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Comparison of ion exchange resins used in reduction of boron in desalinated water for human consumption
Desalination 278 (2011) 244–249
Contents lists available at ScienceDirect
Desalination j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / d e s a l
Comparison of ion exchange resins used in reduction of boron in desalinated water for human consumption María Fernanda Chillón Arias ⁎, Laureano Valero i Bru, Daniel Prats Rico, Pedro Varó Galvañ Institute of Water and Environmental Sciences, University of Alicante, 03080 Ctra. San Vicente s/n, Alicante, Spain
a r t i c l e
i n f o
Article history: Received 13 December 2010 Received in revised form 10 May 2011 Accepted 11 May 2011 Available online 8 June 2011 Keywords: Ion exchange Boron removal Reverse osmosis water
a b s t r a c t There are currently different resins on the market used for the elimination of boron in water. They are composed of the same active group. These are crosslinked macroporous polystyrene resins, with the active group N-methyl-D-glucamine (NMG). The NMG of the resin captures the boron via a covalent bond. The borate ion is complexed by two sorbitol groups. A comparative study of the resins Amberlite IRA 743, Purolite S-108 and XU-43594.00 Filmtec was carried out in a pilot plant of 160 L/h. The retention capacity of boron and its performance compared with other ions was analyzed. The water used as feed comes from the desalination plant of Alicante Canal. The behaviour of the three resins is very similar and the beginning of the appearance of boron in the treated water in all three cases occurred at virtually the same point. To check the selectivity of the resin for boron, the main cations in water, sodium, potassium, calcium and magnesium were analyzed. No reduction in the concentration of the cations tested was observed in any of the resins. The only change experienced by the treated water through the resin was a reduction in the boron concentration. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Ion exchange is a unit operation of transfer between two phases, one solid and one liquid. This is the reversible exchange of ions between a solid and a liquid, in which there is no permanent change in the structure of the solid. There are currently different resins on the market used for the selective disposal of boron in water. Although these resins come from different companies, they are all composed of the same active group. These are crosslinked macroporous polystyrene resins, with the active group N-methyl-D-glucamine (NMG) [1–4] (Fig. 1). The useful operating capacity of the resin depends on the concentration of boron in the feed, the flow, the effectiveness of regeneration and limits of boron in the output [5]. In contrast to standard ion exchange processes, the NMG of the resin captures the boron through a covalent bond and forms a complex of internal coordination (Fig. 2). In a wide range of pH, boric acid is added to the cis–diol pair of the functional group to form a relatively stable complexed ester, cis–diol borate (Fig. 3). In the work carried out by Boëseken and Vermaas [6], Deson and Rosset [7], Pinon et al. [8], the boron is retained as follows: The borate ion is complexed by two sorbitol groups and a proton is retained by a tertiary amine, through a mechanism of anion exchange in a weak base.
⁎ Corresponding author. Tel.: + 34 965909486; fax: + 34 965909418. E-mail address: [email protected] (M.F.C. Arias). 0011-9164/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2011.05.030
The reaction occurs as follows [1]: • Boric acid dissociation: −
BðOHÞ3 ↔½BðOHÞ4 þ H
þ
• Boron complexation -CH-O
B (OH ) −4 + 2 − CHOH − CHOH ↔ 4 H 2O +
O-CHB
-CH-O
O-CH-
• Amine protonation: þ
þ
–CH2 –NðCH3 Þ–CH2 – þ H ↔–CH2 þ N HðCH3 Þ–CH2 –
Nadav et al. [2], Simonnot et al. [1], De la Fuente. [3] and Yilmaz et al. [10] conducted studies with Amberlite IRA 743 resin, but making a comparison with results obtained by them is difficult because this depends on the design of the system used (column height, flow rate, concentration of boron in the feed and temperature). Nadav et al. [2] treated desalinated water from a seawater desalination plant at 25 °C and 1.8 mg/L of boron, using two columns with a resin height of 2.3 m and a total volume of 14 L. They do not specify the flow rate, setting it within a range between 10 and 20 BV/h. They compare the regeneration of the resin using only sulphuric acid and sulphuric acid – sodium hydroxide, observing the second alternative as optimal. Under these circumstances, the appearance of boron in the effluent water was detected after treatment at 546 BV.
M.F.C. Arias et al. / Desalination 278 (2011) 244–249
245
decreases the fraction P is proportional to the increase in A, as shown in the following equation [10]: dA = kAP dt
−
ð1Þ
Eq. (1) is non-linear and can be integrated with initial conditions in that for t0, the concentration of boron in the resin will be A0
j
ln
j
Að1−A0 Þ = kðt0 −t Þ A0 ð1−AÞ
ð2Þ
In the same way, noting that P = 1 − A, Eq. (2) can be rewritten as: Fig. 1. Structure of the selective resin N-methyl glucamine [3].
j
ln
j
P0 ð1−P Þ = kðt0 −t Þ P ð1−P0 Þ
ð3Þ
By definition τ is the time required for the boron concentration in the outlet water to correspond to that of half the incoming water. Eq. (3) could be expressed as:
Simonnot et al. [1] carried out their tests on a laboratory scale and on changing the boron concentration to between 1 mg/L and 210 mg/L, the boron retention obtained by the resin was between 1.66 and 2.35 g. Thus for concentrations between 1 and 3 mg/L in the feed, retentions of between 1.66 g and 1.87 g would be obtained. De la Fuente et al. [3] used the Amberlite IRA-743 resin in a study of methods for the determination of boron and of control of change in the process of wastewater treatment using boron removal resin. They did not directly analyze the behaviour of the resin. Yilmaz et al. [10] suggested the use of this resin for boron removal in wastewater treatment. They analyzed the behaviour at different flows (10, 20 and 30 mL/min), resin beds (71.6, 107.5 and 143.2 cm 3), concentrations of boron (250, 500 and 1000 mg/L) and temperatures (10, 20, 30 and 40 °C). Kabaya et al. [4] conducted studies using Dow XU-43594.00 resin. Their research was carried out at laboratory scale, using a column with a height of 10 cm and a resin volume of 0.5 mL. The water to be treated showed a boron concentration of 1.5 mg/L. Under these conditions they presented results that, when working with a flow of 15 BV/h, detected an occurrence of boron in the treated water from 600 BV. This paper examines comparatively the effectiveness of different resins used in the removal of boron from water previously desalted by reverse osmosis. The selectivity of the same with respect to boron is also tested by not removing other ions in the solution.
According to Eq. (6) time t versus ln[C/(C0 − C)] can be represented, thus the values of τ and 1/k respectively, τ can be obtained. Alternatively, τ can be obtained from the adsorption time when ln[C/(C0 − C)]= 0, as by definition, τ is the adsorption time when C = 1/2C0. Agreeing that the resin bed can be completely saturated at 2τ, the amount of boron retained by the resin (We) can be calculated [10]:
2. Theory
We =
P=
1 1 + exp½kðτ−t Þ
ð4Þ
1 P ln k 1−P
ð5Þ
t ¼τþ
The fraction of boron (P) passing through the resin is equal to C/C0, where C is the concentration of boron in the aqueous solution leaving the resin and C0 is the boron concentration of the feed. Therefore Eq. (1) can be rewritten as: t=τ+
1 C ln k C0 −C
1 C F ð2τÞ = Ce Fτ 2 e
ð6Þ
ð7Þ
Unlike the behaviour of other ion exchange resins, N-methyl glucamine captures the boron through the formation of a covalent bond forming a complex of internal coordination. Therefore, the uptake of boron is carried out through a process of adsorption. In the column adsorption process, the aqueous solution flows through a fixed bed of resin. A portion of boron from the aqueous solution is retained by the resin bed. The fraction of adsorbed boron is A, and the fraction of boron remaining in the aqueous solution that passes through the resin is P. It is reasonable to assume that the amount that
This equation establishes the relationship between the adsorption capacity of the column (We), the concentration of boron in the solution (Ce), the flow of fluid (F) and 50% breakthrough time (τ).
Fig. 2. Methylglucamine resin with complexed boric acid [9].
Fig. 3. Reaction mechanism of boron uptake [5].
246
M.F.C. Arias et al. / Desalination 278 (2011) 244–249
Fig. 4. Flowchart exchange resins pilot plant.
plant. Table 1 shows the ranges of the most significant parameters within which the resins were operated.
3. Experimental 3.1. Pilot plant The pilot plant for ion exchange resins is designed to ensure continuous operation. It has two columns of resins, which work alternately, so that one of them can be regenerated while the other continues running. The treatment capacity of the facility is 160 L/h (3.8 m 3/day). Fig. 4 shows the flow chart of the installation.
3.4. Analytical method The boron analysis was performed using emission spectroscopy by inductively coupled plasma. The equipment used was model 4300 from Perkin Elmer. The LOD for boron calculated for this equipment was 0.02 mg/L and the LOQ 0.08 mg/L.
3.2. Ion exchange resins
3.3. Feed water The feed water comes from the desalination plant of Alicante Canal. To carry out testing, the pilot plant was located in the premises of the desalination plant and can operate continuously using permeate water produced by the desalination plant Alicante Canal. The water is obtained directly from the pressure tubes before remineralization. During the studies, variations in the feed characteristics were produced, due to changes in operating conditions of the industrial
Table 1 Range of parameters of the feed water during experimentation with resins.
3.5. Tests performed Resins were characterized by plotting Breakthrough curves. The physical parameters of the process were measured and samples were taken to analyze the concentration of boron. The pilot plant has been designed to work with a flow rate of 160 L/h, containing a volume of 10 L resin in each column. To study the behaviour of the resins, the operating parameters established by the manufacturers for both their operation and regeneration, were used. Amberlita IRA 743
2,50
Purolite S 108
[B] treated water (mg/L)
Three commercial resins from different manufacturers were selected: IRA 743, Rohm and Haas, Purolite S-108's and Dow XUS43594.00. These resins are specifically used for the removal of boron and are suitable for use with brackish water. The three resins have similar characteristics.
Dow XU-43594.00
2,00 1,50 1,00 0,50 0,00
Parameter
Value
Units
Conductivity at 20 °C Boron Temperature
777–1038 1.38–1.94 15.6–27.4
μS/cm mg/L °C
0
1000
2000
3000
V/Vresin Fig. 5. Boron concentration of treated water.
4000
M.F.C. Arias et al. / Desalination 278 (2011) 244–249 3,0
Table 3 Comparative summary for a boron concentration of 0.5 mg/L in treated water.
2,5
B (gr/L resin)
247
2,0
Parameter
Amberlite IRA 743
Purolite S-108
Dow XU-43594.00
1,5
Start saturation (L/LRESIN) Retention (g B/LRESIN) Regeneration cycle
1200 1.5 75 h (3.1 days)
1100 1.6 71 h (2.9 days)
1000 1.5 66 h (2.7 days)
Amberlita IRA 743 Purolite S 108
1,0
Dow XU-43594.00
0,5 0,0 2000
3000
4000
V/Vresin Fig. 6. Boron accumulated by the resin.
3.6. Calculations The volume of treated water in the ion exchange process is referred to as the bed volume used in the process, in order to analyze and compare the results obtained in different trials. V = V treated water = V resin
ð8Þ
From the data obtained experimentally, time t versusLn[C/(C0 − C)], is shown graphically, thus obtaining the distribution coefficient and the time of Breakthrough. The saturation capacity of the resin in specific working conditions has been calculated using Eq. (7). 4. Results and discussion The behaviour of the three selected resins Amberlite IRA 743, Purolite S-108 and Dow XU-43594.00 was analysed and the operating conditions established. The variation of boron concentration in the treated water has been studied, referring the volume of treated water to the bed volume. To check the reproducibility of results, the trials were tripled for each of the resins, and the most favourable for each of them are presented. The volume of treated water was determined, starting from when the boron concentration begins to increase and the volume of treated water when the concentration of boron in the final product reaches 0.5 mg/L. The range of temperatures in which these tests were carried out varies considerably, due to the length thereof, as work had to be done at different times of the year. Fig. 5 shows data for the concentration of boron in the treated water compared to the volume treated per unit bed volume for the three resins. The behaviour of the three resins is very similar and the beginning of the appearance of boron in the treated water in all three cases, occurs at virtually the same point. The same trend is observed with boron concentrations up to 0.5 mg/L. The data on the amount of boron per litre of resin retained against the volume treated per unit volume of bed is shown in Fig. 6. For the desired final concentration of boron (below the LOD and 0.5 mg/L), the three resins have a similar saturation capacity, as shown in Tables 2 and 3.
Likewise, in the same graph (Fig. 7) the Breakthrough curves calculated for the three resins are represented. Fig. 7 indicates the similarity of the results obtained in all three cases. Ideally one would expect that the three curves are better approximated to the values of [B]/[B]0 = 1, which would mean that total saturation of the resin has been reached. But on an industrial scale this total saturation can be difficult to achieve because the saturation capacity of the resin depends on the operating conditions of the process. The physio-chemical properties of water and the workload considerably affect the final result [10].
4.1. Kinetic parameters Fig. 8 shows the representation of t versus ln[C/(C0 − C)] with each of the resins. Table 4 summarizes the values of τ and k calculated from the lines obtained in Fig. 8. It also presents the value of W calculated for each resin in the operating conditions in which the tests were carried out. For Amberlite IRA 743, if the saturation capacity of the resin is expressed in equivalents, the average value of W = 0.5 eq/L is obtained.
1,20 1,00 0,80
[B]/ [B]0
1000
0,60 0,40 Amberlita IRA 743
0,20
Purolite S108 Dow XU-431594
0,00 0
2000
4000
Parameter
Amberlite IRA 743
Purolite S-108
DowXU-43594.00
900 1.3 56 h (2.3 days)
800 1.3 51 h (2.1 days)
800 1.3 52 h (2.1 days)
10000
12000
14000
8000 7000 6000 5000 4000
y = 1033,1x + 4776
2000
Start saturation (L/LRESIN) Retention (g B/LRESIN) Regeneration cycle
8000
Fig. 7. Breakthrough curve.
3000
Table 2 Comparative summary for a boron concentration in treated water below LOD.
6000
t(min)
t(min)
0
y = 1380,8x + 5113,2
Amberlita IRA743
y = 665,13x + 4513,2
Purolite S108
1000 0 -2,00
Dow XU-431594
-1,50
-1,00
-0,50
0,00
0,50
1,00
1,50
Ln([B]/([B]0-[B])) Fig. 8. t versus ln[C/(C0 − C)] for the three resins.
2,00
248
M.F.C. Arias et al. / Desalination 278 (2011) 244–249
Table 4 Values of τ, k and W.
Amberlite IRA 743 Purolite S 108 Dow XU-43594.00
Table 5 Boron concentration versus time of operation. τ (min)
k (min−1)
W (g B/Lresin)
4776 5113 4513
1.054*10−3 0.724*10−3 1.503*10−3
1.9 2.0 2.0
The specifications of this resin set a maximum capacity of 0.8 eq/L. Given that the manufacturer establishes flow conditions of operation between 4 and 30 BV/h and we established a working flow of 15.6 BV/h, the results seem reasonable. Simonnot et al. [1] carried out their tests on a laboratory scale with Amberlite IRA743. For concentrations between 1 mg/L and 3 mg/L in the feed (which falls within our range of work), they obtained retentions between 1.66 mg/L and 1.87 mg/L. Yilmaz et al. [10] show values of τ (min) and k (min−1) but due to differences in working conditions (boron concentrations of 250, 500 and 1000 mg/L) the results cannot be considered comparable. If the saturation capacity of the Purolite S 108 resin in equivalents is expressed, an average value of W = 0.6 eq/L would be obtained. The specifications of this resin set a maximum capacity of 0.8 eq/L. Moreover, a graph is shown in the specifications representing the storage capacity of boron based on the workflow (Fig. 9). The flow of feed in the tests was 15.6 BV/h. According to Fig. 9, the retention capacity of boron for this flow should be about 2 g B/L which is consistent with experimental results. For the DOW XU-43594.00 resin, the manufacturers set a maximum between 3.4 g/L and 4 g/L in their specifications. Taking into account the workflow established (15.6 BV/h), the results obtained also seem reasonable. Kabay et al. [4] developed their work with this resin but no data is provided of the kinetic parameters calculated. From the values of τ and k in Table 4, the equation can be established which relates the concentration of boron in treated water versus time of operation (Table 5). Fig. 10 shows graphically the results obtained experimentally compared to those calculated from the equations presented in Table 5.
4.2. Study of the removal of other ions To check the selectivity of the resin for boron, the major cations in water were analyzed: sodium, potassium, calcium and magnesium. Very similar results were obtained with all three resins. No reduction in the concentration of the cations tested was observed with any of the resins.
Resin
Equation
Amberlite IRA 743
C=
1 h i C0 1 + exp 0:967⋅10−3 ð4839−t Þ
Purolite S108
C=
1 h i C0 1 = exp 0:724⋅10−3 ð5113−t Þ
Dow XU-43594.00.
C=
1 h i C0 1 + exp 1:503⋅10−3 ð4513−t Þ
5. Conclusions A comparative study was carried out of Amberlite IRA 743, Purolite S-108 and Dow XU-43594.00 resins with a pilot plant, working at a rate of 160 L/h. The retention capacity of boron and its performance against other ions was analyzed. The water used as feed came from the desalination plant of Alicante Canal. In studies performed with Amberlite IRA 743, the beginning of the saturation of the resin occurred after treating 900 L/Lresin which represents a retention of approximately 1.3 g B/Lresin. The concentration of boron in the treated water was kept below 0.5 mg/L until around 1200 L/Lresin was treated, i.e. when the resin retained about 1.5 g B/Lresin. Under these conditions, the resin regeneration should be performed every 56 h (2.3 days) if complete absence of boron is required and 75 h (3.1 days) if the concentration is to be kept below 0.5 mg/L. In studies performed with the Purolite S-108 resin, the beginning of the saturation of the resin occurred after treating 800 L/Lresin, representing a retention of 1.3 g B/Lresin.The concentration of boron in the treated water was kept below 0.5 mg/L until 1100 L/Lresin was treated, i.e. when the retention of the resin was about 1.6 g B/L resin. Under these conditions the resin regeneration should be performed every 51 h (2.1 days) if the total absence of boron is required and 71 h (2.9 days) if the concentration is to be kept below 0.5 mg/L. In studies with the Dow XU-43594.00 resin, the onset of saturation of the resin occurred when 800 L/Lresin was treated. The amount of boron retained by the resin was 1.3 g B/Lresin. The concentration of boron in the treated water was kept below 0.5 mg/L until 1000 L/Lresin was treated, i.e. when the retention of the resin was about 1.5 g B/L resin. The resin regeneration should be performed every 52 h (2.1 days) if the complete absence of boron is required and 66 h (2.7 days) if the concentration is to be kept below 0.5 mg/L. The behaviour of the three resins is very similar and in all three cases, the beginning of the appearance of boron in the treated water
2
[B]product water (mg/L)
1,8 1,6 1,4 1,2 1 0,8
Amberlita IRA 730 experimental
0,6
Amberlita IRA 730 calculado Purolite S108 experimental
0,4
Purolite S108 calculado Dow XU-43594.00 experimental
0,2
Dow XU-4394.00 calculado
0 0
1000
2000
3000
4000
5000
6000
7000
8000
9000 10000
t (min) Fig. 9. Saturation capacity of the resin depending on operating conditions. Purolite S-108. Manufacturer's specifications.
Fig. 10. Experimental and calculated results of the boron concentration in treated water versus time.
M.F.C. Arias et al. / Desalination 278 (2011) 244–249
occurred at virtually the same point. The same trend was observed when working with boron concentrations up to 0.5 mg/L. To check the selectivity of the resin for boron; the major cations in water were analyzed: sodium, potassium, calcium and magnesium. No reduction in the concentration of the cations tested was observed in any of the resins. The only change experienced by the treated water through the resin was a reduction in the concentration of boron. Nomenclature A Fraction of boron adsorbed by the resin P Fraction of boron remaining in the aqueous solution k Constant (min−1) t Time (min) τ Breakthrough time (min) C Concentration of boron in aqueous solution at the outlet of the resin (g/L) C0 Concentration of boron in the feed (g/L) Ce Concentration of boron in the solution (g/L) We Adsorption capacity of the column (g/Lresin) L = Lresin a F Solution flow min Acknowledgements This work has been funded through the project “Technical assistance for applied research on boron reduction in desalinated water
249
(ACUAMED-Waters of the Mediterranean basin, SA) and Treatment and reuse of wastewater for sustainable development” (CSD2006-44). References [1] M. Simonnot, C. Castel, M. Nicolaï, C. Rosin, M. Sardin, Jauffret, Boron removal from drinking water with a boron selective resin: is the treatment really selective? Water Resources 34 (1) (1999) 109–116. [2] N. Nadav, Boron removal from seawater reverse osmosis permeate utilizing selective ion exchange resin, Desalination 124 (1999) 131–135. [3] M.M. De la Fuente García-Soto, E. Muñoz Camacho, Boron removal industrial wastewaters by ion exchange: an analytical control parameter, Desalination 181 (2005) 207–216. [4] N. Kabay, S. Sarp, M. Yuksel, M. Kitis, H. Koseiglu, O. Arar, M. Bryjak, R. Semiat, Removal of boron from SWRO permeate by boron selective ion exchange resins containing N-methyl glucamine groups, Desalination 223 (2008) 49–56. [5] C. Marston, M. Busch, S. Prabhakaran, A boron-selective resin for seawater desalination, European Desalination Society Conference on Desalination and the Environment, 2005. [6] J. Böeseken, N. Vermass, Sur l'existance de complexes de l'acide borique avec une et avec deux moléculas d'un ion dans les solutions aqueuses, Récents Travaux en Chimie 54 (1935) 853–860. [7] J. Deson, R. Rosset, Extraction de traces de bore au moyen de la résine échangeuse d'ions Amberlite XE 243 1968), Bulletin de la Société Chimique de France 8 (1968) 4.307–4.310. [8] F. Pinon, J. Deson, R. Rosset, Propriétés de la résine échangeuse dìons spécifique du bore Amberlite XE 243, Bulletin de la Société Chimique de France 8 (1968) 3.454–3.461. [9] C. Jacob, Seawater desalination: boron removal by ion exchange technology, Desalination 205 (2007) 47–52. [10] A.E. Yilmaz, R. Boncukcuoglu, M.T. Yilmaz, M.M. Kocakerim, Adsorption of boron from boron-containing wastewaters by ion exchange in a continuous reactor, Journal of Hazardous Materials B117 (2005) 221–226.
Contents lists available at ScienceDirect
Desalination j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / d e s a l
Comparison of ion exchange resins used in reduction of boron in desalinated water for human consumption María Fernanda Chillón Arias ⁎, Laureano Valero i Bru, Daniel Prats Rico, Pedro Varó Galvañ Institute of Water and Environmental Sciences, University of Alicante, 03080 Ctra. San Vicente s/n, Alicante, Spain
a r t i c l e
i n f o
Article history: Received 13 December 2010 Received in revised form 10 May 2011 Accepted 11 May 2011 Available online 8 June 2011 Keywords: Ion exchange Boron removal Reverse osmosis water
a b s t r a c t There are currently different resins on the market used for the elimination of boron in water. They are composed of the same active group. These are crosslinked macroporous polystyrene resins, with the active group N-methyl-D-glucamine (NMG). The NMG of the resin captures the boron via a covalent bond. The borate ion is complexed by two sorbitol groups. A comparative study of the resins Amberlite IRA 743, Purolite S-108 and XU-43594.00 Filmtec was carried out in a pilot plant of 160 L/h. The retention capacity of boron and its performance compared with other ions was analyzed. The water used as feed comes from the desalination plant of Alicante Canal. The behaviour of the three resins is very similar and the beginning of the appearance of boron in the treated water in all three cases occurred at virtually the same point. To check the selectivity of the resin for boron, the main cations in water, sodium, potassium, calcium and magnesium were analyzed. No reduction in the concentration of the cations tested was observed in any of the resins. The only change experienced by the treated water through the resin was a reduction in the boron concentration. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Ion exchange is a unit operation of transfer between two phases, one solid and one liquid. This is the reversible exchange of ions between a solid and a liquid, in which there is no permanent change in the structure of the solid. There are currently different resins on the market used for the selective disposal of boron in water. Although these resins come from different companies, they are all composed of the same active group. These are crosslinked macroporous polystyrene resins, with the active group N-methyl-D-glucamine (NMG) [1–4] (Fig. 1). The useful operating capacity of the resin depends on the concentration of boron in the feed, the flow, the effectiveness of regeneration and limits of boron in the output [5]. In contrast to standard ion exchange processes, the NMG of the resin captures the boron through a covalent bond and forms a complex of internal coordination (Fig. 2). In a wide range of pH, boric acid is added to the cis–diol pair of the functional group to form a relatively stable complexed ester, cis–diol borate (Fig. 3). In the work carried out by Boëseken and Vermaas [6], Deson and Rosset [7], Pinon et al. [8], the boron is retained as follows: The borate ion is complexed by two sorbitol groups and a proton is retained by a tertiary amine, through a mechanism of anion exchange in a weak base.
⁎ Corresponding author. Tel.: + 34 965909486; fax: + 34 965909418. E-mail address: [email protected] (M.F.C. Arias). 0011-9164/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2011.05.030
The reaction occurs as follows [1]: • Boric acid dissociation: −
BðOHÞ3 ↔½BðOHÞ4 þ H
þ
• Boron complexation -CH-O
B (OH ) −4 + 2 − CHOH − CHOH ↔ 4 H 2O +
O-CHB
-CH-O
O-CH-
• Amine protonation: þ
þ
–CH2 –NðCH3 Þ–CH2 – þ H ↔–CH2 þ N HðCH3 Þ–CH2 –
Nadav et al. [2], Simonnot et al. [1], De la Fuente. [3] and Yilmaz et al. [10] conducted studies with Amberlite IRA 743 resin, but making a comparison with results obtained by them is difficult because this depends on the design of the system used (column height, flow rate, concentration of boron in the feed and temperature). Nadav et al. [2] treated desalinated water from a seawater desalination plant at 25 °C and 1.8 mg/L of boron, using two columns with a resin height of 2.3 m and a total volume of 14 L. They do not specify the flow rate, setting it within a range between 10 and 20 BV/h. They compare the regeneration of the resin using only sulphuric acid and sulphuric acid – sodium hydroxide, observing the second alternative as optimal. Under these circumstances, the appearance of boron in the effluent water was detected after treatment at 546 BV.
M.F.C. Arias et al. / Desalination 278 (2011) 244–249
245
decreases the fraction P is proportional to the increase in A, as shown in the following equation [10]: dA = kAP dt
−
ð1Þ
Eq. (1) is non-linear and can be integrated with initial conditions in that for t0, the concentration of boron in the resin will be A0
j
ln
j
Að1−A0 Þ = kðt0 −t Þ A0 ð1−AÞ
ð2Þ
In the same way, noting that P = 1 − A, Eq. (2) can be rewritten as: Fig. 1. Structure of the selective resin N-methyl glucamine [3].
j
ln
j
P0 ð1−P Þ = kðt0 −t Þ P ð1−P0 Þ
ð3Þ
By definition τ is the time required for the boron concentration in the outlet water to correspond to that of half the incoming water. Eq. (3) could be expressed as:
Simonnot et al. [1] carried out their tests on a laboratory scale and on changing the boron concentration to between 1 mg/L and 210 mg/L, the boron retention obtained by the resin was between 1.66 and 2.35 g. Thus for concentrations between 1 and 3 mg/L in the feed, retentions of between 1.66 g and 1.87 g would be obtained. De la Fuente et al. [3] used the Amberlite IRA-743 resin in a study of methods for the determination of boron and of control of change in the process of wastewater treatment using boron removal resin. They did not directly analyze the behaviour of the resin. Yilmaz et al. [10] suggested the use of this resin for boron removal in wastewater treatment. They analyzed the behaviour at different flows (10, 20 and 30 mL/min), resin beds (71.6, 107.5 and 143.2 cm 3), concentrations of boron (250, 500 and 1000 mg/L) and temperatures (10, 20, 30 and 40 °C). Kabaya et al. [4] conducted studies using Dow XU-43594.00 resin. Their research was carried out at laboratory scale, using a column with a height of 10 cm and a resin volume of 0.5 mL. The water to be treated showed a boron concentration of 1.5 mg/L. Under these conditions they presented results that, when working with a flow of 15 BV/h, detected an occurrence of boron in the treated water from 600 BV. This paper examines comparatively the effectiveness of different resins used in the removal of boron from water previously desalted by reverse osmosis. The selectivity of the same with respect to boron is also tested by not removing other ions in the solution.
According to Eq. (6) time t versus ln[C/(C0 − C)] can be represented, thus the values of τ and 1/k respectively, τ can be obtained. Alternatively, τ can be obtained from the adsorption time when ln[C/(C0 − C)]= 0, as by definition, τ is the adsorption time when C = 1/2C0. Agreeing that the resin bed can be completely saturated at 2τ, the amount of boron retained by the resin (We) can be calculated [10]:
2. Theory
We =
P=
1 1 + exp½kðτ−t Þ
ð4Þ
1 P ln k 1−P
ð5Þ
t ¼τþ
The fraction of boron (P) passing through the resin is equal to C/C0, where C is the concentration of boron in the aqueous solution leaving the resin and C0 is the boron concentration of the feed. Therefore Eq. (1) can be rewritten as: t=τ+
1 C ln k C0 −C
1 C F ð2τÞ = Ce Fτ 2 e
ð6Þ
ð7Þ
Unlike the behaviour of other ion exchange resins, N-methyl glucamine captures the boron through the formation of a covalent bond forming a complex of internal coordination. Therefore, the uptake of boron is carried out through a process of adsorption. In the column adsorption process, the aqueous solution flows through a fixed bed of resin. A portion of boron from the aqueous solution is retained by the resin bed. The fraction of adsorbed boron is A, and the fraction of boron remaining in the aqueous solution that passes through the resin is P. It is reasonable to assume that the amount that
This equation establishes the relationship between the adsorption capacity of the column (We), the concentration of boron in the solution (Ce), the flow of fluid (F) and 50% breakthrough time (τ).
Fig. 2. Methylglucamine resin with complexed boric acid [9].
Fig. 3. Reaction mechanism of boron uptake [5].
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M.F.C. Arias et al. / Desalination 278 (2011) 244–249
Fig. 4. Flowchart exchange resins pilot plant.
plant. Table 1 shows the ranges of the most significant parameters within which the resins were operated.
3. Experimental 3.1. Pilot plant The pilot plant for ion exchange resins is designed to ensure continuous operation. It has two columns of resins, which work alternately, so that one of them can be regenerated while the other continues running. The treatment capacity of the facility is 160 L/h (3.8 m 3/day). Fig. 4 shows the flow chart of the installation.
3.4. Analytical method The boron analysis was performed using emission spectroscopy by inductively coupled plasma. The equipment used was model 4300 from Perkin Elmer. The LOD for boron calculated for this equipment was 0.02 mg/L and the LOQ 0.08 mg/L.
3.2. Ion exchange resins
3.3. Feed water The feed water comes from the desalination plant of Alicante Canal. To carry out testing, the pilot plant was located in the premises of the desalination plant and can operate continuously using permeate water produced by the desalination plant Alicante Canal. The water is obtained directly from the pressure tubes before remineralization. During the studies, variations in the feed characteristics were produced, due to changes in operating conditions of the industrial
Table 1 Range of parameters of the feed water during experimentation with resins.
3.5. Tests performed Resins were characterized by plotting Breakthrough curves. The physical parameters of the process were measured and samples were taken to analyze the concentration of boron. The pilot plant has been designed to work with a flow rate of 160 L/h, containing a volume of 10 L resin in each column. To study the behaviour of the resins, the operating parameters established by the manufacturers for both their operation and regeneration, were used. Amberlita IRA 743
2,50
Purolite S 108
[B] treated water (mg/L)
Three commercial resins from different manufacturers were selected: IRA 743, Rohm and Haas, Purolite S-108's and Dow XUS43594.00. These resins are specifically used for the removal of boron and are suitable for use with brackish water. The three resins have similar characteristics.
Dow XU-43594.00
2,00 1,50 1,00 0,50 0,00
Parameter
Value
Units
Conductivity at 20 °C Boron Temperature
777–1038 1.38–1.94 15.6–27.4
μS/cm mg/L °C
0
1000
2000
3000
V/Vresin Fig. 5. Boron concentration of treated water.
4000
M.F.C. Arias et al. / Desalination 278 (2011) 244–249 3,0
Table 3 Comparative summary for a boron concentration of 0.5 mg/L in treated water.
2,5
B (gr/L resin)
247
2,0
Parameter
Amberlite IRA 743
Purolite S-108
Dow XU-43594.00
1,5
Start saturation (L/LRESIN) Retention (g B/LRESIN) Regeneration cycle
1200 1.5 75 h (3.1 days)
1100 1.6 71 h (2.9 days)
1000 1.5 66 h (2.7 days)
Amberlita IRA 743 Purolite S 108
1,0
Dow XU-43594.00
0,5 0,0 2000
3000
4000
V/Vresin Fig. 6. Boron accumulated by the resin.
3.6. Calculations The volume of treated water in the ion exchange process is referred to as the bed volume used in the process, in order to analyze and compare the results obtained in different trials. V = V treated water = V resin
ð8Þ
From the data obtained experimentally, time t versusLn[C/(C0 − C)], is shown graphically, thus obtaining the distribution coefficient and the time of Breakthrough. The saturation capacity of the resin in specific working conditions has been calculated using Eq. (7). 4. Results and discussion The behaviour of the three selected resins Amberlite IRA 743, Purolite S-108 and Dow XU-43594.00 was analysed and the operating conditions established. The variation of boron concentration in the treated water has been studied, referring the volume of treated water to the bed volume. To check the reproducibility of results, the trials were tripled for each of the resins, and the most favourable for each of them are presented. The volume of treated water was determined, starting from when the boron concentration begins to increase and the volume of treated water when the concentration of boron in the final product reaches 0.5 mg/L. The range of temperatures in which these tests were carried out varies considerably, due to the length thereof, as work had to be done at different times of the year. Fig. 5 shows data for the concentration of boron in the treated water compared to the volume treated per unit bed volume for the three resins. The behaviour of the three resins is very similar and the beginning of the appearance of boron in the treated water in all three cases, occurs at virtually the same point. The same trend is observed with boron concentrations up to 0.5 mg/L. The data on the amount of boron per litre of resin retained against the volume treated per unit volume of bed is shown in Fig. 6. For the desired final concentration of boron (below the LOD and 0.5 mg/L), the three resins have a similar saturation capacity, as shown in Tables 2 and 3.
Likewise, in the same graph (Fig. 7) the Breakthrough curves calculated for the three resins are represented. Fig. 7 indicates the similarity of the results obtained in all three cases. Ideally one would expect that the three curves are better approximated to the values of [B]/[B]0 = 1, which would mean that total saturation of the resin has been reached. But on an industrial scale this total saturation can be difficult to achieve because the saturation capacity of the resin depends on the operating conditions of the process. The physio-chemical properties of water and the workload considerably affect the final result [10].
4.1. Kinetic parameters Fig. 8 shows the representation of t versus ln[C/(C0 − C)] with each of the resins. Table 4 summarizes the values of τ and k calculated from the lines obtained in Fig. 8. It also presents the value of W calculated for each resin in the operating conditions in which the tests were carried out. For Amberlite IRA 743, if the saturation capacity of the resin is expressed in equivalents, the average value of W = 0.5 eq/L is obtained.
1,20 1,00 0,80
[B]/ [B]0
1000
0,60 0,40 Amberlita IRA 743
0,20
Purolite S108 Dow XU-431594
0,00 0
2000
4000
Parameter
Amberlite IRA 743
Purolite S-108
DowXU-43594.00
900 1.3 56 h (2.3 days)
800 1.3 51 h (2.1 days)
800 1.3 52 h (2.1 days)
10000
12000
14000
8000 7000 6000 5000 4000
y = 1033,1x + 4776
2000
Start saturation (L/LRESIN) Retention (g B/LRESIN) Regeneration cycle
8000
Fig. 7. Breakthrough curve.
3000
Table 2 Comparative summary for a boron concentration in treated water below LOD.
6000
t(min)
t(min)
0
y = 1380,8x + 5113,2
Amberlita IRA743
y = 665,13x + 4513,2
Purolite S108
1000 0 -2,00
Dow XU-431594
-1,50
-1,00
-0,50
0,00
0,50
1,00
1,50
Ln([B]/([B]0-[B])) Fig. 8. t versus ln[C/(C0 − C)] for the three resins.
2,00
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M.F.C. Arias et al. / Desalination 278 (2011) 244–249
Table 4 Values of τ, k and W.
Amberlite IRA 743 Purolite S 108 Dow XU-43594.00
Table 5 Boron concentration versus time of operation. τ (min)
k (min−1)
W (g B/Lresin)
4776 5113 4513
1.054*10−3 0.724*10−3 1.503*10−3
1.9 2.0 2.0
The specifications of this resin set a maximum capacity of 0.8 eq/L. Given that the manufacturer establishes flow conditions of operation between 4 and 30 BV/h and we established a working flow of 15.6 BV/h, the results seem reasonable. Simonnot et al. [1] carried out their tests on a laboratory scale with Amberlite IRA743. For concentrations between 1 mg/L and 3 mg/L in the feed (which falls within our range of work), they obtained retentions between 1.66 mg/L and 1.87 mg/L. Yilmaz et al. [10] show values of τ (min) and k (min−1) but due to differences in working conditions (boron concentrations of 250, 500 and 1000 mg/L) the results cannot be considered comparable. If the saturation capacity of the Purolite S 108 resin in equivalents is expressed, an average value of W = 0.6 eq/L would be obtained. The specifications of this resin set a maximum capacity of 0.8 eq/L. Moreover, a graph is shown in the specifications representing the storage capacity of boron based on the workflow (Fig. 9). The flow of feed in the tests was 15.6 BV/h. According to Fig. 9, the retention capacity of boron for this flow should be about 2 g B/L which is consistent with experimental results. For the DOW XU-43594.00 resin, the manufacturers set a maximum between 3.4 g/L and 4 g/L in their specifications. Taking into account the workflow established (15.6 BV/h), the results obtained also seem reasonable. Kabay et al. [4] developed their work with this resin but no data is provided of the kinetic parameters calculated. From the values of τ and k in Table 4, the equation can be established which relates the concentration of boron in treated water versus time of operation (Table 5). Fig. 10 shows graphically the results obtained experimentally compared to those calculated from the equations presented in Table 5.
4.2. Study of the removal of other ions To check the selectivity of the resin for boron, the major cations in water were analyzed: sodium, potassium, calcium and magnesium. Very similar results were obtained with all three resins. No reduction in the concentration of the cations tested was observed with any of the resins.
Resin
Equation
Amberlite IRA 743
C=
1 h i C0 1 + exp 0:967⋅10−3 ð4839−t Þ
Purolite S108
C=
1 h i C0 1 = exp 0:724⋅10−3 ð5113−t Þ
Dow XU-43594.00.
C=
1 h i C0 1 + exp 1:503⋅10−3 ð4513−t Þ
5. Conclusions A comparative study was carried out of Amberlite IRA 743, Purolite S-108 and Dow XU-43594.00 resins with a pilot plant, working at a rate of 160 L/h. The retention capacity of boron and its performance against other ions was analyzed. The water used as feed came from the desalination plant of Alicante Canal. In studies performed with Amberlite IRA 743, the beginning of the saturation of the resin occurred after treating 900 L/Lresin which represents a retention of approximately 1.3 g B/Lresin. The concentration of boron in the treated water was kept below 0.5 mg/L until around 1200 L/Lresin was treated, i.e. when the resin retained about 1.5 g B/Lresin. Under these conditions, the resin regeneration should be performed every 56 h (2.3 days) if complete absence of boron is required and 75 h (3.1 days) if the concentration is to be kept below 0.5 mg/L. In studies performed with the Purolite S-108 resin, the beginning of the saturation of the resin occurred after treating 800 L/Lresin, representing a retention of 1.3 g B/Lresin.The concentration of boron in the treated water was kept below 0.5 mg/L until 1100 L/Lresin was treated, i.e. when the retention of the resin was about 1.6 g B/L resin. Under these conditions the resin regeneration should be performed every 51 h (2.1 days) if the total absence of boron is required and 71 h (2.9 days) if the concentration is to be kept below 0.5 mg/L. In studies with the Dow XU-43594.00 resin, the onset of saturation of the resin occurred when 800 L/Lresin was treated. The amount of boron retained by the resin was 1.3 g B/Lresin. The concentration of boron in the treated water was kept below 0.5 mg/L until 1000 L/Lresin was treated, i.e. when the retention of the resin was about 1.5 g B/L resin. The resin regeneration should be performed every 52 h (2.1 days) if the complete absence of boron is required and 66 h (2.7 days) if the concentration is to be kept below 0.5 mg/L. The behaviour of the three resins is very similar and in all three cases, the beginning of the appearance of boron in the treated water
2
[B]product water (mg/L)
1,8 1,6 1,4 1,2 1 0,8
Amberlita IRA 730 experimental
0,6
Amberlita IRA 730 calculado Purolite S108 experimental
0,4
Purolite S108 calculado Dow XU-43594.00 experimental
0,2
Dow XU-4394.00 calculado
0 0
1000
2000
3000
4000
5000
6000
7000
8000
9000 10000
t (min) Fig. 9. Saturation capacity of the resin depending on operating conditions. Purolite S-108. Manufacturer's specifications.
Fig. 10. Experimental and calculated results of the boron concentration in treated water versus time.
M.F.C. Arias et al. / Desalination 278 (2011) 244–249
occurred at virtually the same point. The same trend was observed when working with boron concentrations up to 0.5 mg/L. To check the selectivity of the resin for boron; the major cations in water were analyzed: sodium, potassium, calcium and magnesium. No reduction in the concentration of the cations tested was observed in any of the resins. The only change experienced by the treated water through the resin was a reduction in the concentration of boron. Nomenclature A Fraction of boron adsorbed by the resin P Fraction of boron remaining in the aqueous solution k Constant (min−1) t Time (min) τ Breakthrough time (min) C Concentration of boron in aqueous solution at the outlet of the resin (g/L) C0 Concentration of boron in the feed (g/L) Ce Concentration of boron in the solution (g/L) We Adsorption capacity of the column (g/Lresin) L = Lresin a F Solution flow min Acknowledgements This work has been funded through the project “Technical assistance for applied research on boron reduction in desalinated water
249
(ACUAMED-Waters of the Mediterranean basin, SA) and Treatment and reuse of wastewater for sustainable development” (CSD2006-44). References [1] M. Simonnot, C. Castel, M. Nicolaï, C. Rosin, M. Sardin, Jauffret, Boron removal from drinking water with a boron selective resin: is the treatment really selective? Water Resources 34 (1) (1999) 109–116. [2] N. Nadav, Boron removal from seawater reverse osmosis permeate utilizing selective ion exchange resin, Desalination 124 (1999) 131–135. [3] M.M. De la Fuente García-Soto, E. Muñoz Camacho, Boron removal industrial wastewaters by ion exchange: an analytical control parameter, Desalination 181 (2005) 207–216. [4] N. Kabay, S. Sarp, M. Yuksel, M. Kitis, H. Koseiglu, O. Arar, M. Bryjak, R. Semiat, Removal of boron from SWRO permeate by boron selective ion exchange resins containing N-methyl glucamine groups, Desalination 223 (2008) 49–56. [5] C. Marston, M. Busch, S. Prabhakaran, A boron-selective resin for seawater desalination, European Desalination Society Conference on Desalination and the Environment, 2005. [6] J. Böeseken, N. Vermass, Sur l'existance de complexes de l'acide borique avec une et avec deux moléculas d'un ion dans les solutions aqueuses, Récents Travaux en Chimie 54 (1935) 853–860. [7] J. Deson, R. Rosset, Extraction de traces de bore au moyen de la résine échangeuse d'ions Amberlite XE 243 1968), Bulletin de la Société Chimique de France 8 (1968) 4.307–4.310. [8] F. Pinon, J. Deson, R. Rosset, Propriétés de la résine échangeuse dìons spécifique du bore Amberlite XE 243, Bulletin de la Société Chimique de France 8 (1968) 3.454–3.461. [9] C. Jacob, Seawater desalination: boron removal by ion exchange technology, Desalination 205 (2007) 47–52. [10] A.E. Yilmaz, R. Boncukcuoglu, M.T. Yilmaz, M.M. Kocakerim, Adsorption of boron from boron-containing wastewaters by ion exchange in a continuous reactor, Journal of Hazardous Materials B117 (2005) 221–226.