“SSAB air dries its LD sludge for two weeks. The material gets recycled into briquettes that are used in the blast furnace.”

In 2014, steel giant SSAB created a new group-level function for sustainability under Maria Långberg, who simultaneously became CEO of the subsidiary Nortec AB. “It’s really exciting and interesting to lead Nortec’s work. For SSAB, it is important to integrate sustainability into business strategies and operations. Integrating Merox is an important part of this,” says Långberg.

“Merox is focused on optimizing SSAB’s byproduct, scrap and waste management systems with a focus on sustainability. We work with the whole chain from research, development, production, marketing for internal use and external sale. Our product portfolio includes a number of good examples of clever use of byproducts and waste from steel manufacturing. A recent example is a process that we developed to recycle iron-rich sludge that gets formed in steel furnaces.

Useful sludge ended up at the dump

SSAB’s steel mill in Luleå creates sludge with significant amounts of iron, a result of flue-gases created when oxygen is blown into the LD furnace melt.  LD is an oxygenation process named after the Austrian cities of Linz and Donawitz that purifies metal melt from coal. The process is one of several used in the metal industry.

For many years, the sludge was processed in a sintering plant, basically a large compacter, which SSAB closed in 1978 when it started using pellets as iron ore. This LD sludge, 500, 000 tons of it, was instead deposited in landfills.

A new lease on life

“Over the years, many unsuccessful experiments have been carried out to dewater the LD sludge. Our project began in the summer of 2013, and in 2014 we presented a briquette solution,” says Långberg.

There have previously been two major problems with the recirculation of sludge – high zinc content and high moisture content. These days, zinc levels are lower in combination with cleaner steel production. But the high moisture content persists and this is where Merox helps in developing appropriate measures for sludge recirculation.

“Previous efforts have included mixing the sludge with cement and lime to dry it out. We have also tried to roll pellets from the dried material.”

“Today, SSAB transports the LD sludge to a specific area where it air dries for two weeks with the help of a tractor to mix it all up. The material is then turned into briquettes that are then recycled in the blast furnace,” concludes Långberg.

Every year, SSAB’s steel mills produce around 40,000 tons of wet sludge, roughly 25, 000 tons dry. Being able to recycle LD sludge instead of landfilling it provides both environmental benefits and reduced costs for raw materials. Current estimated cost savings amount to between SEK 5-10 million per year.

This article was published in April 2015