2013-03-11_REVISION - M1977300 - Laserfiche WebLink

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Mr. Tom Kaldenbach March 8, 2013 Page 3 The initial pump down of the mine pool, from its current level to 150 feet below the Steve level, in conjunction with incremental in -situ biologic treatment, will serve as pilot -scale testing. The RO Retentate ( "Retentate ") will be blended with barium chloride to cause nucleation of gypsum and barium sulfate precipitation and blended with sugar syrups to further increase the solution density and to support biologically induced formation of metal sulfides that enhances the precipitation of dissolved uranium from solution. The density of the resulting mine backfill slurry ("Slurry ") will be such that the Slurry will rapidly sink to the bottom of the mine pool. If the Slurry does not sink, there will be a conductivity increase in the in -situ monitoring troll suspended at depth in the mine pool that will be detectible as the fluid begins to mix with the mine pool. In the unlikely event there is a 20 percent increase in the concentration of solutes as measured by the conductivity, the addition point of the Slurry will be lowered to a greater depth in the mine pool, and the rate of addition of Slurry slowed by 25 percent. c. The expected secondary effects resulting from the creation of strongly reducing conditions in the mine pool, Creation of strongly reducing conditions in the mine pool will have a primary effect of the formation of metal sulfide and uranyl (IV) dioxide (uraninite) minerals. The metal sulfide (principally FeS) will form through the dissolution of iron oxide from the wall rocks and the reaction of the dissolved iron with newly formed sulfide ion as the result of the action of sulfate reducing biological processes throughout the mine pool. For a short time, iron concentrations in the mine pool will be elevated as a secondary effect of the in -situ treatment process. These concentrations of dissolved iron must be treated through oxidation in a pre - filtration process to avoid plugging the RO membranes with iron minerals. The pre- filtration process will produce an iron oxide particulate that will be backwashed from the filters and these solids will be mixed with the RO Slurry and disposed to the bottom of the mine pool through density —based settling. d. The expected effect of RO treatment residuals on the mine pool treatment process, and As discussed earlier, the RO treatment residuals will become a dense slurry which will settle rapidly in the mine pool. Therefore there is no expected effect on the upper mine pool. The addition of soluble carbon (sugar syrups) will help to densify the slurry, and will convey the beneficial in -situ treatment effects to the deepest parts of the mine pool. In this way the RO Slurry will be re- mineralized as stable metal sulfides and reduced uranium minerals that are highly insoluble in water and will fall out of solution and therefore will be beneficial to the mine pool treatment process. e. The expected effect of organic carbon on the RO treatment process.