File Name: hydrometallurgical extraction and reclamation .zip
Fauconnier and R. Lenahan and R.
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NCBI Bookshelf. This chapter outlines the basic steps involved in mining, processing, and reclamation that might be suitable for uranium ore deposits in the Commonwealth of Virginia. For uranium ore deposits, the choice of mining methods and processing options is very deposit-specific and dependent on many variables such as the quality and quantity of the ore, the shape and depth of the ore deposit, site-specific environmental conditions, and a range of other factors.
Accordingly, the description of how uranium mining is undertaken in this report is generalized and at a high level. Open-pit mining and underground mining are the two types of mining that would be used to exploit uranium deposits in Virginia. These mining techniques can be used individually or combined; for example, many mines start as open-pit operations and continue as underground operations to follow a deposit deeper below the surface.
This chapter presents a short overview of both mining methods, and the considerations involved in using them. After the uranium ore is removed from the ground, it must be treated at a hydrometallurgical processing facility to remove impurities and produce yellow-cake. The specific type of hydrometallurgical process is also deposit-specific, dependent not only on the nature of the uranium mineral but also on the nature of the host rock as well as environmental, safety, and economic factors.
One overarching consideration throughout the entire mining, processing, reclamation, and long-term stewardship process is the need for meaningful and timely public participation throughout the life cycle of a mining project, beginning at the earliest stages of project planning. This requires creating an environment in which the public is both informed about, and can comment upon, any decisions made that could affect their community see additional discussion in Chapter 7.
Based on the current understanding of uranium deposits in the Commonwealth of Virginia, extraction of uranium ore would use open-pit mining, or underground mining, or a combination of both Figure 4. These general terms incorporate a large variety of design possibilities—there are as many methods of mining uranium as there are orebody sizes, shapes, and mineral constituents. The orebody size, location, orientation, rock quality, and the distribution of the valued minerals in it—along with site location and infrastructure—all play a part in the selection of the mining method and the overall plan for developing an orebody.
Mines may range in size from very small underground operations, with considerably less than tons of production per day, to large open-pits that move hundreds of thousands of tons of ore and waste per day.
The descriptions of uranium occurrences in Virginia contained in the previous chapter indicate that most potential deposits will likely be hosted in a hard-rock setting, although geopolitical and market factors may in time enable uranium production as a byproduct of heavy mineral sand mining.
Components of a combined open-pit and underground mine. Site-specific conditions, such as the depth of the ore deposit, its shape, surrounding geological conditions, and other factors, could result in the selection of an underground mining technique. Both vertical and inclined shafts must be equipped with hoists and head-frames, which are the structures at the top of the shafts that enclose and operate the hoists used for transporting ore and mine personnel Figure 4.
Ramps usually spiral downward so that rubber-tired mobile equipment will have access to the mine. In some cases, ramps are driven in a straight line to accommodate conveyor belts. Underground mine headframe and hoist room. Generally, orebodies are either vein type, massive, or tabular in shape, and both the shape and ore thickness influence the mining method used.
Vein-type orebodies usually dip steeply, and this steepness can be used during mining with the ore being allowed to fall to lower levels to an extraction accessway Figure 4. Uranium orebodies are often narrow and irregular. The strength of the ore material and the surrounding host rocks, as well as the ore grade and the distribution of the ore, influences the ore removal method.
Mined openings may be either supported or self-supported. Some supported openings are held up by backfill, that is, waste rock or aggregate placed in the openings shortly after they are mined out. Others are held up by timber, metal supports, concrete, rock bolts, or a combination of methods. The different techniques for underground mining have very specific names—cut and fill, drift and fill, shrinkage stoping, and block caving—and they are described below in very general terms based largely on ILO :.
Underground mine with vertical shaft. All rights reserved. Cut and fill mining is used in steeply dipping or irregular ore zones, where the mineral deposit is contained in a rock mass with good to moderate stability. Cut and fill mining removes the ore in horizontal slices starting from a bottom cut and advances upward, allowing the stope boundaries to be adjusted to follow irregular mineralization. This permits high-grade sections to be mined selectively, leaving low-grade ore in place.
Although cut and fill mining is relatively expensive, it minimizes ore loss and ore dilution. Drift and fill mining is similar to cut and fill, but is used where the ore zone is too wide for a single cut.
As with cut and fill mining, ore is removed after blasting, and the resulting space is packed with fill material. With drift and fill mining, after completion of the first drift, a second drift is driven adjacent to the first.
Additional drifts are developed until the ore zone is mined out to its full width, after which a second cut is started on top of the first cut.
Shrinkage stoping is a mining method that can be used for steeply dipping orebodies. Ore is extracted in horizontal slices, starting at the stope bottoms and advancing upward. Most of the blasted rock remains in the stope to provide a working platform for the miner drilling holes in the roof, and and it also serves to keep the stope walls stable.
Because blasting increases the volume of the rock by about 60 percent, some 40 percent of the ore is drawn at the bottom during stoping in order to maintain a working space between the top of the blasted rock and the roof. The remaining ore is removed after blasting has reached the upper limit of the stope.
Shrinkage stoping allows mining that is very selective, but one disadvantage is that there is a delayed return on capital investment because most of the ore stays underground until mining of the stope is completed. Room and pillar mining is commonly done in flat or gently dipping ore-bodies.
Room and pillar mining accesses an orebody by horizontal drilling advancing along a multifaced front, forming empty rooms behind the producing front. The usual result is a regular pattern of rooms and pillars, with their relative size representing a compromise between maintaining the stability of the rock mass and extracting as much of the ore as possible.
In some room and pillar mines, once the rooms are mined out the pillars can be mined, starting at the farthest point, allowing the roof to collapse. This allows the ore contained in the pillars to be accessed.
Block caving is a large-scale mining method that is used to mine massive orebodies with specific characteristics that enable gravity to do part of the work. Preparation for block caving requires long-range planning and extensive initial development involving a complex system of excavations beneath the orebody. The orebody is drilled and blasted above the undercut, and ore is removed through the accessway.
Because of the characteristics of the orebody, material above the first blast area falls into the collection areas. As ore is removed from the collection areas, subsequent caving provides steady availability of ore.
Extensive rock bolting and concrete lining are required to keep the openings intact, and if caving stops and removal of ore continues, a large void may form that can have the potential for a sudden and massive collapse.
Ground control—the prevention of rock collapse into a mined cavity—is an integral part of mine design to ensure a safe underground working operation.
Ground control design requires consideration of many factors, such as rock type, groundwater inflow, geological features, deposit shape and size, and others.
Ground control may be as simple as leaving adequate support columns during the mining operation, or may involve more complex systems that use cemented backfill to infill voids. Ventilation is a critical consideration for all underground mining. Adequate ventilation is required to provide fresh air to miners and to reduce exposure to gases, products of combustion, dusts including siliceous material , heat and humidity, radioactive gases and solids, and diesel gases and particulate matter.
For many hazardous components, ventilation is used to first dilute contaminants to a safe level, and then to remove them. The most common method for ventilation in the subsurface is by airflow from the surface produced by large fans.
Underground booster fans can also be used to ventilate specific areas of a mine e. Schematic diagram showing a simple mine ventilation system. The design of a major underground ventilation and environmental control system is a complex undertaking Figure 4. It requires a systems engineering approach that encompasses the entire mining process, to ensure that the consequences of changes in the mining techniques and size of the mine, and other factors, are accounted for in the control system design and operation.
Multiple factors interacting in the creation and control of hazards in a subsurface environment. Compared with underground mining, an open-pit mine is usually less expensive. Unlike underground mining, equipment size is not restricted by the size of the opening to the mine and consequently open-pit mining can take advantage of economies of scale, using larger and more powerful shovels and trucks.
Ore production is generally faster in open-pit mines, and lower costs per ton for the mined ore means that lower grades of ore can be mined economically. Open-pit mines do not require the extensive mine ventilation of underground mines, because generally there is sufficient air movement without ventilation equipment. Air monitoring for radon is usually carried out in case there is an atmospheric air inversion; however, these are usually short-lived, and mine operations are reduced in these instances.
Air inversions may also be relevant for other exposures, for example, diesel vapors and particulates. Open-pit mining is appropriate when the ore is near the surface, particularly if the ore deposit is relatively large and there is little overburden. There are several important design considerations for open-pit mines. First, the open-pit walls need to be constructed and angled so that they are strong enough to support a safe slope. Second, the depth to the ore will dictate how much waste overburden will need to be mined before production can begin.
Typical open-pit mine structure. The stripping ratio—the ratio of the amount of waste rock that has to be mined to the amount of ore mined—is a critical element for deciding the economic feasibility of exploiting a particular ore deposit with open-pit or underground mining.
In most cases, this stripping ratio is high for the first bench, and decreases steadily for each successive bench. Obviously, an open-pit mine will only be economically feasible if the cost of mining the waste rock does not exceed the value of the ore.
Ore recovery involves a number of steps that are common to both open-pit and underground mining. Commonly, nitroglycerine dynamites and ANFO i. The blast is initiated by a high explosive blasting cap, usually with a primer. Once the ore has been fragmented by blasting, and a suitable time interval has elapsed to allow safe reentry based on explosive gas dissipation, the ore is loaded into either trucks or rail cars to be transported to the processing area.
In some cases, initial ore processing often crushing occurs underground or in the open-pit, followed by transportation for further processing via a conveyer belt system. After an underground area has been mined out, it is often necessary to backfill it with some waste material—this can occur immediately, or it can be delayed until the stope is completely mined out.
For safety reasons, large blasts in underground mines are usually set off electrically from the surface once all underground workers have reached the surface of the mine, usually at the end of a work shift. This precaution also limits exposure to the dust and fumes caused by a blast, because the ventilation system can flush the underground atmosphere before the next shift goes underground.
A hydrometallurgical process is used to produce uranium from uranium ore, using chemicals and solutions to extract the uranium from the ore matrix. The process is complete when the final uranium product, known as yellowcake, is produced in a sufficient high purity typically 75 to 85 percent U 3 O 8 so that it can be used in the remainder of the nuclear fuel production cycle.
This section provides an overview of these options, with emphasis on the conventional agitated leach process. In situ recovery is briefly discussed for the sake of completeness, but is not evaluated in detail because, as noted previously, it is unlikely to be appropriate for use in Virginia. Also for completeness, this section will briefly describe byproduct recovery. A simplified schematic for uranium processing is shown in Figure 4. There are variations within each unit process as required by the specific uranium ore being processed and the availability of specific chemicals and equipment.
Uranium processing flow diagram showing the unit process steps, from ore produced by an open-pit or underground mine through to yellowcake production.
The state of the art for the recovery of metals from steel industry by-products using hydrometallurgical processes is reviewed. The steel by-products are different slags, dusts, and sludges from a blast furnace BF , basic oxygen furnace BOF , electric arc furnace EAF , and sinter plant, as well as oily mill scale and pickling sludge. The review highlights that dusts and sludges are harder to valorize than slags, while the internal recycling of dusts and sludges in steelmaking is inhibited by their high zinc content. Because wide variations in the mineralogical composition and zinc content occur, it is impossible to develop a one-size-fits-all flow sheet with a fixed set of process conditions. The reason for the interest in EAF dust is its high zinc content, by far the highest of all steel by-products. However, EAF dust is usually studied from the perspective of the zinc industry.
Copper extraction refers to the methods used to obtain copper from its ores. The conversion of copper consists of a series of physical and electrochemical processes. Methods have evolved and vary with country depending on the ore source, local environmental regulations , and other factors.
Not a MyNAP member yet? Register for a free account to start saving and receiving special member only perks. However, uranium mining and processing add another dimension of risk because of the potential for exposure to elevated concentrations of radionuclides.
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Hydrometallurgy is a technique within the field of extractive metallurgy , the obtaining of metals from their ores.
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Hydrometallurgical Extraction and Reclamation. By E. Jackson, Ellis Horwood Limited, Halsted Press, Chichester, , pp., $4 F. M. Doyle. University.
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Hydrometallurgical Extraction and Reclamation. By E. Jackson, Ellis Horwood Limited, Halsted Press, Chichester, , pp., $4 · Related · Information.