Bacteria of the Ferrobacillus-Thiobacillus group -will effectively leach pyrite bearing radioactive conglomerates in abandoned underground workings. Uranium and rare earths can be produced from these ores at a cost comparable to conventional methods, operating solely by bacterial leaching. As an addition to an operating nine, costs can be quite low Thorium is also available for production from these ores when market conditions warrant.
Underground development at the mine began in 1957. The ore bodies are extensive radioactive conglomerate beds, 6 to 40 feet in thickness and dipping from 5 degrees to a maximum of 40 degrees. Thinner un-economic beds also exist. The workings are from 1200 to 2100 feet below sea level. Plant elevation is approximately 1400 feet above sea level. Bio ore is a quarts pebble conglomerate with a pyritized sericitic matrix.
Bacteria of the Ferrobacillus-Thiobacillus group are unicellular organisms 0.25 microns in diameter and 1 micron long. They reproduce by simple division and thrive in acid iron bearing media with a pH range of 1.8 to 3.5 and temperatures of 25 degrees to 40 degree C. Their energy is derived from the oxidation of ferrous iron and/or sulphides and sulphur. Fixed nitrogen and carbon dioxide are required fer body growth. They are sensitive to metal ion concentration, but can be bred to high tolerance levels if the concentrations of ions is increased gradually.
Uranium which occurs in the insoluble tetravalent state is oxidized to the soluble hexavalent state in ferric sulphate solutions by ferric sulphate
UO + Fe2(SO4)3 → UO2SO4 + 2 FeSO4
provided the ferric to ferrous ratio is kept high enough to maintain a redox potential at or above 410 millivolts.
Since test work had shown that high pressure hosing on a three month cycle gave best results, leaching was set up on this basis. Water pipelines were laid exit at intervals through the abandoned areas of the mine with take-off valves at 60 foot intervals. Men working in pairs washed an area approximately 150 feet in length by 35 feet in width each per shift. Each man was equipped with 200 – 250 feet of 1-inch hose and the necessary tools for coupling and repairing hoses.
Water from the washing operation flows through the mine to several points at the lowest elevation. These areas are used as snaps, with 10 B. P. stainless steel R.V.H. pumps, pumping the water to the main settling sump. Laboratory tests show a marked increase in yield using 9K nutrient with the following composition
Tests at Stanrock showed no appreciable increase in recovery for stopes where nutrient was spread after washing and the stopes then rewashed on the regular 3 month cycle. Drying out of the stopes is probably the difficulty.
Mine water is pumped to the surface plant by three 8-stage pumps and one 4-stage pump through 5,000 feet of 6-inch rubber lined steel pipe against a vertical head of 3,500 feet. The pumps are stainless steel, handling the water at a pH of 2.3.
On surface the water is adjusted to pH 2.0. Adjustment of the pH gives a better resin loading in ion exchange. It is now considered economic since the water is returned underground to be used in leaching. Previously it was treated as pumped from underground, usually at a pH of 2.3 – 2.4. After pH adjustment the water flows to a 90′ x 12′ rubber lined thickener tank which acts as a surge tank for the clarifiers. After clarification the water is pumped to ion exchange.
Barren solution or waste from the ion exchange is sent to a holding tank, and from there 4,000 feet through 2″ polyethelene plastic hoses to a sump at the bottom of 2 shaft. From here it is pumped by a stainless steel pump through 1,300 feet of acrylonitrile- butadiene-styrene (ABS) pipe for use in the flooding operation. Previously the barren solution was treated with lime and ammonia to recover a rare earth concentrate. A neutralized slurry containing thorim was sent to tailings.