Neutralization of Red Mud Using CO2 Sequestration and their Utilizations

By: Sahu, Ramesh ChandraContributor(s): Patel, R K [Supervisor] | Ray, B C [Supervisor] | Department of ChemistryMaterial type: TextTextLanguage: English Publisher: 2011Description: 141 pSubject(s): Chemistry | Physical ChemistryOnline resources: Click here to access online Dissertation note: Thesis (Ph.D)- National Institute of Technology, Rourkela Summary: Red mud is a highly caustic wast e product of alumina industry. More than 70 million tons of red mud has been genera ted worldwide per a nnum. It pollutes the industry area due to its alkaline nature. Its storage and maintenance is costly and causes great problem to the industries. Moreover, CO 2 is a global warming gas generated from fossil fuel power plant. Each 500 MW coal power plant emits about 3 million tons of CO 2 per year which may cause serious disr uption to the global climate change. A laboratory study was conducted to i nvestigate the ability of neutralization of red mud (RM) using carbon dioxide gas sequest ration cycle at ambient conditions. The neutralized red mud (NRM) was characte rized by XRD, SEM, EDX, FT-IR, CHNS, TG-DSC and auto titration me thod. X-ray diffraction pattern of NRM was revealed that the intensity of gibbsite wa s increased prominently and formed ilmenite due to dissolution of minerals. EDX analysis was sh owed that the %(w/w) of Na, C, O, Si were higher in the carbonated filtrate as compared to the RM and NRM. The permanently sequestered CO 2 %(w/w) per 10 g of red mud were ~26.33, ~58.01, ~55.37, and ~54.42 in NRM and first, second, third cycles of carbonated filtrate, respectively. Amount of CO 2 removed for cycle 1, 2, 3 of carbonated filtrate and NRM were 3.54, 2.28, 0.63, 0.57 g CO 2 /100 g of red mud, respectively, as determined by CHNS analyzer at 1150°C. So, total calculated CO 2 removal was 7.02 g/100 g of red mud. The pH of red mud was decreased from ~11.8 to ~8.45 and alkalinity was decreased from ~10,789 to ~178 mg/L. The ac id neutralizing capacity of NRM was ~0.23 mol H + /kg of red mud. The specific advantages of these cyclic pr ocesses are that, large amount of CO 2 can be captured as compared to single step. Subsequently, this study has shown the effective neutralization of red mud. Furthermore, the fine iron oxide was extracted from CO 2 –NRM by using biodegradable surfactant and heat treatment. In fact, it is an enrichment process of Fe in red mud. The micro morphologi cal studies of recovered fine iron oxide showed 71.71% of Fe. Therefore, larger amount of fine iron oxide can be utilized in the iron industry. vi Furthermore, a laboratory study was conducted to investigate the ability of activated CO 2 -neutralized red mud (ANRM) for the removal of arsenate from the aqueous solutions. The mechanisms involved in adsorption of ar senate ions on ANRM were characterized by using XRD, FT-IR, UV–vis, SEM/EDX, and chemical methods. The percentage removal was found to incr ease gradually with decrease of pH and maximum removal was achieved at pH ~4. Adso rption kinetic studies revealed that the adsorption process followed pseudo-second-or der kinetics and equilibrates within 24 h. This study has shown that ANRM is highly effective new adsorbent for arsenate removal. Therefore, it is a low-co st environment-friendly material. Therefore, neutralization of red mud using CO 2 sequestration is a nature-bio- inspired absorption method. Today’s most urgent need for CO 2 emission reductions can be possible by using low-cost CO 2 sequestration technology.
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Thesis (Ph.D)- National Institute of Technology, Rourkela

Red mud is a highly caustic wast
e product of alumina industry. More than 70
million tons of red mud has been genera
ted worldwide per a
nnum. It pollutes the
industry area due to its alkaline nature. Its
storage and maintenance is costly and causes
great problem to the industries. Moreover, CO
2
is a global warming gas generated from
fossil fuel power plant. Each 500 MW coal
power plant emits about 3 million tons of
CO
2
per year which may cause serious disr
uption to the global climate change.
A laboratory study was conducted to i
nvestigate the ability of neutralization of red
mud (RM) using carbon dioxide gas sequest
ration cycle at ambient conditions. The
neutralized red mud (NRM) was characte
rized by XRD, SEM, EDX, FT-IR, CHNS,
TG-DSC and auto titration me
thod. X-ray diffraction pattern
of NRM was revealed that
the intensity of gibbsite wa
s increased prominently and formed ilmenite due to
dissolution of minerals. EDX analysis was sh
owed that the %(w/w) of Na, C, O, Si
were higher in the carbonated filtrate
as compared to the RM and NRM. The
permanently sequestered CO
2
%(w/w) per 10 g of red mud were ~26.33, ~58.01,
~55.37, and ~54.42 in NRM and first, second,
third cycles of carbonated filtrate,
respectively. Amount of CO
2
removed for cycle 1, 2, 3 of
carbonated filtrate and NRM
were 3.54, 2.28, 0.63, 0.57
g
CO
2
/100 g of red mud, respectively, as determined by
CHNS analyzer at 1150°C. So, total calculated CO
2
removal was 7.02 g/100 g of red
mud. The pH of red mud was decreased
from ~11.8 to ~8.45 and alkalinity was
decreased from ~10,789 to ~178 mg/L. The ac
id neutralizing capacity of NRM was
~0.23 mol H
+
/kg of red mud. The specific advantages
of these cyclic pr
ocesses are that,
large amount of CO
2
can be captured as compared to single step. Subsequently, this
study has shown the effective
neutralization of red mud.
Furthermore, the fine iron oxide was extracted from CO
2
–NRM by using
biodegradable surfactant and heat treatment. In
fact, it is an enrichment process of Fe in
red mud. The micro morphologi
cal studies of recovered fine iron oxide showed 71.71%
of Fe. Therefore, larger amount of fine iron
oxide can be utilized
in the iron industry.
vi
Furthermore, a laboratory study
was conducted to investigate the ability of
activated CO
2
-neutralized red mud (ANRM) for the removal of arsenate from the
aqueous solutions. The mechanisms involved
in adsorption of ar
senate ions on ANRM
were characterized by using XRD, FT-IR,
UV–vis, SEM/EDX, and chemical methods.
The percentage removal was found to incr
ease gradually with decrease of pH and
maximum removal was achieved at pH ~4. Adso
rption kinetic studies revealed that the
adsorption process followed pseudo-second-or
der kinetics and equilibrates within 24
h.
This study has shown that ANRM is highly
effective new adsorbent for arsenate
removal. Therefore, it is a low-co
st environment-friendly material.
Therefore, neutralization of red mud using CO
2
sequestration is a nature-bio-
inspired absorption method. Today’s most urgent need for CO
2
emission reductions can
be possible by using low-cost CO
2
sequestration technology.

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