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4 Uranium Mining, Processing, and Reclamation
Pages 96-122

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From page 96...
... • Mine design -- whether open-pit or underground -- requires detailed engineering planning that would include pit and rock stability considerations, as well as ventilation design to account for the presence of radon and other respiratory hazards. • With the ore grades expected in Virginia, many of the technical aspects of mining for uranium would be essentially the same as those applying to other hard-rock mining operations.
From page 97...
... 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.
From page 98...
... 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. Underground Mining 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.
From page 99...
... © Atlas Copco 2000 FIGURE 4.1 Components of a combined open-pit and underground mine. SOURCE: Modified; courtesy of Atlas Copco, Underground Rock Excavation Division.
From page 100...
... 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 (2006) : 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.
From page 101...
... 101 URANIUM MINING, PROCESSING, AND RECLAMATION winding tower headframe winding sha pillar ver cal sha elevator room level top road deck chute skip cross cut ore pass manway panel dri landing sump face bo om road winze FIGURE 4.3 Underground mine with vertical shaft. SOURCE: Reproduced with the permission of QA International (http://www.qa-international.com from the book, "The Visual Dictionary" ©QA International 2003.
From page 102...
... Ground Control in Underground Mining 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.
From page 103...
... . 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.
From page 104...
... 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.
From page 105...
... 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 eco nomic 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.
From page 106...
... URANIUM PROCESSING METHODS 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 3O8)
From page 107...
... . suitability of a particular ore deposit for mining suitability, a range of economic, social, and environmental issues are critical.
From page 108...
... . General Uranium Mineralogy While the mining method for a particular uranium ore deposit will be determined by the type and size of the deposit, the choice of process will be primarily determined by the ore type and uranium mineralogy.
From page 109...
... Uranium minerals occurring in ore deposits (as described in Chapter 3) belong to the following general groups: • Oxides, which represent by far the most common group of uranium minerals in ore deposits • Silicates, which are second in importance, and occur in significant concentration in sandstone-hosted deposits • Titanates, which mostly occur in some sodium-metasomatism related uranium deposits
From page 110...
... Worldwide, conventional uranium production is from ores that range from very TABLE 4.1 Chemical Constituents of the Main Uranium Minerals Primary Uranium Minerals Uraninite UO2.x Pitchblende UO2.x (x = 0.2-0.6) Coffinite U(SiO4)
From page 111...
... Ore Pretreatment or Beneficiation A process step that may precede conventional agitation leaching and possible heap leaching is ore pretreatment, or "beneficiation," in order to reduce the quantity of ore that will require chemical treatment. Beneficiation involves separating some of the host rock from the uranium-bearing mineral.
From page 112...
... The choice between an acid leaching process or alkaline leaching process is dependent on the ore and gangue and the uranium mineralogy. Extensive testing, economic studies, and environmental considerations will decide the final process choices.
From page 113...
... A typical conventional agitation leaching process is illustrated in Figure 4.9. The final yellowcake prod FIGURE 4.9 Typical conventional agitated leaching process.
From page 114...
... Although the specific uranium processing method that might be used for an ore deposit in Virginia would be dependent on the specific situation, some of the parameters that would need to be considered for a modern conventional agitated leaching operation, and a typical set of basic design criteria, are shown in Table 4.3. Modern uranium processing operations have very strict mine-plant-product accounting practices to control the process and ensure an accurate accounting of recovery and production.
From page 115...
... 65 (0.01) Degrees Fahrenheit Leach temperature 120 to 135 190 to 205 Hours Leach time 8 to 12 48 to 96 % solids Slurry solids 40 to 60 40 to 60 Pounds per ton Acid consumption 80 to 200 -- Oxidant O2, H2O2, Na2ClO3 O2 or air Gram per liter Carbonate concentration -- 30 to 50 Pounds per ton Carbonate consumption -- 5 to 10 Gram per liter Bicarbonate concentration -- 7 to 12 Pounds per ton Bicarbonate consumption -- 2 to 10 Purification Solvent extraction or Ion exchange Direct precipitation or ion exchange Precipitation H 2O 2 NaOH and then H2O2 Final product UO4 or U3O8 UO4 or U3O8 Tailings treatment Lime neutralization Wash tailings for solution recycle 115
From page 116...
... Recovery of uranium by heap leaching is less common, with acid heap leaching used in Hungary (NEA/IAEA, 2000) and and alkaline heap leaching process used in Namibia (Schnell, 2010)
From page 117...
... This includes a site water balance analysis, including a plant water balance analy sis, that assesses not just water flows and water quality but also identifies water recycle options. This water balance analysis would consider seasonal variations, and consider the use of cutoff berms, stormwater ponds, and possible evaporation ponds, all based on a probable-maximum-precipitation analysis with a suitable safety margin.
From page 118...
... The final selected treatment is dependent upon the plant Clarifiers Tails Thickener Hydroxide Tanks Tailings Reclaim Water Neutralization Tanks Radium Arsenic Radium Polishing Raise Well Water Tailings Management Facility Tailings Neutralization and Disposal Sand Filters Monitoring Ponds Discharge to Sink Reservoir JEB Water Treatment Plant FIGURE 4.11 Example of multistage water treatment flowsheet showing treatment for metal content and radium and including pH adjustment with associated clarification as well as real-time monitoring of water quality before discharge. SOURCE: Schnell and Thiry (2007)
From page 119...
... Such a containment pit may also have an engineered cover to prevent influx of water and oxygen to reduce the risk of acid mine water runoff. The solid waste remaining after recovery of uranium in a processing plant are the tailings, consisting of everything that was in the ore except the extracted uranium.
From page 120...
... HDPE SECONDARY GEOMEMBRANE COMPACTED GEOSYNTHETIC CLAY LINER (GCL) SUBGRADE FIGURE 4.12 A purpose-built tailings impoundment facility was recently approved for the Piñon Ridge processing facility in Colorado: (A)
From page 121...
... Appropriate reclamation and closure are guaranteed by a bond to ensure that sufficient resources are available should the operating company fail prior to final reclamation and closure. It is difficult to envision and describe all postclosure requirements, but modern practice is to review risks and assess opportunities to reduce final closure impacts early in the project design phase.
From page 122...
... Consequently, a final design would require extensive site-specific analysis, and accordingly it is not possible at this stage to predict what specific type of uranium mining or processing might apply to ore deposits in Virginia. • Uranium recovery from ores is primarily a hydrometallurgical process using chemical processes with industrial chemicals, with a lesser dependence on physical processes such as crushing and grinding.


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