Advanced Materials Research Vols 807-809 (2013) pp 1262-1265
© (2013) Trans Tech Publications, Switzerland
doi:10.4028/www.scientific.net/AMR.807-809.1262
Online: 2013-09-10
Investigation on the extraction of aluminum and
iron from fly ash by sodium carbonate fusion method
Hongjing Han1, a, Yanguang Chen1, b, Jia Lu1, c,
Dandan Yuan1, d, Jun Song1, e, Ying Chen1, f
1
Provincial Key Laboratory of oil & Gas Chemical Technology, College of Chemistry & Chemical
Engineering, Northeast Petroleum University, Daqing, P.R.China
a
hongjing_han@163.com, bygchen79310@126.com, clu-jia2008@163.com,
d
yuandandan111@163.com, emsongjun@163.com, fchenying648617@163.com
Keywords: Aluminum extraction, fly ash, sodium carbonate fusion method
Abstract: In recent years, utilization of fly ash has gained much attention in public and industry,
which will help reduce the environmental burden and enhance economic benefit. In the utilizations
of fly ash, the most high value-added applications is extraction of metal elements from fly ash. In
this paper, the aluminum and iron extraction was investigated by orthogonal experiments. The
results show that the optimum extraction condition was reaction temperature 800 oC, reaction time 3
h, the mass ratio of fly ash to Na2CO3 was 1:1.5.
Introduction
Fly ash is a type of solid waste from thermal power plants, steel mills, etc. It is in abundance in the
world. The production of fly ash is about 3.0×109 t at present. With the sustained and rapid
development of China's economy, the energy demand increases. A large amount of fly ash emissions
not only occupied land, but also polluted water and atmosphere resources, moreover, it is harmful to
human health. Fly ash contains many elements can be recycled [1-3], such as silicon, aluminum and
iron, which will help reduce the environmental burden and enhance economic benefit. In the
recycling of aluminum, iron, silicon from fly ash, the key problem is how to effectively break the
Al-Si bond. the aluminum, silicon and other elements can be made full use of [4, 5]. In this paper, a
new method of extracting aluminum and iron was discussed. The calcination reaction between fly
ash and Na2CO3 in the high temperature was investigated. The calcined samples were leached by
acid, the concentration of aluminum ions and iron ions in the leaching solution were analyzed by
titration and spectrophotography, respectively.
Experimental
Experimental materials
The main raw material, coal fly ash samples were collected from Heilongjiang Province of China.
Table 1 presents the composition analysis of fly ash. The raw fly ash samples were first screened to
the size of 150-200 mesh. The unburned carbon (4.5wt%) presented in fly ash were removed by
muffle furnace at 800℃ for 2h. The calcined fly ash samples were treated with distilled water to
removal soluble substances. The slurry was dried at 80℃.
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Advanced Materials Research Vols. 807-809
1263
Table 1 Composition of fly ash
Composition
SiO2
Al2O3
Fe2O3
TiO2
CaO
MgO
K2O
Na2O
Content/wt%
51.44
32.4
6.76
1.58
3.53
1.62
0.80
1.87
Sintered test and leaching test
Take a certain amount of fly ash with addition of Na2CO3 into muffle furnace at different
temperatures ranging from 760-840℃ for 6h, and then cool down to room temperature and obtain
the sample for leaching step.
Sintered product was grinded and put into a flask with a stirring device. The hydrochloric acid
was added to flask, then it was heated by water bath to reaction with continuous stirring at 250 rpm.
In order to prevent hydrochloric acid from evaporation, the flask connected with a condensation
device. After fully reacted, the upper liquid and solid was separated. The concentration of aluminum
ions and iron ions of leaching solution were calculated by the following equation.
ε Al =
3+
mAl
× 100%
ϕ1m flyash
(1)
ε Fe =
mFe
× 100%
ϕ 2 m flyash
(2)
3+
Where, εFe3+, εAl3+ represented the leaching rates of the concentration of aluminum ions and iron
ions. φ1, φ2 represented mass ratio of aluminum and iron elements in fly ash. Process flow diagram
experiment are shown as follows.
Results and discussion
XRD characterization
Figure 1 shows that the main crystalline phase was mullite cordierite by X ray diffraction analysis.
The samples contained both amorphous (mainly SiO2, Al2O3) and crystalline components (mainly
quartz and mullite cordierite).
Fig.1
X ray diffraction pattern of fly ash sample
Orthogonal experiment
To obtain the optimal process condition parameters, orthogonal experiment was designed and
investigated. The sintering time ,reaction temperature, and the mass ratio of fly ash to Na2CO3 as
influencing factors were investigated. The leaching conditions: 80℃, 3mol/L HCl, leaching time
30min and the ratio of solid to liquid 1g:10mL. The leaching of aluminum and iron rate in fly ash
were analyzed as the main indexes of orthogonal experiments, the results was shown in Table 2.
1264
X
Y
Environmental Protection and Resources Exploitation
SN
T/oC
1
2
3
4
5
6
7
8
9
760
760
760
800
800
800
840
840
840
31.99
42.21
51.11
19.11
55.51
80.35
84.85
29.34
K1
K2
K3
R1
K1
K2
K3
R2
Table 2 The results of orthogonal experiments
X (Al3+ leaching rate Y (Fe3+ leaching rate
t/h
mfly ash/mNa2CO3
/%)
/%)
25.40
1
1:1
43.16
24.99
2
1:1.5
57.26
46.70
3
1:2
66.10
40.09
1
1:1.5
57.77
41.38
2
1:2
92.56
54.43
3
1:1
90.72
45.60
1
1:2
75.70
45.15
2
1:1
86.56
52.19
3
1:1.5
92.28
41.66
37.40
39.09
40.27
44.56
47.65
5.47
10.25
58.88
73.48
78.79
69.10
83.03
78.12
24.16
9.018
can determine the impact of various factors on the leaching effect of aluminum and iron ions
after the activation of fly ash: Sintering temperature> reaction time > the ratio of fly ash to
Na2CO3. It can be seen that the factors on the leaching of aluminum and iron ions of fly ash
activated by Na2CO3 are different. the optimal scheme is A3B3C3, however, this scheme is not in our
orthogonal experiments. A proof test was done, the condition is as following: sintering time 3h, the
sintering temperature 840oC, the ratio fly ash to Na2CO3 1:2 and acid concentration 3mol/L. The
leaching ratio of aluminum ion and iron ion was 52.78% and 95.55%. It can be seen from the above
table, the leaching ratio of the proof test was similar with the result of the ninth orthogonal test. In
consideration with saving raw materials, the scheme A3B3C2 was selected.
Extraction without addition of Na2CO3
Fly ash samples without addition of Na2CO3 was also leached by acid directly. Other processing
conditions are the same, the results was shown in Fig. 2. The leaching ratio of aluminum ion and
iron ion were only 14.02% and 42.3%, far lower than 52.78% and 95.55% in Na2CO3 fusion
method. After activation of fly ash under high temperatures with sodium carbonate, Si-Al bond in
the fly ash was broken, the aluminum ion and iron ion leaching ratio increased significantly.
Advanced Materials Research Vols. 807-809
1265
50
aluminum ion
iron ion
Removal rate/%
40
30
20
10
0.5
1.0
1.5
2.0
2.5
Time/h
Fig.2 Results of extraction of aluminum and iron without addition of Na2CO3
Conclusions
The aluminum and iron was extracted from fly ash by using Na2CO3 fusion method, the orthogonal
experiment was designed and investigated, the follow conclusion can be obtained:
(1) Fly ash was activated by Na2CO3 fusion method. The order of the influencing factors is:
sintering temperature> reaction time > the ratio of fly ash to Na2CO3.
(2) The optimum processing parameters are sintering temperature 800oC, reaction time 3 h, the
mass ratio of fly ash to Na2CO3 was 1:1.5 and hydrochloric acid concentration 3mol/L. Under
this condition, the ratio of aluminum and iron ion are 52.78% and 95.55%, respectively.
(3) Fly ash without the activated by Na2CO3, the ratio of aluminum ion and iron ion in leaching test
is 14.02% and 42.3%, lower than that in Na2CO3 fusion method.
Acknowledgements
This work was financially supported by National Natural Science Foundation of China
(No.51204057), National Postdoctoral Science Foundation of China (No.2012M510918), Science
Foundation for Young Scholars of Heilongjiang Province of China (QC2011C034), Foundation for
Key Teacher of Universities by Heilongjiang Province of China (1252G007)， Project of Science
and Technology of Heilongjiang Province of China (No.12521054) and Heilongjiang Postdoctoral
Grant (LBH-Z12274).
References
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Environmental Protection and Resources Exploitation
10.4028/www.scientific.net/AMR.807-809
Investigation on the Extraction of Aluminum and Iron from Fly Ash by Sodium Carbonate Fusion
Method
10.4028/www.scientific.net/AMR.807-809.1262
DOI References
[1] N. Nayak, C.R. Panda. Aluminum extraction and leaching characteristics of Talcher Thermal Power
Station fly ash with sulphuric acid[J]. Fuel, 2010, 89(1): 53-58.
http://dx.doi.org/10.1016/j.fuel.2009.07.019
[2] C. Y Wu, H.F. Yu, H.F. Zhang. Extraction of aluminum by pressure acid-leaching method from coal fly
ash[J]. Transactions of Nonferrous Metals Society of China, 2012, 22(9): 2282-2288.
http://dx.doi.org/10.1016/S1003-6326(11)61461-1
[3] A. Seidel, Y. Zimmels. Mechanism and kinetics of aluminum and iron leaching from coal fly ash by
sulfuric acid[J]. Chemical Engineering Science, 1998, 53(22): 3835-3852.
http://dx.doi.org/10.1016/S0009-2509(98)00201-2
[4] A. Shemi, R.N. Mpana, S. Ndlovu, et al. Alternative techniques for extracting alumina from coal fly
ash[J]. Minerals Engineering, 2012, 34(1): 30-37.
http://dx.doi.org/10.1016/j.mineng.2012.04.007