Resnick Institute

2015 Resonate Award Winners

The Challenge

Steel production is a significant material and energy intensive industry. Nearly 1500 million tons (Mt) of steel is manufactured globally every year resulting in 2700 Mt of CO2, about 7% of global emissions. Steel production also yields 500 Mt of a by-product called slag, which contains 20 to 40% calcium. While slag is used in the production of cement and in road construction, a significant amount is still land filled. Simultaneous to this, 12-14 Mt of precipitated calcium carbonate (PCC or CaCO3) is produced annually from virgin materials around the world for use as fillers in paper, plastics and pharmaceutical products. The challenge of this project is to sequester waste CO2 from the steel industry, while at the same time using its slag waste to produce useful, revenue generating, PCC.

The Response

Järvinen’s group has developed the first Slag-to-PCC (Slag2PCC) pilot plant utilizing steel slag and CO2 from steel mill flue gases to produce highly valued precipitated calcium carbonate (PCC). The process begins by selectively dissolving calcium from the slag using ammonium chloride. CO2 is then bubbled through the solution and calcium carbonate is formed. If all the calcium in steel slag could be recovered this way, approximately 13 Mt of PCC could be produced annually, which meets its global demand. Additionally, 6 Mt of CO2 per year would be sequestered plus the 3 Mt CO2 annually produced by traditional PCC production. By creating a highly valuable product from a material that would have otherwise been landfilled, not only are the landfill related emissions eliminated, but so are those from the mining requirement of virgin limestone.

The Future

The pilot PCC plant was opened at the Otaniemi campus of Aalto University in January 2014. The method used in the pilot is based on the patent owned by the Aalto University Foundation, Åbo Akademi University and steel maker SSAB. The pilot plant is first of its kind and is currently actively used to study how this technology can effectively and most sustainably be brought to industrial scale. The team is looking for the best ways of achieving this as well as new partners to grow towards production on the commercial scale. The team is also working on the commercialization of the process and their objective is to have a bigger demonstration scale plant built next to a steel plant in Finland within the next 2-4 years.