benefits and risks of the agricultural uses of coal fly ash · benefits and risks of the...
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Benefits and Risks of the Agricultural Uses of Coal Fly Ash
P. Fine, U. Mingelgrin and S. Bar-Tal
Inst. Soils, Water and Environmental Sciences, Volcani Center, ARO, P.O.Box 6, Bet-Dagan, 50250, Israel
Coal Fly ash is composed principally of SiO2
(~ 45%) and Al2O3 (~ 35%) and in most cases is highly basic (pH ~12)
It usually also contains significant quantities of calcium and a variety of elements at trace
levels
The fly ash is pozzolanic and serves as an additive in concrete and in cement and road construction.
It can also be used for soil reclamation, e.g., of acid soils (Chang et al., 1977 etc.) and improvement of the hydraulic properties of marginal soils (Ghodrati et al., 1995 etc.).
Possible risk from loads of trace and heavy metals (Adriano et al., 2002)
Adding fly ash to the soil may bring about the following physical and physico-chemical changes:
• Narrow the pore size distribution in sandy soils and slightly cement sand particles especially at the surface. Thus, increase water holding capacity, decrease hydraulic conductivity, and reduce wind erosion.
•Reduce crusting of vulnerable loessial soils thus increasing their infiltration rates.
• Prevent swelling in swelling clayey sodic soils, (high Ca2+ content).
We will also present data on possible adverse effects especially on heavy metals leaching and uptake in plants grown on a soil loaded with fly ash.
ResultsResults
Rain simulator studies (30x50x2 cm3)
Fly ash-treatment of loess
Treated (15%) Untreated
Final infiltration rate after consecutive storms in fly ash-treated loessial loamy soil
Electrical conductivity in the leachates (Na & K; Ca dominates after the 1st storm)
0
1
2
3
4
5
6
7
8
9
1st Rain Storm 2nd Rain Storm 3rd Rain Storm
EC
[ds
/m[
0%Fly Ash 8%Fly Ash 10%Fly Ash 12%Fly Ash 15%Fly Ash
Leaching ratio per storm 9 L/3.5-4.5 kg soil (1:2 – 1:2.5)
Rain simulation study: Leachate composition from dune sand (g/l) Storm # Fly ash (%) B Ni Pb Se Cr
0 75 3 0 10 6 8 77 6 25 30 372 1 106 4 39 27 425
12 102 9 34 23 387 1
15 106 8 47 38 511 8 700 96 36 43 1628
10 500 30 18 32 1911 12 271 81 24 24 833 2
15 323 48 22 17 795 8 640 66 31 34 1303
10 430 19 17 20 1530 12 218 55 18 19 667 3
15 259 33 18 65 655 Israeli drinking water standard 50 10 10 50 Recommended dietary allowances (RDA) & Upper Limit (g/day)
- (20,000)
- (1,000)
55 (400)
35 (nd)
Loessial soil: Ash addition inhibited the formation of crust and increased water infiltration up to 2.5 fold by.
Weakening the crust increased the susceptibility of the soil toward wind erosion.
Sand: The addition of fly-ash (up to 20%) increased water retention by up to 8 fold, reduced the infiltration rate, and reduced the sand's susceptibility to wind erosion.
While the untreated sand moved already at wind speed of 9 m/sec, the ash-treated sands withstood wind speeds of up to 26 m/sec.
Wind Velocity [m/sec] 10m/sec 15m/sec 20m/sec 25m/sec
0
40
80
120
160
200
0 5 10 15 20Time [min]
[impa
cts/
sec]
8% Fly Ash 15% Fly Ash 0% Fly Ash
Wind tunnel study of wind erosion in fly ash treated dune sand
Addition of fly-ash to a swelling clayey, sodium-rich soil reduced swelling to such a degree that the treated soil did not display any cracks, while the untreated soil cracked severely upon drying.
Control 200 T/hectare fly ash
Effect of fly ash addition on cracking of a sodic clayey soil
(summer of the 3rd year after application)
Addition of fly ash (up to 800 tones/ha) to a clayey sodic soil did not result in a reduction in yield of corn in the year of application or of yield of
the crops in consecutive years (cotton, chickpeas, and corn again) nor did it
affect NPK contents.
Addition of fly ash (up to 800 tones/ha) to a clayey sodic soil did not result in a reduction in yield of corn in the year of application or of yield of
the crops in consecutive years (cotton, chickpeas, and corn again) nor did it
affect NPK contents.
P
0500
100015002000250030003500
Can
opy
(mg
kg-1
)
0500100015002000250030003500
Cobs Canopy
N
0
2000
4000
6000
8000
10000
02000400060008000100001200014000
K
Treatment
Control
Fly ash 200t/ha
Fly ash 800t/ha
Cob
s (m
g kg
-1)
0
1000
2000
3000
4000
0
10000
20000
30000
40000
Concentration of elements in corn plants (cobs and canopy)grown of a clayey soil heavily w/wo fly ash
Cd
0.00
0.01
0.02
0.03
0.04
Can
opy
(mg
kg-1
)
0.00
0.01
0.02
0.03
0.04Cobs Canopy
Cr
0
1
2
3
4
0369121518
Pb
Cob
s (m
g kg
-1)
0.00
0.02
0.04
0.06
0.08
0.10
0.00
0.10
0.20
0.30
0.40B
0
2
4
6
8
0
20
40
60
80
Mo
Treatments
Control
Fly ash 200t/ha
Fly ash 800t/ha0.0
0.1
0.2
0.3
0.4
0.5
0.0
0.5
1.0
1.5
2.0
2.5Sr
Control
Fly ash 200t/ha
Fly ash 800t/ha0.00.10.20.30.40.50.60.70.8
0102030405060
b
ab
a
b
a a aab
b
Concentration of trace elements in corn plants (cobs and canopy)grown of a clayey soil heavily amended with fly ash
Mn
0
2
4
6
8
Can
opy
(mg
kg-1
)
0
20
40
60
80
100Cobs Canopy Fe
0
10
20
30
40
0
100
200
300
400
Zn
Cob
s (m
g kg
-1)
0369
121518
0
2
4
6
8
10Cu
0.0
0.5
1.0
1.5
2.0
2.5
0
5
10
15
20
Ni
Treatments
Control
Fly ash 200t/ha
Fly ash 800t/ha0.00.30.60.91.21.51.8
0123456
Co
Control
Fly ash 200t/ha
Fly ash 800t/ha0.0000.0050.0100.0150.0200.0250.0300.035
0.000.050.100.150.200.250.30
Concentration of trace elements in corn plants (cobs and canopy)grown of a clayey soil heavily amended with fly ash
Concentration in corn cobs of Cr in plots receiving 800 tones/hectare fly ash was 3 mg/kg. Yet, no effect on plant
composition was evident in the next three consecutive years (cotton, chickpeas, corn)
Cr
Control
Fly ash 200t/ha
Fly ash 800t/ha
Cob
s (m
g/kg
)
0
1
2
3
4
Can
opy
(mg/
kg)
0369121518
Cobs Canopy
b
ab
a
Fly ash addition improved water infiltration in flood-water collecting systems constructed in
loessial dry-river beds in the Israeli desert
Pond after flood
Date/Hour
Ww
ater
leve
l (cm
)
Rain intensity (m
m/hr))
Water height controlWater height fly ashrain intensity (15 min)
Water height in a pond treated with 8% fly ash and an adjacent control pond
No fly ash
200 tons/hectare fly ash
• Fly ash adds to the soil a significant load of boron and a number of trace metals such as chromium, lead and selenium, as well as soluble salts.
• The effect of the added, undesirable elements can be controlled and attenuated by the rate of ash application, rate of water addition and the pH levels maintained in the soil.
However, the crops grown in a clay soil field plots with 200 tones FA/ha did not display any negative effect on crop yield or quality and did not display accumulation of trace elements. At 200 tones FA/ha, Cr accumulated at significantly higher amounts in the corn cobs grown in the 1st season after application.
Conclusions:
Fly ash can be used to improve soil productivity
Even very high loads, fly ash did not harm yield quantity or quality
Fly ash can be applied to soils without harm to the environment or human health, yet due caution should be practiced mainly with respect to leaching of oxyanions.
