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Long-term brine impacted fly ash. Part 1: chemical and mineralogical composition of the ash residues
Fatoba, O.O.; Petrik, L.F.; Akinyeye, R.O.; Gitari, W.N. & Iwuoha, E.I.
Abstract
The co-disposal of brine and fly ash has become
a common practice in South African power utilities. This
study focuses on the effects of the long-term fly ash–brine
interaction on the chemical and mineralogical composition
of fly ash and the quality of the brine solution after the
interaction test. Long-term fly ash–brine interaction test was
carried out by contacting fly ash and brine for a period of
time varying from 1 week to 12 months under static and
closed conditions. The results of the chemical composition
of the brine decanted after the interaction test revealed that
species such as B, Co, Cu, Pb, Mg, Mn, Zn, Cl and SO4 were
removed to a certain extent from brine during the fly ash–
brine interaction test while Al, Si, Ca, K, Ba, Sr, Fe, As, Cr
and Mo were significantly leached out of the fly ash into the
brine. The X-ray fluorescence results showed that the concentrations
of Na, Mg, Cl and SO4 (as S) in the ash residues
were somewhat higher than their concentrations in the fresh
fly ash. Secondary mineral phases such as wairakite, charlesite,
spinel and celestine which were missing in the X-ray
diffraction analysis of the fresh fly ash were identified in the
ash residues. This study shows that some species contained
in the brine solution could be captured by the fly ash
through secondary mineralization during co-disposal in a
closed static environment, while many other elements could
be significantly leached into the brine.
Keywords
Fly ash; Brine; Chemical and mineralogical composition; Co-disposal; Long-term interaction; Major and minor elements
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