Dumping slag

This is a followon post to the explanation of how steel is made and why the steel industry is not going to return to Pittsburgh.

Once iron ore is melted, the impurities float to the top. Typically silicone dioxide or calcium oxide are added to speed up the removal of the oxygen, converting iron oxide into pure iron and binding with phosphorus and sulfur

So what do you do with this molten waste that is a mix of silicon, calcium, magnesium and aluminum? You dump it in a field called a slag heap.

So what do you do with a slag heap after you have been dumping slag for 100 years and the steel mills close? After slag cools, it is roughly the consistency of hardened concrete. You cover it with asphalt and build a shopping center on top, or you put down some topsoil and build luxury condominiums.

The slag industry has a trade association


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14 Responses to Dumping slag

  1. briand75 says:

    Long story, but I worked at a steel mill back in the 80’s. There are some fascinating and extremely dangerous processes that go on at a mill. The slag you see in the clip is probably around 2000 degrees (+/- 500 degrees). The molten steel right out of the furnace is around 2950 degrees which makes the process of pouring the steel into molds and all of the downstream processes very dangerous – yet fascinating.

  2. Fred Stiening says:

    Well, that was so popular, here is a video of the hot metal train in NW indiana – similar purpose, except carrying the good stuff.


    Any theories on why there are empty gondola cars in between the hot metal cars?

    • briand75 says:

      Okay – next reference point – have you ever been driving in Michigan and seen those molten aluminum carriers? They are very dangerous carrying molten aluminum on the highways if they overturn.

      • briand75 says:

        One example of a “Michigan Train” – these haul crucibles on 11 axles:

        • Fred Stiening says:

          Never saw one of those – where would you typically see them?

          • briand75 says:

            I used to see them all the time on the highway. The key is weight distribution. Michigan allows up to 80,000 lbs. on the highways as long as you have a multiple axle trailer. Most common were the 11 axle single trailers. The aluminum carrying casks were hauled on 10 axle lowboys.

            I always thought I would like to hear the conversation at the toll plaza – they charge $x.xx per axle 🙂

            • Fred Stiening says:

              At least when I lived there, Michigan had no toll roads, just toll tunnels and bridges at the international crossings (the Makinac bridge being the exception). Since Michigan’s economy was based on making cars, the powers that be discouraged using tolls to pay for roads


            • briand75 says:

              I am not sure what term to use – my reference to toll plaza is satirical in nature – I would love to see an 11 axle truck at the toll plaza as it would be a gas to listen to the “that will be $115…” conversation. I lived in St. Joseph – the toll roads I hit were all in Indiana.

    • countess robini says:

      the gondolas are there to spread out the weight and to reduce the effects if there were to be a derailment.

      • Parrott says:

        Yeah, the Countess is correct. Those molten metal cars are mucho- heavy- hombres when loaded!
        They have three trucks on each end. They can’t have that much weight bunched up, it would crush a bridge. The gondolas spread that weight and also help with braking. Pretty wild, they like using those GP-38’s , here is another vid with pulpwood flats for spacers and braking, https://www.youtube.com/watch?v=nhWrjjFx4-E


        • Fred Stiening says:

          From my further research, it appears the time window is 8 hours. They want the metal at the desination in 4 hours… at 6 hours, they got top priority over all other traffic, and at 8 hours, they scrap out the car. Since they don’t have spares, they’ll pour the metal into a hole rather than let it solidify in the car

          Since they were not originally intended for interchange service, the hot metal cars did not have air brakes, but as the finishing mills moved away from the blast furnace, the cars had to be retrofitted with braking gear. They also have a type of bearing that is largely prohibited by the Class 1 railroads

  3. Fred Stiening says:

    Here is an amusing news story from a couple years ago


    Notice the wheels still sitting up on the bridge. What you learned by playing with toy trains was significantly inaccurate.

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