| We talked to North Americas leading In Situ Leach | | | | previously added bicarbonate ion. |
| (ISL) uranium mining engineers, and had them explain | | | | The goal is to get the uranium out of the sandstone |
| exactly how ISL worked. Most of the significant ISL | | | | and soluble. Were accelerating Mother Nature and |
| operations in the United States were designed and/or | | | | making the uranium soluble again, said Doug Norris, |
| constructed by these engineers. They explained how | | | | engineering manager for Uranium Energy. When its |
| ISL mining is really just reversing the process of | | | | soluble, we can just pump it out of the ground. But it |
| Mother Nature. | | | | is dissolved in the water like salt in sea water. You |
| Blossom is what underground uranium miners called | | | | cant see it, but its there. |
| the crystals forming on the tunnel walls. Because the | | | | MINING THE URANIUM |
| ore was in contact with air inside an underground | | | | ISL mining and processing the uranium is a very |
| mine, and as ground water moved slowly against the | | | | simple process. Its a water treatment plant with |
| mines walls, a visible crust of uranium crystals would | | | | hundreds of water wells. There are two types of |
| precipitate, or blossom along those walls. Making the | | | | wells: injection and production. The water plus |
| uranium soluble doesnt require a lot of oxygen and | | | | reagent (oxygen, carbon dioxide) is injected into the |
| water because oxidization is a natural process. Adding | | | | ground via water wells. Outside the United States, |
| more oxygen to the groundwater found in, and | | | | where environmental regulations may be less |
| around, a uranium-mineralized orebody is the principle | | | | restrictive, an ISLs aquifer may be bombarded with |
| upon which present-day In Situ Leach (ISL) uranium | | | | harsh acid leaching. On Harry Anthonys engineering |
| mining is based. | | | | services website, he describes the process he |
| Eons ago, the uranium was soluble and moved, on or | | | | observed in the Czech Republic, Over 4,100,000 tons |
| below the surface, with the ground water. In roll | | | | of H2SO4 (sulfuric acid), 270,000 tons of HNO3 (nitric |
| front uranium deposits the uranium was transported | | | | acid), 100,000 tons of NH3 (ammonia), and 25,000 |
| into the area through the natural groundwater | | | | tons of HF (hydrofloric acid) were consumed by the |
| system and precipitated from solution due to some | | | | mine. |
| reducing environment, explained Harry Anthony, Chief | | | | It would be nearly impossible to get an ISL project |
| Operating Officer of Uranium Energy Corp. Often, the | | | | permitted in the United States using these chemicals |
| reducing agent was something organic, such as coal, | | | | to leach the uranium. The water quality division, within |
| deep-seated oil and gas deposits, or hydrogen sulfide | | | | a states Department of Environmental Quality (DQE), |
| gases. In its reduced form, the uranium crystals are | | | | demands restoration to background, which is about |
| insoluble. It will precipitate as a coating on the existing | | | | where the groundwater was before ISL mining |
| sand grains of the sandstone, added Anthony. As | | | | began. The less things you add, the less you have to |
| more water containing uranium sweeps through this | | | | reclaim at the end of the process, Doug Norris |
| area, and encounters this reducing environment, more | | | | pointed out. The more stuff you add trying to get it |
| uranium is precipitated until there is a sufficient | | | | out of the ground, the more you have to clean up. |
| concentration to make it a commercial deposit. | | | | Dennis Stover explained how the fluids presently |
| After the geological team has delineated a companys | | | | used came about, Historically, most ISL operations |
| uranium roll front deposit and determined it is of | | | | had a great deal of difficulty with plugging or fouling |
| economic value, the company must turn to its ISL | | | | of their injection wells due to the precipitation of |
| design engineers to complete the mining process. | | | | excessive amounts of salts. He pointed out that the |
| While it takes stellar geologists such as David Miller of | | | | chemistry miners were using in conventional milling |
| Strathmore Minerals, Bill Sheriff of Energy Metals, or | | | | operations didnt work in ISL mining. Because they |
| William Boberg of UR-Energy to accumulate large, | | | | had very high concentrated salt solutions, they were |
| proven uranium-mineralized holdings, as they have | | | | trying to accelerate everything, Stover told us. When |
| done in Wyoming, New Mexico, Texas or elsewhere, | | | | you take those concentrated solutions and put them |
| each must turn to their engineers to extract the | | | | underground, Mother Nature is not always happy. |
| uranium from those sand grains and process them to | | | | Other salts that were present in the rock would |
| produce an economic quantity of uranium oxide, or | | | | dissolve, solutions would become supersaturated and |
| U3O8. The overwhelming majority of ISL facilities, | | | | they would precipitate out. The wells would plug up. |
| designed in the United States, were engineered by | | | | Some of the early U.S. operations tried to enhance |
| Harry Anthony, Doug Norris and Dennis Stover. | | | | their production, for example, by using ammonia to |
| Trained as a mechanical engineer, Harry Anthony has | | | | enhance the pH of their water. They forgot that |
| been involved with more than ten ISL uranium | | | | ammonia is easily locked up by clay and almost |
| operations from Union Carbides Palangana in 1976 to | | | | impossible to get back to background, explained |
| Uranium Resources Bruni, Benavides, North Platte, | | | | Norris. Its pretty reactive and doesnt occur that |
| Kingsville Dome and Rosita ISL projects. Anthonys | | | | much in nature. Norris would give anyone using |
| consulting work has taken him to ISL projects in | | | | ammonia during the mining procedure, a 95 percent |
| Kazakhstan, Uzbekistan and the Czech Republic. | | | | chance of having a very bad time. Why, we asked? |
| Dennis Stover is best remembered for designing | | | | Norris responded, Its bad from the fact that nobody |
| Smith Ranch in Wyoming, now owned by Cameco | | | | has been able to successfully clean up a site that has |
| Corp. With a PhD in chemical engineering from the | | | | used ammonia. |
| University of Michigan, Dr. Stover helped develop the | | | | Norris explained that sometimes you have to add a |
| first commercial alkaline ISL project in south Texas | | | | carbonate source, such as carbon dioxide to stabilize |
| for Atlantic Richfield and helped develop an additional | | | | the dissolved uranium as uranyl dicarbonate. Norris |
| five small ISL operations in south Texas. Also a | | | | said, The uranium is in a solid state in the ore, as |
| chemical engineer by training, Doug Norriss paths | | | | Mother Nature left it. We oxidize it and turn it into |
| have crossed with both Stover and Anthony. He | | | | uranyl dicarbonate. What goes to the processing plant |
| helped build the Highland and Smith Ranch ISL | | | | is called lixiviate, the dissolved uranium in its ionic |
| operations in Wyoming, and designed Mestenas Alta | | | | form. According to Anthony, Today, most ISL mining |
| Mesa ISL operation in south Texas. | | | | operates at neutral pH, and the uranium is complexed |
| HOW DOES ISL MINING REVERSE MOTHER | | | | as a dicarbonate. |
| NATURE? | | | | Water is circulated through the injection wells with |
| In its natural, reduced environment, uranium exists as | | | | the expressed purpose of separating the uranium |
| a solid in the +4 valence, Anthony explained. In the | | | | coating the sandstone. Each time you circulate the |
| mining stage, we are reversing Mother Natures | | | | water through the orebody, you are capturing some |
| process by adding oxygen, oxidizing the uranium from | | | | of the uranium. Each pass through is called a pore |
| a valence of +4 to a valence of +6. The uranium | | | | volume. Its like filling up a bucket of sand with water, |
| was oxidized at one time, but then reduced by | | | | explained Anthony. Once you have the bucket full of |
| Mother Nature. By drilling wells into the ore zone, | | | | sand, you can still pour in water. The amount of |
| circulating the water and adding oxygen to it, the | | | | water you can pour in until you just bring it up to the |
| uranium is made soluble again. | | | | top of the sand is termed a pore volume. Pore |
| Is it really this simple? Yes and no. Energy Metals | | | | volume is the interspatial volume. |
| Chief Operating Officer Dennis Stover outlined the | | | | In Anthonys models for operating an economic ISL |
| process, Youre simply adding, into the injection well, | | | | plant, he calculates 20 pore volumes (PV). Porosity, or |
| gaseous oxygen, just pure oxygen, but youre doing | | | | the spaces in between the sand particles, where the |
| it under the water level in the well. The natural | | | | water can travel (permeability), helps determine how |
| pressure, created by that column of water above | | | | much uranium can be recovered. It takes about 20 |
| the injection point, allows the oxygen to dissolve into | | | | PV to 30PV to recover the highest percentage, said |
| the water so that theres no free gas being put into | | | | David Miller, who was Cogemas chief ISL geologist in |
| the well. | | | | the United States, before becoming President of |
| Stover compared the oxygen dissolved in the liquid | | | | Strathmore Minerals. But, as the price of uranium |
| to the carbon dioxide dissolved in a bottle of soda. | | | | keeps going higher, it may be economic to recover a |
| The soda remains clear, dissolved in the liquid, when | | | | higher percentage of the orebody. Maybe 40PV to |
| stationery. But when you shake it up, the gas will | | | | 50PV will be possible with the direction the prices are |
| break out, added Stover. The pressure thats available | | | | moving. Of course, your average processed grade will |
| that lets you dissolve the oxygen is determined by | | | | go down. A few years ago, you would want to shut |
| the amount of naturally occurring water pressure | | | | wells off at 15 parts per million (ppm), but now you |
| thats on the uranium deposit. Stover explained that if | | | | might want to run them at 10ppm. At $50/pound |
| the deposit is 100 feet below the water table, you | | | | uranium, you may be able to run at 7 or 8ppm. |
| can dissolve a certain amount of oxygen. If the | | | | Typically, an ISL operation should recover about 70 |
| uranium deposit is 200 feet below the water table, or | | | | percent of the uranium in the ore, under the 20PV to |
| twice as deep, you can dissolve twice as much | | | | 30PV scenario. However, in the case of the Czech |
| oxygen. | | | | Republics Diamo project, once Europes largest |
| Historically, ISL mining evolved from acid leaching to | | | | uranium mining operation, only 55 percent was |
| leaching with sodium bicarbonate or sodium | | | | recovered. Clearly, the more uranium recovered with |
| carbonate. Most people add only carbon dioxide in | | | | the least number of pore volumes, the lower the |
| dissolved oxygen at this point, Stover explained. | | | | operating costs. Trying to recover more uranium is |
| Theres a chemical relationship between carbon | | | | only possible if you have the plant capacity. Because |
| dioxide gas, bicarbonate, and the carbonate ion. The | | | | of the rising price of uranium, we would expect more |
| host rock typically contains calcium carbonate or | | | | companies to attempt to recover a higher |
| sodium carbonate minerals. By adding the carbon | | | | percentage of uranium. Miller warns, however, You |
| dioxide, Stover said, It will lower the PH of the | | | | will not make your production quota if your plant is |
| solution just slightly. That enhances the solubility of | | | | sized at a certain gallons per minutes at a certain |
| the naturally occurring calcium carbonate. According | | | | grade to meet your annual production. If you lower |
| to Stover and the other experts, the addition of | | | | the average grade and fail to increase your flow |
| carbon dioxide is an effective replacement for the | | | | rate, your annual production will decrease. |