Some ores may be treated by heap-leaching. This involves sprinkling a weak cyanide solution over an open pile of ore stacked on an impervious base. The solution percolates through the ore, leaching gold as it goes, and is drawn off at the base and then treated to recover the gold. The pellet load is moved through a number of linked tanks containing slurry in a direction opposite to the slurry movement. Pellets, loaded with gold, are removed and gold is stripped from them by washing in a solution of hot cyanide.
Carbon used in the process is recycled.
An electric current is passed through the new solution and the gold is deposited on a steel wool cathode. The gold laden cathode is treated with hydrochloric acid to dissolve any residual steel. The gold sludge is filtered and dried and is then ready for smelting. At this stage the gold-bearing material may still contain silver and base metals. Gold is smelted in a crucible furnace to produce unrefined bullion.