Leaching of ore

The metallic or semi-metallic character of many common sulfides implies the significance of electrochemical factors in the study of their oxidation, which is relevant to environmental, energy, and metallurgical issues, e.g., in connection with the direct electrochemical conversion of sulfide ores to metals, the pressure leaching of ore materials, or flotation processes. 

Figure 5.5 Various cases of in-situ leaching of ore deposits below the water table (I = injection of leach solutions P = recovery of pregnant solutions). 

Leaching of ores, i.e. the separation of Fe oxides from silicate minerals has prompted investigations into the acid dissolution behaviour of natural goethites and hematites (Surana Warren, 1969 Warren Roach, 1971). Dissolution curves... 

Leaching of ores Cryo processing 100-300 aluminium (from bauxite) technical gases (N2, 02, H2, He. ..) gas liquefaction... 

The loss of dissolved metals during the leaching of ores was studied by Osseo-Asare and Fuerstenau (22). These investigators... 

Solvent extraction plays an important role in many commercial processes for the extraction of uranium from ore. In this case, the radioactivity levels are quite low compared with those in spent fuel extraction. The liquors from hy-drometallurgical leaching of ores are typically fairly dilute in uranium (0.5-5 g/L) and contain iron and other metals in solution. Depending on conditions, solvent extraction or ion exchange may be used to separate and concentrate the uranium from the leach liquor. 

Figure 2 Typical arrangement of a five-hole pattern for in situ leaching of ores. The central hole is used to inject the leachant, which flows radially to the outer holes from which the metal-laden solutions are withdrawn.

In Chapters 4 and 6, considerable emphasis is placed on the environmental significance of biotransformation as opposed to biodegradation. It therefore seems appropriate to draw brief attention also to their use in biotechnology. Microorganisms play important roles in widely diverse technical processes ranging from the leaching of ores and the preservation of food, to the production of antibiotics and food additives. It is worth drawing attention to some features of these applications. 

Some of these processes are carried out by specific groups of organisms for example, by acid-tolerant thiobadlli in the leaching of ores, by lactobacilli in food preservation, or by fungi and actino-myces in the production of antibiotics. 

Bacterial leaching of ores for the recovery of metals by natural adhesion on solid materials. 

Pressures above atmospheric have been employed for the leaching of ores in recent years, and this necessitates a completely new design of equipment. The process is usually operated on a batch basis with individual pressure vessels. 

Dilute alkali leaching of ores, principally with solutions of sodium carbonate or ammonium carbonate, is a technique of some commercial importance. In the rare metal field, however, its use is almost entirely restricted to two elements, uranium and vanadium, which form soluble complexes in carbonate solutions. The relatively inexpensive soda-ash grade of sodium carbonate is adequate for the purpose. 

Two of the most well-known applications of the sodium carbonate leaching of ores are the extraction of uranium from pitchblende in Canada and extraction of both uranium and vanadium from camotite, which is mined in numerous localities of the Colorado Plateau area of the United States. The latter deposits were originally worked for their vanadium content but since the 1939-45 war the emphasis has been on uranium, with vanadium a subsidiary product. 

Figure 9.2 presents a number of less commonly used stages, but all of them have commercial application in special cases. Pressure carbonate leaching of ores, which contain limestone can be cheaper than acid leaching and ion-exchange. This is followed by TBP extraction of the concentrate for final purification since any alternative would normally be based upon the same general chemical engineering principles and would only involve a different solvent. The older type of dryway process is then shown, with ammonia precipitation as the first step, since this still has applications for the production of special types of uranium dioxide. The final calcium reduction of oxide finds application on a relatively small scale, where the uranium metal product is required in powder form. 

During hydrothermal synthesis one can also expect the occurrence of chemical reactions such as synthesis of new phases, stabilization of new complexes, crystal growth, preparation of finely divided materials and microcrystallites with well-defined size and morphology, leaching of ores in metal extraction, decomposition, alteration, corrosion and etching. 

The occurrence of heavy metals in water bodies can be of natural origin (i.e., eroded minerals within sediments, leaching of ore deposits, and vulcanism extruded products) or... 

Soluble material is leached from a slurry of porous spherical particles by suspending them in a well-stirred liquid solvent of constant volume. This type of operation finds frequent use in the leaching of ores, and in the extraction of edible oils from seeds. Show that the model for this system is made up of a single PDE for the spheres and an ODE for the stirred tank. What are the relevant boundary and initial conditions ... 

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