base tub of the sand screw means a suspension of the finer particles are carried upward by a flow of water and pass over a weir into a mixing tank while the coarser particles are conveyed by the auger and are substantially drained and squeezed dry of water for example to a water content of about 18 25 w in the preferred embodiment the salinity of the water drained from the coarse sand sized particles is measured by an electrical resistivity measuring device not shown arranged to control a flop gate 4 for directing separated particles to either a stockpile or a salty particle return if the water drained from or remaining on the surfaces of such particles has a salinity equivalent to no more than a selected target concentration such as less than about 2500 ppm nacl equivalent the particles are sent to a stockpile the target concentration may be set by criteria for non hazardous waste disposal where the salt concentration of such water which amounts to a salt leaching water which contacted the particles is higher than the target concentration the particles are returned for remixing and reseparation within the sand screw 3 as indicated by the arrow labeled 34 salty particle return 34 such remixing and reseparating is repeated until a selected level of salt concentration is reached during this processing feeding of the new batches of contaminated materials into the hopper 1 and on the blade mill 2 may be delayed.