Method and apparatus for countercurrent washing of particulate solids

A continuous countercurrent washing unit for washing particulate solids with a washing solution, wherein the particulate solids are microspherical particles containing fissile and/or fertile material, the washing solution being selected to remove foreign material from the microspherical particles, comprising

• means defining a washing tower including a plurality of washing sections disposed one above the other,
• each washing section of the tower including
• a tapered floor forming a centrally arranged restricted opening at the base of the respective washing section,
• a recirculation loop interconneted at one end with an upper portion of the respective washing section, the other end of the loop being in communication with a nozzle means extending upwardly through the restricted opening in the base of the respective section, and
• a pump and throttle valve means arranged in each respective recirculation loop for drawing washing solution from the upper portion of the section and recirculating it into the base of the section through the nozzle means,
• the recirculation loop for the lowermost washing section including means for introducing fresh washing solution into the lowermost washing section,
• the washing unit further comprising,
• means in communication with the uppermost washing section for introducing particulate solids to be washed,
• an outlet section arranged beneath the lowermost washing section for receiving washed solids therefore, said outlet section including a restricted passage means for regulating the flow of washing solution in the tower,
• overflow means in communication with an upper portion of an uppermost washing section, and
• means for introducing additional washing solution into the outlet section of the tower above the restricted passage in order to minimize the flow of washing solution from the tower through the restricted passage.

In a method of washing particulate solids to remove foreign material, the steps comprising,

• forming a washing tower with a plurality of washing sections arranged one above the other and an outlet section at the base of the tower, each washing section including a restricted opening at its lower end,
• introducing fresh washing solution into the washing tower beneath the restricted opening for the lowermost washing section,
• withdrawing washing solution from an upper portion of each washing section and recirculating said withdrawn washing solution for introduction through the restricted opening in the bottom of the respective washing section, regulating the rate of washing solution recirculation for each washing section in order to selectively adjust the dwell time for particulate solids in each respective washing section, and
• restricting passage of particulate solids from the outlet section of the wash tower in order to regulate the flow of washing solution in the tower.