Mineral Carbonation


Mineral carbonation

CARMAT process scheme

Carbonation is a process that uses carbon dioxide as a reactive material to create carbonates. This process can be used to convert the fine fraction that remains after steel slag treatment into artificial sand, aggregates or building elements.

The fine fraction from steel slags is carbonatised with exhaust carbon dioxide to produce aggregates.



This technology provides a valorization route for the fine fraction from steel slags. Various applications in construction industry are possible, such as road construction, tiles and pavers . The carbonation process can also be extended to other streams, e.g. non ferrous slags, bottom ash, soil, dredging sludge.



The aim of the CARMAT Project is to develop a pilot plant dedicated to mineral carbonation of steel slags.

Difference to BAU technology/approach:

In the business-as-usual scenario, steel slags are crushed and demetallized. These treatment processes lead to a coarse and fine fraction. Coarse fractions can be applied in road construction without further treatment. However, the fine fraction is difficult to reclaim and is typically sent to landfill.

crushing and demetallisation

coarse fraction

fine fraction


Input stream requirements:

Steel slags. The carbonation process can also be extended to other streams, e.g. non ferrous slags, bottom ash, soil, dredging sludge.

fine fraction of steel slag

non ferrous slag

bottom ash


Available quantity:

Approximately 3000 kton of steel slag are deposited yearly in Belgium.

Drivers for treating this stream:

It is difficult to find suitable applications for the fine fraction. It usually goes to landfill. 

Potential environmental risks related to this waste stream:

The fine fraction has limited environmental impact.     

Economic/technical barriers to collect this stream:

Various composition of slag are available, and there are disseminated over various locations. It is not easy to have constant stream of material (in terms of both composition, location, and amount).

Output stream:

Depending on the envisaged application, the carbonation process can be adjusted to artificial sand/aggregates and shaped bulk parts.

The carbonated material can be shaped into pavers.

Potential uses of this output stream:

The shaped parts include interlocking pavers and tiles. The aggregates can be used in road construction. They have sound and vibration damping properties and they improve thermal insultation.

tiles interlocking pavers

aggregates for road construction


Potential environmental risks/benefits related to this output stream:

Interlocking pavers: specific chemical agents have to be added to reduce the heavy metals leaching (Cr, Mo, Ni).

Economic barriers/drivers for market introduction of this output stream:

Suitable business model needed : compromise between (transport operating) cost / value of the final product.

Technical barriers for market introduction of this output stream:

Technical validation of the final characteristics of the material (for each field of application).

Legislative barriers for market introduction of this output stream:

Official approval by the region needed for the use of waste (the slag) in each field of application, based on a detailed technical datasheet of the final product.

Pilot description:

The Carmat process consists of 4 main steps: (1) slag pretreatment, (2) fine fraction hydration, (3) shaping of the slag into artificial sand/aggregates (using a pelletisation table or a granulator) and bulk parts (using a hydraulic press), (4) carbonation using synthetic gas containing different CO2 amounts and pressures. Depending on the product, a different curing process is used.

The CARMAT carbonation process consists of 4 main steps.



The pilot location is situated near APERAM (stainless steel producer) in Farciennes (Wallonia, Belgium). The pilot is still under construction and is planned to start up in the beginning of 2014. The first products are expected Mid 2014.

Pilot location in Farciennes (Wallonia)


no detailed information available.

Scale of the equipment:

Large pilot scale

Main technological barriers for market introduction:

Leaching of heavy metals can be a problem in carbonation products from low pressure processes, such as pavers and aggregates. Additives need to be added to limit leaching. High pressure products, such as tiles, show less leaching.

Main economic barriers/drivers for market introduction:

Carbonation of the fine fraction from steel slags can produce a range of various products for different applications. The process can also be extended to other mineral waste streams.

Research steps:

The concept is proven at pilot scale (thousands of pieces produced in industrial conditions).

Economic steps:

The business model is suitable in a limited area around the plant (to limit transport cost, and to be supplied in CO2).

Legislative steps:

Regional authorities need to approve the process. A first approval is under examination by the Walloon region, Belgium.


Pilot start up: beginning of 2014.
Expected time to market: no information available

Contact details:
Organisation: CTP

Department: Research Department

Leading projet manager: Hervé Bréquel

Leading researcher: Philippe Descamps

Phone number: +32 69 88 42 51

E-mail: herve.brequel@ctp.be



Presentation: CARMAT PROJECT “Development of a pilot plant dedicated to mineral carbonation of steel slags”, Descamps, RENEW Technology Foresight Conference 24/04/2013