Discussion on Achieving Carbon Emission Reduction by Using Red
Mud to Absorb CO2
YANG Chao, WANG Jie
School of Resources and Environment Engineering, Shandong University of Technology, China,
255049
[email protected]
Abstract: This paper studies the hydration reaction mechanism of industrial waste (red mud) from
alumina plant adsorbing CO2, and by measuring changes in red mud carbon content as well as
microcosmic analysis of mineral constituents in red mud reveals that red mud possesses strong
adsorption capacity for CO2 in its dry curing process. At the same time, this paper also puts forward the
industrial thinking of reducing carbon emission by making use of red mud piling. Adsorbing CO2 by red
mud not only reduces CO2 emission, but also helps the safety storage of red mud, so as to realize control
of waste by waste and to achieve a double win of economic benefit and social benefit.
Keywords: characteristics of red mud, red mud adsorption, reduction of carbon emission, X diffraction
scanning analysis, energy spectrum analysis, control of waste by waste
1.
Foreword
Global warming has become the focus of international attention and it seriously affects the sustainable
development of mankind. In addition to natural causes, climate change is also closely related with
human activities, especially the CO2 emission during the use of fossil fuel[1]. According to statistics,
every year CO2 emission from fuel burning, cement plants, oil refineries, and the process of
fermentation exceeds 240 × 108t, of which 150 × 108t absorbed by plants, annual net increase of 90 ×
108t [2]. December 2009, in Copenhagen, the Chinese Government promised that "by 2020, unit GDP
carbon emission will decrease by 40% -45% compared to that of 2005." Therefore, in order to achieve
this challenging goal, continuous efforts of our various enterprises, academics and technology workers is
needed to reduce carbon emission through technological innovation, system innovation, industrial
restructuring, new energy exploitation and so on. The final goal is to achieve a low carbon economy to
realize a double win economic development pattern which balances economic and social development
and ecological environment protection.
This paper discusses the idea of using industrial waste from alumina plant - red mud to adsorb CO2 in
order to reduce carbon emission from alumina plant and surrounding enterprises, which not only reduces
carbon emission, but also is conducive to the safety storage of red mud, and moreover, can provide
opportunities for the comprehensive reuse of red mud. The ultimate purpose is to realize control of
waste by waste and to achieve a double win of economic benefit and social benefit.
2.
Hydration Reaction Mechanism of Red Mud Absorbing CO2
CO2 is usually a kind of colorless, non-toxic, and slightly pungent little sour gas which can be dissolved
in water and produces acidic aqueous solution. Red mud is the residue after leaching of alumina from
bauxite by use of alkali in alumina plants. PH value of red mud is very high. The PH value of the
leaching solution is from 12.1 to 13.0, while red mud PH value is from 10.29 to 1.13 [3]. Therefore, we
can use the alkaline material of red mud to absorb the acid gas CO2. As the red mud is generated under
alkaline conditions, there will be a large number of OH- ions, and the CaO in red mud will also produce
OH- ions in alkaline solution. The red mud will absorb atmospheric CO2 to produce HCO3- in alkaline
environment, and HCO3- will continue to produce CO32- ions under alkaline conditions. Eventually,
products like Na2CO3 , CaCO3 will be produced. Below is the main chemical reaction mechanism:
104
CaO + H2O=Ca(OH)2
Ca2++ 2OHCa(OH)2
NaOH
Na++ OHHCO3CO2 + OH
CO32-+ H2O
HCO3- + OH+
22Na + CO3
Na2CO3
CaCO3
Ca2+ + CO32In addition, red mud has relatively stable chemical constituent, very fine dispersion, high surface area
and good adsorption properties, which is conducive to better absorption of CO2. In order to test the
existence of the above reaction mechanism, carbon absorption capacity of red mud, X diffraction scan
analysis and energy spectrum analysis of mineral constituent in red mud are separately conducted by the
author.
3.
Test of Red Mud Absorbing CO2
3.1 Chemical constituent of red mud
The chemical constituent of red mud mainly depends on the constituent of bauxite, alumina production
methods, the additive material constituent used in production processes and the ingredients of
compounds generated in production processes. The raw material for test is Bayer red mud from
Shandong Branch of China Alumina. Its chemical constituents are shown in Table 1.
Constituent
SiO2
Fe2O3
Table1
Al2O3
Content/%
23.68
27.59
20.01
Dominant constituents of red mud/%
CaO MgO
TiO2
K2O
Na2O
2.66
0.10
1.65
12.18
0.37
3.2 Test for carbon absorption capacity of red mud
Carbon absorption test uses deionized water "wet" conditions, because it is closer to red mud watering─
curing conditions. The initial carbon content of red mud under test and the carbon content of products
after different absorption time are shown in Table 2.
Table2 Carbon content in air drying red mud after different adsorption time
C absorption time
C content /%
Initial
1.31
4d
2.73
4.5d
3.53
6d
3.77
8d
4.70
12d
5.16
As the "initial red mud" used for test actually lasts more than 10 days after it is discharged from the
aluminum plant in the wetting state, it could be assumed that the 1.31% carbon content is mainly
absorbed from environment. The above test result shows that over time the carbon content in red mud is
gradually increasing, which indicates that red mud is continually absorbing CO2 from surrounding
environment.
3.3 X diffraction scanning analysis of red mud under different time
To further understand the mineral constituents of red mud before and after absorption of carbon, X
diffraction scanning analysis is conducted separately for fresh red mud and red mud placed for 28 days.
Sample is fresh red mud extracted from the filter of Shandong Aluminum Company, water content about
30%. The red mud is placed for one week and then made into powder. X diffraction scanning analysis
result is shown in Figure 1.
105
d=1.3820
d=1.3724
d=1.6936
d=1.8162
d=1.5914
d=1.5417
d=1.5063
d=1.4976
d=1.4827
d=1.4536
50
d=2.1233
d=2.6964
d=2.6044
d=2.5127
d=2.4493
d=2.4030
100
d=9.9817
Intensity(Counts)
150
d=4.8405
d=4.1679
d=3.6748
d=3.3421
[BAIER.MDI]
d=6.3873
200
0
10
20
30
40
50
60
70
80
90
2-Theta(°
Fig.1 X diffraction of Bayer Red Mud
d=1.1836
d=1.3730
d=1.4496
d=1.8399
d=1.7635
d=1.6936
d=2.1247
d=1.9976
50
d=2.6965
d=2.5128
d=2.4216
d=3.6809
d=3.3422
d=3.0359
d=6.3866
100
d=9.9794
Intensity(Counts)
150
d=4.8441
[28-BAI.MDI]
d=4.1667
200
0
10
20
30
40
50
60
70
80
90
2-Theta(°
Fig.2 X diffraction of Completely Dried Bayer Red Mud
The result of Figure 1 shows that the dominant mineral components of the Bayer Red Mud are as below:
high water kaolin (d = 9.98), Gibbsite (d = 4.84, d = 3.34, d = 2.44, d = 1.81), sodium Silicon Slag (d =
6.387, d = 3.67), goethite (d = 4.16, d = 2.60), iron oxide (d = 2.696, d = 2.51), sodium aluminate (d =
2.12) and so on.
The sample is placed for 28 days and X-diffraction scanning analysis is re-conducted to study whether
the mineral constituents are changed, especially to examine whether there is carbonation reaction and
whether new carbon materials are generated. X diffraction scanning analysis result is shown in Figure 2.
The data of Figure 2 shows that X diffraction pattern of completely dried Bayer red mud is very clear,
which indicates relatively full crystallization of minerals. Major minerals such as kaolinite, sodium
silicate slime, gibbsite, goethite, hematite still exist, but a new carbon material (d = 3.03, d = 1.997)
appears. Investigation indicates that this mineral is calcite CaCO3, which shows that carbonation
reaction of red mud has occurred in the air environment.
106
3.4 Energy spectrum analysis of the white precipitate material attached to the surface of dried red
mud
During the storage process of red mud, a white precipitate material is formed on the surface of red mud
because of evaporation and drying. Analysis indicates [4] that this is formed by the water-soluble
substances after evaporation ─drying which leaked through micro hole along with the water solution
during red mud storage process. Energy spectrum analysis is conducted for the white precipitate material
on the surface of red mud which has been placed for 20 days. Its dominant constituents are shown in
Figure 3. Energy spectrum analysis result proves the formation of Na2CO3. Na2CO3 further illustrates
that red mud is continually absorbing CO2 from the surrounding environment and carbonation reaction
is occurring during its storage process.
Fig.3 Energy spectrum of white material On red mud heap surface
4.
Discussion on Industrial Application
The above analysis and test results show that red mud has a certain adsorption capacity for CO2, and red
mud can be deposited to adsorb CO2 from alumina plant and the surrounding environment, thus
reducing CO2 emission and achieving low carbon economy purpose. The author puts forward an
industrial thinking on using red mud to reduce carbon emission. The general idea is described by
following steps. First, set CO2 collection device for the alumina plant, power plants, lime kilns and other
sources of CO2 emission. Part of the collected CO2 is purified to be used for beer and other carbonated
beverages, gas welding, refrigeration of food and refrigerants, fertilizer plants and other industry
products for sale. The other part of CO2 is discharged into the red mud slurry to be adsorbed by red mud.
The dried red mud after the pressure filtration process can be stored. As the CO2 in the red mud
generates CaCO3 (test shows the storage strength of dried red mud after pressure filtration process
increases 0.73Mpa than the original strength of the direct storage), the dried red mud storage strength
will be increased. Finally, the dried red mud can also be utilized[5-9], such as: extraction of valuable
107
metals by using red mud, production of cement and bricks by using red mud, paving, the production of
desulfurization and other applications. Specific implementation is shown in Figure 4.
Figure 4 Industrial application plan
5.
Conclusion
According to theoretical analysis and laboratory tests, we obtain the following conclusions: (1) Red mud
can effectively absorb carbon dioxide, and reduction of carbon dioxide emission by using red mud
adsorption to achieve control of waste by waste is feasible. (2) The author puts forward an industrial
application thinking for using red mud to absorb carbon dioxide and comprehensive utilization of red
mud. (3) The best conditions for the use of red mud in absorbing carbon dioxide and the optimum plan
for industrial applications need further studies in order to optimize the carbon dioxide adsorption
capacity and economic indicators.
：
Author in brief or Acknowledgment
YANG Chao(1962- ) ,Male , Master in Mineral Processing Engineering of Shandong University of
Technology , research direction for the comprehensive utilization of mineral resources.
E-mail: [email protected]
mailing address: School of Resources and Environment Engineering ,Shandong University of
Technology, Zibo 255049, Shandong.
mobile phone:13012713546
References
[1]. LIU Zhan fu .Development of low-carbon economy is the best choice to achieve energy saving. Nei
Meng Gu statistics, 2009(4): 9-10(in Chinese)
[2]. LI Zhong lai .Preparation of carbon dioxide and chemical applications. Small N design, 2005, 26
(1): 11-17(in Chinese).
[3]. LI Pei, CHEN Su ying. Comprehensive utilization of red mud and security stockpiling. Chemical
industry Technology & Development, 2005, 26(1): 11-17(in Chinese).
[4]. WANG Ping sheng. Characteristics and Rapid Hardening Mechinsm of Red Mud from Alumina
production with Sintering Process. Nonferrous Metals, 2005,57(3):115-118(in Chinese)
108
[5]. LAI Lan ping ZHOU Li lei HAN Lei etc. The Red Mud Reclaims Synthetically and Makes use of
Current Situation and Progress. Sichuan Nonferrous Metals, 2008,1:43-48(in Chinese)
[6]. M aneesh S, S N Upadhayay. Preparation of iron rich cements using red mud [J]. Cement and
Concrete Re-search, 1997, (7):1037 – 1046.
[7]. REN Dong mei MAO Ya nan. Comprehensive utilization of red mud. Nonferrous Metals Industry,
2002, (5):57-58. (in Chinese)
[8]. PAN Zhi hua FANG Yong hao LV Yi nong. Alkali - slag - Red Mud Cement. Cement Engineering,
2000, (1):53-57. (in Chinese)
[9]. Vincenzo M S,Renzo C.Bauxite’red mud’in the ceramic industry. Partl: thermal behaviour [J].
Journal of the Eu-ropean Ceramic Society, 2000, (20) :235 – 244
109