A greener approach for resource recycling: Manganese bioleaching.

In view of unremitting diminution of mineral resources, rising energy economics along with increasing global consumption of Manganese (Mn), development of environment friendly technologies for tapping alternate sources of Mn has gained importance lately. Mn recovery from mining residues using conventional approaches is extremely expensive due to high capital and energy costs involved. However lean grade ores present in millions of tons awaits the development of competent and cost effective extractive process. Mn recovery by biomining with diverse microbes is thereby recommended as a superior and green alternative to the current pyro metallurgical techniques. The synergistic effects of different factors are known to influence microbial leaching of mineral ores which includes microbiological, mineralogical, physicochemical and process parameters. Bacterial bioleaching is mostly due to enzymatic influence, however fungal bioleaching is non enzymatic. Genomic studies on microbial diversity and an insight of its metabolic pathways provides unique dimension to the mechanism of biomining microorganisms. The extraction of Mn has a massive future prospective and will play a remarkable role in altering the situation of ever-decreasing grades of ore. This review aims to encompass the different aspects of Mn bioleaching, the plethora of organisms involved, the mechanisms driving the process and the recent trends and future prospects of this green technology.

Degradation mechanism and control of blended eri and tasar silk nanofiber.

Fabrication of nanofibers from wild varieties of silk such as eri and tasar is very promising for tissue engineering application because of the presence of RGD (arginine-glycine-aspartic acid) ligand and high content of hydrophilic amino acids. In this study, the biodegradation of silk fibroin (SF) nanofibers have been studied in protease XIV solution to analyze the degradation behavior. The present study reveals that the degradation of nanofibrous mat strongly depends on hydrophilic amino acid fragments possessing bulky groups connecting the crystalline portion in nanofibrous structure. The newly found mechanism shows that ß sheet content and percentage of crystal in nanofibers play a major role in addition to hydrophilic fragments in degradation processes. Understanding of this mechanism can optimize the preparation of nanofibers with controlled and flexible degradation behavior without affecting essential biomaterial properties such as hydrophilicity, mechanical strength, and morphological property. This knowledge would widen the application of silk-based biomaterial for several tissues engineering application.

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 nickel by microbial reduction of lateritic chromite overburden of Sukinda, India.

Microbial extraction of nickel from lateritic chromite overburden (COB), Sukinda by Acidithiobacillus ferrooxidans has been investigated in this work. In anoxic environment, A. ferrooxidans reduced the ferric iron in goethite [Fe(O)OH] mineral of COB by using elemental sulphur as electron donor. Nickel embedded in the complex goethite matrix of COB was successfully recovered by cumulative action of sulphuric acid, generated by oxidation of elemental sulphur and reduction of ferric iron in goethite matrix by A. ferrooxidans. Forty one percent of the nickel present in COB was extracted in a 3 L scale bioreactor (pH of 1.8 ± 0.05, temperature of 28 ± 2°C) maintained in anoxic environment. In contrast, only 11% of the nickel present in COB was extracted with continuous supply of air to the bioreactor keeping all the parameters unchanged. Kinetics study of anoxic microbial processing of COB revealed that the chemical reaction rate control model fits to the rate of nickel dissolution (R(2)=0.975).

Manganese biomining: A review.

Biomining comprises of processing and extraction of metal from their ores and concentrates using microbial techniques. Currently this is used by the mining industry to extract copper, uranium and gold from low grade ores but not for low grade manganese ore in industrial scale. The study of microbial genomes, metabolites and regulatory pathways provide novel insights to the metabolism of bioleaching microorganisms and their synergistic action during bioleaching operations. This will promote understanding of the universal regulatory responses that the biomining microbial community uses to adapt to their changing environment leading to high metal recovery. Possibility exists of findings ways to imitate the entire process during industrial manganese biomining endeavor. This paper reviews the current status of manganese biomining research operations around the world, identifies factors that drive the selection of biomining as a processing technology, describes challenges in exploiting these innovations, and concludes with a discussion of Mn biomining's future.

Bioleaching of low-grade uranium ore using Acidithiobacillus ferrooxidans.

Bioleaching of uranium was carried out with Turamdih ore sample procured from Uranium Corporation of India Limited, Jaduguda. The bacterial strain that was used in the leaching experiments was isolated from the Jaduguda mine water sample. Efficiency of bioleaching was studied by varying parameters like pulp density and initial ferrous concentration as source of energy. It is observed that the efficiency of bioleaching was 49% at 10% pulp density (w/v) and initial pH 2.0. Addition of external has no effect on efficiency of bioleaching showing domination of direct leaching mechanism over indirect.

Differential bioleaching of copper by mesophilic and moderately thermophilic acidophilic consortium enriched from same copper mine water sample.

Three acidophilic enrichment consortium were developed from mine water sample of copper mine site at Khetri, India were compared for their copper leaching efficiency. Out of these one was mesophilic (35 degrees C) and two were moderately thermophilic (50 degrees C). Consortia were named as mesophilic acidophilic chemolithotrophic consortia (MACC), thermophilic acidophilic chemolithotrophic consortia (TACC), and Sulfobacillus acidophilic consortia (SAC). Copper extraction ability of both the thermophilic consortia (77-78% extraction) was almost double to that of mesophilic consortia (40% extraction) at 10% pulp density after 55 days. Both the thermophilic consortia were equally effective in leaching of other metals like Ni, Co, Zn, Mn. After 55 days, the percentage of extractions of copper by TACC was 76, 74, 67, 48 and 45 at 5%, 10%, 15%, 20% and 30% pulp density, respectively. Total number of bacteria was maximum at 5% pulp density which decreases with increase in pulp density. Sulfobacillus-like bacteria were seen in the Sulfobacillus enrichment cultures. Moderately thermophilic consortia proved to be better in leaching performance than the mesophilic counterpart.

Beneficiation of iron ore slime using Aspergillus niger and Bacillus circulans.

Studies were carried out on the removal of alumina from iron ore slime containing (%) Fe(2)O(3) 75.7, Al(2)O(3) 9.95, SiO(2) 6.1, Fe (total) 52.94 with the help of Bacillus circulans and Aspergillus niger. B. circulans and A. niger showed 39% and 38% alumina removal after six and 15 days of in situ leaching at 10% pulp density, respectively. Culture filtrate leaching with A. niger removed 20% alumina at 2% pulp density with 13 day old culture filtrate. B. circulans was more efficient than A. niger for selective removal of alumina. In case of A. niger in situ leaching rather than culture filtrate leaching was found to be more effective.

Microbial desulfurization of different coals.

Coal is the most important nonrenewable energy source of fossil origin. It is also the most common fuel in thermal power plants. However, during coal incineration in power plants, high sulfur content of coal poses serious environmental problems owing to sulfur dioxide emission. We studied the application of microbial methods for removal of sulfur from three types of high sulfur coals-two samples collected from Assam and Rajasthan in India and one from Libiaz, Poland. These coal samples were desulfurized using indigenous Acidithiobacillus sp. After investigation of the effect of various parameters, the conditions optimized for the maximum removal of total sulfur (91.87% for lignite, 63.13% for Polish coal, and only 9.44% for Assam coal) were as follows: initial pH of 1.5 (2.5 in the case of Assam coal), particle size of 45 micro, pulp density of 2% (w/v), incubation period of 30 d at -35 degrees C in presence of 44.2 g/L of ferrous sulfate in the media with shaking at 140 rpm. Poor removal of sulfur in the case of Assam coal was owing to extensive precipitation of jarosites. In addition, the sulfur in Assam coal is mostly found in organic form, which is difficult to remove with Acidithiobacillus sp. The removal of sulfur from the three coal samples was demonstrated with photomicrographic studies.

Microbial leaching of lateritic nickel ore.

Lateritic nickel ore from the Sukinda Mines, Orissa, India, was leached using Thiobacillus ferrooxidans, Bacillus circulans, Bacillus licheniformis and Aspergillus niger at 5% (w/v) solid: liquid ratio for 5-20 days. Maximum leaching of Ni was achieved with B. circulans (85%) and Aspergillus niger (92%) after 20 days. Bacillus circulans showed significantly higher rate of leaching than the other organisms giving 80% Ni extraction after 15 days. The importance and usefulness of heterotrophic organisms in metal extraction are discussed.