42 MANUFACTURE OF FERTILIZING MATERIALS 



ficient pressure head to work against and prevent 

 vibrations in the pump. 



After the material reaches the washer from the 

 mines it is delivered to a relay pump without going 

 into a sump. This pump lifts the material to 

 the top of the washer, where it is discharged into a 

 launder that feeds a rotary screen having IJ-in. 

 holes. The screen makes two products; an over- 

 size consisting of mud balls and coarse rock 

 which is sent directly to the tailing pond, and an 

 undersize which is discharged on to an inclined 

 stationary screen with A-in. slop openings, where 

 some of the sand is removed, the operation being 

 assisted by sprays of water. The oversize from 

 this screen passes to a 16-ft. double log washer 

 which discharges the material into another 16-ft. 

 single log washer. These logs separate the par- 

 ticles of phosphate, sand, and pebble from the 

 silica by reason of their grinding and mixing action. 

 Wash water is also supplied to the logs, which 

 assists the separation by moving the silica sand 

 backwards and over the tail-gate of the log-box. 

 The last set of logs discharges on to a shaking 

 screen which further eliminates all but about 6 

 to 8 per cent of the remaining silica and the greater 

 part of the water. The dewatered material from 

 this screen goes directly into a hopper-bottom 

 storage bin over the railroad tracks, where it is 

 ready for transportation. 



