Why this matters—now
Every few decades mining absorbs a technology that changes the cost curve. Flotation (early 1900s) unlocked low-grade sulphides and became the default concentrator front-end. Solvent extraction–electrowinning (SX-EW) (commercialised from the 1960s–80s) turned dilute leach liquors into cathode metal and catalysed modern heap leaching (HL) at scale, particularly from the 1980s onward. oai_citation:0‡mininghistoryassociation.org
Today the energy transition and grade decline are rewriting copper’s demand/supply math. SX-EW—essentially the downstream engine for heap operations—now accounts for roughly ~17–20% of mine output/capacity, and has been growing faster than concentrates in several recent periods. oai_citation:1‡ScienceDirect
The question: can we push HL from “good when you have oxides” to a first-choice route that competes with concentrators on cost, schedule, risk and CO₂ per tonne Cu?
Where heap leach is strongest today
Best fit ores (now)
- Oxides (malachite/azurite/tenorite): fast kinetics; lab/column work frequently shows very high extractions over short durations. Field recoveries depend on permeability and acid balance. oai_citation:2‡MDPI
- Secondary sulphides (chalcocite/covellite): viable with oxygen supply (forced aeration), Eh/pH control, and chloride assistance; recoveries can be strong but are very sensitive to operating control. oai_citation:3‡ScienceDirect
Where it struggles
- Primary chalcopyrite remains the “hard rock” of ambient-temperature leaching: passivation and slow kinetics limit economic recovery and/or time, though pilot/column studies show progress under specific regimes (bio-assist, chloride, temperature). oai_citation:4‡MDPI
Scale indicator
- The SX-EW side of the business is ~5.3 Mt/y of mine capacity (2022), a reasonable proxy for leach-derived production headroom in the system. Not all of this is pad leach, but it signals the installed base ready to benefit from better HL practice. oai_citation:5‡PRS – Copper EPC Supplier
There isn’t an authoritative public split of global copper resources by oxidation state (oxide vs. secondary vs. primary sulphide)—deposits are mixed and reported inconsistently. A practical planning proxy is regional SX-EW capacity + oxide/secondary proportions in local resource models. oai_citation:6‡International Copper Study Group
Why recoveries lag—and how to close the gap
Typical outcomes (directional):
- Oxides: often 70–90%+ extraction in well-run columns/labs; field outcomes drop when permeability and solution management aren’t engineered. oai_citation:7‡MDPI
- Secondary sulphides: ~50–80% possible with right aeration/Eh/chloride control; mis-managed pads underperform. oai_citation:8‡MDPI
- Primary chalcopyrite: <~30–50% at long times at ambient conditions unless special regimes are used. oai_citation:9‡911Metallurgist
What usually holds HL back
- Permeability & liquids routing – segregation, fines migration and poor agglomeration kill uniform contact. oai_citation:10‡ScienceDirect
- Oxygen & redox management – secondary sulphides need oxygen delivered through the pad; sparging design and control matter. oai_citation:11‡journal.austms.org.au
- Chemistry windows – chloride, Eh/pH, acid balance, ammonia/chloride variants for certain minerals. oai_citation:12‡ScienceDirect
- Instrumentation & control – few pads run with the same sensor density and decision discipline as mills; recoveries suffer. oai_citation:13‡MDPI
What it takes to make HL a first-choice copper route
1) Engineer the rock first (not the pipework).
Pad performance is dictated by particle size distributions, agglomeration recipe, cure time, lift heights, stacking method, and permeability management—not just irrigation rate. Build pad physics into the flowsheet from day one. oai_citation:14‡ScienceDirect
2) Treat air like a reagent.
For secondary sulphides, design aeration like you would a reactor: blower selection, manifold layout, pressure drops, and control loops tied to Eh in raffinate/PLS. oai_citation:15‡journal.austms.org.au
3) Run inside the right chemistry window.
For chalcocite systems, chloride catalysis and Eh control can materially shift kinetics; for chalcopyrite, be explicit about the trade between time, temperature, chloride, and bio-assist. oai_citation:16‡MDPI
4) Close the loop with SX-EW.
SX-EW capacity and performance are the gating factors for HL value. System-level design (PLS grade stability, crud control, electrolyte management) increases copper per square metre of pad. SX-EW is now ~17–20% of mine capacity/output globally—optimising the hydromet loop compounds value. oai_citation:17‡vernycapital.com
5) Decide with evidence, not averages.
Pad pilots and scenario/TEA models should drive go/no-go and covenant-level KPIs (NPV sensitivity to recovery/time, acid cost, air power, water balance). This is where HL can compete with concentrators: lower capex, modular scale-up, faster first production, and optionality.
Applying the 100-year lesson
- Flotation won because it delivered step-change economics across many ore bodies, not because it worked in a lab. oai_citation:18‡mininghistoryassociation.org
- SX-EW won when it integrated chemistry, equipment and operations into a repeatable system. oai_citation:19‡saimm.co.za
- Heap leach can do the same—if we design pads as engineered reactors, instrument them accordingly, and run them with the same discipline as mills. oai_citation:20‡ScienceDirect
What Persephone does next for copper HL
- Diagnostic: ore-through-to-SXEW audit (pad physics, air, chemistry, control).
- Design: lift plans, agglomeration recipe, aeration manifolds, reagent strategy, monitoring.
- Decision model: integrated process + TEA linking recovery curves and time to NPV/IRR.
- Pilot: KPI-driven sighter → on-pad trial → scale-up plan with value proof.
If you’re sitting on mixed oxide/secondary sulphide inventories—or planning a new operation around them—let’s test whether HL can be your primary route, not a side project.