Heap, dump and vat leaching

There is a whole family of leaching that never makes a slurry. Instead of grinding the ore and agitating it in tanks, the percolation family stacks coarse ore in a bed and lets leach solution trickle down through it, dissolving the metal on the way and draining out the bottom as a pregnant solution. It trades the speed and recovery of tank leaching for a fraction of the cost, and knowing where that trade pays is the point of the topic.

The percolation family

The members differ mainly in how the bed is built and how much engineering goes under it. Heap leaching stacks crushed ore on a prepared, lined pad and irrigates the top with leach solution — raffinate — which percolates through and is collected as pregnant leach solution for recovery downstream. Dump leaching is the same idea applied to run-of-mine or waste-grade material with little or no preparation, the lowest-cost and lowest-recovery end of the family. Vat leaching holds coarse ore in a tank and floods it with solution rather than irrigating a heap, a more contained and faster percolation variant. All three contact solution with a static bed of solids, which is the defining difference from the agitated slurry of tank leaching.

Where heaps win

The economics are the whole story. A heap needs no fine grinding, no agitators, no large tanks and little energy; it is cheap to build and cheap to run, and it can treat low-grade material that could never carry the cost of a tank circuit. What it gives up is recovery and time. Solution cannot reach every grain in a coarse, unstirred bed the way it does in an agitated slurry, so recovery is lower and some value is left behind; and percolation is slow, so a heap leaches over weeks to months or longer against the hours of a tank. Channelling, bed permeability and irrigation distribution all shape how completely the bed is contacted.

So the percolation family wins where the grade is too low or the tonnage too large for tank leaching to pay, and where time is available — many copper oxide and low-grade gold operations, and the copper end of the heap-leach–solvent-extraction–electrowinning flowsheet. It loses where high recovery in a short time is the requirement. This page places the family and names the trade; the irrigation-rate and percolation sizing are a circuit-specific design matter, and it lands as cited connective tissue rather than on a tool.