Material Insights · Understanding the Material World

Copper and Sulfur

Copper smelters make sulphuric acid as a by-product and copper leaching consumes it, so copper is both a rival to sulphur burning and one of its customers; in 2026 an acid shortage became a cost shock for leach mines.

Copper (commodity) and Sulfur (commodity): 3 relationships.

How they are linked

1. Smelter acid

Joint production · Strong · Copper smelting yields sulphuric acid

Copper concentrate is mostly copper and iron sulphides; smelting drives off the sulphur as sulphur dioxide, which smelters must capture and convert to sulphuric acid.

  • about 3 to 4 t sulphuric acid produced per tonne of copper cathode made by smelting
  • about 90% of US sulphur consumed as sulphuric acid
  • about 6% of US sulphur output in all forms that came as by-product acid from nonferrous smelters, 2025

Smelter acid is produced whether or not anyone wants it, so it competes directly with acid made by burning elemental sulphur from oil and gas. When smelter output rises, acid prices tend to fall and sulphur burners lose share; smelter maintenance or closures tighten acid markets.

Sources: US Geological Survey; Shanghai Metals Market

2. Acid for leaching copper

Physical flow · Strong · Sulphuric acid to copper (leach and SX-EW)

Oxide copper ores are leached with sulphuric acid and the copper recovered by solvent extraction and electrowinning, so these mines are large acid buyers.

  • 2 to 5 t sulphuric acid consumed per tonne of SX-EW copper
  • nearly 4 Mt sulphuric acid imported by Chile in 2025, 1.5 Mt from China
  • 22 to 33% possible share of acid in average operating costs (C1) at Chilean leach operations, 2026 estimate

Leached copper is about 20% of the copper Chile exports. China suspended ordinary sulphuric acid exports from May 2026, and with sulphur CFR quotations above $1,000 per tonne in May 2026, acid became a major cost risk for leach mines in Chile and the DRC.

Sources: Shanghai Metals Market; Plusmining

3. Price link: competing acid supply

Cost and price · Weak · Both ways

Smelter acid adds supply that lowers sulphur demand, while leaching adds acid demand; the two effects partly cancel, so prices are only loosely linked.

  • 0.12 monthly change correlation
  • 0.21 12-month change correlation
  • 0.61 fitted elasticity

Sulphur prices are driven mainly by fertiliser demand and oil and gas refining, so the price link to copper is weak. The tie shows up instead as a cost: in 2025 the Tampa sulphur contract price rose from $116 per long ton in January to $310 in October, and leach mines faced higher acid bills as a result.

Sources: Material Insights (World Bank, FRED, IMF data); US Geological Survey; Shanghai Metals Market

For investors

Key learnings

  1. Smelter acid is a by-product revenue for copper smelters and a supply source that competes with sulphur burning.
  2. Leach and SX-EW copper mines are exposed to sulphur and acid prices; one 2026 estimate put acid at 22 to 33% of average operating costs at Chilean leach operations.
  3. China's acid export policy links Chinese smelting to Chilean and African leach mine costs.

What to track

  • Sulphur CFR price (China, India, Middle East): Higher prices raise acid costs for leach mines (Weekly · Argus, CRU)
  • China sulphuric acid exports: Restrictions tighten acid supply to Chile and the DRC (Monthly · China Customs)
  • Chile sulphuric acid imports by origin: Direct supply and cost signal for leach copper (Monthly · Chile customs, Cochilco)

For policymakers

Key learnings

  1. A copper smelter is also a large acid plant, so its closure can disrupt fertiliser and chemical makers, as India saw in 2018.
  2. Smelter acid also feeds phosphoric acid and fertiliser production, so domestic smelter capacity supports farm inputs as well as copper.
  3. Acid availability can limit copper output from leaching, a factor in national copper supply plans.

What to track

  • India sulphuric acid prices: Signal tightness after smelter outages (Monthly · trade press, DGCI&S import data)
  • India copper smelter utilisation: Determines domestic by-product acid supply (Quarterly · company reports)

India

The 400,000 t per year Sterlite smelter in Tuticorin produced about 1.2 Mt of sulphuric acid a year before it closed in May 2018; its chief executive said acid prices rose about fourfold in the following six months. India produced about 3.7 Mt of sulphur in 2024.

Sources

  1. Price correlation, Material Insights, Material Insights (World Bank, FRED, IMF data)
  2. Mineral Commodity Summaries 2026: Sulfur, US Geological Survey (2026)
  3. Sulphuric acid: a key variable reshaping copper pricing logic (SMM analysis), Shanghai Metals Market (2026)
  4. Copper expert: Chinese sulfuric acid restrictions could represent 33% of production costs, Plusmining (2026)
  5. Sterlite's Tuticorin plant closure spiked sulphuric acid prices 4-fold in 6 months: CEO, Millennium Post (2018)