Click here to sign up. Download Free PDF. Dr Abhilash. A short summary of this paper. Download Download PDF. Translate PDF. Version of record f irst published: 04 Oct Any subst ant ial or syst em at ic reproduct ion, redist ribut ion, reselling, loan, sub- licensing, syst em at ic supply, or dist ribut ion in any form t o anyone is expressly forbidden. The publisher does not give any warrant y express or im plied or m ake any represent at ion t hat t he cont ent s will be com plet e or accurat e or up t o dat e.
The accuracy of any inst ruct ions, form ulae, and drug doses should be independent ly verified wit h prim ary sources. The publisher shall not be liable for any loss, act ions, claim s, proceedings, dem and, or cost s or dam ages what soever or howsoever caused arising direct ly or indirect ly in connect ion wit h or arising out of t he use of t his m at erial. Pandey CSIR-National Metallurgical Laboratory CSIR-NML , Jamshedpur, India Downloaded by [National Metallurgical Laboratory] at 23 October Due to depletion of high-grade deposits of uranium and generation of large quantities of tailings produced by mining and metallurgical activities, there is a need to find an economi- cal way to recover uranium from low-grade deposits and secondary resources.
Bioleaching of uranium from the ores, minerals, and wastes in heap and dumps, besides in-situ biodisso- lution processes, is rapidly expanding globally, and its economic values may exceed that of the underground mining.
The biodissolution of uranium is a consequence of hydrometallur- gical treatment of ore with microbial intervention. Uranium bioleaching is mainly driven by the combined action of Fe III and the protons that are produced by the activity of chemo- lithotrophic micro-organisms which use either iron or sulfur as their energy source for their growth.
The processes developed or in vogue for bioleaching of uranium are described in some detail, along with recent initiatives. Hydrometallurgical methods have some disadvantages such as poor recovery, involvement of high process and energy cost, and increase in pollution load of water resources Bruynesteyn ; Dwivedy and Mathur Industrial-scale bioleaching of uranium is carried out by spraying stope walls with acid mine drainage and the in-situ irrigation of fractured underground ore deposits.
E-mail: biometnml gmail. PANDEY and is environmentally benign; it is due to the uranium solubilizing and accumulating properties of certain micro-organisms. The commercial appli- cation of bioleaching of uranium from low-grade ores has been practiced since the s. The seven leading uranium-producing countries in descending order are Canada, Australia, Niger, the Russian Federation, Kazakhstan, Namibia, and Uzbekistan.
Currently, the two largest producers viz. As regards bioleaching, Canada produced about 70, lb of U3O8 in using Acidithiobacillus ferrooxidans Downloaded by [National Metallurgical Laboratory] at 23 October A. Currently this technology is applied on a commercial scale not only for the recovery of uranium but also for extraction of copper, nickel, gold, etc. The microbial consortia responsible for removing uranium from its minerals are considered to be complex mixtures of acidophilic, autotrophic, and heterotrophic bacterial strains de Siloniz et al.
U IV can be oxidized to the soluble form by ferric ion as reported by Dutrizac and MacDonald , and the oxidation occurs much more rapidly in the presence of A. For the leaching to be effective, it must reach the potential Eh above mV in accordance with Eh-pH Diagram Figure 2.
The solubility of uraninite in the form of U IV is typically observed at higher acidity, i. The leaching rate is faster in acid solution as com- pared to alkali carbonate solution. Higher temperature and lea chant concentration though leads to favor uranium recovery, but more refractory matrix materials also get decomposed thereby increasing the amount of impurity. At the industrial level, the Fe III regeneration is carried out by adding strong oxidizing agents which are capable of maintaining the redox potential between mV to mV.
MnO2 and pyrolusite Shakir, Aziz, and Beheir Shakir et al. Ketzinel et al. Amme et al. The percentage extractability of uranium from different ores through bioleaching is summarized in Table 1. A look at the table shows various degree of leachability of uranium from different locations depending upon the type of minerals present, their association with other ore minerals and gangue, and their leachability under standard practiced conditions. The role of micro-organisms in mining, ore processing, and waste-water treatment is likely to become increasingly important.
A comparison of acid, alkali, and bio-leaching is shown in Table 2. Leonardos et al. Rutherfordine UO2 CO3 It is applied to large operations. It is also applied to large operations. It may be applied to small and large Brierley and Brierley operations.
Acid leaching achieves a high uranium Extraction from alkaline leaching is low, Bioleaching using micro-organisms Fisher ; Bhatti et al. Acid leaching yields faster dissolution Slower kinetics of uranium dissolution; Bioleaching yields very slower dissolution Taylor et al. High acid consumption of carbonate Potential to treat ores containing high Potential to treat all minerals including Gupta et al.
Mandatory use of anti-corrosive Common material and equipment can be Common material and simple equipments Taylor et al. Addition of oxidant not always Addition of oxidant always required and Addition of oxidant not required as it is Taylor et al.
The excess acid in recycled solution, with accurate generated must be neutralized. Possibility of recovering by-products. Leaching chemistry is very selective. Leaching chemistry is highly selective. Taylor et al. Additional processing on surface may Product dissolution from ion-exchange Additional processing is not required. Acid leaching causes the emission of Alkali leaching causes the emission of No emission of gaseous pollutants Taylor et al.
The air pollution by sulfur gaseous pollutants. The air pollution by eco-friendly. The air pollution by sulfur oxides cannot be eliminated but sulfur oxides cannot be eliminated but oxides can be eliminated but sulfur sulfur byproducts can be recovered. Ore cannot be upgraded at mining site.
Ore can be upgraded at mining site. Brierley and Brierley Leaching agents are to be Leaching agents are transported. Leaching agents are produced in situ no 88 transported. It is not dependent on the climate. It is also not dependent on the climate. Dependence on the climate. Brierley and Brierley Capital costs are high. Capital costs are low compared to acid Capital costs are low. Krebs et al.
High energy demand. Low energy intensive. A further advantageous characteristic of bioleaching processes is that they are usually not contaminated by unwanted micro-organisms. Table 3 shows different micro-organisms capable of leaching uranium from its ores and the optimum conditions. The applicability of the various classes of microbes is cor- related with their characteristics by virtue of which they utilize these raw materials.
For instance, Acidithiobacillus group of bacteria utilizes the energy from Fe III in acid medium in presence of oxygen at an optimum pH of 1. The optimum levels of nutrients, pH and temperature are very essential to maintain the exponential phase activity of these microbes. In case of fungus, the primary action is initiated through the metabolite Downloaded by [National Metallurgical Laboratory] at 23 October mediated reactions.
The important micro-organisms involved in dissolving uranium from minerals are those which are responsible for producing Fe III and H2SO4 required for the bioleaching reactions. These are the iron- and sulfur-oxidizing chemolithrophic bac- teria and archaea Rossi The micro-organisms have a number of features in common that make them especially suitable for their role in mineral solubilization. These chemolithotrophs obtain their energy by using either Fe II or reduced inorganic sulfur compounds some use both as an electron donor, and oxygen as the electron acceptor.
As sulfuric acid is produced during the oxidation of inorganic sulfur, and the micro-organisms grow at low pH environments, most mineral dissolution processes operate at a pH between 1.
This ability is relevant in non-aerated heap leaching in which oxygen might not penetrate to the bottom of the heap. As may be expected, micro-organisms that grow in mineral-rich environments are remarkably tolerant to a wide range of metal ions, though there are considerable variations within and between the species Waksman and Joffe These include the iron- and sulfur-oxidizing A.
Limited investigations have been carried out on with the micro-organisms like A. Archaea belong to the genus Acidianus such as Ad. There are a few reports on the evaluation of microbial species in the leaching environment, in which eukaryotic life appears to be restricted largely to certain fungi including yeasts and protozoa de Siloniz et al. So far A.
In the leaching of uranium, the bacteria do not directly attack the uranium mineral. The schematic representation of the mechanisms for bioleaching of uranium from its ore by A. Direct mechanism: In direct leaching, there is a physical contact between the microbial cell and the ore surface. In the process of obtaining energy from the inorganic material the microbial cell causes electrons to be transferred from Fe or S to O2 Chander and Briceno ; Sand et al. The transferred electrons give up energy, which is coupled to the forma- tion of adenosine tri-phosphate ATP , the energy currency of the cell Mignone and Donati Most of iron containing uranium ores, or iron externally added in the form of salt, is oxidized to iron III sulphate according to the following reactions Sand et al.
How- ever, the mechanism of attachment and the initiation of uranium solubilization are not completely understood. Indirect Mechanism: Indirect leaching is usually referred to as microbial assisted leaching with A. The micro-organisms need not be in contact with the ore surface but they accelerate the reoxidation of Fe II in solution to generate Fe III which chemically oxidizes the sulfur present in the ore Figure 3b. The bio-oxidation is about — times faster than the chemical oxidation Dziurla et al.
In practice, the leaching of uranium is far more complex than the above analysis might suggest. There are numerous processes in addition to direct enzymatic oxidation and bac- terial generation of Fe III. When sulfur is formed, A. Bioleaching by Heterotrophs: Since the minerals are not sterile and cannot be sterilized on a commercial scale, bioleaching using heterotrophs presents some pro- cess design challenges that are not realized in the bioleaching with autotrophic acid- ophiles.
The acidophilic autotrophs grow in highly selective environments which tolerate hardly any competitor that can displace them, but it is not the case with the heterotrophs.
The free-living and symbiotic fungi secrete carboxylic acids such as oxalic, citric, and gluconic acids, which decrease the pH of the media and also act as metal chelators Mishra et al. The fungal species like Penicillium sp. The microbiological processes for the removal of metals from solution can be divided into three categories: the adsorption of metal ions onto the surface of a micro-organism, the intracellular uptake of metals and the chemical transformation of metals by biological agents.
Aspergillus species which synthesizes oxalic acid as a metabolite could leach appreciable amount of uranium from geological rocks Strasser, Burgs taller, and Schinner The leach ability of uranium from the ferruginous siltstone Hefnawy et al.
The ores with high SiO2 Greater quantity of uranium leached by these fungal species may be attributed to the production of carboxylic acids in the media that shift the pH to a lower acidity while forming soluble com- plexes.
Quartz sand, kaolins, and clays which lower the quality of minerals can be removed by these micro-organisms. Best results were achieved when oxalic and citric acids were the main components in the lea chant solution. Bioleaching of uranium needs to be optimized with respect to the rate of bio- leaching reactions and growth of the micro-organism involved.
In order to optimize the leaching, it is necessary to understand the nature of biotic and abiotic reactions of the system.
The maximum yields of uranium can be achieved only when the leaching conditions correspond to the optimum growth conditions of the micro-organisms. Mineralogy of the ore: No two ores are identical, and within each ore deposit the mineralogical composition and the concentration of uranium display heterogen- eity. Miller et al. However, the bacterial leaching has been used with good results in the mines near Elliot Lake, Canada where the brannerite ore abounds.
Hence, the most suitable quantity of pyrite depends on the mineral content and the characteristics of the pyrite to be added. Micro-organisms: A variety of bacteria as well as fungi are known for the Downloaded by [National Metallurgical Laboratory] at 23 October dissolution of uranium.
The process is affected by the bacterial population density, its metal tolerance Phyllis et al. The rate and the extent of dissolution also depend on the microbial strain within the same species.
Inoculum density has been found to affect the bio- leaching rate. These parameters are reported to be as much critical for chemical leaching of uranium in acidic conditions Bhatti et al. So far, A. Temperature: Temperature plays a decisive role in uranium extraction since the behavior of certain species depends on it. Seasonal variation in the temperature greatly affects the bioleaching processes. During summer, when the temperature and humidity are high, high rates of uranium dissolution will be observed compared to the lower temperature.
The effect of temperature can be very well seen with application of the thermophiles that can grow at higher temperature, so oxidation kinetics may be compared when mesophiles and moderate thermophiles are used. The bioleaching kinetics in presence of thermo- philes Sulfolobus sp. The bioleaching dissolution reaction is exothermic; therefore, the tempera- ture increases during the reaction.
Norris et al. Higher temperature leads to more uranium recovery but the more refractory matrix materials also get decomposed and impurity level increases in the leach solutions Blake et al. The pH values in the range 1. Lower activity limit of A.
McCready, Wadden, and Marchbank have studied the effects of various nutrients on the growth of A. The energy source is the oxidation of Fe II , elemental sulfur, and other sulfur containing ura- nium minerals which is mediated primarily by the genera like Acidithiobacillus, Lep- tospirillum, Sulfolobus, Sulfobacilli, and Acidianus at low pH values to release uranium Norris et al. In industries, Fe III generation has been carried out by adding strong oxi- dizing agents while maintaining Eh between — mV.
The vast amounts of Fe II need to be oxidized to produce relatively little cell mass Kawatra, Eisele, and Bagley The large quantity of iron is not trans- ported through cell membrane but remain outside of the cell and each Fe II ion sim- ply delivers its electron to a carrier situated in the cell envelope. Earlier, it was reported that A.
Blake et al. Other soluble metal ions are frequently present in fairly high concentrations in highly acidic environments. Sulfur reduction: The acid responsible for the very low pH environment in which extreme acidophiles are found is most often sulfuric acid which is produced by the oxidation of inorganic sulfur compounds.
For bio-oxidation to occur, the reduced inorganic sulfur serves as an electron donor with O2 serving as the energeti- cally most favorable electron acceptor. The kinetics of sulfur oxidation is greatly depressed for bacteria grown with sulfur as substrate Espejo et al. Sugio et al. It is a very effective method and has the advantage that it can easily be controlled and regulated.
It may be poss- ible to choose a favorable temperature and to add phosphate, ammonia, carbon dioxide, sulfuric acid, iron, or other additives to accelerate the leaching process. However, it has major limitations of continu- ously changing conditions. It is also an expensive tool and its application is restricted to special purposes, for instance to the leaching of concentrates. Bhatti et al. Recently, Abhilash et al. A feature characteristic of column leaching is that it appears to results in the formation of dif- ferent zones within the ore sample that have distinct chemical and physical gradients.
These zones may exhibit differences in redox potential, iron precipitation, and elemental sulfur formation. These zones may have some analogy with those in large-scale dump and heap bioleaching operations Qiu et al.
In industrial operations, such zones have not been characterized at mine sites and are likely to include temperature gradients also. Sometimes, air lift percolator 5 mm diameter and 30—60 cm height can be considered the smallest and the simplest of the class of percolation devices.
The ore charge of the percolator ranges from g to g and average particle size up to 10 mm. The leach liquor trickling through the column is pumped up by the compressed sterile air to the top of the column for recirculation.
Simultaneously, the stream of air takes care of the aeration of the sys- Downloaded by [National Metallurgical Laboratory] at 23 October tem. To monitor the course of leaching the samples are taken at intervals and the state of the process is determined on the basis of pH measurements, microbiological investigations and the chemical analysis of iron and uranium.
The correct operation of percolation leaching needs periodic addition of distilled water to compensate for evaporation while restoring liquor volume.
In a column leaching experiment 40 cm height and 7. Abhilash et al. The rate of recovery of uranium values from heap and dump leach operations has been simulated by mathematically modeled reactions of several minerals and reagents.
The rates of all reactions are controlled by molecular dif- fusion within the particles of heap or dump leaching Box and Prosser It is still arguable that no fundamental differences exist among dump, heap, and in-situ bioleaching since all these processes are carried out on coarse and unsized frag- mented ore.
PANDEY The residence time of leach liquor ranges from a few hours for dump limited in height to three days for dumps of 80 m height and as much as 12 days for m high dumps. In commercial dump-leaching operations million tons of ore over-burden and waste rock containing small but valuable quantities of uranium are transported by truck or train from open-pit uranium mines to the dump site.
Sprinkling introduces air, a vital component of both the chemical and the biological oxidation reactions in the leach liquor. The dumps are not inocu- lated with the leaching micro-organism. They are ubiquitous and when conditions in the rock pile become suitable for their growth then they proliferate. The leach liquor percolates through the leach dump and the pregnant or uranium-laden solution is Downloaded by [National Metallurgical Laboratory] at 23 October collected in catch basins or reservoirs at the foot of the dump Figure 4.
Uranium is recovered from solution by solvent extraction or ion exchange. The barren or uranium-free solution is then recycled to the top of the dump. Because of the con- struction methods employed and the volume of the solid material treated, dump leaching is a crude operation. The oxidation of mining heaps containing pyrite is mod- eled based on the coupling of macroscopic transport and the microscopic particle reaction kinetics by incorporating oxygen and heat transport based on the two major mechanisms of convection and diffusion Fisher It was established that the interaction of macroscopic transport with the microscopic particle kinetics, water Figure 4 Various industrial operations of bioleaching Box and Prosser ; Taylor et al.
The macroscopic transport is the main limiting factor in dump leach- ing. Heap leaching: Heap leaching offers somewhat more regulation of biological, chemical, and engineering factors than dump leaching.
In heap leaching, the rocks are often crushed to avoid the solution Downloaded by [National Metallurgical Laboratory] at 23 October contact problems encountered when leaching large boulders and the heaps are built up on impermeable pads to prevent loss of the leach solution into the underlying soil Figure 4. The controlling dimension being heaps height which can range from 2—3 m to as much 7—8 m when the greater part of the ore is of 60— mm or greater lumps McCready and Gould ; Rossi The volume of heap can range from a few thousand to 15, tons accordingly.
The degree of compaction ranges from 80 to proctor for a slope heap leaching. However, commercial applica- tions of heap method are relatively few since preference has usually been given to the much simpler although less effective dump leaching method for sub marginal ores and to richer run-off-mines ore.
Mashbir reported the commercial application of heap leaching from low-grade ores and mine wastes in North America. In-situ leaching: Many problems encountered with the conventional mining techniques such as exposure to radon gas and mine roof failures are avoided with in-situ mining.
It has the advantage that the ore does not need to be removed from the ground and is usually carried out on the haloes of the low-grade ore that are left behind after the high-grade ores have been removed. It is most economical when old mine workings can be used to access the low-grade deposits. It is a promising tech- nique for the recovery of uranium from low-grade ores in inaccessible sites. This involves fracturing underground working using explosives, percolating with acidic leach liquors containing bacteria, pumping the pregnant liquor to the surface and extraction of solubilized uranium.
M e t a llurgy, Art , H ist ory by Fathi Habashi. Published April ISBN: 2- The present volume is a collection of selected papers dealing with the extractive metallurgy of copper published by the author and his coworkers plus ten new chapters specially written.
The book is fully illustrated by many coloured pictures, flowsheets, and diagrams - - should be useful for students, engineers, chemists, geologists, and for research workers. Published in ISBN , pages 6" x 9". The book included the chemistry of copper, its history, ores, beneficiation, pyrometallurgy, hydrometallurgy, electrometallurgy, and kinetics of leaching copper minerals. H ist ory, M e t a llurgy, Cult ure by Fathi Habashi.
This collection of articles gives a rapid and fully illustrated review of the history and extractive metallurgy of gold. Social responsibility of scientists 2. Migration and movement of scholars 3. Philanthropy and its role in education and culture 4. Enlightened despots and their influence on science and culture 5.
Social aspects of mining The book is meant for the general reader but can benefit scientists as well. Pictures have an important role to convey a message and for this reason some time was spent in selecting them from a variety of sources. Pe rsona l Re c olle c t ions by Fathi Habashi. The book is illustrated with numerous photographs, many of them in colour and contains facsimile of 12 letters and 4 historical papers by Ida Noddack.
Published February The history of the Copts is briefly told by Fathi Habashi in 92 pages, fully illustrated by coloured pictures. Published , ISBN An I llust ra t e d H ist ory by Fathi Habashi. Fully illustrated in color, pages, published August , covers history of mining and quarrying in relation to world civilization. An audio course for students and engineers in 5 hours, published by the American Chemical Society, composed of a page reference manual and a CD.
In pages incorporating illustrations 50 in color and numerous Tables. Published August T e x t book of H ydrom e t a llurgy, by Fathi Habashi.
The book covers the general principles of solution chemistry, engineering aspects, and detailed studies of hydrometallurgical processes in pages fully illustrated with drawings and photographs. Ou t of pr in t T e x t book of H ydrom e t a llurgy, 2 e dit ion by Fathi nd Habashi.
Pre ssure H ydrom e t a llurgy, by Fathi Habashi. It is an update to the new processes described in the literature dealing with recovering metals from ores and concentrates using this technology. Out of print Princ iple s of Ex t ra c t ive M e t a llurgy, vol. The book covers the general principles of heterogeneous non-catalyzed reactions which are the basis of extractive metallurgy. ISBN: , pages. September ISBN , published The book outlines the problems faced in the industry and how they were solved.
The book explains what is a metal, a nonmetal, and a metalloid, and summarises the processes is use for extracting metals from their ores. Published , is a collection of some papers published by the author during the period — The collection gives a rapid and fully illustrated review of the history and extractive metallurgy of aluminum. A selected collection of papers by the author and his co-workers to which an outline on the recovery of rare earths from different sources has been specially written.
The position of rare earths in the Periodic Table is also discussed. Cha lc opyrit e. I t s Che m ist ry a nd M e t a llurgy by Fathi Habashi, pages. H ist ory, Che m ist ry, a nd M e t a llurgy by Fathi Habashi, pages.
The book contains articles on the history and structure of asbestos, surface modification of its surface by organic dyes, and the toxicity issue.
Published by St. Boyan Kamenov Street, Sofia , Bulgaria. The book is in 8 chapters: 1.
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