# Copper and Sulphuric acid Copper and sulphuric acid are tied both ways: smelting sulphide concentrates makes roughly 4 tonnes of acid per tonne of copper, while leach mines consume acid to dissolve oxide ore. Acid sales now prop up smelter margins when treatment charges are weak, and acid shortages raise costs at leach mines, notably in Chile. Source page: https://www.materialinsights.org/links/copper-and-sulphuric-acid/ [Copper](https://www.materialinsights.org/commodities/copper/) (commodity) and [Sulphuric acid](https://www.materialinsights.org/chemicals/sulphuric_acid/) (chemical): 5 relationships. ## How they are linked ### 1. Smelter by-product acid *Joint production · Strong · Copper smelting to sulphuric acid* Copper concentrates are largely copper iron sulphides; smelting drives off the sulphur as sulphur dioxide, which smelters must capture and convert to sulphuric acid to meet air rules. - **about 4 t** sulphuric acid made per tonne of copper cathode (rough figure) - **568 kt** US by-product acid from smelters, sulphur content, 2022 The acid comes out whether or not there is demand for it, so smelter acid is a forced output that must be sold or stored, and its price can swing widely. Acid from smelters competes with acid made by burning elemental sulphur, which is the main source for fertiliser plants. Sources: [Shanghai Metals Market](https://news.metal.com/en/newscontent/103364346-Strong-profits-from-smelting-acid-strongly-support-copper-smelting-business-SMM-Analysis); [USGS](https://pubs.usgs.gov/myb/vol1/2022/myb1-2022-copper.pdf) ### 2. Leaching reagent *Physical flow · Strong · Sulphuric acid to copper (SX-EW)* Oxide and some secondary sulphide ores are leached with sulphuric acid and the copper is recovered by solvent extraction and electrowinning (SX-EW), so acid is a direct operating input for these mines. - **20%** of world mine output produced by SX-EW, 2022 - **nearly 4 Mt** sulphuric acid imported by Chile in 2025, 1.5 Mt of it from China Acid consumption per tonne has risen in Chile as ores get harder to leach: leachable copper output fell from 2.1 Mt in 2009 to 1.1 Mt in 2025 while acid use rose from 6.9 Mt to nearly 8 Mt. After China announced a halt to acid exports in 2026, spot acid in Chile traded at about USD 330 a tonne against 2026 contract prices of about USD 160 to 175 agreed in late 2025, and one expert estimated acid at 22 to 33% of average C1 cash costs at Chilean leach operations. Sources: [USGS](https://pubs.usgs.gov/myb/vol1/2022/myb1-2022-copper.pdf); [PlusMining](https://plusmining.com/en/2026/05/05/copper-expert-chinese-sulfuric-acid-restrictions-could-represent-33-of-production-costs/) ### 3. Acid credit in smelter margins *Cost and price · Rising · Acid revenue supports copper smelting* A smelter earns treatment and refining charges on concentrate plus revenue from by-products, so when treatment charges are low or negative, acid sales can decide whether a smelter covers its costs. - **600 to 650 yuan per tonne** smelter acid delivered price in major Chinese provinces, June 2025 - **about USD 43** estimated acid profit per tonne of copper, China, June 2025 In 2025 the acid credit largely made up for weak spot treatment charges and helps explain why Chinese smelters kept running at high rates. The credit is fragile: acid was long seen as a burden for smelters, and its value depends on fertiliser and leaching demand rather than on copper. Sources: [Shanghai Metals Market](https://news.metal.com/en/newscontent/103364346-Strong-profits-from-smelting-acid-strongly-support-copper-smelting-business-SMM-Analysis) ### 4. Price link: by-product *Cost and price · Weak · Both ways* Acid supply from smelters rises with copper output, but acid prices are set mainly by phosphate fertiliser and leaching demand and by sulphur prices, so the two prices move only loosely together. - **0.12** monthly change correlation - **0.21** 12-month change correlation - **0.60** fitted elasticity The low correlation is expected for a by-product: a smelter cannot cut acid output without cutting copper output, so acid prices absorb the mismatch between smelter supply and fertiliser demand. Sources: [Material Insights (World Bank, FRED, IMF data)](https://www.materialinsights.org/chemicals/sulphuric_acid/correlation/) ### 5. Smelter outages cut acid supply *Shared risk · High in India · Copper smelter closures to acid buyers* Where a large smelter is a regional acid supplier, its closure removes acid for nearby fertiliser and chemical users at the same time as it removes copper. - **about 400 kt a year** copper output of Sterlite's Thoothukudi smelter before its May 2018 closure The Tamil Nadu government shut the Sterlite plant in May 2018. The closure cut the supply of sulphuric acid that fertiliser and detergent makers in the region had relied on, and India became more dependent on imported copper. Sources: [ChemAnalyst](https://www.chemanalyst.com/NewsAndDeals/NewsDetails/closure-of-sterlite-copper--50) ## For investors ### Key learnings 1. For smelters, sulphuric acid has turned from a disposal problem into a meaningful profit line when treatment charges are low, so smelter earnings now depend partly on fertiliser markets. 2. Leach mines are acid buyers, so the same acid price that helps smelters raises costs at SX-EW operations, which supplied about a fifth of world mine output in 2022. 3. The monthly price correlation is weak because acid is a by-product; the useful signal is the gap between smelter acid supply and fertiliser and leaching demand. ### What to track - **Copper concentrate treatment and refining charges**: Low charges make acid credits more important to smelter margins (Annual benchmark and monthly spot · industry reports, company filings) - **Sulphuric acid prices, Chile delivered and China ex-works**: High prices lift smelter credits and raise leach mine costs (Weekly · Argus, CRU, SMM) - **China sulphuric acid export policy**: Export curbs tighten supply for Chilean and African leach mines (As announced · Chinese customs and commerce ministry) ## For policymakers ### Key learnings 1. Copper smelting capacity is also sulphuric acid capacity, so smelter closures can hurt fertiliser and chemical supply chains as well as copper supply. 2. Air rules that require sulphur dioxide capture create the acid by-product; planning for smelters should include where the acid will go. 3. India's Thoothukudi closure in 2018 showed that one plant can move both copper imports and regional acid supply. ### What to track - **Domestic smelter output and utilisation**: Lower output means less acid for fertiliser makers and more copper imports (Monthly · Ministry of Mines, company filings) - **Sulphuric acid imports**: Rising imports show acid supply falling short of fertiliser and chemical demand (Monthly · DGCI&S) - **New smelter projects and acid offtake plans**: Projects with no acid outlet risk storage problems or cut runs (As announced · environment clearances, company releases) ## India India's copper smelters also supply sulphuric acid to fertiliser and detergent makers; the 2018 closure of Sterlite's Thoothukudi smelter removed about 400 kt a year of copper and a regional acid source. ## Sources 1. [Price correlation, Material Insights](https://www.materialinsights.org/chemicals/sulphuric_acid/correlation/), Material Insights (World Bank, FRED, IMF data) 2. [Strong profits from smelting acid strongly support copper smelting business (SMM Analysis)](https://news.metal.com/en/newscontent/103364346-Strong-profits-from-smelting-acid-strongly-support-copper-smelting-business-SMM-Analysis), Shanghai Metals Market (2025) 3. [2022 Minerals Yearbook: Copper](https://pubs.usgs.gov/myb/vol1/2022/myb1-2022-copper.pdf), USGS (2022) 4. [Copper expert: Chinese sulfuric acid restrictions could represent 33% of production costs](https://plusmining.com/en/2026/05/05/copper-expert-chinese-sulfuric-acid-restrictions-could-represent-33-of-production-costs/), PlusMining (2026) 5. [Closure of Sterlite Copper jeopardizes downstream industries](https://www.chemanalyst.com/NewsAndDeals/NewsDetails/closure-of-sterlite-copper--50), ChemAnalyst (2018)