Civil Engineering Reference
In-Depth Information
of unburned and partially burned raw materials present in the combustion
gases of the cement kiln, are considered as a potential hazardous waste due
to their caustic and irritative nature. as mentioned in table 1.2, the amount
of CKD generated per kg of clinker produced equals about 15-20% (by
mass) (Van Oss and Padovani, 2003). Nowadays, both the environmental
and health risks associated with CKD can be reduced significantly by means
of mineral carbonation. Sequestering carbon in CKD stabilizes the waste.
the reduction in pH reduces health risks and the generation of harmful
leachate (Huntzinger and eatmon, 2009). In addition, the utilization of
CKD for sequestration appears to have an advantage on the global scale,
since about 7% of the carbon emissions can be captured this way. On the
local scale, attention should be paid to the chromium content of cement. For
instance, the sale of cement containing more than 2 ppm of soluble Cr(VI)
when hydrated is prohibited by european Directive 2003/53/eC (european
Union, 2003). Hexavalent chromium or Cr(VI) is not stable. When dissolved,
Cr(VI) can penetrate the unprotected skin and be transformed into to Cr(III)
which combines with epidermal proteins to form the allergen to which some
people are sensitive. the Cr(VI) content can originate from (i) raw materials
and fuel entering the system, (ii) magnesia-chrome refractory blocks, (iii)
wear metal from crushers containing chromium alloys and (iv) additions of
gypsum, pozzolans, ground granulated bFS, mineral components, CKD and
set regulators (Hills and Johansen, 2007).
Finally a number of additional pollutants such as polychlorinated dibenzo-
p
-
dioxins, dibenzofurans and heavy metals can be potentially released (abad et
al., 2004; Schumacher
et al., 2003). recent studies that evaluate the potential
health risk for populations living in the neighbourhood of a cement plant show
that a seasonal pattern were observed with higher values recorded during the
colder periods. However, the carcinogenic and non-carcinogenic risks derived
from human exposure to metals and polychlorinated dibenzodioxins/Furans
(PCDD/Fs) were within the ranges considered acceptable by international
regulatory organisms (rovira
et al., 2011). Furthermore, the intensive use
of alternative fuels such as sewage sludge or municipal solid waste which
would otherwise be disposed somehow/somewhere or refuse-derived fuels
allow a significant decrease in PCDD/Fs levels as well as in some metal
concentrations (rovira
et al., 2010).
1.4 Future trends
1.4.1 Alternative materials
Alternative fuels
the use of alternative fuels and raw materials (aFr) for cement and clinker
production is certainly of high importance for the cement manufacturer but
