Sulfuric Acid Alternatives in Mining: 7 Options Compared

The main sulfuric acid alternatives in mining are alkaline carbonate leaching, ammonia leaching, chloride-assisted leaching, hydrochloric acid, methanesulfonic acid, alkaline pressure oxidation and acid made from pyrite in the ore itself. None replaces sulfuric acid everywhere. Each works only for certain ores, and each brings its own costs and trade-offs.

The question matters more now because acid has become expensive. Ivanhoe Mines reported an average net realized price of about US$900 per tonne for high-strength sulfuric (sulphuric) acid in the Democratic Republic of Congo (DRC) in the third quarter of 2026, roughly double the previous quarter. This guide compares the seven options for a consultant screening a flowsheet, shows what each one has done at real sites and includes a calculator for your own acid bill.

Seven sulfuric acid alternatives compared

A lixiviant is the solution that dissolves metal out of ore. The table compares the seven routes by the ore they suit and how far they have gone. “Reduces” means the route lowers acid use but does not end it.

Why miners want to use less sulfuric acid

Sulfuric acid is cheap only when supply is easy. World output was estimated at 260 million tonnes in 2022, and most of it has gone to fertilizer, so mines compete with phosphate plants for the same tonnes. Fertilizer demand therefore reaches a leach mine’s reagent budget. See how minerals used in fertilizer and crop-yield steps on farms create that demand. In the United States, about 90% of sulfur consumed was in the form of sulfuric acid in 2025 (USGS, 2026).

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US sulfur price, a driver of acid cost

average unit value, US$ per metric ton of elemental sulfur

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Reported sulfuric acid prices vary by market

US$ per tonne or ton, company-reported, 2026; bases differ

Three events pushed the issue up the agenda in 2026:

• Sulfur supply. The World Bank warned in April 2026 that disruption to Middle East sulfur exports and a planned Chinese acid export ban could raise processing costs and limit copper and nickel output.
• Chile. Reuters reported that Chinese acid exports to Chile fell to zero in March 2026. Morgan Stanley said Chile’s 1.1 million tons a year of leached copper could be at risk, over half its refined output.
• Central Africa. Zambia banned acid exports in September 2025, moved to permits in March 2026 and eased limits in May 2026. DRC miners cut usage and considered output reductions.

Demand is also growing outside copper. CRU puts nickel-related acid demand at 16 million tonnes a year in 2025, up from 3.5 million in 2021, driven by Indonesian high-pressure acid leach plants. Kazakhstan’s in-situ uranium fields used 1.85 million tonnes in 2025 (Acuity Commodities, quoted by World Nuclear Association).

What acid costs depends on where you buy it

There is no single world price. Grupo Mexico reported an average acid price of about US$178 per ton for the third quarter of 2026, while the Kamoa-Kakula smelter in the DRC sold at about US$900 per tonne. Ivanhoe’s figure is for acid sold from the mine gate into a tight local market, so freight does not explain it, and neither source breaks down the gap. Always price acid delivered to your site. Our sister guide on sulphuric acid production trends and plant upgrades covers the supply side.

The alternatives, one by one

1. Alkaline carbonate leaching

Best for: uranium in rock rich in calcium. World Nuclear Association says that alkaline leaching must be used when an orebody holds more than about 2% calcium, as limestone or gypsum, because those minerals would consume the acid. US in-situ mines use it for this reason.

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In-situ uranium recovery: acid against alkaline

percent of uranium recovered, low to high of the published range

Pros: it takes acid out of the supply chain and suits ground that acid cannot treat economically. Cons: the same source gives 60-70% recovery against 70-90% for acid, and acid operating costs are about half those of alkaline leaching. So this is a geological choice first, and a cost-saving move rarely.

2. Ammonia leaching

Best for: copper oxide and carbonate minerals in carbonate host rock. Tenorite, malachite and azurite dissolve readily in ammonia solutions, and some impurities stay out of solution because of the higher pH. The US National Park Service records ammonia leaching tanks at Kennecott in Alaska, where it recovered copper from waste gravel in limestone.

Pros: limestone does not eat the reagent the way it eats acid, which is the issue that Mantoverde faces with high-carbonate ore (below). Cons: ammonia is volatile, so it needs containment and recovery. It also needs testing on your own minerals.

3. Chloride-assisted leaching

Best for: copper ore with natural chloride, and possibly primary sulfides. This route still uses sulfuric acid, but less of it. Ivanhoe Electric’s 2026 preliminary feasibility study for Santa Cruz in Arizona gives about 9 kg of acid per tonne of ore, with acid under 5% of cash operating costs. A preliminary study is not a production record, so treat those as study figures.

Antofagasta is developing Cuprochlor-T, its proprietary primary sulfide leaching technology, aimed at ore that ordinary acid leaching struggles with. Cons: high chloride brine demands corrosion-resistant materials and careful water planning, and results depend heavily on the ore.

4. Hydrochloric acid leaching

Best for: lithium claystone in the plans reviewed here. Century Lithium’s Angel Island feasibility study in Nevada pairs hydrochloric acid leaching with direct lithium extraction and an on-site chlor-alkali plant, after pilot work. Compare Thacker Pass, also Nevada claystone, whose plan includes its own sulfuric acid plant.

Pros: reduces dependence on bought sulfuric acid. Cons: it swaps one reagent system for another, and hydrochloric acid is corrosive. Angel Island is a study, not an operating mine, so the comparison is between two plans and not two track records.

5. Methanesulfonic acid

Best for: research flowsheets. Methanesulfonic acid (MSA) can dissolve many metal salts at higher concentrations than hydrochloric or sulfuric acid, has low vapor pressure and is not an oxidant. Those traits make it attractive on paper.

Cons: the sources reviewed for this guide document industrial and laboratory use and not a mine leaching at scale. Ask any vendor for pilot data on your ore, reagent loss per tonne and recycling rate before giving it weight in a study.

6. Alkaline pressure oxidation for refractory gold

Best for: refractory gold ore, where minerals lock up the gold; so far this rests on test work in the source reviewed. The study notes that alkaline oxidation runs at lower temperatures with less autoclave corrosion, but its reagents cost more. One published test on a floated concentrate found acid oxidation at 220°C and 500 kPa oxygen gave a gold result 19% higher than a sodium hydroxide route. That study covers one ore, so it shows the size of the possible penalty and not a rule.

7. Acid made from pyrite in the ore

Best for: heaps where pyrite is available. Pyrite is iron sulfide, and it can generate acid as it oxidizes. Capstone’s Mantoverde Pyrite Augmentation project, a US$45 million plan approved by its board in July 2026, is expected to cut acid consumption by about 20% and add about 3,500 tonnes of copper cathode a year, with completion expected in early 2028. Joint-venture approval was still expected when Capstone reported.

Bioleaching works on similar chemistry, with native bacteria speeding up oxidation of sulfur products to acid. Cons: it depends on the sulfide present in the ore, and carbonate still consumes acid however it is made.

A related option: use less through better control

Sometimes the best substitute is less waste. Antofagasta reports that a predictive system saved more than 1,000 tonnes of acid in 2025 while raising copper recovery by 0.8 percentage points. Capstone also cut throughput of high-carbonate ore at Mantoverde because it was uneconomic at spot acid prices. In-situ recovery is another angle: Florence Copper in Arizona produced first cathode in February 2026, though acid-consuming rock remains a limit on that method.

How much acid different ores consume

Acid use per tonne of ore varies by more than fifty times, which is why ore testing comes before reagent choice. Reported figures run from about 9 kg per tonne at Santa Cruz to 10-11 kg per tonne in Haib heap tests, nearly 300 kg per tonne of flotation concentrate (not ore) in one Haib bacterial test, and 500 kg or more per tonne for some nickel heap leaching. These come from different ores and tests, so they show the spread and not a benchmark.

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Acid use spans a very wide range

kg of acid per tonne of feed (ore; concentrate for the Haib test); studies and tests, not benchmarks

Calcium carbonate is the usual culprit. When limestone meets acid it neutralizes it, and the mine pays for acid that dissolves no metal. A simple acid-consumption test on representative samples is the cheapest step in this whole decision.

Sulfuric acid in gold mining: what it really does

What does sulfuric acid do to gold? On its own, almost nothing: gold does not react with sulfuric acid. Gold dissolves in cyanide solution or in aqua regia, a mix of nitric and hydrochloric acids. In gold plants, sulfuric acid is mainly about the minerals around the gold.

• Pressure oxidation. Sulfide minerals lock up fine gold. Autoclaves break them down so that cyanide can reach it. Pueblo Viejo in the Dominican Republic uses four autoclaves in parallel ahead of cyanidation, in a plant designed for about 14 million tonnes a year.
• Roasting by-product. Roasting sulfide ore gives off sulfur dioxide, which can be captured and converted into sulfuric acid (US EPA).
• Biological oxidation. Bacteria break down gold-bearing pyrite, producing acid as they go.

Two claims from older articles on this topic need correcting. First, cyanide leaching itself runs alkaline, at pH above about 10.5, controlled with lime, so acid is never added to control pH in that circuit. Second, the acid wash used on activated carbon in gold plants is usually hydrochloric acid, with nitric acid also used, per the US EPA. Our guide to cyanide heap leaching explains the circuit.

On the cyanide side, reagent substitution has also reached a plant: CSIRO reported that a thiosulfate process poured its first gold bar at Barrick’s Goldstrike in late 2014. That replaces cyanide and not acid, but it shows the path a new lixiviant has to travel.

▶ How gold moves from rock to refined metal, including dissolving and carbon recovery · 5:27

How to choose a route: a screening checklist

1. Identify the metal mineral. Oxide, secondary sulfide and primary sulfide copper behave very differently.
2. Measure carbonate. Calcium carbonate decides whether acid is viable at all. Above about 2% calcium, uranium in-situ work moves to alkaline.
3. Run acid-consumption tests. Use representative samples, and record net consumption with solution recycling, since one-pass columns can mislead.
4. Price delivered acid. Get quotes with freight, and model a high case as well as a low one.
5. Price the alternative in full. Include reagent loss, recycling, corrosion-resistant materials, water and any extra plant.
6. Check permits. Ammonia, chloride brine and in-ground solutions each raise different questions for the regulator.
7. Compare recovery and not only cost. A cheaper reagent that recovers less metal can be the more expensive choice.

Infographic

Screening a reagent in 4 steps

1. 1MineralogyName the metal mineral and measure carbonate.
2. 2TestMeasure net acid use on representative samples.
3. 3PriceCompare delivered acid with the full cost of the alternative.
4. 4PilotConfirm recovery and reagent loss on your own ore.

Location also drives the answer. A project next to a smelter may have by-product acid nearby, as copper mining in the DRC shows, and knowing where copper is found helps you judge how far acid must travel. At the earliest stage, satellite mapping can flag carbonate and iron-oxide patterns across a licence before samples are collected. Farmonaut’s satellite mineral detection produces exploration targets of this kind; they sit ahead of metallurgical testing and do not replace it.

Environmental controls on acid and its alternatives

Changing reagent does not remove environmental duties. Acid heaps need lined pads and solution ponds, and spent wash solutions must be neutralized; the US EPA describes neutralizing spent acid wash to a stable pH of 10 before it goes to a tailings impoundment. In-situ fields use monitor wells above, below and around the ore zone to check that solutions stay inside the permitted area.

Some articles on this topic claim universal global acid standards or compulsory worldwide traceability. Rules are set by each country and permit, so check the regulator for your site.

▶ The environmental impacts of mining explained in clay animation · 2:31

Frequently asked questions

What can replace sulfuric acid in mining?

It depends on the ore. Alkaline carbonate suits calcium-rich uranium, ammonia suits copper oxides in carbonate rock, hydrochloric acid is planned for some lithium clay, and chloride-assisted or pyrite-based routes reduce acid use in copper.

What does sulfuric acid do to gold?

On its own it leaves gold largely untouched. In processing it helps attack the sulfide minerals that lock gold up, so cyanide can then dissolve the gold.

Does sulfuric acid dissolve gold?

It is not used to dissolve gold in mining. Plants use cyanide solution, and laboratories and refiners may use aqua regia.

Why is sulfuric acid used in copper leaching?

It dissolves copper from oxide ore on a heap. The acid is recycled from the solvent extraction circuit and reused on the pad, and the copper is plated out as cathode.

Why is sulfuric acid so expensive now?

Sulfur supply from the Middle East was disrupted in 2026, and China planned export limits. Smelters that sell acid as a by-product have benefited, as Ivanhoe and Teck described in 2026 reports.

Is alkaline leaching better than acid leaching for uranium?

Not by default. World Nuclear Association reports higher recovery and about half the operating cost for acid, but alkaline is required where calcium is high.

Can chloride leaching eliminate sulfuric acid?

In the study cited here, no. Santa Cruz still uses about 9 kg of acid per tonne; chloride lowers the amount.

Is methanesulfonic acid used in mines?

It has industrial and laboratory uses and has been promoted as a replacement acid. Ask for pilot data on your own ore before relying on it.

How much acid does a copper heap leach use?

It varies widely by ore. Net figures near 10 kg per tonne appear in some test work, while carbonate-rich ore can use far more. Only testing your own samples gives a usable number.

What are sulphuric acid plant upgrades for?

Typically to add capacity, recover more sulfur dioxide or secure supply for a mine. Thacker Pass plans its own acid plant, and our production guide covers the plant side in more detail.

Questions about this guide or a site of your own? Contact our team or use the mining query form.