Remedial Design of a Uranium Tailings Repository

Further, we can show that Kd values vary both spatially and temporally. For example, effective K values for sulfate can be calculated from simulation results based on the 

Chemical equilibrium conditions are assumed for all reactions. The chemical model consists of eight components UOj 1 , VO4-, CO2-, K+, Ca2+, H+, and HFO as the sorbent. Four minerals, carnotite (K2(U02)2(V04)2), tyuyamunite (Ca(U02)2(V04)2), calcite (CaC03), and gypsum (CaS04 2H2O), are allowed to participate in precipitation-dissolution reactions. The detailed chemical model (reactions and parameters) is presented in Morrison et al. (1995a). No ionic strength correction was made for activity coefficients. 

The initial conditions for the transport model were the total analytical concentrations of components estimated from the complete digestions of tailings samples. Four tailings piles exist at the site and will be filled in the repository Carbonate, Vanadium, Acid and East Piles. The Vanadium Pile contains pore fluids with pH values from 7 to 13 and 

The boundary concentrations for the transport model are the same low-concentrations as in the pediment gravel. Oxidizing conditions were assumed to exist throughout the system Eh from 400 to 500 mV). Only advection was considered, and dispersivity was set to zero. A period of 216 years was simulated. 

The coupled reaction transport modeling effort provided a few insights for the design of remedial action. It was found that  

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