Sandeep Panda

Fe (III) reduction strategies of dissimilatory iron reducing bacteria

Advances in applied and industrial microbial biotechnology have opened up many new avenues for application of several microorganisms. A group of certain metal reducers such as the dissimilatory iron reducing microorganisms possess an inherent potential to reduce oxidized metals under strict anaerobic/facultative anaerobic condition, thereby opening possibilities to combat environmental pollution. This unique property has invited researchers towards understanding the metabolic regulatory pathways that enables the microbes to thrive under extreme environmental conditions. Currently, dissimilatory iron reducing bacteria (DIRB) is in the focus of researchers to elucidate the specific mechanisms responsible for microbial metal reduction. The recent advances towards understanding the metabolism of iron reduction in Shewanella and Geobacter, the model DIRB has been covered in this review. It is believed that the metabolic insights into the Fe (III) reduction systems of the model DIRB; Shewanella and Geobacter (as discussed in the review) can be a basis for metabolic engineering to provide improved practical applications. With the advancement of our existing knowledge on the metabolic processes of the model iron reducers, applications ranging from laboratory to field scale practices can be carried out. DIRB has gained immense interest for its application in the field of bioremediation, electrobiosynthesis, and bioelectronics in this decade. It can therefore be anticipated that the forthcoming years will see more applications of microbial iron reducers based on the existing as well as advanced metabolic informations available in open source literature.

Current scenario of chalcopyrite bioleaching: a review on the recent advances to its heap-leach technology.

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.

Two step meso-acidophilic bioleaching of chalcopyrite containing ball mill spillage and removal of the surface passivation layer.

Meso-acidophilic bacterial leaching of ball mill spillage (containing chalcopyrite >80%) was carried out in an innovative two-step bioleaching method. The major drawback of meso-acidophilic bioleaching limiting industrial application is the passivation phenomenon over the ore surfaces in iron-sulfur rich environments. In the present study, we present a novel wash solution that efficiently removed the passivation layer. FTIR characterization of the bioleached sample indicated that the residues could be further leached to recover extra copper after wash solution application. XRD study indicated accumulation of sulfates (SO(4)(-)) of Na, K, Fe and oxy hydroxides of iron [FeO(OH)] in the form of jarosite outlining the passivation layer. SEM, FESEM-EDS studies indicated severe corrosion effects of the wash solution on the passivation layer. Two step bioleaching of the ore sample yielded 32.6% copper in 68days in the first interlude and post wash solution application yielded 10.8% additional copper.

Extraction of copper from copper slag: Mineralogical insights, physical beneficiation and bioleaching studies

Copper slag was subjected to in-depth mineralogical characterization by integrated instrumental techniques and evaluated for the efficacy of physical beneficiation and mixed meso-acidophilic bioleaching tests towards recovery of copper. Point-to-point mineral chemistry of the copper slag is discussed in detail to give better insight into the association of copper in slag. Characterization studies of the representative sample revealed the presence of fayalite and magnetite along with metallic copper disseminated within the iron and silicate phases. Physical beneficiation of the feed slag (~0.6% Cu) in a 2 L working volume flotation cell using sodium isopropyl xanthate resulted in Cu beneficiation up to 2–4% and final recovery within 42–46%. On the other hand, a mixed meso-acidophilic bacterial consortium comprised of a group of iron and/or sulfur oxidizing bacteria resulted in enhanced recovery of Cu (~92–96%) from the slag sample. SEM characterization of the bioleached slag residue also showed massive coagulated texture with severe weathered structures. FE-SEM elemental mapping with EDS analysis indicated that the bioleached residues were devoid of copper.

Recovery of copper from a surface altered chalcopyrite contained ball mill spillage through bio-hydrometallurgical route

Bioleaching studies for chalcopyrite contained ball mill spillages are very scarce in the literature. We developed a process flow sheet for the recovery of copper metal from surface activated (600 °C, 15 min) ball mill spillage through bio-hydrometallurgical processing route. Bioleaching of the activated sample using a mixed meso-acidophilic bacterial consortium predominantly A. ferrooxidans strains was found to be effective at a lixiviant flow rate of 1.5 L/h, enabling a maximum 72.36% copper recovery in 20 days. Mineralogical as well as morphological changes over the sample surface were seen to trigger the bioleaching efficiency of meso-acidophiles, thereby contributing towards an enhanced copper recovery from the ball mill spillage. The bio-leach liquor containing 1.84 g/L Cu was purified through solvent extraction using LIX 84I in kerosene prior to the recovery of copper metal by electrowinning. Purity of the copper produced through this process was 99.99%.

Bioleaching of copper from pre and post thermally activated low grade chalcopyrite contained ball mill spillage

Bioleaching of a low grade chalcopyrite (ball mill spillage material) was tested for copper recovery in shake flasks. The original samples (as received) were thermally activated (600°C, 30 min) to notice the change in physico-chemical and mineralogical characteristics of the host rock and subsequently its effect on copper recovery. A mixed culture of acidophilic chemolithotrophic bacterial consortium predominantly entailing Acidithiobacillus ferrooxidans strain was used for bioleaching studies and optimization of process parameters of both original and thermally activated samples. Mineralogical characterization studies indicated the presence of chalcopyrite, pyrite in the silicate matrix of the granitic rock. Field emission scanning electron microscopy coupled with Energy dispersive spectroscopy (FESEM-EDS) and X-ray Fluorescence (XRF) analysis indicated mostly SiO2. With pH 2, pulp density 10% w/v, inoculum 10% v/v, temperature 30°C, 150 r·min−1, 49% copper could be recovered in 30 days from the finest particle size (−1 + 0.75 mm) of the original spillage sample. Under similar conditions 95% copper could be recovered from the thermally activated sample with the same size fraction in 10 days. The study revealed that thermal activation leads to volume expansion in the rock with the development of cracks, micro and macro pores on its surface, thereby enabling bacterial solution to penetrate more easily into the body, facilitating enhanced copper dissolution.

Bio-hydrometallurgical processing of low grade chalcopyrite for the recovery of copper metal

A process flowsheet was developed to recover copper metal from the lean sulfide ore of copper available at Malanjkhand, Hindustan Copper Limited (HCL), India. Copper pregnant leach solution (PLS) obtained from bio-heap leaching of chalcopyrite containing 0.3% copper was purified through solvent extraction (SX) and the copper recovered by electrowinning (EW). The copper-free raffinate obtained from SX stripping unit was returned back to the bioleaching circuit. The purity of the electrolytic copper produced at pilot scale was found to be 99.96%. During electrowinning, the effect of flow rate of electrolyte on current efficiency and energy consumption was also studied.

Effect of dissimilatory Fe(III) reducers on bio-reduction and nickel–cobalt recovery from Sukinda chromite-overburden

The effect of an adapted dissimilatory iron reducing bacterial consortium (DIRB) towards bio-reduction of Sukinda chromite overburden (COB) with enhanced recovery of nickel and cobalt is being reported for the first time. The remarkable ability of DIRB to utilize Fe(III) as terminal electron acceptor reducing it to Fe(II) proved beneficial for treatment of COB as compared to previous reports for nickel leaching. XRD studies showed goethite as the major iron-bearing phase in COB. Under facultative anaerobic conditions, goethite was reduced to hematite and magnetite with the exposure of nickel oxide. FESEM studies showed DIRB to be associated with COB through biofilm formation with secondary mineral precipitates of magnetite deposited as tiny globular clusters on the extra polymeric substances. The morphological and mineralogical changes in COB, post DIRB application, yielded a maximum of 68.5% nickel and 80.98% cobalt in 10 days using 8M H2SO4.

Synergistic effect of biogenic Fe(3+) coupled to S° oxidation on simultaneous bioleaching of Cu, Co, Zn and As from hazardous Pyrite Ash Waste.

Pyrite ash, a waste by-product formed during roasting of pyrite ores, is a good source of valuable metals. The waste is associated with several environmental issues due to its dumping in sea and/or land filling. Although several other management practices are available for its utilization, the waste still awaits and calls for an eco-friendly biotechnological application for metal recovery. In the present study, chemolithotrophic meso-acidophilic iron and sulphur oxidisers were evaluated for the first time towards simultaneous mutli-metal recovery from pyrite ash. XRD and XRF analysis indicated higher amount of Hematite (Fe2O3) in the sample. ICP-OES analysis indicated concentrations of Cu>Zn>Co>As that were considered for bioleaching. Optimization studies indicated Cu - 95%, Co - 97%, Zn - 78% and As - 60% recovery within 8days at 10% pulp density, pH - 1.75, 10% (v/v) inoculum and 9g/L Fe2+. The productivity of the bioleaching system was found to be Cu - 1696ppm/d (12% dissolution/d), Co - 338ppm/d (12.2% dissolution/d), Zn k 576ppm/d (9.8% dissolution/d) and As - 75ppm/d (7.5% dissolution/d). Synergistic actions for Fe2+ - S° oxidation by iron and sulphur oxidisers were identified as the key drivers for enhanced metal dissolution from pyrite ash sample.

BBProF: An Asynchronous Application Server for Rapid Identification of Proteins Associated with Bacterial Bioleaching

Recovery of metal value, especially from low-grade ores and overburden minerals using acidophilic bacteria through the process of bioleaching is an environmentally benign and commercially scalable biotechnology. In recent years, while the “OMICS” landscape has been witnessing extensive application of computational tools to understand and interpret global biological sequence data, a dedicated bioinformatic server for analysis of bacterial information in the context of its bioleaching ability is not available. We have developed an on-line Bacterial Bioleaching Protein Finder (BBProF) System, which rapidly identifies novel proteins involved in a bacterial bioleaching process and also performs phylogenetic analysis of 16S rRNA genes. BBProF uses the features of Asynchronous Java Script and XML (AJAX) to provide an efficient and fast user experience with minimal requirement of network bandwidth. In the input module the server accepts any bacterial or archaeal complete genome sequence in RAW format and provides a list of proteins involved in the microbial leaching process. BBProF web server is integrated with the European Bioinformatics Institute (EBI) web services such as BLAST for homology search and InterProScan for functional characterization of output protein sequences. Studying evolutionary relationship of bacterial strains of interest using Muscle and ClustalW2 phylogeny web services from EBI is another key feature of our server, where 16S rRNA gene sequences are considered as input through a JQUERY interface along with the sequences present in the BBProF database library. Complete genome sequences of 24 bioleaching microorganism characterized by genomic and physiological study in the laboratory and their respective 16S rRNA gene sequences were stored in the database of the BBProF library. To our knowledge BBProF is the first integrated bioinformatic web server that demonstrates its utility in identifying potential bioleaching bacteria. We hope that the server facilitate ongoing comparative genomic studies on of bioleaching microorganisms and also assist in identification and design of novel microbial consortia that are optimally efficient bioleaching agents.