Industries ramp up efforts to reduce sulfur dioxide emissions

In the face of growing environmental concerns, key industrial sectors such as base metal smelters and coal-fired power plants are intensifying efforts to curb sulfur dioxide (SO₂) emissions. These industries, traditionally significant contributors to atmospheric SO₂, are now actively remodeling their facilities with effective emission-reducing technologies.

This article explores the origins of sulfur dioxide emissions, their impact on the environment, and the current strategies industries are employing to minimize their ecological footprint.

What is SO₂ and where does it come from?

Sulfur dioxide is a colorless hazardous gas. Though it is not toxic when its content in the air is low, it causes environmental damage in higher concentrations. Heavy emissions of SO₂ can provoke local acid rains, as the gas reacts with moisture in the atmosphere and turns into sulfuric acid.

The main natural source of SO₂ is volcanic activity. Large industrial emissions of SO₂ are associated with the smelting of base metals like copper and nickel, as well as the burning of sulfur-bearing fossil fuels.

Who emits the most SO₂?

The world’s largest SO₂ emitter is South Africa’s debt-laden power utility Eskom. The coal-reliant company emits more sulfur dioxide than energy sectors of entire countries including the United States and China.

A lot of sulfur dioxide is also released during the production of non-ferrous metals. Concentrates of copper, zinc and nickel sulfides are heated to separate metal from sulfur, and the sulfur is oxidized when heated. The volume of harmful emissions depends on the sulfur content in the ore. For example, the Mexican Southern Copper Corporation’s smelter in Peru’s Ilo, which processes concentrate with a high sulfur content (33%), emitted a lot of sulfur dioxide before modernization.

How can SO₂ emissions be reduced?

Capturing and recycling sulfur dioxide is an important challenge for industrial companies around the world. Some of them manage to deal with the issue successfully, thereby reducing environmental damage. These projects are always very costly, however, and are technologically challenging.

One proven technology for reducing SO₂ emissions is converting sulfur dioxide into sulfuric acid. Unfortunately, the acid is expensive to store and transport, and SO₂ requires thorough prior cleaning. If this is not done, the acid with impurities will be unsuitable for further use, such as in the production of fertilizers.

Programmes to reduce SO₂ emissions require significant investment from businesses. They entail costs for gas purification and emissions monitoring systems, construction of acid plants, acid storage, and the modernization of pipelines and other production facilities.

What are the global best practices for dealing with SO₂?

In the early 1990s, diversified miner Rio Tinto modernized a copper smelter located near Salt Lake City, Utah. To reduce SO₂ emissions, the company began producing sulfuric acid there in addition to copper.

Over a 20-year span, the company invested $5 billion in the project. During this time, the plant produced more than 16 million tons of sulfuric acid, becoming one of the largest producers in North America. Thanks to this project, the Salt Lake City plant has become one of the cleanest smelters in the world and has significantly reduced SO₂ pollution, with a sulfur recovery rate of 99.93%.

A similar project was implemented by the aforementioned Southern Copper Corporation’s plant in Peru, which also began sulfuric acid production after being modernized. This allowed the company to increase its SO₂ capture rate to more than 92% from 33%. Investments in the project amounted to $600 million.

The problem of air pollution as a result of sulfur dioxide production also concerns Russia. As of 2022, total SO₂ emissions reached 1.8 million tons, mostly from nickel smelters in Norilsk.

Nornickel is one of the largest producers of nickel, platinum, and copper in the world, and it has now launched the first stage of its Sulphur Programme at the Nadezhda Metallurgical Plant in order to reduce SO₂ emissions radically. It aims to replace old SO₂ capture technologies with an alternative solution that will allow it to turn SO₂ into elemental sulfur and gypsum.

According to the company’s estimations, the implementation of the Sulfur Programme will enable the capture of 1.5–1.7 million tons of sulfur dioxide per year. It will produce up to 280,000 tons of elemental sulfur and up to 5 million tons of gypsum annually.

At the first stage of the project at the Nadezhda Metallurgical Plant, investments in the programme stand at about 180 billion rubles ($2 billion at current rates) and the volume of SO₂ emissions in the company’s Norilsk Division is set to be reduced by 45%.

The total cost of the programme is estimated at 300 billion rubles ($3.25 billion), while total spending could even reach 950 billion rubles ($10.3 billion) through 2050, including maintenance and amortization costs.

Sulfur emissions remain an issue for industrial enterprises across the globe, and companies are dealing with them differently. Although these financially challenging initiatives do not bring returns to shareholders, they help minimize the impact on the environment and people’s health.