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What is a Copper Slag?

B. Turner
B. Turner

Copper slag is a by-product created during the copper smelting and refining process. As refineries draw metal out of copper ore, they produce a large volume of non-metallic dust, soot, and rock. Collectively, these materials make up slag, which can be used for a surprising number of applications in the building and industrial fields.

This material represents a popular alternative to sand as a blasting medium in industrial cleaning. Using blasting or high-pressure spraying techniques, companies can use copper slag to clean large smelting furnaces or equipment. Slag blasting is also used to remove rust, paint, and other materials from the surface of metal or stone. This helps to prep the surface for painting, or simply to remove unwanted finishes or residue.

Small nuggets of pure copper.
Small nuggets of pure copper.

Copper slag has also gained popularity in the building industry for use as a fill material. Unlike many other fill materials, it poses relatively little threat to the environment. This means it can be used to build up the earth to support roads, buildings, or other surfaces.

Contractors may also use copper slag in place of sand during concrete construction. The slag serves as a fine, or binding agent, which helps hold the larger gravel particles within the concrete together. When used in this manner, the slag helps to improve the properties of the concrete, and also serves as a form of recycling.

Copper slag is a by-product created during the extraction of copper from copper ore.
Copper slag is a by-product created during the extraction of copper from copper ore.

One of the primary advantages to copper slag is the low risk it poses to health and the environment. Silica sand, which represents the most popular blasting medium and concrete fine currently in use, poses serious health risks when inhaled. It may also contribute to pollution and other environmental concerns.

Copper slag also has a high strength-to-weight ratio, making it an effective option in concrete, or as a fill material under the roadway. When added to concrete, it makes the paved surface less porous, which minimizes problems with moisture and freezing. It also makes concrete more fire resistant, and helps to slow the spread of heat and flames.

This material also has several limitations that users should be aware of before using copper slag. Some versions may contain heavy metal traces, which can contribute to air and water pollution. It's commonly classified as hazardous waste due to this risk. Another issue to consider is the shear volume of slag produced during copper refining. Typically, refineries end up with two units of slag for every one unit of copper produced during smelting.

Discussion Comments


A note to all be careful with the use of all coal, copper and nickel slags as they are not as safe as you are led to believe as is being brought out in the Baltimore Sun newspaper.

Are you are an abrasive blast worker or employer, inspector, engineer, industrial hygienist, plant/facility owner or government/military employee who performs work associated with the use of coal and copper slag abrasives? If you or a person you know can answer yes, you really need to read and share the below article that was published on The Baltimore Sun's front page, by Tim Wheeler, titled "Federal agency investigating sand-blasting hazards Contaminants in coal and copper slag pose risks, critics say."

It is a thorough and objective factual analysis of the potential significant impact on human health to both workers, their families and even retail consumers from the use of coal and copper slag abrasives due to the high levels of the cancer causing toxin beryllium in the dust. Ironically, according to OSHA, beryllium is most dangerous when inhaled in small particles thus making abrasive blasting with coal or copper slag a potentially perfect delivery vehicle of beryllium-laden dust particles into a person's lungs.

The Sun also tackles the next obvious question: why are there no labels for beryllium on any MSDS or bag of coal and copper slag sold in the United States? It now appears from this article, OSHA has decided to soon ask the coal and copper slag companies that same question.


How does using copper slag blasting compare to using sand or other materials? Is one material better than the other for certain situations, or are they both about equal? Also, what is the price difference between the two?

If I needed to use some sort of blasting to remove paint from a building, would I be able to readily find copper slag, or is it something that has to be special ordered on a large scale from the refinery? Also, would you be able to use the copper in a regular sand blasting machine, or would you need special equipment?


Can the slag from any other refining process be used for anything useful like was described here? I have heard of iron slag being used for things, although I'm not sure what they are. All metals would have some sort of waste products, but I don't know what qualities make something good for other uses. I don't know whether other materials would be harmful for the environment or not, either.


What are the slag properties? The article says it is a dust, but with the rock and other materials combined, it the slag powdery or it it more grainy like the consistency of sand?

I was also curious how the copper slag can be less harmful for your health compared to silica. Maybe this all depends on the size of the particles, but I thought most of the danger with breathing in dust was due to the size of the particles being able to enter the lungs. I didn't think it was really connected to the material that was being used. Is this right? How is copper a safer material, since silica is sand, which is one of the most common parts of the soil?


@JimmyT - You are right that mining copper can have a major negative impact on the habitat around a mine, especially for the streams and waterways. I believe most of the problem is not with the ore itself, but with the process that removes the ore.

When mines extract copper, they often use sulfuric acid, which helps to separate the ore from the rest of the surrounding rock. When the mines aren't careful, the sulfuric acid will leach into surrounding streams and cause major problems among the fish, wildlife, and plant communities.

Another problem can come simply from the fact that the ground has been opened up to expose new areas. There are many other compounds besides copper that line the mines. These materials are usually fine, but when they react with water thanks to the mine opening, they can turn to liquid form and create dangerous chemicals that also run into the water system. Very good question.


I have always heard of copper mining as being extremely harmful for the environment. What happens between the mining and refining process that makes the copper by-products nearly harmless?

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    • Small nuggets of pure copper.
      By: Ekaterina Fribus
      Small nuggets of pure copper.
    • Copper slag is a by-product created during the extraction of copper from copper ore.
      By: jonnysek
      Copper slag is a by-product created during the extraction of copper from copper ore.