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In the current era, the alarming rate at which coal is being burned as a fuel is causing concern with regard to the release of sulphur oxides. According to reports, global coal consumption has increased by 0.4% in 2014. While countries like UK, Ukraine etc. have witnessed a decline in coal consumption, some others like India, China, Africa and North America have increased their use of coal to meet the energy requirements of the growing human population. The increasing use of coal has led to extensive investigations for finding an ecofriendly clean coal technology. Dibenzothiophene (DBT) and some of its alkylated derivatives present in the form of organic sulphur in coal have received a great deal of attention in the past few years because of their recalcitrant nature. Considering the economic and environmental prospects, biodesulphurization is being regarded as an effective tool for the degradation of DBT, with concomitant application towards sulphur removal from coal. Owing to the importance of microbial applications towards production of clean coal, the present review discusses some of the recent findings in the area of DBT biodegradation. In addition, current advances in coal biodesulphurization are reviewed, concluding with a consideration of future prospects for the rapidly growing energy sector. [ABSTRACT FROM AUTHOR]

Abstract: Acidithiobacillus ferrooxidans biofilm grown on uranium ore substrate was analyzed by a micro-Raman spectrometer and an atomic force microscope (AFM). The bacterium employed for this study, A. ferrooxidans BM1, was isolated from a uranium mine (Jaduguda, India). Micro-Raman analysis revealed the different constituents of molecular fragments present in microbial cells and in secreted extracellular polymeric substances (EPSs). AFM images clearly revealed bacterial cells surrounded by EPS. From Raman spectral data, the composition of EPS from A. ferrooxidans BM1 appeared to be similar to that of EPS secreted in a different Pseudomonas bacterium. [Copyright &y& Elsevier]

A bacterial strain isolated from a contaminated soil degraded phenol as the sole source of carbon and energy. It was identified as Serratia plymuthica with the help of its biochemical, physiological and morphological characteristics. The bacterium was able to tolerate and degrade phenol up to a concentration of 1050mgl−1. High concentration of phenol in minimal medium had inhibitory effect on bacteria. The bacterium was able to degrade other aromatic compounds like benzoic acid, ortho-, meta-, para-cresol, protocatechuate, catechol and tryptophan. Phenol was degraded through ortho-pathway. Crude cell extract showed presence of ring cleavage enzyme catechol 1,2-dioxygenase. Specific activity of catechol 1,2-dioxygenase was 0.134μmolemin−1 mg−1 protein. Effect of phenol as inhibitory substrate show that higher the concentration of phenol in the medium more is the negative effect on growth of bacteria and subsequent biodegradation. This bacterium grew well in pH range of 5 to 9 and temperature range of 30 to 40°C. Presence of other carbon source like glucose in the phenol minimal medium affects negatively the rate of degradation of phenol but increases the specific growth rate of the bacteria. [Copyright &y& Elsevier]

A native isolate, 9C, identified as Rhodococcus ruber (Genbank Accession number – KY029073) was studied for dibenzothiophene degradation and subsequent bio-desulphurization of three different sulphur bearing materials (NE coal containing organic sulphur; lignite containing pyritic sulphur and a calcined petroleum-coke) of Indian origin. The isolate could degrade 0.25 mM DBT through the 4S pathway within 7 days. Preliminary studies for sulphur removal using the 9C isolate indicated NE coal to be more amenable (29% sulphur removal) followed by Lignite (15.87%) and CPC (14.83%) respectively. Characterization through XRD and FTIR along with the proximate and ultimate analysis of all the samples provided more insights into the changes in calorific values as well as the chemical constitution of the samples following microbial treatment. Owing to the amenability of NE coal, the effect of time, size fraction and pulp density were optimized. The best bio-desulphurization conditions for NE coal indicated 36% total sulphur removal (organic–53%, pyritic–18% and sulphate sulphur–14% respectively). Analytical characterization studies confirmed that the energy value of the NE coal was not affected due to biodesulphurization, rather it contributed towards an increase in gross calorific value from 6698 cal/g to 6812 cal/g following microbial treatment. [ABSTRACT FROM AUTHOR]

Chalcopyrite is the primary copper mineral used for production of copper metal. Today, as a result of rapid industrialization, there has been enormous demand to profitably process the low grade chalcopyrite and “dirty” concentrates through bioleaching. In the current scenario, heap bioleaching is the most advanced and preferred eco-friendly technology for processing of low grade, uneconomic/difficult-to-enrich ores for copper extraction. This paper reviews the current status of chalcopyrite bioleaching. Advanced information with the attempts made for understanding the diversity of bioleaching microorganisms; role of OMICs based research for future applications to industrial sectors and chemical/microbial aspects of chalcopyrite bioleaching is discussed. Additionally, the current progress made to overcome the problems of passivation as seen in chalcopyrite bioleaching systems have been conversed. Furthermore, advances in the designing of heap bioleaching plant along with microbial and environmental factors of importance have been reviewed with conclusions into the future prospects of chalcopyrite bioleaching. [ABSTRACT FROM AUTHOR]

Two ore samples, one obtained from a partially leached heap with suspended operations for about four years and the other through sonic drilling of a discarded dump were tested for the amenability/feasibility of copper extraction through reactor and column leaching. Mineralogical analysis of the samples indicated the dominant sulphide minerals to be chalcopyrite and pyrite. Various process parameters such as the effect of acid concentration, time, oxidant, pulverization and temperature were studied for the reactor leaching experiments. A maximum of 91% Cu extraction can be achieved while leaching the pulverized sonic drilled sample at 90 °C for 3 h. On the other hand, column leaching studies at 1 kg scale showed 65–70% Cu extraction with an acid concentration of 2.7% ( v / v ) for both the samples. Sequential leaching of the chemically leached residues of both sonic drilled and heap leached pad sample yielded additional 13.2% and 22.2% Cu, respectively in 20 days of bacterial leaching using a mixed culture of meso-acidophilic bacterial consortium. Column leaching studies showed that the heap leached pad sample was more amenable to leaching than the sonic drilled one. Further, during the downstream processing of the leach liquors, the solvent extraction efficiency was about 95% and the Cu metal deposited by electrowinning was of 99.9% purity. A tentative process flowsheet for the recovery of copper was also prepared. [ABSTRACT FROM AUTHOR]

Dumping of poor but metal containing industrial waste is associated with several environmental issues. Exposure of these wastes to the natural environment offers serious concerns for the mineral processing industries to utilize them for metal recovery and check environmental pollution. In the present study, a novel sequential bioreduction–bioleaching and bioreduction–chemical leaching route as a hybrid process is compared and discussed for the enhanced recovery of copper from an industrial concentrator plant ball milling unit rejected sample. A mixed consortium of metal reducing bacteria (DMRB) initially adapted to high Fe(III) concentrations was found to cause mineralogical/matrix alteration (possibly silicate weathering) including Fe(III) bioreduction in the sample and dissolute 29.73% copper during the first 35 days under facultative anaerobic conditions. Sequential leaching of the bioreduced waste sample (generated from the first step) using a mixed meso-acidophilic bacterial consortium predominantly Acidithiobacillus ferrooxidans showed additional 28.72% copper dissolution within 2 days using 1 gL − 1 Fe(II). On the other hand, a comparative chemical leaching of the same bioreduced sample using 0.5 M H 2 SO 4 yielded additional 32.17% copper within 4 days of leaching and indicated better performance than the bioleaching tests. [ABSTRACT FROM AUTHOR]

The nickeliferous chromite overburden (COB) awaits a suitable technology to extract the obstinate nickel ingrained in its goethite matrix. In the present study, a novel Bio-Reduction Acid Leaching (BRAL) approach has been proposed using dissimilatory iron reducing bacteria (DIRB) which is inherently capable of transforming iron mineral phases via bio-reduction (BR). Mineralogical characterization of the bio-reduced COB using XRD and FTIR confirmed the phase transformation of goethite to hematite and magnetite with exposure of the nickel oxide peaks. Further, morphological characterization using FESEM vividly highlighted the changes of acicular goethite to granular magnetite deposits on the extra polymeric substance (a scaffold for electron transfer) secreted by DIRB consortium over the surface of COB. Further, enhanced nickel extraction was achieved with a reductive acid leaching (AL) approach with 6N sulfuric acid and 2% glucose (reducing agent) at 65 °C for 6 h. A cumulative of 83.6% nickel was achieved through this BRAL approach. The pregnant leach solution (PLS) generated as a result of the AL approach was subjected to a hydrometallurgical route to recover metallic nickel. Solvent extraction (SX) of the PLS was performed using 0.5 M NaD2EHPA as extractant. The pregnant nickel-loaded electrolyte was subjected to electrowinning (EW) to recover metallic nickel of 99.6% purity. The process flow-sheet is believed to provide a suitable eco-friendly, potential method to efficiently extract nickel from low grade nickel laterites to meet the ever growing demands caused by depletion of high grade nickel sulfidic ores. [ABSTRACT FROM AUTHOR]

Dumping of low-grade chalcopyrite encompasses several environmental problems. Despite slow dissolution rate, meso-acidophilic bioleaching is preferred for the extraction of copper from such ores. In the present study, meso-acidophilic bioleaching of a low-grade chalcopyrite in the presence of an acid-processed waste newspaper (PWp) is discussed for the first time. The study illustrated a strong catalytic response of PWp with enhanced bio-recovery of copper from acid-conditioned chalcopyrite. A maximum of 99.13% copper recovery (0.36% Cu dissolution/day) was obtained in 6 days of bioleaching in the presence of 2 gL − 1 PWp in contrast to only 5.7% copper in its absence. FTIR analysis of bioleached residues revealed similar spectral patterns to the original acid-conditioned ore in the presence of PWp, thus indicating less development of passivation layer which was also confirmed through a complementary Raman characterization of the bioleached residues. Further, a reaction mechanism (chemistry) was proposed suggesting the possible role of PWp as the electron donor under oxygen limiting conditions which facilitated microbial reduction of Fe (III). The resulting biochemical changes provided an energy source for the bacteria, thus allowing free flow of electrons through the ore surface, thus contributing towards enhanced bioleaching of copper. [ABSTRACT FROM AUTHOR]

Highlights: [•] Iron reducing bacteria reduced goethite to hematite in chromite overburden. [•] An adapted consortium showed efficient bio-reduction in chromite overburden (COB). [•] Phase changes lead to exposure of metals embedded in the goethite matrix. [•] Leaching of treated COB yielded enhanced nickel and cobalt recovery with 8M H2SO4. [Copyright &y& Elsevier]

The most adverse outcome of increasing industrialization is contamination of the ecosystem with heavy metals. Toxic heavy metals possess a deleterious effect on all forms of biota; however, they affect the microbial system directly. These heavy metals form complexes with the microbial system by forming covalent and ionic bonds and affecting them at the cellular level and biochemical and molecular levels, ultimately leading to mutation affecting the microbial population. Microbes, in turn, have developed efficient resistance mechanisms to cope with metal toxicity. This review focuses on the vital tolerance mechanisms employed by the fungus to resist the toxicity caused by heavy metals. The tolerance mechanisms have been basically categorized into biosorption, bioaccumulation, biotransformation, and efflux of metal ions. The mechanisms of tolerance to some toxic metals as copper, arsenic, zinc, cadmium, and nickel have been discussed. The article summarizes and provides a detailed illustration of the tolerance means with specific examples in each case. Exposure of metals to fungal cells leads to a response that may lead to the formation of metal nanoparticles to overcome the toxicity by immobilization in less toxic forms. Therefore, fungal-mediated green synthesis of metal nanoparticles, their mechanism of synthesis, and applications have also been discussed. An understanding of how fungus resists metal toxicity can provide insights into the development of adaption techniques and methodologies for detoxification and removal of metals from the environment. • Review focuses on mechanisms used by fungus to resist the toxicity by heavy metals. • Mechanisms:biosorption, bioaccumulation, biotransformation, and efflux of metal ions. • Interaction with toxic metals-copper, arsenic, zinc, cadmium, nickel is discussed. • Exposure of metals to fungal cells leads formation of metal nanoparticles. • Fungal-mediated metal nanoparticles synthesis-mechanism-applications discussed. [ABSTRACT FROM AUTHOR]