When people ask what ArcelorMittal produces, the answer is easy – steel. But we also produce byproducts – materials generated in the course of making steel.
Some of the byproducts, like mill scale, are recycled right on site through sinter plants to make iron-bearing raw material for our blast furnaces. Others, like coal tar or ammonium sulfate from the coke plants, are highly valued as raw materials in the chemical industry or for use as fertilizers.
One of our highest volume byproducts is steelmaking dust (also known as steelmaking oxide). This fine material is captured in the fume collection systems of steel shops as either a dry dust or a wet filter cake. The dust is a mix of oxides that are inert and harmless, not much different than iron ore itself. But due to either size (too fine), moisture (too high) or chemistry (high zinc) they would be difficult to recycle through our sinter plants or blast furnaces. Only a portion of the dry oxides are recycled to the blast furnace through the sinter plant.
In the past, most of the reddish brown oxides were sent to landfills. In 2015, in an effort to decrease costs and improve sustainability at our Indiana Harbor facility, the oxides produced began to be marketed to the cement industry as a raw material. Limestone is the prime raw material for cement, but all cement plants require a small amount of iron in their raw material mix. The iron promotes a reaction in the high temperature kiln which lowers the production cost of cement. Before shipping to the cement plants, the fine materials are micro-pelletized on site at Indiana Harbor to form an oxide that is dry, but not dusty – about the size of sand.
In addition to reusing 38,000 tons of steelmaking oxide in our own facilities in 2015, we also sold 33,000 tons to the cement industry and 2,000 tons to a fertilizer company for reuse. The price at which we sell the material to external companies does not fully cover our cost of moving the materials and micro-pelletizing them – but it is much less costly than landfilling. More importantly, it fully contributes to our goals of beneficially reusing byproducts and directly supports our core value of sustainability. Our goal is to sell 50,000 tons to other companies for reuse in 2016.
Another excellent example of our recycling efforts is seen in our reuse of slag and sludge within our steelmaking process. Recent innovations by our research and development team are allowing us to reuse more of these resources onsite.
Steel slag is a byproduct that is produced through the basic oxygen furnace. Sludge is a byproduct generated from the basic oxygen furnace process when dust is combined with water. Both of these byproducts contain unwanted components, such as zinc, sulfur and phosphorus, which can limit our ability to recycle them. To be a viable recycling option, our solutions need to be efficient, sustainable and cost effective.
In order to increase the amount of materials recycled through reduction of those unwanted components, ArcelorMittal’s research and development team developed new technologies that remove the sulfur from slag and a method to manage dust and sludge. The result of these processes is that we are able to significantly increase the recyclability of these byproducts. These technologies were implemented at virtually no capital or operational cost to ArcelorMittal.
To better recycle slag, our research and development team optimized a magnetic separation process. As a result, it is now possible to significantly improve the iron content and to reduce sulfur and phosphorus. This allows us to reuse the slag at our sinter plants. The sustainability benefit is significant, as we are able to greatly reduce costs, landfilling and the consumption of virgin raw materials: iron ore and fluxes. The implementation of this new technology began in August 2015. In 2016, we anticipate being able to reuse 80,000 tons of this recycled slag at our Indiana Harbor facility.
Our facility in Burns Harbor, Indiana, is another example of a plant where our slag is being significantly recycled. Examples of products that are created from the recycled slag include:
-Dark colored glass, including medicine and beer bottles
-The mineral wool industry, including ceiling tiles, insulation, fire proofing and sound proofing
-Construction applications, including heavy highway and bridge materials, base for roads, concrete, hot mix asphalt and under drains for piping
Sludge is a byproduct of the steelmaking process that is rich in iron and fluxes. Unfortunately, the level of zinc found in the material severely limits its recyclability to be used in our plants by our sinters and blast furnaces. Through processes created by our research and development team, we are now removing zinc-containing scrap at one of our facilities and using zinc-free scrap in others. As a result, low-zinc steelmaking dust/sludge has been produced. This has resulted in an additional 136,000 NT/year of the byproduct being recycled per year at our Indiana Harbor facility.