Macquarie University – upcycling of steelmaking slag for material reuse project

Summary

Need

This project was selected as part of the competitive Iron and Steel R&D Funding Round under the Transformative Research Accelerating Commercialisation (TRAC) Program to create solutions for Australian iron ore, predominantly comprised of lower grade ore from the Pilbara, and to decarbonise domestic steel production. Near-term investment in innovative R&D is a critical enabler to rapidly develop the technologies required to transition to a net zero future state. Projects supported by the Iron and Steel R&D Funding Round seek to accelerate novel and innovative low emissions iron and steel technologies using Australian iron ore. 

Annually, Australia produces one million tonnes of steelmaking furnace slag (SFS), which contains between 20-30% of iron oxide, 40-60% calcium oxide and up to 5% phosphates. Techniques for extracting and recycling of these oxides into iron and steelmaking processes are not currently commercially viable due to difficulties in separating phosphates from the oxides.  

The project proposes a novel SFS processing method which integrates a staged pyro-enrichment and hydro-leaching precipitation process for the separation of the higher value components present in SFS (calcium oxide, iron and phosphorous) for recycling and reuse.

Action

The project involves developing a technology for upcycling of steelmaking furnace slag (SFS) through a hydro-separation process in which different high value components are separated from the slag for reuse. The technology applies leaching of calcium silicate, iron phases and phosphorus from the slag, and then separates each component through a staged precipitation process. The intent is for the calcium oxide and iron to be recycled back into the blast furnace and steelmaking operations as substitutes for lime and iron oxide, while phosphorus is used to produce fertilizers.  

The project is also aiming to develop a pyro-separation process that will modify the phase transformation of molten steelmaking slag during cooling to maximise the enrichment of phosphate-containing phases in the slag. This process will significantly improve the efficiency of slag separation and its upcycling in the hydro-separation process. 

Outcome

The objectives for the project will be achieved through the following Outcomes: 

1. Reduction in or removal of barriers associated with using lower-grade Australian iron ores in low emissions steel production through decreased use of virgin fluxes (calcium oxide) 
2. Increased research capacity in the Australian iron and steel sector, and the facilitation of collaboration between research groups and industry, and 
3. Development and improvement in the technology readiness and commercial readiness of upcycling processes for SFS, separating calcium, iron and phosphorous.