RADIOACTIVE WASTE DISPOSAL IN THE SHIPROCK-TYPE URANIUM MILLING FLOWSHEET
A study was made of possible modifications in conventional uranium ore- processing steps to confine and permit controlled disposal of radioactive wastes. A potential method of minimizing pollution from radioactive nuclides, principally radium-226, in uranium mill waste streams is to reuse the waste solutions within the mill. Such reuse of waste solution in the Kerr-McGee Shiprock-type process was investigated in the laboratory. The Shiprock mill employs a two-stage acid- leaching process for dissolution of the uranium, countercurrent decantation for liquidsolid separation and washing, and organophosphorus solvent extraction for recovery of the uranium and vanadium from solution. The simulated use of barren raffinate instead of fresh water in the mill circuit was carried through a laboratory campaign of 28 interlocked leaching, washing, and solvent extraction cycles. About 99 percent of the uranium and 91 percent of the vanadium were dissolved from the ore. Washing efficiency in the thickener circuit averaged about 99.5 percent when the pulp was washed with enough barren raffinate and makeup water to recover 2.5 tons of pregnant solution per ton of ore. The only solution discarded was that contained in the washed and thickened leach residue. A buildup of salts due to recycling of solutions did not adversely affect operation of the washing circuit. In preparation for separately recovering uranium and vanadium by solvent extraction, the pregnant solution was reduced to a redox potential of minus 240 millivolts with sulfur dioxide, and the pH was adjusted to 1.4 by the addition of ammonlum hydroxide. About 99.5 percent of the uranium and less than 0.5 percent of the vanadium were extracted by organic feed consisting of 4 percent di-2-ethylhexyl phosphoric acid (EHPA) and 4 percent tributyl phosphate (TBP) in kerosine. Loaded organic feed from the extraction step was stripped with sodium carbonate solution to yield loaded strip liquor containing 50 grams of U/sub 3/O/sub 8/ per liter. The uranium-barren solution was treated in a separate circuit for vanadium recovery using organic feed composed of 8.5 percent EHPA and 4 percent TBP in kerosine. The loaded organic feed was stripped with 20-percent sulfuric acid solution, yielding strip liquor containing about 98 percent of the dissolved vanadium in a solution containing 100 grams of V/sub 2/O/sub 5/ per liter. Raffinate from the vanadium solvent extraction circuit was reused in washing the leach residue. The rafflnates from the vanadium eMraction circuit were routinely analyzed for radium-226 by the radon-emanation method. Radium in the raffinate ranged from 900 to 2,000 disintegrations per minute (d.p.m.) per liter. An upward trend was not evident, and no radium buildup occurred. Thus, reuse of raffinate in the Shiprock process appears feasible. Such reuse of raffinate would result in about a 75percent decrease in the amount of contaminated solution discarded from the mill. (auth)
- Research Organization:
- Bureau of Mines. Salt Lake City Metallurgy Research Center
- NSA Number:
- NSA-16-031340
- OSTI ID:
- 4777474
- Report Number(s):
- BM-RI-6045
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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Related Subjects
ACIDS
AMMONIUM COMPOUNDS
BUTYL PHOSPHATES
CLEANING
CONTAMINATION
CONTROL
COUNTER CURRENT
HYDROXIDES
LEACHING
LIQUIDS
ORE PROCESSING
ORGANIC COMPOUNDS
PHOSPHORUS COMPOUNDS
RADIUM 226
RADON
RECOVERY
SEPARATION PROCESSES
SODIUM CARBONATES
SOLIDS
SOLUTIONS
SOLVENT EXTRACTION
SULFUR OXIDES
SULFURIC ACID
URANIUM
URANIUM ORES
URANIUM OXIDES
VANADIUM
VANADIUM OXIDES
WASTE DISPOSAL
WASTE DISPOSAL AND PROCESSING
WASTE SOLUTIONS