This byproduct of mineral treatments has many uses

metals treatment for slag

metals treatment for slag

But this is not the only slag to be produced during the production of steel. In an integrated steel plant the molten iron from the blast furnace is combined with steel scrap in a ratio of typically four parts molten iron to one part scrap. Lime is also added and oxygen is blasted through the resultant mixture. This process results in the production of steel and basic oxygen steelmaking (BOS) slag. Apart from the chemical differences, BOS slag is about 50 per cent more dense than its blast furnace counterpart.

Copper smelting also produces copper slag and coal slag is produced from coal fired power generation plants – so where does all this “man made mineral” end up? Blast furnace slag has a myriad of uses of which perhaps the most intriguing is for the production of mineral wool. It’s difficult to believe that a lump of dense slag can be turned into a low density material with a high insulating capacity. However the process for this is familiar on any fairground.

fibre glass wool-slag by-product

fibre glass wool-slag by-product

Just as candyfloss (cotton candy in North America or barbe à papa in French speaking parts of the world) is made by melting and spinning sugar, mineral wool is made by melting and spinning mixtures of basalt rock and slag (or slag on its own). This material is then processed into the low density wadding used in roofing to reduce energy consumption.

slag in raod surfacing

slag in raod surfacing

Have you looked at an asphalt surfaced road and wondered how such a smooth looking surface can react so well with your car’s tyres when you hit the brakes as the car in front slows down unexpectedly? You were able to brake safely because the wearing course of the asphalt contained steel slag – and it’s also very likely that the subsurface also contains the same material. Steel slag adheres to asphalt enhancing the overall performance of the road in spite of rain, sun or applied salt.

Have you heard the term pozzolan? Granulated blast furnace slag is a pozzolan and when this is further ground down it produces a fine powder that has cement-like properties when mixed with water.

Sourced and published by Henry Sapiecha Feb 2009

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