Geochemical modeling and laboratory studies of aquifer restoration at an in situ leach uranium mine
Flow-through column experiments were performed at Pacific Northwest Laboratory to simulate aquifer restoration by contacting aquifer sediment with leaching solution (lixiviant) under anoxic conditions. The chemical composition of the effluent solutions were determined to monitor the progress of restoration. The results were used to identify chemical mechanisms in the water/sediment system that occur during aquifer restoration. The movement of uranium through the column was initially retarded as a result of interactions with the sediment. A possible mechanism to explain the behavior of uranium involves the presence of pyrite. When pyrite is oxidized, the Fe(III) produced forms ferric hydroxide minerals, which have a strong sorption affinity for uranium. Adsorption of uranium onto the ferric hydroxide and clay surfaces could lower the concentration of uranium in solution. As the lixiviant displaced the residual pore water in the column, the calcium, magnesium, and sulfate concentrations decreased and the sodium concentration and pH increased. This effect probably was caused by ion exchange between dissolved constituents and cations on the sediments' surfaces. After examining the data, we developed a conceptual chemical model of the system that incorporated the reactants and chemical processes that appeared to be important. Then, we modeled the interaction of the lixiviant with the sediment during flow through the column. The chemical processes incorporated in the model included oxidation of pyrite, the dissolution and equilibration of magnesian calcite, ion exchange, and aqueous complexation of dissolved constituents. The equilibrium geochemical computer code, MINTEQ, was used to make the necessary speciation and mass transfer calculations. The model results were then compared with the observed effluent solution compositions. 7 refs., 8 figs., 5 tabs.
- Research Organization:
- Pacific Northwest Labs., Richland, WA (USA)
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 5353131
- Report Number(s):
- PNL-SA-13119; CONF-850893-2; ON: TI85017902
- Resource Relation:
- Conference: Practical applications of ground water models conference, Columbus, OH, USA, 19 Aug 1985
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
58 GEOSCIENCES
GROUND WATER
WATER QUALITY
ROCK-FLUID INTERACTIONS
SOLUTION MINING
ENVIRONMENTAL EFFECTS
GEOCHEMISTRY
URANIUM ORES
BENCH-SCALE EXPERIMENTS
LEACHING
M CODES
SEDIMENTS
URANIUM MINES
CHEMISTRY
COMPUTER CODES
DISSOLUTION
ENVIRONMENTAL QUALITY
HYDROGEN COMPOUNDS
MINES
MINING
ORES
OXYGEN COMPOUNDS
SEPARATION PROCESSES
UNDERGROUND FACILITIES
WATER
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