text: Leached pulp and carbon are transferred in a countercurrent flow arrangement involving a series of tanks, usually numbering 4 to 6. In the final tank, fresh or barren carbon is put in contact with low grade or tailings solution.  At this tank the fresh carbon has a high affinity for gold and can remove trace amounts of gold (to levels below 0.01 mg/L Au in solution). 
  As it moves up the train, the carbon loads to higher and higher concentrations of gold, as it comes in contact with higher grade solutions.  Typically concentrations as high as 4000 to 8000 grams of gold per tonne of carbon (g/t Au) can be achieved on the final loaded carbon, as it comes in contact with freshly leached ore and pregnant leach solution (PLS).