Blog

Jun 25, 2023

Application of slag in steel, other industries

The steel industry of Pakistan has been facing a number of challenges including but not limited to import of raw materials at a competitive price owing to currency fluctuations as well as the hike in

The steel industry of Pakistan has been facing a number of challenges including but not limited to import of raw materials at a competitive price owing to currency fluctuations as well as the hike in power tariffs. Amongst many other challenges, there is an ongoing debate on what raw materials are relevant to the industry.

A number of inputs have been disallowed to the steel industry through Sales Tax General Order (STGO) 12/2022 dated April 07, 2022. The analysis of data pertaining to inputs claimed by the steel sector had led the FBR to conclude that these sectors are misusing the facility of filing automated sales tax returns. Some of the inputs claimed by the sector are not relevant to their business.

An in-depth investigation into the relevance of these inputs that were disallowed to the steel sector has shown that the STGO was rightly guided for a variety of reasons ever since the steel industry is lobbying to get the STGO rescinded.

One such input claimed by a few of the steel players in the market is slag. The analysis of data revealed that input adjustment on slag was claimed by only a few steel manufacturers and not all of them. This surprising observation led the writer to further dig out why slag is not claimed as an input across the steel industry since their industrial processes are almost the same.

The process of steelmaking produces valuable by-products that are profitable for the companies if they are sold off in the appropriate industries. The by-products or waste produced from steelmaking generates revenues for steel manufacturers all over the world. These by-products are rich in elements that make them economically viable to be recycled and reused in several industries. One such by-product of the steel manufacturing process is steel slag. The slag basically occurs in the form of molten liquid melt that solidifies upon cooling.

Slag is a primary by-product of steelmaking and is produced during the separation of molten steel from impurities in steelmaking furnaces. It is first produced during the melting of steel scrap in heating furnace-such a type of slag is called Electric Arc Furnace Slag (EAFS).

Some slag is also produced during the secondary refining stage of steel in Ladle Furnace-such a type of slag is called Ladle Furnace Slag (LFS). If we analyze the composition of any classification of slag, we find that it is primarily a solution of silicates and various oxides such as calcium oxide, silicate oxide, aluminum oxide, ferrous oxide, and manganese oxide etc.

Looking at a typical composition of slag we see that there is no scientific reason to substantiate its use in making steel. It’s a by-product of the steel industry and not the raw material needed for making steel.

It’s akin to suggesting that bread crumbs are a raw material used in the process of making bread since we all know that bread crumbs are a by-product of bread itself. The main raw material in making bread is flour, not bread crumbs. The bread crumbs may be separately used and sold since it’s a cooking ingredient in many dishes; however, it is not used to make bread. In a similar manner, slag is just a by-product, albeit a very useful one.

Once separated from the molten metal or scrap during the melting process, it can be recycled by the steel industry for metal recovery using jaw crushers and magnetic separators; however, the rate of metal recovery is extremely low. Any piece of steel that may have remained intact during the steel-melting and refining processes can be recovered from slag; however, there is a difference between recovering any piece of steel from slag and claiming slag as a raw material for making steel.

Slag is not composed of steel though it may contain any un-molten piece of steel scrap. The rate of recovery of steel scrap from slag is so low that any left-out pieces of steel are manually removed from slag by the labour employed by steel manufacturers.

While examining the raw materials employed by the local steel industry, it is important to compare the information acquired in the process with the global standards. Globally speaking, none of the steel industries claim slag as a raw material used in the process.

According to the World Steel Association’s Fact Sheet on Steel and Raw Materials, the key raw materials used for steelmaking include iron ore, steel scrap (or recycled steel), coal and limestone. The OECD’s steel committee report titled ‘Steelmaking Raw Materials: Market and Policy Developments’ lists the raw materials used in steelmaking which include iron ore, ferrous scrap (steel scrap), coking coal, silicon, zinc, chromium, etc. There is no evidence anywhere in the world that slag is an input of steel industry. All the major international steel and slag associations such as ‘Nippon Slag Association’ acknowledge slag as a by-product of steel with immense benefits for other allied industries.

Slag is a sustainable by-product of steel industry. While slag has little use in the steel industry, it has several applications as a raw material for other industrial processes. Not all slag is created equal-the chemical composition and properties of slag may vary slightly depending upon factors such as the rate of cooling, etc. The rate of cooling or the method of cooling of slag significantly affects the particle morphology, and subsequently determines its utilization.

The air-cooled slag (ACS) is produced through cooling under ambient temperature conditions while the granulated blast furnace slag (GBFS) or water quenching blast furnace slag is produced through cooling with water sprays. The air-cooled slag is predominantly crystalline in nature and is effectively used as an aggregate in the construction industry. The water quenched slag is amorphous in nature and is used in making Portland cement. One of the main benefits of slag are associated with environmental remediation since it can be used to alleviate heavy metal contamination in soil or water.

The evidence clearly points to the fact that slag is not a raw material used in the production of steel; it is a by-product with many applications in other industries. The STGO 12/2022 has rightly disallowed slag and other wastages or byproducts of steel industry as inputs since claiming their own waste products or by-products as inputs has little foundation.

Having said that, the steel industry of Pakistan should up the ante by developing a robust research team that is in line with the recent international developments on finding cost-effective alternatives to various raw materials currently in use. This would not only help the industry gain a competitive advantage but also greatly help the national exchequer.

Copyright Business Recorder, 2022

Rosheen Hussain Syed

The writer is Deputy Commissioner-IR FBR