Copper Mining Shifts Output Toward Sulfuric Acid Sales
Summary
Capstone paused heap leach while First Quantum sacrificed about 1,000 tonnes of copper to sell 70,000 tonnes of high-priced sulfuric acid.
On October 29, 2026, Capstone Copper (CS) and First Quantum Minerals (FM) disclosed that regional sulfuric acid prices had begun to change copper production decisions. Capstone paused part of its acid-intensive heap-leach output, while First Quantum accepted roughly 1,000 tonnes of lower copper production to generate and sell 70,000 tonnes of sulfuric acid.[1][2]
Sulfuric acid is becoming a production-allocation constraint
Sulfuric acid can be both an input and an output in copper mining. Oxide and lower-grade ores may be heap leached, a process that applies acid to ore so copper can be recovered from solution. Sulfide ores more often move through concentration or smelting, and smelting sulfur-bearing concentrate can itself produce sulfuric acid. A miner may therefore consume acid in one operation and produce it in another.
When regional acid supply tightens and spot prices rise sharply, the production sequence changes. Marginal tonnes that require substantial purchased acid lose profitability first. A miner with smelter-produced acid can compare using that acid internally with reducing low-margin copper processing and selling the acid. The reagent then becomes a factor in choosing ore routes and output levels.
Capstone and First Quantum changed operating choices
Capstone reduced the part of its production most exposed to purchased acid. The company reported a spot sulfuric acid price of about $360 per tonne and said 2027 fixed contracts could land at $250 to $300 per tonne. It paused heap leach during price spikes and shifted its mix toward lower-cost sulfides.[1] Capstone plans to start bio-oxidative heap leaching in late Q1 or Q2 2027 to generate some acid internally, and an early-2028 pyrite project is expected to cut acid use by about 20%.[1]
First Quantum put the market value of its own acid ahead of marginal copper volume. It said sulfuric acid rose from $180 per tonne in Q1 to $460 in Q3. The company sold 70,000 tonnes of surplus acid, generated $33 million of revenue, and recorded a 14-cent-per-pound by-product credit to copper C1 costs.[2]
"CFO explained that processing low-margin copper material generated 70,000 tonnes of high-value acid, sacrificing ~1,000 tonnes of copper production. This strategy is expected to continue into Q4 and beyond given strong acid prices."[2]
In other words, First Quantum accepted about 1,000 tonnes of lower copper output to continue selling high-priced acid.
Economics are diverging across processing routes
High acid prices are widening the economic gap between acid-consuming mines and operations that produce acid. Heap-leach operations can face higher unit costs and fewer profitable marginal tonnes. Smelter-linked operations may receive acid sales revenue and a by-product credit that partly offsets copper costs. Freeport-McMoRan (FCX) also reported about $500 million of combined energy and sulfuric acid cost pressure, while its internal acid production provided partial protection.[3]
The effect has a clear boundary. It is concentrated in regions with tight sulfuric acid supply, limited transport radius, and production routes that depend on leaching. It is not a universal copper constraint. Freeport still plans to expand leach output through additives, while Teck's concentrator-led portfolio did not identify sulfuric acid as a Q3 operating bottleneck. Useful follow-up measures include regional contract prices, heap-leach restart timing, internal acid-project milestones, and whether by-product credits persist.
Companies exposed to the same mechanism
- Freeport-McMoRan (FCX): Its US leach program consumes sulfuric acid, exposing it to higher prices, while internal acid production offers partial protection and the company continues to pursue leach growth.
- Southern Copper (SCCO): Its integrated smelters in Mexico and Peru produce sulfuric acid, creating producer-side exposure similar to First Quantum, although the reviewed disclosure did not quantify a benefit from the current price move.
Sources
[1] Drillr · Capstone Copper · October 29, 2026 · Q3 2026 earnings-call summary and Q&A
[2] Drillr · First Quantum Minerals · October 29, 2026 · Q3 2026 earnings-call summary and Q&A
"CFO explained that processing low-margin copper material generated 70,000 tonnes of high-value acid, sacrificing ~1,000 tonnes of copper production. This strategy is expected to continue into Q4 and beyond given strong acid prices."
[3] Drillr · Freeport-McMoRan · October 27, 2026 · Q3 2026 earnings-call summary
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