International Slag Valorisation SymposiumLeuven6-7/4/2009 - Third ...

low costs and possibly higher reactivity, relative to mineral ores. Although their total
CO 2 sequestration capacity is limited relative to total anthropogenic CO 2 emissions, the
use of residues as feedstock can contribute to make the first mineral CO 2 sequestration
(demonstration) plants economically feasible. 2)
In addition to its possible contribution to the reduction of CO 2 emissions, carbonation of
alkaline solid residues has been demonstrated to have potentially beneficial effects on
the leaching of constituents from these materials to the environment. For example,
reduced leaching of potentially harmful constituents has been reported for residues such
as municipal solid waste incineration (MSWI) bottom ash, fly ash from coal fired power
plants, air pollution control residues, and steel slag (see Huijgen & Comans 3) , and
references therein). In such studies, a number of possible carbonation mechanisms has
been distinguished that affect leaching, such as (1) precipitation of carbonates, (2) pHneutralisation,
(3) formation of minerals other than carbonates, (4) co-precipitation and
(5) sorption on freshly precipitated surfaces. Leaching experiments combined with
geochemical modelling, and mineralogical characterisation (e.g. by X-ray diffraction
and electron microscopic analyses) have been shown to be valuable tools to study the
leaching properties and underlying mechanisms of these residues.
This paper reviews a number of recent studies in which the authors have focused on the
mineral carbonation mechanisms and potential of steel slag, as well as on the leaching
properties of freshly produced steel slag and steel slag at various degrees of carbonation.
By combining controlled carbonation and leaching experiments, geochemical modelling
and mineralogical analyses, these studied are aimed to provide a mechanistic insight
into (1) the mineral CO2 sequestration potential of steel slag and (2) the effects of the
carbonation processes on the leaching properties of steel slag, including pH, redox
potential (Eh), major and trace elements. As such, these studies are intended to
contribute to the development of a treatment process that can facilitate the beneficial
utilisation of steel slag.
Materials and Methods
Steel slag samples
Two types of converter slags have been selected for carbonation experiments at
atmospheric pressure (see below), each derived from a single heat, representing the
maximum difference in primary mineralogy: K1 slag, which consists mainly of C2S
(2CaO.(Si,P,V)O 4), C 2F (2CaO.(Fe,Ti,Al,V) 2O 3) and magnesio-wuestite (MW;
(Fe,Mg,Mn)O), and K3 slag, which contains C3S (Ca3SiO5), C2S, C2F, MW and freelime
(CaO). 1) The C3S is a high-temperature phase which decomposes to C2S + lime
during cooling, but leaves a characteristic intergrowth texture, possibly with a different
1 st International Slag Valorisation Symposium│Leuven│6-7/4/2009
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