Civil Engineering Reference
In-Depth Information
using renewable energy sources for the low-temperature calcination process
(~700 °C) and the significant CO
2
sequestration within porous blocks would
significantly reduce the emissions above.
A number of research and development projects and commercial initiatives,
which are directly or indirectly addressing more environmentally sustainable
production of reactive MgO, have been reported and are ongoing. Examples
include:
∑ development of a closed system low-temperature kiln (without releases
to the atmosphere) in which grinding and calcination of MgCO
3
occur
simultaneously; this system makes use of the heat generated in grinding
to assist with calcination, thereby giving up to 30% better efficiency
(Harrison and Cuff, 2006; Harrison, 2009);
∑ production of nesquehonite, through a low-energy low-maintenance
precipitation process, from seawater or brine, including waste brines
from desalination plants or produced water, through CO
2
sequestration
(Ferrini et al., 2009; Constantz et al., 2009; Mignardi et al., 2011; Hassan
forthcoming);
∑ production of reprocessed MgO from the hydroxide/carbonate slurry
carbon capture cycle technology used in the leaching of MgO from
low-grade MgCO
3
and dolomites (Fernandez et al., 1999; butt et al.,
1996; bearat et al., 2002);
∑ precipitation of brucite from magnesium silicates through hydrochloric
acid or sodium hydroxide digestion processes as intermediate stages
within the mineral carbonation process of magnesium silicates (IPCC,
2004; Nduagu, 2008; Zevenhoven and Fagerlund, 2011);
∑ precipitation of hydrated magnesium carbonates from magnesium silicates
through mineral carbonation at high pressures and temperatures (O'Connor
et al., 2005; Huijgen and Comans, 2005; Sipilä et al., 2008)
∑ precipitation of magnesium carbonates through mineral carbonation of
MgO-rich industrial waste streams such as slags (Stolaroff et al., 2005;
Teir et al., 2007; bobicki et al., 2012).
Current work at the University of Cambridge is investigating the second
initiative above, producing nesquehonite from a range of different source
brines and waste brines and assessing the performance of the resulting MgOs
produced from different reactions followed by different calcinations conditions
(Hassan, forthcoming; Jin, forthcoming). The produced nesquehonites with
those from different reactions, e.g. Wang et al. (2008) and Cheng and li
(2009) are also being compared. The work is also performing carbon footprint
calculations for these processes and comparing them with the processes from
a number of the other initiatives above (Hassan, forthcoming).
It is expected that some of the above developments will lead to commercial
production of MgO in much reduced or even carbon negative processes.
