Abstract
Mineral carbonation involves the capture and storage of carbon dioxide in carbonate minerals. Mineral carbonation presents opportunities for the recycling of steel slags and other alkaline residues that are currently landfilled. The Carbstone process was initially developed to transform non-hydraulic steel slags (stainless steel slag and basic oxygen furnace slags) in high quality construction materials. The process makes use of accelerated mineral carbonation by treating different types of steel slags with CO2 at elevated pressure (up to 2 MPa) and temperatures (20 to 140°C). For stainless steel slags raising the temperature from 20 to 140°C had a positive effect on the CO2 uptake, strength development and the environmental properties (i.e. leaching of Cr and Mo) of the carbonated slag compacts. For BOF slags raising the temperature was not beneficial for the carbonation process. Elevated CO2 pressure and CO2 concentration of the feed gas had a positive effect on the CO2 uptake and strength development for both types of steel slags. In addition also the compaction force had a positive effect on the strength development. The carbonates that are produced in-situ during the carbonation reaction act as a binder, cementing the slag particles together. The carbonated compacts (Carbstones) have technical properties that are equivalent to conventional concrete products. An additional advantage is that the carbonated materials sequester 100 to 150 g CO2/kg slag. The technology was developed on lab scale by optimisation of process parameters with regard to compressive strength development, CO2 uptake and environmental properties of the carbonated construction materials. The Carbstone technology was validated using (semi-)industrial equipment and process conditions.
Highlights
An estimated 170–250 Mt of steel slags were generated worldwide in 2014 (U.S Geological Survey, 2015)
The calculated maximum theoretical CO2 sequestration capacity based on the total Ca and Mg concentrations of the slags is ~460 g CO2/kg for the steel slags and 360 g CO2/kg for the basic oxygen furnace (BOF) steel slags
A carbonation process has been developed for the production of construction materials using slags and CO2 as raw materials without the need for any additional binder
Summary
An estimated 170–250 Mt of steel slags were generated worldwide in 2014 (U.S Geological Survey, 2015) The recycling of these slags provides a number of environmental benefits, including the preservation of natural resources, the recovery of valuable metals, and a reduction in the volume of solid waste. Accelerated Carbonation of Steel Slag Compacts in asphalt and waterway embankment material The use of these slag aggregates is, often hampered by their volumetric instability. In Belgium, about 0.5 Mt of stainless steel (SS) slags are processed each year to recover the enclosed metal (Van Mechelen et al, 2011). These slags contain on average ~5% of SS. Solutions to reduce the volumetric instability of the slag aggregates and improve the environmental quality of the fine grained powder slags are necessary
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