- Email: [email protected]
Effect of hydroxyl and nitrate ions on the sorption of ammonium ions by sulphonic cation exchangers
DESALINATION Desalination 175 (2005) 259-268
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Effect of hydroxyl and nitrate ions on the sorption of ammonium ions by sulphonic cation exchangers A. Ancuta a, D. Kau~p6dien6 b, A. Gefenien6 b, J. Snuki~kis b*, E.
Vasilevi6ifit6a aConcern "Achema Group '" Jonalaukio k., Ruklos sen., donavos r. 5005, Lithuania bInstitute of Chemistry, A. Gogtauto 9, 2600 Vilnius, Lithuania Tel. +370 (5) 261-0042; Fax +370 (5) 261-701& email: [email protected] Received 25 January 2004; accepted 24 September 2004
Abstract
The sorption of ammonium ions and ammonia by the H+ form of sulphonic acid cation exchangers Amberlite 252, Lewatit 2629 and Relite C 360 from a solution containing NH4NO3 in the range of 0 to 0.214 equ/L and NH3 in the range of 0.353 to 0 equ/L was investigated to establish the possibility of their application for the recovery of ammonium from caustic condensate generated in nitrogen fertilizer production. Breakthrough and elution curves were obtained, determining the concentration of ammonium with Nessler's reagent. The sorption of ammonium and ammonia depends on the concentration ratio of ammonia to ammonium nitrate [NH3]][NH4NO3]. On decreasing [NH3]][NH4NO3] , the concentration ratio of hydroxyl to nitrate ions [OH']/[NO~] and the effluent pH prior to NH] breakthrough also decrease. This results in a decrease in the NH~ sorption because of a deficiency in the neutralization of hydrogen ions released (ordinary cation-exchange process). Thus, adverse circumstances create an unfavorable medium for NH~ removal from the caustic condensate. Maximum sorption of NH~ is attained at [NI-I3]/[NH4NO3] -1.2. A further decrease in [NH3]/[NH4NO3] is followed by a significant decrease in the effluent pH, which leads to an increase in the concentration ofprotonated sulphonie acid groups (-SOaH), resulting in a decrease in the ion-exchange ability of the cation exchangers under investigation with respect to NH] removal. The concentration (g/L) ofNH4NOa in the eluate from the cation-exchanger regeneration, carried out using 0.7 bed volumes (BV) of 20% HNO3, amounts to 136.7 for Relite C 360, 119.5 for Lewatit K 2629 and 96.7 for Amberlite 252. The content of undamaged beads after 100 cycles (each cycle comprises saturation with caustic condensate, containing ammonia and ammonium, successive regeneration with 20% nitric acid and washing) is from 97 to 99.8%. Resistance to boiling in 20% HNO3 solution is from 97 to 99.8%. These are applicable for the recovery of NH4NO3 from the caustic condensate in the nitrogen fertilizers production, preventing economic damage and environmental contamination from nitrogen compounds. Keywords: Cation exchangers; Ammonia; Ammonium nitrate; Sorption; Nitrogen fertilizers
*Corresponding author.
0011-9164/05/$- See front matter © 2005 Elsevier B.V. All fights reserved doi: 10.1016/j.desal.2004.09.029
260
A. Ancuta et al. / Desalination 175 (2005) 259-268
I. Introduction
Large amounts of condensed caustic water are generated by the production of nitrogenous fertilizers, related to the replacement ofprilled ammonium nitrate by granular products. They must be treated, bearing in mind not only economic but also environmental considerations. The loss of nitrogen with waste effluents is also unacceptable. Taking into account the necessity of water recycling, the loss of pure water, led out as waste effluent, is 0.5-2.5 m3/ton of the ammonia capacity [1]. Ion-exchange processes are still considered effective to apply for condensed water treatment [2-9]. Using the Varion KSM cation exchanger and Varion ADAM anion exchanger (Hungary), the concentration of NH4NO3 in the condensed water, containing 2.5 g/L, can be diminished to 10 mg/L [5]. The systems of the condensed water treatment on the basis of ion exchange have been designed. The treatment is carded out using strong acid cation exchangers and weak basic anion exchangers: Duolite A 374, Purolite A 104/2561 and Amberlit IRA 93SP [7]. Short cycle systems with the external regeneration of cation exchangers are the most advanced since they avoid hazardous explosions at the regeneration of the cation exchanger, saturated with ammonium ions [1,9,10]. Condensed water, comprising condensate from the nitrogen fertilizer production, contains not only ammonium nitrate but also ammonia. When dissolved in water, the NH 3 molecule exists in hydrated form, surrounded by four molecules of water, bounded to NH 3 by hydrogen [11]; the oxygen atoms, contained in three molecules of water, are bounded to three hydrogen atoms in the NH 3 molecule, whereas the hydrogen atom in the fourth molecule of water is bounded to the NH3 molecule because of the free pair of electrons in the nitrogen atom. Although the molecule of ammonia can accept a proton from the molecule of water to form ammonium ions NH 3 + H20 ~
NH~ + OH-
(1)
not all of the dissolved ammonia interacts with water. A substantial fraction of ammonia remains in molecular form. A quantitative indication of equilibrium (1) is given by the base ionization constant (Kb, mol/L) [11]:
K b--
[NH4] [OH -]
[NH3]
= 1.8× 10s
(1)
At pH<7, equilibrium (1) is displaced to the right so that nitrogen exists in the form of NH~ ions. In spite of the experience in the field of the condensate treatment by cation exchangers, the data concerning the sorption of NH] ions in the presence of dissolved ammonia, and also the effect of hydroxyl and nitrate coions as well as the dependence of the sorption as a whole on the concentration ratio between ammonia and ammonium, are not available. The purpose of this study was to establish the effect of dissolved ammonia, hydroxyl and nitrate ions on the sorption of ammonium by sulphonic acid cation exchangers, the resistance of the cation exchangers investigated to nitric acid and the possibility of their application for the recovery of ammonium ions from the condensate generated in nitrogen fertilizer production.
2. Materials and methods
Amberlite 252 (Rohm and Haas, UK), Lewatit K 2629 (Bayer) and a Relite C 360 (Mitsubishi Chemical, Italy), containing sulph-onic acid fixed groups (-SO3H) in H ÷ form were used. Cation exchangers were transferred into glass columns and subjected to swelling in distilled water. The conversion into H ÷ form was carded out passing five bed volumes (BV) of 5% HC1 solution through 1 BV of the cation exchanger at a flow rate of 4 ml/min. BV is defined as BV = volume of treated solution/volume of cation exchanger
A. Ancuta et at/Desalination 175 (2005) 259-268
The fraction >0.315 mm in bead diameter was separated by sieving. Ion-exchange capacity with respect to NH4 ions was determined under static conditions using 1 BV of the cation exchanger for 3 BV of model caustic condensate, corresponding to an average of an overall concentration of caustic condensate generated in nitrogen fertilizer production: (NH3, 0.176; NH4NO3, 0.038 equ/L). When measuring the solution pH, it was established that the equilibrium between the solution and cation exchanger is attained in no longer than 15 min from the beginning of the interaction. The volume distribution coefficient (Dr) for NH~ was calculated as the ratio between the concentration of NH~ (g per ml of cation exchanger) and the concentration of NH 4 (g per ml of the solution) [12]. The ion-exchange capacity was also determined under .dynamic conditions: the model condensed water was passed through the glass column (2 cm in diameter), loaded with 25 ml of the H + form cation exchanger at a flow rate of 1.13 ml/min, corresponding to velocity, acceptable for industrial process. Twenty-five ml of effluent samples were collected, the concentration of NH~ determined and pH measured; 0.2 g/L NH~ concentration in the effluent was considered as one, corresponding to a 5% breakthrough. "Breakthrough" is defined as a phenomenon when the effluent concentration amounts to 0.2 g NH~/L (5% of the initial concentration in the model caustic condensate, containing: NH3, 0.176 and NH4NO3, 0.038 equ/L). To determine the cation-exchanger resistance to oxidation by nitric acid, 2.55 ml samples were subjected to boiling with 100 ml of 20% nitric acid in the flasks, supplied with reverse coolers, for 30 min. The samples were separated from the solution using a glass filter and washed with distilled water until metilorange did not change its color. The samples were transferred into flasks, and 100 ml of 0.1 N NaOH solution were added; in 24 h the maximum ion-exchange capacity was determined when titrating 25 ml of the solution with 0.1N HC1. The effect of 20% nitric
261
acid onto the recovery of the ion-exchange capacity was evaluated. The microscopic analysis was also carried out: the stability (S, %) of the matrix with respect to boiling with 20% nitric acid was calculated: s = x 2 × 100
x,
(2)
where XI is the number of undamaged beads prior to boiling andX2 the number of undamaged beads after boiling. To determine the stability of the matrix, the cation exchangers were subjected to 100-fold recycling, each cycle comprising the saturation with 3 BV of the model condensed water, regeneration with 0.7 BV of 20% nitric acid and washing with distilled water. The condition of the cation exchangers before and after recycling was evaluated using a MBS-9 microscope (Russia). The concentration of NH~ was determined using Nessler's reagent [13] with a KFK-2 concentration photoelectric colorimeter (Russia); a concentration of HNO3 with 0.1 N NaOH and a methyl red 211. A microprocessor pH meter (Portugal) was used for the measurement of pH. The effect of the ratio between the free ammonia concentration and the ammonium ions concentration onto the sorption was determined under dynamic conditions. A 25 ml sample of the cation exchanger was saturated with model solutions containing NH 3 in the range of 0.353 to 0 equ/L and NH4NO3 in the range of 0 to 0.214 equ/L (inherent to the caustic condensate, generated in the nitrogen fertilizers production) (Table 1). The concentration of NH~ ions in the effluent BV of the solution treated prior to the 5% breakthrough were measured and ion-exchange capacity calculated. The desorption of NH~ and the regeneration of the cation exchangers, previously saturated with test solutions (Table 1) at a flow rate of 1.13 ml/ min, was carried out by passing 0.7 BV of 20% nitric acid solution through 25 ml of the cation
262
A. Ancuta et al. / Desalination 175 (2005) 259-268
Table 1 Composition and characteristics of the test solutions Test solution [NH3],
[NH4NO3],
[NH3]+[NH4],
no.
equ/L
equ/L
equ/L
1 2 3 4 5 6
0.353 0.176 0.118 0.059 0.006 0
0 0.038 0.096 0.155 0.208 0.214
0.353 0.214 0.214 0.214 0.214 0.214
exchanger at the flow rate of 0.4 ml/min. The samples of the eluate were collected, the concentration of NH~ ions and free nitric acid determined, pH measured and the recovery of NHaNO3 from the condensate calculated.
[NH3]/[NH;]
pH
[OH-], equ/L
[OH-l/[NO3-]
74.8 4.63 1.23 0.38 0.03 3x 10-4
11.7 10.53 9.97 9.46 8.32 5.74
5x10 -3 3.39x10 -4
[NO3] = 0 8.9x10 -3
9.35x10-5 2.9x10-5 2.1×10-6 5.5x10-9
9.7x10-4 1.9x10-4 1.0xl0-5 2.3x10-s
The counterion (H+) released from the cation exchanger is consumed by the reaction with the coion (OH-). Consequently, a conventional ion exchange is accompanied by the irreversible reaction. Taking into account that chemical reaction results in an elimination of coions (OH-), one could expect that, after the attainment of equilibrium with the cation exchanger, the solution should be near neutrality. Nevertheless, the effluent acidity from pH 3.1 to pH 4.4 was observed (Table 2, solution No. 1). This is because the equilibrium of the ionization of sulphonic acid cation exchangers
is displaced to the right: the apparent ionization constant (K,) is 10 -2 to 10-3 [14]. Consequently, the concentration of hydrogen ions is sufficiently high to displace equilibrium (1) to the fight, resulting in an increase in the concentration of NH~ ions, and to promote the sorption of NH4, proceeding accordingly to Eq. (4). At 5% (0.2 g NH~/L) breakthrough, the sorption cycle is interrupted, and the regeneration of cation exchanger carried out. A 5% breakthrough occurs after treating 5 BV of solution No. 1 with Amberlite 252 (Fig. 1, curve I), 6 BV with Lewatit K 2629 (Fig. 2, curve 1) and 7 BV with Relite C 360 (Fig. 3, curve 1). The sorption capacity ofRelite C 360 at a 5% breakthrough is the highest one amongst the cation exchangers investigated (Table 2). With the addition of NH4NO3 into solution and the corresponding decrease in the concentration ratio [NH3]/[NH4NO3], the concentration ratio [OH-]/ [NO;] also decreases (Table 1). As a result, a decrease in the effluent pH from 10.5 to 1.5 was observed (Table 2, solution no. 2). This is because, besides the sorption of NH~, proceeding on the basis of ion exchange and followed by the neutralization reaction accordingly to equilibrium (4), the sorption of NH~, proceeding on the basis of conventional ion exchange and leading to an increase in the concentration of hydrogen ions
R SO3H ~-+ R SO3 + H +
RSO3H + NH4NO3 ~-+RSO3NH4 + H + + NO3 (6)
3. Results and discussion
As the aqueous solution of ammonia is treated with the sulphonic acid cation exchanger in H + form, the substitution of H + ions by NH~ ones, leading to the sorption of NH~ ions, occurs as follows: R SO3H + N H 4 O H
~-~ R S O 3 N H 4 q- H20
(4)
(5)
A. Ancuta et al. / Desalination 175 (2005) 259-268 Q;
0 o
Q eel 0
(o
0
0
o
£.)
0
t~ cq
~"~ •
0
°
rg
0
't'l
eg
N 6
.
°
.
,
- -
263
A. Ancuta et al. / Desalination 175 (2005) 259--268
264
3000
3000
2500
4
1 + ,~
3
2
2000
5
~
o
500
2
4
6
8
10
12
500
Fig. 1. Breakthroughcurves for the sorption of NH~ from NH3-NH4NO3 solutions by Amberlite 252. The number of the curve corresponds to number of the test solution (Table 1). 6
2500
1
4
32 X5
13
20oo
E
+.; 1500
looo 5o0 L
-
2
_
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4
6
8
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4
6
8
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Volume of effluent (bed volumes)
Volume ~emue~(bedvolumes)
o 0
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0
O,
w
3
lOOO
10oo
..I
2500
E +~ •1- 2000 z o
1soo
f?2 4
10
12
Volume of effluent (bed volumes)
Fig. 2. Breakthroughcurves for the s o r p t i o n of NH~ from NH3-NH4NO3 solutions with the Lewatit K 2629. Number of the curve corresponds to number of the test solution (Table 1).
takes place. When NH4NO 3 concentration in the initial solution is increased, maximum sorption at 5% breakthrough, followed by a decrease in the effluent pH to 1, is observed (Table 2, solution no. 3). The acidity, corresponding to pH 1, is not so high as to interfere significantly with the deprotonation of sulphonic groups, and, consequently, with the sorption of NH~, proceeding
Fig. 3. Breakthroughcurves for the sorption of NH4 from NH3-NH4NO3solutions by Relite C 360. The number of the curve corresponds to number of the test solution (Table 1). accordingly to equilibrium (6). With a further decrease in [ N H 3 ] / [ N H 4 N O 3 ] , the effluent pH ecreases to 0.8-0.9 (Table 2, solutions nos 4-6). This is because the sorption of NH~, proceeding accordingly to equilibrium (6), becomes overwhelming. However, a strongly acidic medium results in a displacement of equilibrium (5) to the left, followed by a decrease in the concentration of deprotonated functional groups, which consequently results in a decrease in the sorption of NH~. In this connection the diminution of the sorption capacity at a 5% breakthrough was observed (Table 2, solution nos 4-6). Nevertheless, the diminution of the sorption is only slightly affected by a decrease in pH because the value of the ionization constant (K,) is rather high [14]. The sorption capacity at a 50% breakthrough is significantly higher when compared to that at 5%, especially for the Relite C 360. If the cation exchanger, saturated with NH4, is subjected to an action by the nitric acid solution, the displacement of equilibrium (6) to the left takes place, resulting in both the desorption of NH~ and the regeneration of the sorption capacity. The higher the concentration maximum in
265
A. Ancuta et aL / Desalination 175 (2005) 259-268 10
8
g
7 7
o¢
g
5
5 4
z ~
24 a
4 s
3 2
2
8
3
1
o
o 0
0.3
0.6
0.g
1.2
1.5
0
C360, saturated with NH3-NH4NO3 solutions. The number of the curve corresponds to the number of the test solution (Table 1). the eluate and the less the volume of the eluate, needed to attain the maximum, the higher the regeneration efficiency. The maximum ratio C/Co between the eluate concentration (C) and the saturation liquid concentration (Co) is attained with 0.2-0.5 BV of the eluent for Relite C360 (Fig. 4) and with 0.2 BV for Amberlite 252 (Fig. 5), whereas the C/Co maximum for Lewatit K2629 is displaced by 0.4--0.6 BV (Fig. 6). An important parameter of practical significance is the decontamination factor (DF) [15], indicating the ratio between the concentration of ammonium in the effluent prior to a 5% breakthrough and the corresponding concentration in the eluate from the regeneration. Experimental data indicate D F decreases with the ammonium concentration decrease in the initial solution (Table 2). To avoid excessive evaporation expenses, the volume of the eluate from the regeneration of the cation exchanger, saturated with caustic condensate, must be no more than 0.7 BV. When 0.7 BV 20% HNO3 is used as eluent, the highest concentration of NH~ (136.7 g/L) and the highest regeneration degree (70.3% o f the sorption
0.6
0.9
1.2
1.5
Volume of effluent (bed volumes)
Volume of effluent (bed volumes)
Fig. 4. Elution of NH; by 20% I-IN03 from the Relite
0.3
Fig. 5. Elution ofNH4+by 20% HNO3from the Amberlite 252, saturated with NH3-NH4NOa solutions. The number of the curve corresponds to the number of the test solution (Table 1).
7
G z
i
o 10/ 0
%ol 0.3
0,6
0,9
1.2
1.5
Volume of effluent (bed volumes)
Fig. 6. Elution of NH~ by 20% HNO 3 from the Lewatit K 2629, saturated with NH3-NH4NO 3 solutions. The number of the curve corresponds to the number of the test solution (Table 1). capacity), as well as the lowest concentration of free nitric acid have been obtained in the eluate from Relite C 360 (Table 3). Considering the ammonium concentration 0.2 g/L in the effluent at a 5% breakthrough as a treatment objective, the total ammonium concentration in the solution after treatment (until
266
.4..4ncuta et al. / Desalination 175 (2005) 259-268
_=
P~
0
"0
0 o.)
0
0 t~
< Z
o.)
_=
°i p~
.
.
.
.
° °
¢'4
oJ
267
A. Ancuta et at/Desalination 175 (2005) 259-268
Table 4 Parameters for the recovery of NH~ from NH3-NH4NO3test solutions (average for solutions Nos. 1-6) Cation exchanger
Co, equ/L" V, L
Ce, equ/L
C,, g/L
V,, L
C, equ/L
N, %
Lewatit I(2629 Amberlite 252 Relite C360
0.24 0.214 0.214
1.103 1.120 1.523
88.2 89.6 122.3
0.0175 0.0175 0.0175
0.128 0.127 0.108
40.1 40.7 50.5
0.225 0.225 0.250
'Co = [NH3]+ [NI1;]. breakthrough) (C, equ/L) can be determined from the arrangement of the mass balance equation: K C = Co - ~ × C~ V
(7)
where Co is the initial concentration of ammonium in the solution before treatment (equ/L), C, the total concentration of NH4NO3 in the eluate (equ/L), V the volume (L) of the solution treated until C/Co = 0.05, and Ve the volume of the eluate (L). Ammonium recovery efficiency (N), defined as the percentage of ammonium in the eluate compared to the total amount in the solution before treatment,
N - C, V, x 100
CoY
(8)
is presented in Table 4. To predetermine the osmotic stability of the cation exchangers, 100 cycles (each of them comprises the saturation with NH~ ions from the solution, containing 0.176 equ/L of NH 3 and 0.038 equ/L ofNH4NO 3 at pH 10.53, the successive regeneration with 20% HNO3 and washing with distilled water) were carded out. Most of the beads aider 100 cycles remained undamaged. 4. Conclusions
The sorption of ammonium ions and ammonia by the H ÷ form of sulphonic cation exchangers (Amberlite 252, Lewatit 2629, Relite C360) from
the solution containing NH 3 in the range of 0.353 to 0 equ/L and NH4NO3 in the range of 0 to 0.214 equ/L and corresponding to the composition of the caustic condensate, generated in the nitrogen fertilizers production, depends on the concentration ratio of ammonia to ammonium nitrate [NH3]/[NH4NO3], as well as on the initial solution pH. When [NH3]/[NH4NO3] decreases, the ratio of hydroxyl to nitrate [OH]/[NO~] and pH of the effluent prior to NH~ breakthrough (0.2 g NH~/L) also decrease. A decrease in [OH']/ [NO3] results in a decrease in that portion of the NH~ sorption, which proceeds on the basis of ion exchange, accompanied by irreversible reaction (neutralization of hydrogen ions, released from the cation exchanger), and leads to an increase in that portion of NH~"sorption, which proceeds on the basis of the conventional ion exchange. As a result, the effluent pH and, subsequently, the concentration ofdeprotonated functional (-SO3H) groups decrease, leading also to a decrease in the NH~ total sorption. The maximum sorption of NH~ corresponds to [NH3]/[NH4NO3] -1.2. The concentration (g/L) of NH4NO3 in the eluate from the cation exchanger regeneration, carded out with 0.7 BV 20% HNO3, amounts to 136.7 for Relite C360, 119.5 for Lewatit L2629 and 96.7 for the Amberlite 252. The cation exchangers investigated are resistant to boiling in 20% HNO3 solution. Osmotic stability is 97-99.8%. The exchangers are applicable for the recovery of NH4NO3 from caustic condensate, providing a new opportunity for economic consideration and environmental issues.
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A. Ancuta et al. / Desalination 175 (2005) 259-268
Acknowledgements A Bayer Company, Bang & Bonsomer and Technical Projects Company are acknowledged for supplying the cation exchangers.
References [1] J. Jaqust, Z. Dzendo and N. Arion, Nitrogen, 163 (1986) 28-34. [2] M. Philipot, G. De Laminat, Nitrate removal by ion exchange, Water Supply, 6(3) (1988) 45-50. [3] D. Clifford and X. Xiaosha, J. AWWA, 85 (1993) 135-143. [4] R. Bohm, Application of Ion Exchanger for Cleaning Waste Waters of Fertilizer Production. 4. Symp. of Ion Exchanger, Siofok, 1980. [5] F. Orszag, F. Ratkocics and B. Szeiler, Hung. J. Indus. Chem., 9 (1981) 241-250. [6] N. Arion, J. Jagust and 7.. Dzendo, Nitrogen, 8-9 (1986) 28--34.
[7] S. Leakovi~, I. Mijatovi~, ~. Cerjan-Stefanovi~ and E. Hod,~i6,Water Res., 34(1) (2000) 185-190. [8] R. Davies, Chem. Engn. Progress, 1 (1994) 63-71. [9] C. Caiman, Explosion hazards of using nitric acid in ion-exchange equipment, Chem. Engn., 87(23) (1980) 271-274. [10] G. Keenan, K. Notz and N.B. Franeo, Synergistic catalysis of ammonium nitrates decomposition, J. Amer. Chem. Soc., 91(12) (1969) 3168-3171. [11] D.G. Peters, J.M. Hayes and G.M. HieRje, Chemical Separations and Measurements. Theory and Practice of Analytical Chemistry, W.B. Saunders, Bloomington, 1974, p. 117. [12] K. Dorfner, Ion Exchangers, Valter de Guyter, Berlin, New York, p. 70. [13] Y.Y. Lur'e and A.J. Ribnikova, Chemical Analysis of Industrial Waste Waters, Khimiya, Moscow, 1974, pp. 67-68 (in Russian). [14] E.Y. Zakharov, B.E. Rebchikov and B.D. D'yakov, Ion Exchange Installation in Nuclear Industry, Energoatomizdat, Moscow, 1987,p. 22 (in Russian). [15] T.H. Karpipinen and A. Yuli-Pentti, Sep. Sci. Technol., 35(10) (2000) 1619.
ELSEVIER
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Effect of hydroxyl and nitrate ions on the sorption of ammonium ions by sulphonic cation exchangers A. Ancuta a, D. Kau~p6dien6 b, A. Gefenien6 b, J. Snuki~kis b*, E.
Vasilevi6ifit6a aConcern "Achema Group '" Jonalaukio k., Ruklos sen., donavos r. 5005, Lithuania bInstitute of Chemistry, A. Gogtauto 9, 2600 Vilnius, Lithuania Tel. +370 (5) 261-0042; Fax +370 (5) 261-701& email: [email protected] Received 25 January 2004; accepted 24 September 2004
Abstract
The sorption of ammonium ions and ammonia by the H+ form of sulphonic acid cation exchangers Amberlite 252, Lewatit 2629 and Relite C 360 from a solution containing NH4NO3 in the range of 0 to 0.214 equ/L and NH3 in the range of 0.353 to 0 equ/L was investigated to establish the possibility of their application for the recovery of ammonium from caustic condensate generated in nitrogen fertilizer production. Breakthrough and elution curves were obtained, determining the concentration of ammonium with Nessler's reagent. The sorption of ammonium and ammonia depends on the concentration ratio of ammonia to ammonium nitrate [NH3]][NH4NO3]. On decreasing [NH3]][NH4NO3] , the concentration ratio of hydroxyl to nitrate ions [OH']/[NO~] and the effluent pH prior to NH] breakthrough also decrease. This results in a decrease in the NH~ sorption because of a deficiency in the neutralization of hydrogen ions released (ordinary cation-exchange process). Thus, adverse circumstances create an unfavorable medium for NH~ removal from the caustic condensate. Maximum sorption of NH~ is attained at [NI-I3]/[NH4NO3] -1.2. A further decrease in [NH3]/[NH4NO3] is followed by a significant decrease in the effluent pH, which leads to an increase in the concentration ofprotonated sulphonie acid groups (-SOaH), resulting in a decrease in the ion-exchange ability of the cation exchangers under investigation with respect to NH] removal. The concentration (g/L) ofNH4NOa in the eluate from the cation-exchanger regeneration, carried out using 0.7 bed volumes (BV) of 20% HNO3, amounts to 136.7 for Relite C 360, 119.5 for Lewatit K 2629 and 96.7 for Amberlite 252. The content of undamaged beads after 100 cycles (each cycle comprises saturation with caustic condensate, containing ammonia and ammonium, successive regeneration with 20% nitric acid and washing) is from 97 to 99.8%. Resistance to boiling in 20% HNO3 solution is from 97 to 99.8%. These are applicable for the recovery of NH4NO3 from the caustic condensate in the nitrogen fertilizers production, preventing economic damage and environmental contamination from nitrogen compounds. Keywords: Cation exchangers; Ammonia; Ammonium nitrate; Sorption; Nitrogen fertilizers
*Corresponding author.
0011-9164/05/$- See front matter © 2005 Elsevier B.V. All fights reserved doi: 10.1016/j.desal.2004.09.029
260
A. Ancuta et al. / Desalination 175 (2005) 259-268
I. Introduction
Large amounts of condensed caustic water are generated by the production of nitrogenous fertilizers, related to the replacement ofprilled ammonium nitrate by granular products. They must be treated, bearing in mind not only economic but also environmental considerations. The loss of nitrogen with waste effluents is also unacceptable. Taking into account the necessity of water recycling, the loss of pure water, led out as waste effluent, is 0.5-2.5 m3/ton of the ammonia capacity [1]. Ion-exchange processes are still considered effective to apply for condensed water treatment [2-9]. Using the Varion KSM cation exchanger and Varion ADAM anion exchanger (Hungary), the concentration of NH4NO3 in the condensed water, containing 2.5 g/L, can be diminished to 10 mg/L [5]. The systems of the condensed water treatment on the basis of ion exchange have been designed. The treatment is carded out using strong acid cation exchangers and weak basic anion exchangers: Duolite A 374, Purolite A 104/2561 and Amberlit IRA 93SP [7]. Short cycle systems with the external regeneration of cation exchangers are the most advanced since they avoid hazardous explosions at the regeneration of the cation exchanger, saturated with ammonium ions [1,9,10]. Condensed water, comprising condensate from the nitrogen fertilizer production, contains not only ammonium nitrate but also ammonia. When dissolved in water, the NH 3 molecule exists in hydrated form, surrounded by four molecules of water, bounded to NH 3 by hydrogen [11]; the oxygen atoms, contained in three molecules of water, are bounded to three hydrogen atoms in the NH 3 molecule, whereas the hydrogen atom in the fourth molecule of water is bounded to the NH3 molecule because of the free pair of electrons in the nitrogen atom. Although the molecule of ammonia can accept a proton from the molecule of water to form ammonium ions NH 3 + H20 ~
NH~ + OH-
(1)
not all of the dissolved ammonia interacts with water. A substantial fraction of ammonia remains in molecular form. A quantitative indication of equilibrium (1) is given by the base ionization constant (Kb, mol/L) [11]:
K b--
[NH4] [OH -]
[NH3]
= 1.8× 10s
(1)
At pH<7, equilibrium (1) is displaced to the right so that nitrogen exists in the form of NH~ ions. In spite of the experience in the field of the condensate treatment by cation exchangers, the data concerning the sorption of NH] ions in the presence of dissolved ammonia, and also the effect of hydroxyl and nitrate coions as well as the dependence of the sorption as a whole on the concentration ratio between ammonia and ammonium, are not available. The purpose of this study was to establish the effect of dissolved ammonia, hydroxyl and nitrate ions on the sorption of ammonium by sulphonic acid cation exchangers, the resistance of the cation exchangers investigated to nitric acid and the possibility of their application for the recovery of ammonium ions from the condensate generated in nitrogen fertilizer production.
2. Materials and methods
Amberlite 252 (Rohm and Haas, UK), Lewatit K 2629 (Bayer) and a Relite C 360 (Mitsubishi Chemical, Italy), containing sulph-onic acid fixed groups (-SO3H) in H ÷ form were used. Cation exchangers were transferred into glass columns and subjected to swelling in distilled water. The conversion into H ÷ form was carded out passing five bed volumes (BV) of 5% HC1 solution through 1 BV of the cation exchanger at a flow rate of 4 ml/min. BV is defined as BV = volume of treated solution/volume of cation exchanger
A. Ancuta et at/Desalination 175 (2005) 259-268
The fraction >0.315 mm in bead diameter was separated by sieving. Ion-exchange capacity with respect to NH4 ions was determined under static conditions using 1 BV of the cation exchanger for 3 BV of model caustic condensate, corresponding to an average of an overall concentration of caustic condensate generated in nitrogen fertilizer production: (NH3, 0.176; NH4NO3, 0.038 equ/L). When measuring the solution pH, it was established that the equilibrium between the solution and cation exchanger is attained in no longer than 15 min from the beginning of the interaction. The volume distribution coefficient (Dr) for NH~ was calculated as the ratio between the concentration of NH~ (g per ml of cation exchanger) and the concentration of NH 4 (g per ml of the solution) [12]. The ion-exchange capacity was also determined under .dynamic conditions: the model condensed water was passed through the glass column (2 cm in diameter), loaded with 25 ml of the H + form cation exchanger at a flow rate of 1.13 ml/min, corresponding to velocity, acceptable for industrial process. Twenty-five ml of effluent samples were collected, the concentration of NH~ determined and pH measured; 0.2 g/L NH~ concentration in the effluent was considered as one, corresponding to a 5% breakthrough. "Breakthrough" is defined as a phenomenon when the effluent concentration amounts to 0.2 g NH~/L (5% of the initial concentration in the model caustic condensate, containing: NH3, 0.176 and NH4NO3, 0.038 equ/L). To determine the cation-exchanger resistance to oxidation by nitric acid, 2.55 ml samples were subjected to boiling with 100 ml of 20% nitric acid in the flasks, supplied with reverse coolers, for 30 min. The samples were separated from the solution using a glass filter and washed with distilled water until metilorange did not change its color. The samples were transferred into flasks, and 100 ml of 0.1 N NaOH solution were added; in 24 h the maximum ion-exchange capacity was determined when titrating 25 ml of the solution with 0.1N HC1. The effect of 20% nitric
261
acid onto the recovery of the ion-exchange capacity was evaluated. The microscopic analysis was also carried out: the stability (S, %) of the matrix with respect to boiling with 20% nitric acid was calculated: s = x 2 × 100
x,
(2)
where XI is the number of undamaged beads prior to boiling andX2 the number of undamaged beads after boiling. To determine the stability of the matrix, the cation exchangers were subjected to 100-fold recycling, each cycle comprising the saturation with 3 BV of the model condensed water, regeneration with 0.7 BV of 20% nitric acid and washing with distilled water. The condition of the cation exchangers before and after recycling was evaluated using a MBS-9 microscope (Russia). The concentration of NH~ was determined using Nessler's reagent [13] with a KFK-2 concentration photoelectric colorimeter (Russia); a concentration of HNO3 with 0.1 N NaOH and a methyl red 211. A microprocessor pH meter (Portugal) was used for the measurement of pH. The effect of the ratio between the free ammonia concentration and the ammonium ions concentration onto the sorption was determined under dynamic conditions. A 25 ml sample of the cation exchanger was saturated with model solutions containing NH 3 in the range of 0.353 to 0 equ/L and NH4NO3 in the range of 0 to 0.214 equ/L (inherent to the caustic condensate, generated in the nitrogen fertilizers production) (Table 1). The concentration of NH~ ions in the effluent BV of the solution treated prior to the 5% breakthrough were measured and ion-exchange capacity calculated. The desorption of NH~ and the regeneration of the cation exchangers, previously saturated with test solutions (Table 1) at a flow rate of 1.13 ml/ min, was carried out by passing 0.7 BV of 20% nitric acid solution through 25 ml of the cation
262
A. Ancuta et al. / Desalination 175 (2005) 259-268
Table 1 Composition and characteristics of the test solutions Test solution [NH3],
[NH4NO3],
[NH3]+[NH4],
no.
equ/L
equ/L
equ/L
1 2 3 4 5 6
0.353 0.176 0.118 0.059 0.006 0
0 0.038 0.096 0.155 0.208 0.214
0.353 0.214 0.214 0.214 0.214 0.214
exchanger at the flow rate of 0.4 ml/min. The samples of the eluate were collected, the concentration of NH~ ions and free nitric acid determined, pH measured and the recovery of NHaNO3 from the condensate calculated.
[NH3]/[NH;]
pH
[OH-], equ/L
[OH-l/[NO3-]
74.8 4.63 1.23 0.38 0.03 3x 10-4
11.7 10.53 9.97 9.46 8.32 5.74
5x10 -3 3.39x10 -4
[NO3] = 0 8.9x10 -3
9.35x10-5 2.9x10-5 2.1×10-6 5.5x10-9
9.7x10-4 1.9x10-4 1.0xl0-5 2.3x10-s
The counterion (H+) released from the cation exchanger is consumed by the reaction with the coion (OH-). Consequently, a conventional ion exchange is accompanied by the irreversible reaction. Taking into account that chemical reaction results in an elimination of coions (OH-), one could expect that, after the attainment of equilibrium with the cation exchanger, the solution should be near neutrality. Nevertheless, the effluent acidity from pH 3.1 to pH 4.4 was observed (Table 2, solution No. 1). This is because the equilibrium of the ionization of sulphonic acid cation exchangers
is displaced to the right: the apparent ionization constant (K,) is 10 -2 to 10-3 [14]. Consequently, the concentration of hydrogen ions is sufficiently high to displace equilibrium (1) to the fight, resulting in an increase in the concentration of NH~ ions, and to promote the sorption of NH4, proceeding accordingly to Eq. (4). At 5% (0.2 g NH~/L) breakthrough, the sorption cycle is interrupted, and the regeneration of cation exchanger carried out. A 5% breakthrough occurs after treating 5 BV of solution No. 1 with Amberlite 252 (Fig. 1, curve I), 6 BV with Lewatit K 2629 (Fig. 2, curve 1) and 7 BV with Relite C 360 (Fig. 3, curve 1). The sorption capacity ofRelite C 360 at a 5% breakthrough is the highest one amongst the cation exchangers investigated (Table 2). With the addition of NH4NO3 into solution and the corresponding decrease in the concentration ratio [NH3]/[NH4NO3], the concentration ratio [OH-]/ [NO;] also decreases (Table 1). As a result, a decrease in the effluent pH from 10.5 to 1.5 was observed (Table 2, solution no. 2). This is because, besides the sorption of NH~, proceeding on the basis of ion exchange and followed by the neutralization reaction accordingly to equilibrium (4), the sorption of NH~, proceeding on the basis of conventional ion exchange and leading to an increase in the concentration of hydrogen ions
R SO3H ~-+ R SO3 + H +
RSO3H + NH4NO3 ~-+RSO3NH4 + H + + NO3 (6)
3. Results and discussion
As the aqueous solution of ammonia is treated with the sulphonic acid cation exchanger in H + form, the substitution of H + ions by NH~ ones, leading to the sorption of NH~ ions, occurs as follows: R SO3H + N H 4 O H
~-~ R S O 3 N H 4 q- H20
(4)
(5)
A. Ancuta et al. / Desalination 175 (2005) 259-268 Q;
0 o
Q eel 0
(o
0
0
o
£.)
0
t~ cq
~"~ •
0
°
rg
0
't'l
eg
N 6
.
°
.
,
- -
263
A. Ancuta et al. / Desalination 175 (2005) 259--268
264
3000
3000
2500
4
1 + ,~
3
2
2000
5
~
o
500
2
4
6
8
10
12
500
Fig. 1. Breakthroughcurves for the sorption of NH~ from NH3-NH4NO3 solutions by Amberlite 252. The number of the curve corresponds to number of the test solution (Table 1). 6
2500
1
4
32 X5
13
20oo
E
+.; 1500
looo 5o0 L
-
2
_
m
4
6
8
2
4
6
8
10
12
14
Volume of effluent (bed volumes)
Volume ~emue~(bedvolumes)
o 0
1500
0
O,
w
3
lOOO
10oo
..I
2500
E +~ •1- 2000 z o
1soo
f?2 4
10
12
Volume of effluent (bed volumes)
Fig. 2. Breakthroughcurves for the s o r p t i o n of NH~ from NH3-NH4NO3 solutions with the Lewatit K 2629. Number of the curve corresponds to number of the test solution (Table 1).
takes place. When NH4NO 3 concentration in the initial solution is increased, maximum sorption at 5% breakthrough, followed by a decrease in the effluent pH to 1, is observed (Table 2, solution no. 3). The acidity, corresponding to pH 1, is not so high as to interfere significantly with the deprotonation of sulphonic groups, and, consequently, with the sorption of NH~, proceeding
Fig. 3. Breakthroughcurves for the sorption of NH4 from NH3-NH4NO3solutions by Relite C 360. The number of the curve corresponds to number of the test solution (Table 1). accordingly to equilibrium (6). With a further decrease in [ N H 3 ] / [ N H 4 N O 3 ] , the effluent pH ecreases to 0.8-0.9 (Table 2, solutions nos 4-6). This is because the sorption of NH~, proceeding accordingly to equilibrium (6), becomes overwhelming. However, a strongly acidic medium results in a displacement of equilibrium (5) to the left, followed by a decrease in the concentration of deprotonated functional groups, which consequently results in a decrease in the sorption of NH~. In this connection the diminution of the sorption capacity at a 5% breakthrough was observed (Table 2, solution nos 4-6). Nevertheless, the diminution of the sorption is only slightly affected by a decrease in pH because the value of the ionization constant (K,) is rather high [14]. The sorption capacity at a 50% breakthrough is significantly higher when compared to that at 5%, especially for the Relite C 360. If the cation exchanger, saturated with NH4, is subjected to an action by the nitric acid solution, the displacement of equilibrium (6) to the left takes place, resulting in both the desorption of NH~ and the regeneration of the sorption capacity. The higher the concentration maximum in
265
A. Ancuta et aL / Desalination 175 (2005) 259-268 10
8
g
7 7
o¢
g
5
5 4
z ~
24 a
4 s
3 2
2
8
3
1
o
o 0
0.3
0.6
0.g
1.2
1.5
0
C360, saturated with NH3-NH4NO3 solutions. The number of the curve corresponds to the number of the test solution (Table 1). the eluate and the less the volume of the eluate, needed to attain the maximum, the higher the regeneration efficiency. The maximum ratio C/Co between the eluate concentration (C) and the saturation liquid concentration (Co) is attained with 0.2-0.5 BV of the eluent for Relite C360 (Fig. 4) and with 0.2 BV for Amberlite 252 (Fig. 5), whereas the C/Co maximum for Lewatit K2629 is displaced by 0.4--0.6 BV (Fig. 6). An important parameter of practical significance is the decontamination factor (DF) [15], indicating the ratio between the concentration of ammonium in the effluent prior to a 5% breakthrough and the corresponding concentration in the eluate from the regeneration. Experimental data indicate D F decreases with the ammonium concentration decrease in the initial solution (Table 2). To avoid excessive evaporation expenses, the volume of the eluate from the regeneration of the cation exchanger, saturated with caustic condensate, must be no more than 0.7 BV. When 0.7 BV 20% HNO3 is used as eluent, the highest concentration of NH~ (136.7 g/L) and the highest regeneration degree (70.3% o f the sorption
0.6
0.9
1.2
1.5
Volume of effluent (bed volumes)
Volume of effluent (bed volumes)
Fig. 4. Elution of NH; by 20% I-IN03 from the Relite
0.3
Fig. 5. Elution ofNH4+by 20% HNO3from the Amberlite 252, saturated with NH3-NH4NOa solutions. The number of the curve corresponds to the number of the test solution (Table 1).
7
G z
i
o 10/ 0
%ol 0.3
0,6
0,9
1.2
1.5
Volume of effluent (bed volumes)
Fig. 6. Elution of NH~ by 20% HNO 3 from the Lewatit K 2629, saturated with NH3-NH4NO 3 solutions. The number of the curve corresponds to the number of the test solution (Table 1). capacity), as well as the lowest concentration of free nitric acid have been obtained in the eluate from Relite C 360 (Table 3). Considering the ammonium concentration 0.2 g/L in the effluent at a 5% breakthrough as a treatment objective, the total ammonium concentration in the solution after treatment (until
266
.4..4ncuta et al. / Desalination 175 (2005) 259-268
_=
P~
0
"0
0 o.)
0
0 t~
< Z
o.)
_=
°i p~
.
.
.
.
° °
¢'4
oJ
267
A. Ancuta et at/Desalination 175 (2005) 259-268
Table 4 Parameters for the recovery of NH~ from NH3-NH4NO3test solutions (average for solutions Nos. 1-6) Cation exchanger
Co, equ/L" V, L
Ce, equ/L
C,, g/L
V,, L
C, equ/L
N, %
Lewatit I(2629 Amberlite 252 Relite C360
0.24 0.214 0.214
1.103 1.120 1.523
88.2 89.6 122.3
0.0175 0.0175 0.0175
0.128 0.127 0.108
40.1 40.7 50.5
0.225 0.225 0.250
'Co = [NH3]+ [NI1;]. breakthrough) (C, equ/L) can be determined from the arrangement of the mass balance equation: K C = Co - ~ × C~ V
(7)
where Co is the initial concentration of ammonium in the solution before treatment (equ/L), C, the total concentration of NH4NO3 in the eluate (equ/L), V the volume (L) of the solution treated until C/Co = 0.05, and Ve the volume of the eluate (L). Ammonium recovery efficiency (N), defined as the percentage of ammonium in the eluate compared to the total amount in the solution before treatment,
N - C, V, x 100
CoY
(8)
is presented in Table 4. To predetermine the osmotic stability of the cation exchangers, 100 cycles (each of them comprises the saturation with NH~ ions from the solution, containing 0.176 equ/L of NH 3 and 0.038 equ/L ofNH4NO 3 at pH 10.53, the successive regeneration with 20% HNO3 and washing with distilled water) were carded out. Most of the beads aider 100 cycles remained undamaged. 4. Conclusions
The sorption of ammonium ions and ammonia by the H ÷ form of sulphonic cation exchangers (Amberlite 252, Lewatit 2629, Relite C360) from
the solution containing NH 3 in the range of 0.353 to 0 equ/L and NH4NO3 in the range of 0 to 0.214 equ/L and corresponding to the composition of the caustic condensate, generated in the nitrogen fertilizers production, depends on the concentration ratio of ammonia to ammonium nitrate [NH3]/[NH4NO3], as well as on the initial solution pH. When [NH3]/[NH4NO3] decreases, the ratio of hydroxyl to nitrate [OH]/[NO~] and pH of the effluent prior to NH~ breakthrough (0.2 g NH~/L) also decrease. A decrease in [OH']/ [NO3] results in a decrease in that portion of the NH~ sorption, which proceeds on the basis of ion exchange, accompanied by irreversible reaction (neutralization of hydrogen ions, released from the cation exchanger), and leads to an increase in that portion of NH~"sorption, which proceeds on the basis of the conventional ion exchange. As a result, the effluent pH and, subsequently, the concentration ofdeprotonated functional (-SO3H) groups decrease, leading also to a decrease in the NH~ total sorption. The maximum sorption of NH~ corresponds to [NH3]/[NH4NO3] -1.2. The concentration (g/L) of NH4NO3 in the eluate from the cation exchanger regeneration, carded out with 0.7 BV 20% HNO3, amounts to 136.7 for Relite C360, 119.5 for Lewatit L2629 and 96.7 for the Amberlite 252. The cation exchangers investigated are resistant to boiling in 20% HNO3 solution. Osmotic stability is 97-99.8%. The exchangers are applicable for the recovery of NH4NO3 from caustic condensate, providing a new opportunity for economic consideration and environmental issues.
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A. Ancuta et al. / Desalination 175 (2005) 259-268
Acknowledgements A Bayer Company, Bang & Bonsomer and Technical Projects Company are acknowledged for supplying the cation exchangers.
References [1] J. Jaqust, Z. Dzendo and N. Arion, Nitrogen, 163 (1986) 28-34. [2] M. Philipot, G. De Laminat, Nitrate removal by ion exchange, Water Supply, 6(3) (1988) 45-50. [3] D. Clifford and X. Xiaosha, J. AWWA, 85 (1993) 135-143. [4] R. Bohm, Application of Ion Exchanger for Cleaning Waste Waters of Fertilizer Production. 4. Symp. of Ion Exchanger, Siofok, 1980. [5] F. Orszag, F. Ratkocics and B. Szeiler, Hung. J. Indus. Chem., 9 (1981) 241-250. [6] N. Arion, J. Jagust and 7.. Dzendo, Nitrogen, 8-9 (1986) 28--34.
[7] S. Leakovi~, I. Mijatovi~, ~. Cerjan-Stefanovi~ and E. Hod,~i6,Water Res., 34(1) (2000) 185-190. [8] R. Davies, Chem. Engn. Progress, 1 (1994) 63-71. [9] C. Caiman, Explosion hazards of using nitric acid in ion-exchange equipment, Chem. Engn., 87(23) (1980) 271-274. [10] G. Keenan, K. Notz and N.B. Franeo, Synergistic catalysis of ammonium nitrates decomposition, J. Amer. Chem. Soc., 91(12) (1969) 3168-3171. [11] D.G. Peters, J.M. Hayes and G.M. HieRje, Chemical Separations and Measurements. Theory and Practice of Analytical Chemistry, W.B. Saunders, Bloomington, 1974, p. 117. [12] K. Dorfner, Ion Exchangers, Valter de Guyter, Berlin, New York, p. 70. [13] Y.Y. Lur'e and A.J. Ribnikova, Chemical Analysis of Industrial Waste Waters, Khimiya, Moscow, 1974, pp. 67-68 (in Russian). [14] E.Y. Zakharov, B.E. Rebchikov and B.D. D'yakov, Ion Exchange Installation in Nuclear Industry, Energoatomizdat, Moscow, 1987,p. 22 (in Russian). [15] T.H. Karpipinen and A. Yuli-Pentti, Sep. Sci. Technol., 35(10) (2000) 1619.