the present study was to evaluate the application of Bioleaching technique to recover heavy metals (Zn, Cu, Ni, Pb, Cd and Cr) in dewatered metal plating sludge not containing sulphide or sulphate compounds. The effects of pH, pulp density of the sludge and agitation time were investigated in both shake flask and completely mixed batch reactor experiments. The leaching of heavy metals increased with decrease of pH and pulp density and increase of agitation time for both Bioleaching experiments. The maximum metal leaching efficiencies of 93 and 97% Zn, 86 and 96% Cu, 85 and 93% Ni, 70 and 84% Pb, 65 and 67% Cd and 30 and 34% Cr were attained with the shake flask and the completely mixed batch reactor experiments, respectively, at a pH 2, a solid content of 2% (w/v) and a reaction temperature of 25 ± 2°C during the Bioleaching process (20 days). The rates of metal leaching for both Bioleaching systems are well described by a kinetic equation related to time. Although the rates of metal leaching were in the decreasing order: Zn > Cu > Ni > Pb > Cd > Cr for both leaching experiments, Bioleaching using the completely mixed batch reactor was slightly more efficient than the shake flask due to aeration of system. These results suggest that Bioleaching may be an alternative or adjunct to conventional physicochemical treatment of dewatered metal plating sludge for the removal of hazardous heavy metals. Key words: Bioleaching, waste sludge, heavy metals, Acidithiobacillus ferrooxidans
Bin Lian - One of the best experts on this subject based on the ideXlab platform.
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Bioleaching of rare earth and radioactive elements from red mud using penicillium tricolor rm 10
Bioresource Technology, 2013Co-Authors: Bin LianAbstract:The aim of this work is to investigate biological leaching of rare earth elements (REEs) and radioactive elements from red mud, and to evaluate the radioactivity of the bioleached red mud used for construction materials. A filamentous, acid-producing fungi named RM-10, identified as Penicillium tricolor, is isolated from red mud. In our Bioleaching experiments by using RM-10, a total concentration of 2% (w/v) red mud under one-step Bioleaching process was generally found to give the maximum leaching ratios of the REEs and radioactive elements. However, the highest extraction yields are achieved under two-step Bioleaching process at 10% (w/v) pulp density. At pulp densities of 2% and 5% (w/v), red mud processed under both one- and two-step Bioleaching can meet the radioactivity regulations in China.
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Bioleaching of heavy metals from red mud using Aspergillus niger
Hydrometallurgy, 2013Co-Authors: Bin Lian, Congqiang LiuAbstract:Abstract Red mud (bauxite residue) is the main waste product of the alkaline extraction of alumina from bauxite with high amounts of metals. In this study, Bioleaching of heavy metals from red mud by using the fungus Aspergillus niger was investigated. Bioleaching experiments were examined in batch cultures with the red mud at various pulp densities (1–5%, w/v) under various Bioleaching conditions (one-step, two-step and spent medium Bioleaching). It was shown that the main lixiviant excreted by A. niger was citric acid. The highest leaching ratios of most various heavy metals were achieved under spent medium leaching at 1% pulp density. The increase in red mud pulp densities resulted in a general decrease in leaching ratios under all Bioleaching conditions. However, in the case of the spent medium leaching the decrease in leaching ratios was lowest. The Toxicity Characteristic Leaching Procedure (TCLP) tests showed that the leaching toxicity of the Bioleaching residue was far below the levels of relevant regulations. The micromorphology of the red mud particles were changed by the fungal activity during Bioleaching process.