Journal of Minerals & Materials Characteri zation & Enginee r ing, Vol. 10, No.6, pp.561-571, 2011
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561
Removal of Cu2+ from Aqueous Solution using Fly Ash
Jinjing Luo*, Huazhen Shen, Hanna Markström, Zhongye Wang, Qiang Niu
Environment Science Research Center, Xiamen Univeristy, China
*Corresponding Author:
ABSTRACT
This research aims at investigating the utilization of fly ash as a low-cost adsorbent to
remove copper ions from aqueous solutions such as wastewater. Fly ash dosage as well as
initial copper ion con centration
， temperature and pH value were varied to find the optimum
conditions for Cu2+ adsorption by fly ash. The results from sorption process showed that the
maximum adsorption rate was obtained at 50 mg/L when different dosage of fly ash was
added into the solution, and it could be concluded that decreasing the initial concentration of
copper ion is beneficial to the adsorption ability of fly ash. With the increase of pH value, the
removal rate increased. When pH was 6, the removal rate reached the maximum of 99.60%.
When initial copper content was 50 mg/L, pH value was 6, the adsorption capacity of fly ash
sample reached 0.98 mg/mg. The main removal mechanisms were assumed to be the
adsorption at the surface of the fly ash together with the precipitation from the solution.
Keywords: Fly ash; Mercury; Adsorption; Copper
1. INTRODUCTION
Fly ash is a particulate material generated from coal-fired power plants. Every year, there is a
large amount of fly ash produced during combustion of coal all over the world, which
requires large dumping sites for the safe disposal or investigation for reuse and recycling of
those fly ash waste. This demand is more intense in current China. The amount of fly ash
produced in China was 0.7 billion tons in 2010, and this number is going to be rising.
However, the utilization rate of fly ash is still in a relatively low level. The major use of fly

562 J. Luo, H. Shen, H. Markström, Z. Wang, Q. Niu Vol.10, No.6
ash has been as an additive to cement concrete and other building materials, also as soil
amendments. As the amount of fly ash increases, there is a need to develop alternative uses of
fly ash.
This study aims at investigating the utilization of fly ash as an adsorbent to remove copper
ions from aqueous solution, such as wastewater. Fly ash is strong alkali material, and its pH
value normally varied from 10 to 13 when added to water. Thereby, it can be expected that
copper ions can be removed from aqueous solutions by precipitation or electrostatic
adsorption [1]. As a matter of fact, a number of studies were undertaken to verify the
influence of fly ash in the removal of heavy metal ions from aqueous solutions [2-6].
However, the results appeared to less comprehensive, and more practical factors should be
chose to test the effectiveness of fly ash to remove copper ions from aqueous solution.
In this work, batch experiments were designed for the sorption process, and the effects of
temperature, pH value, initial concentrations of copper ions and fly ash dosages on adsorption
were evaluated. The optimum condition was also discussed for copper ions removal.
2. MATERIAL AND METHOD
2.1 Chemicals and Instruments
Fly ash samples from a thermo-electric power plant in Xiamen, China was sieved, and the
particle size that less than 100 mesh was collected and dried at 105°C. Cu(NO3)2 was used to
prepare for copper ions solution. Reagents used in the experiments were 40% (NH4)3C6H5O7
solution, 0.2% Cl4H22N4O2 solution (BCO-solution) and ammonia-ammonium chloride buffer
solution with pH value of 9. Other chemicals used were C2H6O, C2H4O, HCl, NH3 and
MilliQ-water.
The instruments used in the experiments were Sartorius BS223S electric balance, Sartorius
TE6101-L electric balance, DHG-9036A heating & drying oven, 510 pH/Ion/mV Meter,
SKY-2102C rocking incubator, DL-5C centrifuge, thermostatic water bath, suction filtration
equipment and UV-9200 ultraviolet and visible spectrophotometer.
2.2 Experimental Method
2.2.1 Characteristics of fly ash samples
X′Pert PRO X-ray diffractometer (PAN/analytical Inc., Netherland) was used to obtain x-ray
diffraction pattern of coal fly ash samples. The parameters were set as: Cu/K-alpha1;

Vol.10, No.6 Removal of Cu
2+ from Aqueous Solution using Fly Ash 563
Cu(40kV,30mA); scan scale: 2θ=10～90°.
MALVERN MS2000 laser particle size analyzer (Malvern Instruments, UK) was used to
analyze the particle size of fly ash samples.
2.2.2 Calibration curve and spectrophotometric method
25 ml aqueous solutions containing 0, 0.1, 0.2, 0.4, 0.8 and 1.2 mg/L of Cu2+ were added to
colorimetric cylinder flasks. 2 ml of 40% (NH4)3C6H5O7 solution was added to each flask and
pH was adjusted to 9 with ammonia solution. 5 ml ammonia-ammonium chloride buffer
solution was added and the flasks were shaken before adding 5 ml of 0.2% Cl4H22N4O2
solution (BCO-solution). 1 ml C2H4O was added and then adding MilliQ-water to 50 ml and
the flasks were shaken. After this, they were put into a water bath in 50°C for 10 min. When
cooled to room temperature the spectrophotometer was used to measure copper
concentrations in the solution at the wavelength of 546 nm.
2.2.3 Effect of initial Cu2+ concentration
25 ml aqueous solutions containing 5, 10, 50, 100, 200, 300 and 400 mg/L Cu2+ were added
to 250 ml conical flasks, and added Milli-Q water to 60ml. 1.2 g of fly ash was added and the
pH-value was adjusted to 6. After 1 h shaking in the rocking incubator, at room temperature
with a speed of 150 r/min, the fly ash was separated from the solution by suction filtration
and the Cu2+ residue in the solution was measured in the spectrophotometer (method
described above).
2.2.4 Effect of fly ash dosage
25 ml aqueous solution containing 50 mg/L Cu2+ were added to 250 ml conical flasks, and
added Milli-Q water to 60ml. 0.3, 0.6, 0.9, 1.2, 1.5, 1.8 g and 2.1 g fly ash were added and
the pH-value was adjusted to 6. After 1 h shaking in the rocking incubator at room
temperature, with a speed of 150 r/min, the fly ash was separated from the solution by suction
filtration and the Cu2+ residue in the solution was measured in the spectrophotometer.
2.2.5 Effect of pH
25 ml aqueous solution containing 50 mg/L Cu2+ and 1.2 g fly ash was added to 250 ml
conical flasks and the pH-value was adjusted to 3, 3.5, 4, 5, 6, 8 and 10. After 1 h shaking in
the rocking incubator at room temperature, with a speed of 150 r/min, the fly ash was
separated from the solution by suction filtration and the Cu2+ residue in the solution was

564 J. Luo, H. Shen, H. Markström, Z. Wang, Q. Niu Vol.10, No.6
measured in the spectrophotometer.
2.2.6 Effect of Temperature on the Cu2+ removal
25 ml aqueous solution containing 50 mg/L Cu2+ and 1.2 g fly ash was added to 250 ml
conical flasks and the temperature was set at 10, 15, 25, 35, 45, 55 and 65 ℃. After 1 h
shaking in the rocking incubator, with a speed of 150 r/min, the fly ash was separated from
the solution by suction filtration and the Cu2+ residue in the solution was measured in the
spectrophotometer.
3. RESULTS
3.1 Characteristics of Fly Ash Samples
The x-ray diffraction pattern of fly ash samples was illustrated in Figure 1. The XRD results
show there is a characteristic diffraction peak at 22～35° (2θmaxCuKα), which means large
amount of amorphous glassiness in the fly ash, and Quartz (SiO2) and Mullite (3Al2O3·2SiO2)
are two major crystal-constituents. Besides, there are other mineral compositions, such as
magnetite (Fe3O4) and sodalite (3Al2O3·3Na2O·6SiO2·NaCl).
0 20406080100
0
200
400
600
800
1000
1200
Mt
S
S
M
MM
M
M
Mt
Q
M
Q
Intensity
M
M=mullite; Q=quartz; Mt=magnetite; S=sodalite
Fig. 1 X-ray diffraction pattern of coal fly ash
Figure 2 shows the particle size distribution of fly ash samples. It illustrates that the majority
of particle size is between 5~200 μm. Among them, coarse granule (10~50 μm) is around
40%, followed by medium size (5~10 μm) particle, which is around 9 %, fine particle (2~5

Vol.10, No.6 Removal of Cu
2+ from Aqueous Solution using Fly Ash 565
μm) is around 2~3%, and clay particle (<2 μm) is around 2%.
Fig. 2 Particle size distribution of fly ash
PH value of fly ash sample was measured by 510 pH/Ion/mV meter. 1.2 g fly ash sample was
added into 250 mL conical flask and mixed with 60 mL Mili-Q water, before testing the pH.
The results show that the pH value of fly ash sample in this study is between 10.00~10.20.
3.2 Calibration Curve
Calibration curves made prior to operating UV-9200 ultraviolet and visible
spectrophotometer to measure copper ions in the solution to obtain accurate results. Figure 3
presents an example.
Fig. 3 Calibration curve
3.3 Effect of Initial Cu2+ Concentration
The influence of initial copper ion concentration to the removal rate was shown in Fig 4.

566 J. Luo, H. Shen, H. Markström, Z. Wang, Q. Niu Vol.10, No.6
With the increasing concentration from 5 to 50 mg/L, removal rate of copper ion was
increased to 99.52%. While with the copper ion concentration increased from 50 to 400 mg/L,
the tendency of removal rate decreased. Meanwhile blank test indicated the removal rate of
copper ion dropping with the initial concentration increasing, which represented precipitation
trend of copper ions in the solution. In Figure 5 the adsorption performance of the fly ash
surface was shown and the maximum adsorption rate was obtained at 50 mg/L. From Fig. 5,
it could be concluded that decreasing the initial concentration of copper ion is beneficial to
the adsorption ability of fly ash.
0100 200 300 400
0
10
20
30
40
50
60
70
80
90
100
A
B
Removal Rate(%)
C op p er C o ncen tration (m g /L)
A:add fly ash;B:no fly ash
Fig. 4 Effect of initial Cu2+ concentration on the removal of rate with fly ash and without
fly ash
0100 200 300 400
25
30
35
40
45
50
55
Removal Rate(%)
C op p er Co n centra tion(mg/L )
Fig. 5 Effect of initial Cu2+ concentration on the adsorption of Cu2+ using fly ash

Vol.10, No.6 Removal of Cu
2+ from Aqueous Solution using Fly Ash 567
3.4 Effect of Fly Ash Dosage
Fig. 6 illustrates the influence of fly ash dosage on the removal rate of copper ion. The
removal rate was 98.06% with adding 0.3 g fly ash in the solution, and removal rate
increasing with increasing fly ash dosage. The maximum removal rate of 99.75% occurred
when 2.1 g fly ash was added into the solution. In this study, since the removal rate was
pretty high with even the minimum dosage of fly ash added in the solution, resulted in the
ascending trend of adsorption rate was not large enough. Fig 7 showed the adsorption ability
of fly ash sample. The adsorption capacity of fly ash is over 0.98 mg/mg. Other researches
[7-9] found similar trend of increasing fly ash dosage resulted in increasing the percentage
removal of Cu2+.
0.2 0.4 0.6 0.8 1.0 1.21.4 1.6 1.82.0 2.2
50
55
60
65
70
75
80
85
90
95
100
A
B
Removal Rate(%)
Fly Ash Dose(g)
A;add fly ash;B:no fly ash
Fig. 6 Effect of Fly Ash dosage on the removal rate with Fly Ash and without Fly Ash
3.5 Effect of pH Value
The influence of pH value of aqueous solution on the removal rate was shown in Fig 8. With
the increasing of pH value, the removal rate increased. When pH was 6, the removal rate
reached the maximum of 99.60%. In the blank test, the removal rate didn’t change much with
pH increasing, as showed in Fig. 9. The pH value of the solution could affect the surface
electricity property of fly ash, ionic strength and the existing form of metal ions in the
solution. Under the strong acidic condition, the H+ ions in the solution could neutralize the
basic anhydride on the surface of fly ash, which decreased the adsorption ability of fly ash.
Under the strong alkaline condition, precipitation could occur, and which may inhibit the
adsorption process. The mechanism of removing copper ions from aqueous solution was

568 J. Luo, H. Shen, H. Markström, Z. Wang, Q. Niu Vol.10, No.6
assumed to be the combination of the adsorption at the surface of fly ash together with the
precipitation from the solution.
0.2 0.40.6 0.8 1.0 1.2 1.4 1.6 1.82.0 2.2
33.5
34.0
34.5
35.0
35.5
36.0
36.5
37.0
Removal Rate(%)
Fly Ash Dose(g)
Fig. 7 Effect of fly ash dosage on the adsorption rate with fly ash
234567891011
0
10
20
30
40
50
60
70
80
90
100
A
B
Removal Rate(%)
pH
A:add fly ash; B:no fly ash
Fig. 8 Effect of pH on the removal rate with and without Fly Ash
3.6 Effect of Temperature
Fig 10 & Fig. 11 illustrate the influence of temperature on copper ion removal rate &
adsorption ability. They showed increasing temperature help increase removal rate and

Vol.10, No.6 Removal of Cu
2+ from Aqueous Solution using Fly Ash 569
adsorption ability. The removal rate is over 99% when temperature is between 10~65℃. And
the adsorption ability of fly ash increased from 32.63% to 51.16% in this temperature range.
Based on this result, it could be concluded that for the realistic experiment, room temperature
is the best choice for using fly ash to remove copper ion from aqueous solution.
234567891011
0
10
20
30
40
50
60
70
80
90
100
Removal Rate(%)
pH
Fig. 9 Effect of pH on the adsorption rate of Cu2+ with fly ash
10 20 30 40 50 60 70
0
10
20
30
40
50
60
70
80
90
100
A
B
Removal Rate(%)
A:add fly ash;B:no fly ash
Fig. 3 Effect of temperature on the removal rate of Cu2+ with fly ash and without fly ash

570 J. Luo, H. Shen, H. Markström, Z. Wang, Q. Niu Vol.10, No.6
10 20 30 40 50 60 70
30
35
40
45
50
55
Removal Rate(% )
Fig. 41 Effect of temperature on the adsorption rate of Cu2+ using fly ash
4. CONCLUSION
Experimental results showed there was a high removal rate even without adding any fly ash
and this removal is probably due to precipitation of Cu(OH)2. This means the removal of
copper ion from solution is the combination of adsorption process and the precipitation
phenomena.
Based on the results obtained above, the main chemical composition of fly ash sample tested
in this study is SiO2, Al2O3, and Fe3O4, and its pH value is between 10.00~10.20. The particle
size of fly ash is mostly dropped in 5~200 μm. The results from sorption process showed that
the maximum adsorption rate was obtained at 50 mg/L when added different dosage of fly
ash into the solution. And it could be concluded that decreasing the initial concentration of
copper ion is beneficial to the adsorption ability of fly ash. With the increase of pH value, the
removal rate showed increased. When pH was 6, the removal rate reached the maximum of
99.60%. When initial copper content was 50 mg/L, pH value was 6, the adsorption capacity
of fly ash sample reached 0.98 mg/mg. When temperature was set between 10~65℃, the
adsorption ability of fly ash increased from 32.63% to 51.16%.
To sum up, fly ash could be used as an effective adsorbent to remove Cu2+ from aqueous
solutions under the optimal conditions.
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