In the case of oxide copper ore, a heap leaching pad will dissolve a dilute copper sulfate solution in a weak sulfuric acid solution.  This pregnant leach solution (PLS) is pumped to an extraction mixer settler where it is mixed with the organic phase (a kerosene hosted extractant).  The copper transfers to the organic phase, and the aqueous phase (now called raffinate) is pumped back to the heap to recover more copper.
In a high-chloride environment typical of Chilean copper mines, a wash stage will rinse any residual pregnant solution entrained in the organic with clean water.
The copper is then stripped from organic phase in the strip stage into a strong sulfuric acid solution suitable for electrowinning.  This strong acid solution is called barren electrolyte when it enters the cell, and strong electrolyte when it is copper bearing after reacting in the cell.