Trash to treasure: Turning steel-mill waste into bricks

May 25, 2011

Scientists are reporting development and successful testing of a promising new way of using a troublesome byproduct of the global steel industry as raw materials for bricks that can be used in construction projects. Their study appears in ACS' Industrial & Engineering Chemistry Research.

In the report, Ana Andrés and colleagues note that steel mills around the world produce vast quantities of waste dust each year — 8 million – 12 million tons in the United States, for instance, and 700,000 tons in the European Union countries. The dust often is converted into a rock-like material known as Waelz slag, which is usually disposed of in landfills.

The slag contains iron, calcium, silicon oxide and other minor oxides as manganese, lead or zinc oxide. Scientists have been searching for practical and safe uses for Waelz slag. In earlier research, scientists showed that Waelz slag had potential as an ingredient in bricks, roof tiles and other ceramic products. The new research moves large-scale recycling of Waelz slag closer to reality, establishing at two real-world brick factories that the material can successfully be incorporated into commercial-size bricks.

It showed existing commercial equipment could be used to make bricks with Waelz slag, and eased concerns about large amounts of potentially toxic metals leaching out of such bricks. A small amount of potentially toxic material came out of the slag-made bricks over time, not in excess of European Union regulations. "Overall, it may be summarized that Waelz slag containing meet the highest quality standards set for construction ceramic materials," the researchers say.

Explore further: Researchers open possible avenue to better electrolyte for lithium ion batteries

More information: Incorporation of Waelz Slag into Commercial Ceramic Bricks: A Practical Example of Industrial Ecology, Ind. Eng. Chem. Res., 2011, 50 (9), pp 5806–5814. DOI: 10.1021/ie102145h

Abstract
The recovery of electric arc furnace (EAF) dust generates large amounts of an industrial byproduct called Waelz slag. This residue, consisting primarily of iron oxide contaminated with other metal oxides (including zinc and lead), is usually disposed of in landfill sites at a high economic and environmental cost. This paper investigates an alternative based on industrial ecology principles, which involves the incorporation of Waelz slag into clay ceramic construction bricks. For the purpose of this work, Waelz slag and raw materials employed in the manufacture of ceramic bricks (natural clays, wood pulp) were characterized. Subsequently, a series of brick specimens were manufactured according to commercial mixes and using industrial equipment and procedures. Similar specimens were also produced replacing 20−30 wt % of the clay with Waelz slag. The resulting products were analyzed for their physical (bulk density, water absorption, open porosity), mechanical (modulus of rupture), and chemical properties (soluble salts content) in order to evaluate compliance with quality standards for construction materials. The environmental consequences of incorporating slag into ceramic products were also investigated at three stages of their life cycle: release of potentially toxic species during their use (NEN 7345), leaching of heavy metals after disposal in landfill sites (EN 12457 1 and 2), and emission of atmospheric pollutants during the firing process. The experimental results demonstrate that incorporation of Waelz slag does not deteriorate the physical, mechanical, and chemical properties of the resulting products. The leaching of species during its useful lives show compliance with threshold values established according to the Dutch Building Materials Decree (DBMD), and Waelz slag containing bricks fall into the category of nonhazardous waste landfill, just like conventional bricks used at this work. Emissions of CO2 and NOx were reduced versus the emissions of halogenated gases and SO2, which were favored due to the thermal decomposition of S, Cl, and F contained in the waste material.

add to favorites email to friend print save as pdf

Related Stories

Making Steel Recycling Greener

Jan 26, 2010

A new process developed by Siemens cuts the energy required to recycle steel and also lowers carbon dioxide (CO2) emissions.

Byproduct of steel shows potential in CO2 sequestration

Oct 13, 2008

With steelworks around the world emitting huge amounts of carbon dioxide, scientists are reporting that a byproduct of steel production could be used to absorb that greenhouse gas to help control global warming. The study ...

Follow the 'Green' Brick Road?

May 22, 2007

Researchers have found that bricks made from fly ash--fine ash particles captured as waste by coal-fired power plants--may be even safer than predicted. Instead of leaching minute amounts of mercury as some ...

Bricks made with wool

Oct 05, 2010

Spanish and Scottish researchers have added wool fibres to the clay material used to make bricks and combined these with an alginate, a natural polymer extracted from seaweed. The result is bricks that are ...

Laying the foundations for a green industry

Jul 31, 2006

Australian university researchers have developed a strong, lightweight building material that they believe could generate a thriving new "green" industry for countries such as China and India.

Recommended for you

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.