Radium is a chemical element with the symbol Ra and an atomic number of 88. It was discovered in 1898 by Marie and Pierre Curie. They extracted it from uranium ore. Twelve years later, Marie Curie and Andre Debierne isolated the pure metallic form of radium by electrolysis from radium chloride. It was given the French name radium from Latin radius or ray. The curie unit of radioactivity was named for Marie Curie and is based on the radioactivity of Ra-226.
Radon is a tasteless, colorless, odorless elemental noble gas in the family with helium, neon, argon, krypton and xenon. Its chemical symbol is Rn and it has an atomic number of 86. It is the densest noble gas and one of the densest gases that exist. As with the other noble gases, radon is chemically inert and rarely forms compounds with other substances. It was discovered in 1900 by Friedrich Ernst Dorn as a gas given off by radium.
When enriched uranium is used in nuclear reactors, the exhausted fuel consists mainly of U-238 with small amounts of U-235, plutonium and minor actinides such as neptunium, americium, curium, berkelium, californium, einsteinium, and fermium. There are commercial facilities in France, the United Kingdom and Japan for reprocessing spent fuel. Reprocessing is also carried out at nuclear weapons facilities. Reprocessing is currently carried out in eleven countries.
When uranium metal is processed to increase the proportion of U-235, a byproduct of the process is a great deal of uranium metal containing smaller amounts of U-235 than the natural proportion of 0.72 %. This byproduct is known as “depleted” uranium(DU). The U-238 in DU emits alpha particles which contain 2 protons and 2 neutrons. These alpha particles only travel a few centimeters in open air and can be blocked by a sheet of paper or plastic, a layer of clothing.
When uranium metal is processed to increase the proportion of U-235, a byproduct of the process is a great deal of uranium metal containing smaller amounts of U-235 than the natural proportion of 0.72 %. This byproduct is known as “depleted” uranium. To produce 1 pound of 10% enriched uranium, 24 pounds of uranium must be processed leaving 23 pounds of deplete uranium. Depleted uranium usually contains from 0.2 % to 0.4 percent U-235. Processes have been developed to recover more U-235 from the deplete uranium as the price of uranium has risen. Deplete uranium metal is 1.67 times as dense as lead and almost as dense as gold or tungsten. In a powdered or vaporized state, it is highly flammable.
The U-238 in depleted uranium emits alpha particles which contain 2 protons and 2 neutrons. These alpha particles only travel a few centimeters in open air and can be blocked by a sheet of paper or plastic, a layer of clothing or even human skin. Their primary danger to human health lies in their danger when inhaled or swallowed.
Depleted uranium is store near the uranium processing facilities. It is mainly stored in steel cylinders in a crystalline solid form of uranium hexafluoride (UF6). Each cylinder contains about 14 tons of UF6. As of 2008, there were about 760,000 tons of UF6 in the US in Kentucky and Ohio. These stores of UF6 pose an environmental threat because the UF6 can interact with water moisture in the air to produce solid uranyl fluoride(UO2F2) and hydrogen fluoride(HF) gas both of which are highly toxic. Fortunately, the solid UO2F2 tends to plug leaks in the steel cylinder which would allow the HF gas to escape.
In the 1970, research on the use of depleted uranium as a projectile was begun in response to developments in armor plating for tanks. It has also been used as armor plating because of its density.
Armor piercing incendiary ammunition is currently in use by the U.S. military. In calibers of 20 to 30 mm, it is fired from tanks, armored personnel carriers, jet fighters, helicopters and naval vessels. Long thin penetrators made of depleted uranium are fired from tanks to defeat armored tanks and other vehicles. When they penetrate the armor of a tank, they can disintegrate, catch fire and burn everything inside the vehicle. Grenades, cluster bombs and mines were also developed by the U.S. military but they are no longer used.
There are minor civilian uses for depleted uranium such as shielding for radiographic cameras, chemical reagents, detectors in high energy physics and other scientific and industrial application. Other civilian uses for depleted uranium that have been discontinued include coloring agents for glass and ceramics, trim weights in aircraft and keels in sailboats.
Depleted uranium penetrator of a 30 mm round:
If the concentration of uranium in the ore from underground mines or open pit mines is too low to be processed in the mill, the heaps of ore are subjected to leaching liquids such as acids, alkaline chemicals or peroxide solutions. The liquid flows down through the heap and dissolves uranium minerals. The liquid runs down a layer of plastic under the heap and collects in pools.
Uranium is mined in 20 countries with a world annual production in the range of 60,000 tons. Just 10 mines in six countries provide over half of the total world production of uranium ore. These six countries produce over 85% of the annual mined uranium in the world.
Uranium is mined all over the world. There a number of different techniques that have been developed to extract uranium from various types of sources.
Uranium is a common element. It forms compounds with many other elements and is present in a wide variety of minerals. Four common geological processes distribute uranium minerals in many different forms across the earth. Only a few of the many minerals are considered suitable for extraction to obtain useful uranium and only a few of their deposits are currently exploited. .About one third of the worlds uranium resources are in the form of unconformity-related deposits.
The primary uranium minerals in commercial ores are uraninite (UO2), pitchblende (U3O8), coffinite (U(SiO4), brannerite (UTi2O6), davidite ((REE)(Y,U)(Ti,Fe3)20O38) and thucholite (Uranium-bearing pyrobitumen). There are a number of other common uranium minerals which form hydrated crystals incorporating water molecules.
The mineralogy of the host minerals, the reduction-oxidation potential of the uranium mineral and the porosity which determines water infiltration are important factors in the formation of uranium deposits. Since uranium is highly soluble, it can be easily moved around by the flow of water underground. This contributed to the variety of places and manners in which uranium may accumulate. The way in which uranium interacts with other elements and compounds in melted rock also influences its distribution.
Combinations of surface weathering, sedimentation, diagenetic, magmatic and hydropthermal geological processes mentioned in a previous post produce fifteen general types of uranium deposits.
The richest uranium ore deposits are found near unconformities. An unconformity is a break in between two layers of rock that have been laid down at different times. In the case of uranium deposits, the two layers are a quartz rich sedimentary layer and a metamorphic layer has been altered by heat and pressure. These deposits were formed between two billion five hundred million years ago and five hundred million years ago.
The second best uranium ore deposits form in sedimentary deposits on continental shelves and freshwater areas such as river deltas, lakes, etc. In an oxygen rich environment, the uranium dissolves and then moves with the water. When it encounters an oxygen poor or reducing environment, it precipitates out of solution.
Tabular deposits occur parallel to groundwater flow in sandstone. The ores are rich but the deposits are small.
Roll front uranium deposits form when ground water dissolves the uranium in sandstone and, after flowing underground, collides with some sort of organic matter rich in carbon. The uranium precipitates out at the “front” when the water encounters the organic material.
Basal channel deposits form from moving ground water like the tabular and roll front deposits, but the deposition occurs along channels of moving surface water such are rivers. When the water evaporates along desert margins or in shallow saline ponds, the uranium is deposited.
Quartz-pebble conglomerate deposits are created by the separation and movement of particles of uranium in flows of surface water and their deposit in river beds, river deltas and lakes. These deposits generally contain large quantities of low grade ore
Breccia complex deposits contain uranium along with iron oxide, copper, gold, silver and rare earth elements. Hydrothermal processes enriched the uranium content of the quartz-hematite breccias.
Vein deposits are uranium minerals filling in cracks, veins, fractures and breccias in steeply dipping fault systems. Magmatic processes in molten rock create the veins and later hydrothermal activity can concentrate the uranium. Some veins contain a variety of other metals in combination with the uranium.
Intrusive uranium deposits form when magma is forced into older rocks deep within the Earth’s crust.
Marine sedimentary deposits of phosphorite (which contain large amounts of phosphorus) sometimes contain uranium.
Collapsed breccia pipe deposits are created when vertical cylindrical cavities formed by groundwater dissolving limestone are filled with fragments of rock when they collapse. Uranium fills cavities and coats other rocks.
Volcanic deposits of uranium may be formed by magmatic processes in the molten rock or later mineralization by groundwater and chemical processes. Such deposits are usually small with low grade ore.
Surface deposits can form in peat bogs, karst caverns and in soil from the weathering of shallow sedimentary deposits of uranium.
Metasomite deposits are the result of uranium minerals being distributed in rocks that have been subjected to sodium metasomatism which is chemical alteration by hot subsurface solutions of sodium.
Metamorphic deposits were laid down by sedimentary or magmatic processes and then remained unaltered by any other processes.
Lignite is a soft brown young coal derived from wood. Some deposits contain significant amounts of uranium minerals.
Black shale deposits form in oxygen-free submarine sedimentation processes. The uranium is not mineralized by organic materials due to the lack of oxygen. These deposits are considered very low grade ores.
There are many other types of uranium minerals but these fifteen types constitute the pool from which uranium ores are chosen for extraction.
Sedimentary layers:
