Interaction of Potassium and Ammonium ions in Soil

Interaction of Potassium and
Ammonium ions in Soil
XQ Chen, JM Zhou, PM Huang,
et al.
Institute of Soil Science,
Chinese Academy of Sciences
About
+
K
and
+
NH4
A pair of ions with some special and interesting
characteristics
Similarity
Similar crystal ionic radii, 0.133nm and
0.143nm for K+ and NH4+, respectively ;
Relatively low hydration energies;
Both ions may be trapped into the hexagonal
cavity in the basal oxygen plane of 2:1
phyllosilicates and thought to be fixed by the
similar or same mechanism
With these similarities …
Ð If one of the two ions was added into soil
prior to another one , then the amount of
the ion added later would be reduced in
proportion to the amount of the one
previously adsorbed.
Ð If added together, the amount and rate of
adsorption of the 2 ions would be the same.
However, …
When added simultaneously to an Hsaturated Mt, more K+ than NH4+ was fixed
at lower concentrations, reversed results
found at higher concentrations (Joffe and
Levine,1947).
Other works observed a preference of
NH4+ to K+ (Bower, 1950; Nommik, 1957;
Nielsen, 1972)
Objective of this study
h To compare the adsorption
characteristics of K+ and NH4+ on soil;
h To compare the effect of K+ and
NH4+ interaction on the adsorption of
these two ions
By some kinetics experiments
Materials and methods
Original soil sample:
Rego Chernozem, from Saskatoon.
Texture: clay (with 20.0% of sand,
36.3% of silt, and 43.7% of clay).
Organic C: 1.102
Materials and methods
Preparation of Ca-saturated clay samples
z The sedimentation method was used to obtain the
< 2μm clay fractions from the soil samples.
z The < 2μm clay fractions were then washed with
0.5 M CaCl2 for 5 times to obtain the Ca-saturated
clay samples for the purpose of kinetics study.
z The excess Ca2+ was removed by the subsequent
washing with deionized distilled water until a
negative test for Cl- was obtained by AgNO3.
z The Ca-saturated < 2μm clay samples were then
dispersed in deionized distilled water by a Sonifier
and stored in a 10-L plastic bottle.
z The clay concentration was kept at 0.14 g of clay
(DW) in every 10 mL of the well mixed suspension.
Materials and methods
Adsorption kinetics experiment
z The batch technique was used in the kinetics
experiments.
z 10 mL of 5.12 mM KCl, NH4Cl or KCl and NH4Cl was
added into a 125-mL triangular flask with 10 mL of the
clay suspension, placed on a shaker bath, and
maintained at the temperatures of 5, 25, and 45 oC.
z Then shake for 2, 4, 8, 16, 30, 60, 120, 240, 360, 840,
and 1440 min.
z At the end of each reaction period, the suspension
was filtered through a Millipore membrane with 0.25 μm
pore size by a vacuum pump.
z The concentration of K in the filtrate was determined
directly by flame emition. And the concentration of NH4
was determined by the automatic analyzer.
z Each experiment was done in triplicate.
Adsorption of K+ from KCl solution on
soil clay at different temperatures
K adsorbed (m m ol/kg)
100
KCl-K
90
80
70
5
25
45
60
0
300
600
900
1200Time (min)
1500
Adsorption of NH4+ from NH4Cl solution
on soil clay at different temperatures
NH4 adsorbed (mmol/kg)
100
90
80
NH4Cl-NH4
5
70
25
45
60
0
300
600
900
1200
1500
Time (min)
Comparison of K+ and NH4+ adsorption
amount from single solution
Temp (oC)
5
25
45
Ion
Amount adsorbed
2min
Balanced
K
68.71
79.29
NH4
77.29
91.00
K
75.71
88.26
NH4
79.81
93.43
K
76.71
90.00
NH4
83.00
97.71
Elovich equation fitting curve of K+
adsorption from KCl solution
K adsorbed (m m ol/kg)
100
KCl-K
y = 1.8266Ln(x) + 77.362
2
R = 0.9361
90
80
y = 1.6884Ln(x) + 76.846
2
R = 0.9038
70
25
对数 ( 5 )
对数 ( 4 5 )
5
45
对数 ( 2 5 )
y = 1.5479Ln(x) + 69.83
2
R = 0.8579
60
0
300
600
900
Time (min)
1200
1500
Elovich equation fitting curve of NH4+
adsorption from NH4Cl solution
NH4 adsorbed (m m ol/kg)
100
90
NH4Cl-NH4
80
y = 2.1226Ln(x) + 80.354
R 2 = 0.9361
70
y = 1.998Ln(x) + 76.574
2
R
= 0.9898
60
0
300
600
y = 2.3257Ln(x) + 83.325
R 2 = 0.946
5
25
45
对数 ( 5 )
对数 ( 2 5 )
对数 ( 4 5 )
900
Time (min)
1200
1500
According to
Arrhenius Equation
Ea
+ ln A
ln k = −
RT

A: pre-exponential factor（frequency
factor）；

Ea：Arrhenius activation energy
Arrhenius plots of K+ adsorption kinetics
from KCl solution
0.70
0.65
lnk
0.60
0.55
y = -365.75x + 1.7521
R 2 = 0.9999
0.50
0.45
0.40
0.0031 0.0032 0.0033 0.0034 0.0035 0.0036 0.0037
1/T
Arrhenius plots of NH4+ adsorption
kinetics from NH4Cl solution
0.90
0.85
lnk
0.80
0.75
0.70
0.65
y = -333.63x + 1.8859
R2 = 0.976
0.60
0.0031 0.0032 0.0033 0.0034 0.0035 0.0036 0.0037
1/T
Effect of temperature on K+ and NH4+
adsorption from single solution
Temp (oC)
Rate constant
KCl-K
NH4Cl-NH4
5
1.548
1.998
25
1.688
2.123
45
1.827
2.326
Ea
3.04
2.77
A
5.77
6.59
Adsorption of K+ from mixed KCl and NH4Cl
solution on soil clay at different temperatures
K adsorbed (mmol/kg)
80.00
75.00
70.00
65.00
NK-K
60.00
5
55.00
45
25
50.00
0
300
600
900
1200
Time (min)
1500
Adsorption of NH4+ from mixed KCl and NH4Cl
solution on soil clay at different temperatures
NH4 adsorbed (mmol/kg)
110.00
100.00
NK-NH4
90.00
80.00
70.00
60.00
5
50.00
25
45
40.00
30.00
0
300
600
900
1200
Time (min)
1500
Comparison of K+ and NH4+
adsorption from mixed solution
Temp
5
25
45
(oC)
Ion
K
NH4
K
NH4
K
NH4
Amount adsorbed
2min
Balanced
61.82
73.00
46.71
78.14
64.00
76.43
51.43
88.57
65.43
78.29
57.86
107.00
Elovich equation fitting curve of K+ adsorption
from mixed KCl and NH4Cl solution
K adsorbed (mmol/kg)
85.00
y = 2.017Ln(x) + 65.383
R 2 = 0.9481
NK-K
80.00
75.00
y = 1.915Ln(x) + 64.432
R 2 = 0.9295
70.00
65.00
60.00
y = 1.769Ln(x) + 61.417
R 2 = 0.974
55.00
5
25
45
对数 (45 )
对数 (5)
对数 (25 )
50.00
0
300
600
900
1200
Time (min)
1500
Elovich equation fitting curve of NH4+ adsorption
from mixed KCl and NH4Cl solution
NH4 adsorbed (mmol/kg)
120.00
NK-NH4
110.00
y = 7.4923Ln(x) + 59.41
2
R = 0.9142
100.00
90.00
80.00
70.00
60.00
y = 4.4571Ln(x) + 47.622
50.00
R = 0.9538
y = 6.0001Ln(x) + 49.459
2
R = 0.9596
5
45
对数 ( 2 5 )
2
40.00
25
对数 ( 4 5 )
对数 ( 5 )
30.00
0
300
600
900
1200
Time (min)
1500
Arrhenius plots of K+ adsorption kinetics
from mixed KCl and NH4Cl solution
0.75
lnk
0.70
0.65
0.60
0.55
y = -290.88x + 1.6196
R2 = 0.9934
0.50
0.0031 0.0032 0.0033 0.0034 0.0035 0.0036 0.0037
1/T
Arrhenius plots of NH4+ adsorption kinetics
from mixed KCl and NH4Cl solution
2.2
2
lnk
1.8
1.6
1.4
1.2
y = -1480.2x + 2.757
R2 = 0.9997
1
0.0031 0.0032 0.0033 0.0034 0.0035 0.0036 0.0037
1/T
Effect of temperature on K+ and NH4+
adsorption from mixed KCl and NH4Cl solution
Temp (oC)
Rate constant
KCl-K
NH4Cl-NH4
5
1.769
4.457
25
1.915
6.000
45
2.017
7.492
Ea
2.42
9.56
A
5.05
13.97
Comparison of K+ and NH4+ adsorption
amount from single and mixed solution
45 o C
110.00
90.00
Amount adsorbed (mmol/kg)
Amount adsorbed (mmol/kg)
A mo u n t ad so rb ed (mmo l/kg )
100.00
100.00
90.00
25 o C
5 C
o
100.00
80.00
80.00
90.00
70.00
70.00
80.00
60.00
KCl
KCl
NK-K
NK-K
60.00
70.00
50.00
50.00
40.00
50.00 0
0
NH4Cl
KCl
60.00
40.00
0
300
300
300
600
600NK-K
900 NK-NH41200
Time (min)
900
1200
1500
Time (min)
600
NH4Cl
NH4Cl
NK-NH4
NK-NH4
900
Time (min)
1200
1500
150
Amount ratio of K+ to NH4+ adsorbed from
KCl and NH4Cl mixed solution
Time (min)
Temperture (oC)
5
25
45
2
1.32
1.24
1.13
4
1.22
1.19
1.05
8
1.10
1.12
0.92
16
1.08
1.07
0.84
30
1.06
1.01
0.78
60
0.99
0.95
0.79
120
1.00
0.91
0.78
240
0.99
0.90
0.76
360
0.99
0.89
0.75
840
0.97
0.88
0.73
1440
0.93
0.86
0.73
Conclusion
The adsorption amount of both K and NH4
enlarged with the increase of temperature
z The amount of NH4 was higher than that of K
adsorbed at the same temperature
z The adsorption of K was greatly retarded by NH4
co-application; the adsorption of NH4 was also
reduced by K at low temperature, but facilitated
at high temperature
z Arrhenius activation energy (Ea) and preexponential factor (A) could bring a clue to
explore the mechanism of effect of K and NH4
interaction on the adsorption of these two
special ions
z
活化能 Ea 的求算
作图法：
Ea 1
ln k = ( − ) ⋅ + ln A
R T
由实验测得不同温度 T 时的速率常数 k，
作图 ln k ~ 1/ T，曲线的在某一温度的
斜率为：
Ea
−
⇒ 该温度的活化能： E a
R

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