<Tr> <Td> </Td> <Td> </Td> </Tr> <Tr> <Td> Relative concentrations of the different chemical forms of uranium in a non-complexing aqueous medium (e.g. perchloric acid / sodium hydroxide). </Td> <Td> Relative concentrations of the different chemical forms of uranium in an aqueous carbonate solution . </Td> </Tr> <P> The uranium fraction diagrams in the presence of carbonate illustrate this further: when the pH of a uranium (VI) solution increases, the uranium is converted to a hydrated uranium oxide hydroxide and at high pHs it becomes an anionic hydroxide complex . </P> <P> When carbonate is added, uranium is converted to a series of carbonate complexes if the pH is increased . One effect of these reactions is increased solubility of uranium in the pH range 6 to 8, a fact that has a direct bearing on the long term stability of spent uranium dioxide nuclear fuels . </P>

Where are natural sources of uranium found and how is it obtained