Leach process complex

The dissolution time for the unreprocessed fuel would be at least 1 million years due to the limited water supply, even if a rapid oxidation of uranium to the hexavalent state and a subse-guent formation of water soluble carbonate complexes are assumed (15). Since the conditions are reducing in the groundwater (see beTow) the dissolution time would probably be several orders of magnitude larger. The unsignificant dissolution of uranium and fission products observed in the Oklo-deposit (16) is an example of a similar extremely slow leaching process in the natural environment. 

In order to be truly predictive, models for the complex leaching process must contain equilibrium, kinetic, and chromatographic parameters. Development of such comprehensive models will not only aid in the optimization of solution compositions for the most effective uranium recovery, but will also allow a more realistic environmental impact assessment. 

In other reactions, particularly where strongly complexing reactants, e. g., carbon monoxide, are involved, leaching of the immobilized metal center may take place. Generally, the parameters to be considered in a polymer-anchored metal complex catalyst are of a manifold nature. It is still an unsolved problem and an incompatible situation that, on the one hand, a leaching process should be avoided while, on the other hand, sufficient activity and the selectivity necessary for industrial applications are to be maintained. As a consequence it has become... 

In the carbonate. basic leaching process, both carbonate and bicarbonate ions are required to buffer the solution and prevent precipitation of uranium salts. In both acidic and basic leaching, complex anions are formed. The solutions may therefore be upgraded by anion exchange or anion solvant extraction (SX) processes. The upgraded solution is normally treated by selective precipitation of umaium by pH adjustment. 

The mined zinc ores retrieved from the mines are too low in zinc content for direct reduction to refined metal thus, they are first concentrated. Production of concentrates requires crushing and grinding followed by gravity or magnetic methods of separation or flotation. These processes may be combined, depending on the complexity of the ore. A caustic-leach process is used to decrease the extent of metal loss during the concentration process. In this process, the metal is leached by caustic soda, the resulting electrolyte is purified with zinc dust and lime, and the zinc is electrodeposited. The crude zinc may be dissolved in sulfuric acid and purified by electrodeposition. 

Various continuous leaching processes have also been employed. Usually the powder and leaching acid are fed in a co-current manner into a rotating or stirred vessel and at some point it is necessary to separate the resulting metal powder under conditions where it is not allowed to remain static for long periods. The complexity of a safe continuous system, coupled with the relatively small scale of operation, usually leads to a preference for a batch leaching system. 

It is relatively complex, with two different leach processes. 

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