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The book discusses the manufacturing and use of materials in electronic devices while presenting an overview of separation methods for industrial materials. Readers will also benefit from a global overview of various national and international regulations related to the topic of electronic and electrical waste.
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It begins with general concepts like definitions of mineral resources, mineral resources and humans, recycling mineral resources, distribution of minerals resources across Earth, and international standards in mining, among others.
Then it turns to a classification of mineral resources, covering the main types from a geological standpoint. The exploration of mineral resources is also treated, including geophysical methods of exploration, borehole geophysical logging, geochemical methods, drilling methods, and mineral deposit models in exploration. Further, the book addresses the evaluation of mineral resources, from sampling techniques to the economic evaluation of mining projects i.
It subsequently describes key mineral resource exploitation methods open pit and underground mining and the mineral processing required to obtain saleable products crushing, grinding, sizing, ore separation, and concentrate dewatering, also with some text devoted to tailings dams. Lastly, the book discusses the environmental impact of mining, covering all the aspects of this very important topic, from the description of diverse impacts to the environmental impact assessment EIA , which is essential in modern mining projects.
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It will inspire and inform current and future generations of minerals and metallurgy professionals. Mineral processing and extractive metallurgy are atypical disciplines, requiring a combination of knowledge, experience, and art. Investing in this trove of valuable information is a must for all those involved in the industry—students, engineers, mill managers, and operators. 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. PANDEY environment, is currently employed to extract residual minerals from abandoned mine working and to recover uranium from the low-grade deposits.
To dissolve ura- nium from depleted mine working, the leaching liquor is applied directly to the walls and the roof of an intact stope or to the rubble of fractured working Figure 4. Best known is the in-situ leaching operations in the underground uranium mines in the Elliot Lake district of Canada including the Stanrock, Milliken, and Denison mines. At that time, the annual production of uranium from the Stanrock Mine was about 50, kg U3O8 whereas 60, kg U3O8 was produced in the Milliken Mine after improvement of the leaching conditions McCready and Gould Young ura- nium deposits post glacial are of apparent economic interest in view of their com- mon occurrence and amenability to in-situ leaching and lack of radioactive Downloaded by [National Metallurgical Laboratory] at 23 October components Culbert and Leighton Nguyen et al.
However, with the reduction in demand for uranium in subsequent years, this mine stopped production and no microbially assisted ura- nium recovery is currently taking place. About tons of uranium was produced in at Beverley mine, Australia with A. There are several in-situ mining opera- tions which have experienced decreased production due to heavy accumulations of inorganic particles and bacteria on well screens, casings, and submersible pumps. It is more expensive to construct and to operate tank leaching than dump, heap or in-situ leaching processes, but the rate of uranium extraction is much higher and can be used successfully.
The dissolution of uranium takes place in days when compared with weeks and months in heap or dump leaching operations. The major constraint using tank reactor is the PD that should be maintained in the suspension. This limitation in PD, higher capital, and running costs as compared to heap or dump leaching dis- courages their use in uranium dissolution.
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