Copper hit record highs this year. The reason is not a mine strike, not a landslide, not a grade decline.
It is a chemical you last thought about in high school chemistry.
Sulphuric acid. Without it, over 15% of the world's primary copper output cannot be produced. And right now, the two largest sources of that acid have been severed within six weeks of each other.
The International Energy Agency now confirms what the supply chain has been screaming. In its Global Critical Minerals Outlook 2026, the agency warns the short- and medium-term copper supply outlook has "worsened considerably" because of constraints on sulphuric acid availability. Those constraints pose "a significant risk to SxEW production," the report states, citing a market already tight from slow recoveries at major mines.
The binding constraint on copper is no longer geology. It is logistics. Specifically, the logistics of a heavy, corrosive liquid that is expensive to ship and impossible to substitute at scale.
28 February. Then 10 April.
Two dates. Two shocks. One market.
On 28 February 2026, the Strait of Hormuz closed to commercial dry bulk traffic. The strait carries roughly half of all seaborne sulphur traded globally — sulphur being the essential feedstock for sulphuric acid production. The closure immediately stranded cargoes from Gulf countries and Iran, which together supply a quarter of the world's sulphur.
By April, over 600,000 tonnes of sulphur sat on vessels in the Mideast Gulf with no exit. Global sulphur exports fell 45% below end-February levels. Gulf sulphur loadings in March collapsed to nearly 400,000 tonnes, a 74.5% year-on-year decline.
Then on 10 April, China announced a full ban on sulphuric acid exports through August 2026, replacing a 700,000-tonne annual quota with a complete cessation. China is the world's largest acid exporter. Its primary customers in 2026 are Chile, Indonesia, and Saudi Arabia. The ban cut off nearly a quarter of acid supply outside China overnight.
Kpler, the commodities data firm that tracked the buildup in near-real time, calls the resulting shock "the most acute sulphur supply disruption in a generation." Three simultaneous blows: a chokepoint closure, an export ban, and a structural deficit in Asia.
Why a chemical shortage kills copper mines
Over 15% of global primary copper output comes from a process called SxEW — leaching, solvent extraction, and electrowinning. It turns acid-leached ore directly into finished cathode at the mine site. No acid, no cathode. The process does not slow down. It stops.
Two countries are exposed to a degree that should alarm anyone long copper.
The Democratic Republic of Congo has roughly 1.5 million tonnes of leached copper output, with almost 45% of its production dependent on sulphuric acid leaching. Chile has roughly 1.2 million tonnes of leached output and was already facing an acid supply crunch before the Strait closed. China's ban removes the largest alternative supplier for Chilean operations that had been relying on imported acid.
Together, the DRC and Chile account for 2.7 million tonnes of leached copper. A sustained acid shortage does not trim output at the margin. It forces cathode lines to idle.
The trap most analysts are missing
Sulphuric acid is heavy, corrosive, and expensive to ship long distances. The economics dictate that it is produced near sulphur sources or as a byproduct of smelting, then consumed regionally. The Hormuz closure severed the main artery for sulphur feedstock. China's ban removed the backup acid supplier.
A handful of vessels still move. The UAE was the only Mideast Gulf country able to transit sulphur via the Strait in May 2026, with 3 confirmed shipments. Three vessels. That is a rounding error in a market that has lost 600,000 tonnes of stranded cargo and a major exporter.
The consensus frames this as a temporary logistics hiccup. That framing misses the most important structural reality in this crisis.
The 600,000 tonnes of sulphur stranded in the Mideast Gulf will not simply flow to copper smelters when the Strait reopens. That sulphur is committed under long-term contracts to fertilizer buyers. The sulphur supply chain was optimized for a different demand profile entirely — agriculture, not metals. When the Strait reopens, those cargoes will go to their contracted destinations. The copper industry's acid crisis does not resolve when the ships start moving again. It resolves when new sulphur supply routes are built. That takes 12 to 18 months.
This is not a logistics hiccup. It is a structural supply shock with a built-in delay on the remedy.
400,000 tonnes. $12,000 copper. And what comes after.
Here is the chain of consequence.
By mid-2027, at least 400,000 tonnes of SxEW production will be lost — roughly 2% of global copper supply. The mechanism is straightforward: DRC and Chilean operations without long-term acid contracts or on-site production will cut output rather than pay spot prices that have detached from any historical norm. The IEA's warning that sulphuric acid constraints pose a "significant risk" is not a forecast of inconvenience. It is a forecast of idled capacity.
The first-order effect is price. Copper has already risen 33% between January 2025 and April 2026 to record highs. Removing 400,000 tonnes of supply from a tight market will push prices above $12,000 per tonne. That is not a spike. It is a structural repricing driven by a physical input constraint.
Then the substitutions begin. At $12,000 copper, the economics of aluminum wiring and fiber optics shift decisively. Downstream manufacturers who have been testing alternatives will accelerate deployment. Some of that demand destruction will be permanent. Copper substituted out of wiring during a supply crisis does not automatically return when prices ease.
Then the scramble. Ferric chloride, bioleaching, and other technologies that reduce or eliminate sulphuric acid dependence move from pilot projects to operational necessity. The winners are Canadian and Australian sulphur producers with secure shipping routes that bypass Hormuz entirely. Their product will command a premium that reflects not just sulphur content but supply-chain security.
The losers are any copper miner reliant on imported acid without long-term contracts, especially in the DRC. Those operations face a binary choice: pay any price for acid or stop producing cathode. There is no third option.
The IEA estimates that if China's export controls are fully implemented, $6.5 trillion in annual production outside China could be put at risk. Copper is the first critical mineral to feel the full force of that risk. It will not be the last.
What would prove this thesis wrong? A rapid resolution to the Strait of Hormuz closure combined with China lifting its export ban on schedule in August 2026, plus a faster-than-expected ramp of alternative sulphur supply from Canada and Australia. If all three conditions are met by Q4 2026, the 400,000-tonne loss estimate is too high. If any one of them fails, the estimate is conservative.
What operators must do now
For copper miners, the window to act is closing. Lock in long-term acid contracts immediately, even at elevated rates. Diversify sulphur sources away from the Gulf. Invest in on-site acid production or alternative leaching technologies. The miners who move fastest will preserve output while competitors idle.
For traders, the sulphuric acid market has become the leading indicator for copper supply. Track acid deliveries in the DRC and Chile, not mine production guidance. Mine output numbers are a lagging indicator. Acid availability is the binding constraint.
For downstream users, hedge copper exposure now. Accelerate substitution plans. The market will not rebalance until new sulphur supply routes come online from Canada, Australia, or recovered sulphur from oil sands. That takes 12 to 18 months. The copper price will reflect the acid shortage long before new supply arrives.
The canary is still breathing. Barely.
The chemical most investors ignored is now the binding constraint on a $200 billion market.
Copper's future for at least the next 18 months is written in sulphuric acid logistics, not mine grades. The IEA's warning is the canary. The question is whether the market adapts before the acid runs out — and 400,000 tonnes of annual production hangs on the answer.
