28
Water for Energy and Fuel Production
Froth from the hot water process may be mixed with a hydrocarbon diluent
such as coker naphtha and centrifuged. The Suncor process described by Speight
[16,17,44] employs a two-stage centrifuging operation. The final bitumen product
contains 1–2 wt% mineral and 5–15 wt% water. About 2 tons of tar sands is required
to produce one bbl of oil. Roughly 75% of the bitumen can be recovered from sand.
More details on oil recovery from tar sands are given in excellent reviews of Speight
[16,17,44].
Relatively large amount of water is required to process tar sands. Currently, tar
sand extraction and processing require several bbl of water for each bbl of oil produced, though some of the water can be recycled. In situ production methods are
used on bitumen deposits buried too deep for mining to be economically recovered.
These techniques include steam injection, solvent injection, and firefloods (see various EOR methods in Sections 2.3.1 and 2.3.2).
2.5.3 urAnium mining And leAChing
Uranium, a substance essential for nuclear energy, is recovered from the ground by
the extraction process [41]. In 2009, a worldwide production of uranium amounted to
50,572 tons [41]. While this number is small compared to that for coal, oil shale, and
tar sands, this mining process also requires a large amount of water. As with other
types of hard rock mining, uranium is extracted by the three main methods: box cut
mining, open pit mining, and in situ leaching (ISL). While water requirement for
open pit mining or underground mining of uranium is similar to that of other minerals, coal, oil shale, and tar sand, the major water usage in uranium mining is in the
implementation of the ISL process.
The ISL process is also known as solution mining, which involves leaving the
ore where it is in the ground and recovering uranium from it by dissolving it and
pumping the pregnant solution to the surface where the uranium is recovered. This
process has a little surface disturbance and no waste is generated. Uranium ISL
uses the native groundwater in the ore body that is fortified with a complexing
agent and in most cases an oxidant such as hydrogen peroxide. In many cases, the
complexing agent used is sulfuric acid. It is then pumped through the underground
ore body to recover the minerals in it by leaching. Once the pregnant solution is
returned to the surface, uranium is recovered in much the same way as in other
uranium plants [41].
Often, the use of oxidant is replaced by high concentration of acid solution. In the
United States, ISL mines use an alkali leach due to the presence of significant quantities of acid-consuming minerals such as gypsum and limestone in the host aquifers.
Any more than two to five percent carbonate minerals means that alkali leach must
be used in preference to the more efficient acid leach.
In uranium mine near Moab, Utah, uranium deposits were formed when oxygenated groundwater, which had leached uranium from crystal rocks, flowed
down into aquifers, where it was reduced to form precipitate uraninite; the main
ore of uranium. This corresponds to oxidized and reduced conditions in groundwater redox chemistry. The rocks formed in the oxidizing conditions are reduced
by a reducing fluid. The reduced fluid carries uranium-bearing minerals [41].
Water for Energy and Fuel Production
Froth from the hot water process may be mixed with a hydrocarbon diluent
such as coker naphtha and centrifuged. The Suncor process described by Speight
[16,17,44] employs a two-stage centrifuging operation. The final bitumen product
contains 1–2 wt% mineral and 5–15 wt% water. About 2 tons of tar sands is required
to produce one bbl of oil. Roughly 75% of the bitumen can be recovered from sand.
More details on oil recovery from tar sands are given in excellent reviews of Speight
[16,17,44].
Relatively large amount of water is required to process tar sands. Currently, tar
sand extraction and processing require several bbl of water for each bbl of oil produced, though some of the water can be recycled. In situ production methods are
used on bitumen deposits buried too deep for mining to be economically recovered.
These techniques include steam injection, solvent injection, and firefloods (see various EOR methods in Sections 2.3.1 and 2.3.2).
2.5.3 urAnium mining And leAChing
Uranium, a substance essential for nuclear energy, is recovered from the ground by
the extraction process [41]. In 2009, a worldwide production of uranium amounted to
50,572 tons [41]. While this number is small compared to that for coal, oil shale, and
tar sands, this mining process also requires a large amount of water. As with other
types of hard rock mining, uranium is extracted by the three main methods: box cut
mining, open pit mining, and in situ leaching (ISL). While water requirement for
open pit mining or underground mining of uranium is similar to that of other minerals, coal, oil shale, and tar sand, the major water usage in uranium mining is in the
implementation of the ISL process.
The ISL process is also known as solution mining, which involves leaving the
ore where it is in the ground and recovering uranium from it by dissolving it and
pumping the pregnant solution to the surface where the uranium is recovered. This
process has a little surface disturbance and no waste is generated. Uranium ISL
uses the native groundwater in the ore body that is fortified with a complexing
agent and in most cases an oxidant such as hydrogen peroxide. In many cases, the
complexing agent used is sulfuric acid. It is then pumped through the underground
ore body to recover the minerals in it by leaching. Once the pregnant solution is
returned to the surface, uranium is recovered in much the same way as in other
uranium plants [41].
Often, the use of oxidant is replaced by high concentration of acid solution. In the
United States, ISL mines use an alkali leach due to the presence of significant quantities of acid-consuming minerals such as gypsum and limestone in the host aquifers.
Any more than two to five percent carbonate minerals means that alkali leach must
be used in preference to the more efficient acid leach.
In uranium mine near Moab, Utah, uranium deposits were formed when oxygenated groundwater, which had leached uranium from crystal rocks, flowed
down into aquifers, where it was reduced to form precipitate uraninite; the main
ore of uranium. This corresponds to oxidized and reduced conditions in groundwater redox chemistry. The rocks formed in the oxidizing conditions are reduced
by a reducing fluid. The reduced fluid carries uranium-bearing minerals [41].