Why Copper Smelting Plants Concern Environmental Regulators

A smelter heats copper ore concentrate to separate the metal from sulphur and other impurities. The usual stages are roasting, smelting and converting. The US Federal Highway Administration says sulphur leaves the ore as sulphur dioxide (SO2) in the roasting step. The EPA says SO2 is also released in smelting and converting.

The US EPA says primary smelters mainly release particulates and sulphur oxides.

What is in the dust?

• The EPA says the particles may also contain oxides of arsenic, antimony, cadmium, lead, mercury and zinc.
• They may also contain sulphuric acid mist.
• Converter gas that is captured is treated in electrostatic precipitators. It then goes to sulphuric acid plants.

Why does SO2 matter?

• The WHO says SO2 comes from burning coal and oil. It also comes from smelting sulphur-bearing ores.
• The US EPA says SO2 harms breathing. It also feeds acid rain.
• The US health agency ATSDR names copper smelting as a source of SO2.
• Carbon monoxide is not the documented concern here. The UPSC question in card 2 tests exactly this point.

The Civil Services Preliminary Examination 2021 (General Studies Paper I, Q17) asked this question, word for word:

“Why is there a concern about copper smelting plants?”

1. “They may release lethal quantities of carbon monoxide into environment.” 2. “The copper slag can cause the leaching of some heavy metals into environment.” 3. “They may release sulphur dioxide as a pollutant.”

The question ended: “Select the correct answer using the code given below.”

The options were (a) 1 and 2 only, (b) 2 and 3 only, (c) 1 and 3 only, and (d) 1, 2 and 3. UPSC’s official key is (b). Statements 2 and 3 are correct.

Why is statement 1 the trap?

• The sources in card 1 name sulphur oxides and particulates as the main releases. None names carbon monoxide as the concern.
• A real-sounding but false claim is mixed with true ones. Knowing what a process releases beats knowing that “it releases something toxic”.

How do you solve it?

• Sulphur dioxide is documented, so statement 3 is correct.
• Slag leaching is documented, so statement 2 is correct.
• Statement 1 is wrong. Only option (b) leaves it out.

Impurities in the ore form a molten waste called slag. Workers skim it off. The EPA describes this step in its smelter notes.

Is slag always dangerous?

• A 2025 review says copper slags mostly consist of stable compounds. The main concern is leaching of heavy metals into the ground.
• The FHWA says tests on some copper slags found non-hazardous leachate. It adds that slags from sulphide ores may leach sulphur.
• A leaching test on one waste slag found lead above the regulatory limit (TCLP).

Where does slag go?

• The same review says only 15% of copper slag worldwide is used commercially.
• Slag has been used for years as granular base on mining roads, says the FHWA.
• Indian road guidelines (IRC:SP:121-2018) name Dahej and Tuticorin as copper-slag generators.
• Abrasive blasting with copper slag can raise worker exposure to lead, arsenic and chromium above OSHA limits.

Each pollutant from a smelter has its own main target. UPSC likes such pairings.

Which pollutant harms which organ?

• Sulphur dioxide: it harms breathing. ATSDR says people with asthma are sensitive even to low levels.
• Arsenic: the WHO names skin lesions and skin cancer as characteristic effects. ATSDR lists copper or lead smelting as an arsenic exposure job.
• Cadmium: it damages the kidney and bones, says ATSDR. The WHO adds the lungs and calls cadmium a human carcinogen.
• Lead: the nervous system is the main target. Children are more vulnerable, says ATSDR.

How serious is lead?

• The WHO names smelting as a source of lead contamination.
• It says no blood lead level is known to be safe.
• ATSDR says lower lead levels can reduce mental development.

Is there a real-world example?

• A study in Morales, Mexico, tested soil near a copper-arsenic smelter.
• It found 90% of samples above US EPA guidelines for lead and arsenic.

The plant at Tuticorin (Thoothukudi) began operations in 1996. Its story ran through the Pollution Control Board, the NGT, the High Court and the Supreme Court. The dates are easy to mix up.

What is the dated timeline?

• April 2013: the Supreme Court asked Sterlite to pay Rs 100 crore.
• 31 May 2013: the NGT reversed a closure order that followed a suspected gas leak.
• 22 May 2018: police firing during protests killed at least 11 people, says an early report. Later counts differ.
• 28 May 2018: the Tamil Nadu government endorsed the closure under the Water Act. The plant shut that day.
• 15 December 2018: the NGT set aside the closure order.
• 18 February 2019: the Supreme Court held that the NGT had no jurisdiction to order reopening.
• 18 August 2020: the Madras High Court held that the plant must stay shut.
• 29 February 2024: the Supreme Court dismissed Vedanta’s appeals against the High Court order.
• November 2024: the Supreme Court dismissed Vedanta’s review plea.

What findings did the Supreme Court leave in place in 2024?

• The High Court had found that the unit dumped large amounts of copper slag. This led to air and water pollution.
• It also found about ten years of operation without hazardous waste authorisation.
• The Supreme Court did not disturb these findings.
• It cited the repeated nature and severity of the breaches.
• A show-cause notice of the state board had earlier noted 3.52 lakh tonnes of slag on a water-body site.

Why does the 2019 ruling confuse people?

• The 2019 ruling was about jurisdiction only. It did not decide whether the plant should reopen.
• The 2024 ruling dealt with the plant’s conduct.

Dahej in Gujarat hosts Hindalco’s Birla Copper. Hindalco calls it one of the largest single-location copper smelters.

Did Dahej shut down?

• No. Hindalco’s 2024-25 report says a brownfield expansion at Dahej will add 300 KTPA.
• That would raise refined copper output to 721 KTPA.
• So the two plants took different paths. Sterlite faced repeated breaches and a closure order. Dahej is growing.

What did Tuticorin’s closure do to supply?

• India has been a net importer of copper cathodes since the closure, says the Mines Ministry.
• Net import was 0.335 MT in FY24. Refined copper output had peaked at 0.843 MT in FY18.
• Concentrate imports fell from 1.488 MT in FY18 to 0.824 MT in FY19.
• Kutch Copper (Adani) began a 0.5 MT unit at Mundra in March 2024.
• The ministry sees 1.285 MT of capacity rising to 1.785 MT by 2029.

Modern plants try to catch sulphur before it leaves the chimney.

How does cleaner smelting work?

• Converter gas is cleaned in electrostatic precipitators and routed to sulphuric acid plants, says the EPA.
• The EPA calls flash converting an environmentally superior alternative.
• Glencore says its ISASMELT process uses a single submerged lance. It reports low fugitive emissions and efficient off-gas capture.
• One Utah smelter reported sulphur capture above 99.9%. That is one plant’s figure, not an industry average.

Who regulates smelters in India?

• The Air Act was enacted in 1981 and amended in 1987. The Water Act dates from 1974.
• The CPCB’s Red category list includes the copper smelter. Red means industries that pollute the most.
• State boards and the CPCB monitor emissions under these laws.

India is rebuilding smelting capacity. Court stories also get retold with small errors.

What is new?

• In March 2025, Tamil Nadu’s government gave Sterlite 80 days to move machinery. Deccan Herald says the machinery was meant for an expansion project. It is likely to move to Silvassa.
• Activists still wanted the plant dismantled. The report does not say it is being dismantled.
• Hindalco’s Q4 FY26 release calls it India’s largest copper producer.
• Reports say Hindalco will add 250-280 kilotonnes of capacity in Gujarat.

Where do sources differ?

• Date of the ruling: the judgment is dated 29 February 2024. Some pages say 28 February.
• Who gave 80 days: the Tamil Nadu government did, not the Supreme Court.
• Death toll: the first report said at least 11. Later counts differ. This lesson gives no final number.
• Emission limits: the gazette limits for smelters could not be machine-read. This lesson quotes none.