In the extraction of uranium in leaching when bismuth and phosphoric acid is added to the leach liquor bismuth phosphate precipitates and it coprecipitates plotonium(un wanted solute)?? Why it coprecipitates plotonium??

In the extraction of uranium in leaching when bismuth and phosphoric acid is added to the leach liquor bismuth phosphate precipitates and it coprecipitates plotonium(un wanted solute)?? Why it coprecipitates plotonium??