Modelling seawater intrusion in a resin-filled column to...
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Boluda Botella, N., Gomis Yagües, V., Pedraza Berenguer, R. and Torres Prieto, N. Chemical Engineering Department, University of Alicante. Apdo. 99. E-03080 Alicante. Spain. E-mail: [email protected] REFERENCES 55. [1] Appelo, C.A.J. and Postma, D., 2005. Geochemistry, groundwater and pollution. 2nd Ed. Balkema, Rotterdam, Netherlands. 535 pp. [6] Boluda-Botella, N., Gomis-Yagües, V., Ruiz-Beviá, F. and Saquete-Ferrándiz, MD., [2] Gomis, V., Boluda, N. and Ruiz, F., 1997. J. Cont. Hydrol., 29, 81-91. 2004. 18th SWIM. Cartagena (Spain). [3] Boluda-Botella, N., Gomis-Yagües, V. and Ruiz-Beviá, F., 2008. J. of Hydrol. (in press). [7] Boluda Botella, N., Gomis, V. and Pedraza, R., 2006. 1st SWIM-SWICA. Cagliary [4] Gomis, V., Boluda, N. and Ruiz, F., 1996. J. Cont. Hydrol., 22: 67-81. (Italy). [5] Gomis-Yagües, V., Boluda-Botella, N. and Ruiz-Beviá, F., 2000. J. of Hydrol., 228, 48- [8] Parkhurst, D.L. and Appelo, C.A.J., 1999. U.S. Geological Survey. Water Res. Inv. INTRODUCTION Laboratory column experiments are necessary to the understanding of the reactive transport behavior of inorganic chemical species when dealing with environmental problems such as fresh- or seawater intrusions into aquifers, landfill leaching plumes, or transport of heavy metals in soils and aquifers. In the case of seawater intrusion, cationic exchange is one of the main chemical reactions analyzed [1]. This process occurs when cations from seawater (mainly sodium and magnesium) displace calcium ions on sediment exchange sites. In previous studies of the reactive transport processes of seawater intrusion [2,3], column experiments were carried out by displacing synthetic freshwater with seawater along a sediment column 100 cm in length. Moreover, application of a multicomponent reactive model [4] to the experimental data showed gypsum precipitation dissolution [5] to be taking place, in addition to cation exchange. Modelling seawater intrusion in a resin-filled column to study cationic exchange and gypsum precipitation Water composition Freshwater (mmol/L) (mmol/L) Sodium 0 522 Potassium 0 10.3 Calcium 3.13 11.3 Magnesium 0 61.7 Chloride 2.96 606 Sulphate 0 30.2 Bicarbonate 0 2.13 Seawater Figure 1. Previous experimental results 0 5 10 15 20 25 30 35 40 0 100 200 300 400 500 600 700 800 Time (h) Concentration (mmol/L) S Mg/2 Cl/25 Na/40 K Ca/10 COLUMN TRANSPORT PARAMETERS ACUAINTRUSION [7] a graphical user interface was designed with Microsoft Visual Basic 6.0 to calculate the best fit of the experimental data [chloride concentration (mmol/L) versus experimental time (h)]. This code uses the analytical solution of the convection-dispersion equation (Lapidus and Amundson, 1952) is Where C(L,t) is the chloride concentration at the output stream of the column, C , the initial concentration of the chloride in the freshwater, i, C , the concentration of chloride in the seawater, 0 L, column length, t, time, v, interstitial water velocity in the direction of propagation (equal to Darcy velocity divided by porosity, or u/e), and D , longitudinal dispersion coefficient. L ( ) ( ) ú û ù ê ë é ÷ ÷ ø ö ç ç è æ + ÷ ÷ ø ö ç ç è æ + ÷ ÷ ø ö ç ç è æ - - + = t D 4 vt L erfc D vL exp t D 4 vt L erfc 2 C C C t , L C L L L i 0 i Column properties Column length 19 cm Column diameter 2.5 cm Flow 50 mg/min Transport parameters Peclet number 167.6 Residence time 14.67 h Darcy’s velocity 0.61 cm/h Porosity 0.47 Interstitial velocity 1.29 cm/h 2 Dispersion 0.146 cm /h Dispersivity 0.113 cm Chloride breakthrough curve 0 0.2 0.4 0.6 0.8 1 1.2 0 20 40 60 80 100 T ime (h) Dimensionless c hloride Experimental Calculated Figure 2. Chloride breakthrough curves: experimental (symbol), calculated 0 5 10 15 20 25 30 35 40 45 50 0 100 200 300 400 500 600 700 800 T im e (h) Concentration (mmol/L) Symbols: experimental. Lines: simulated (SI = 0). Cl/25 S Mg/2 Ca/10 K Na/40 Symbols: experimental. Lines: simulated (SI = 0.65). 0 5 10 15 20 25 30 35 40 0 100 200 300 400 500 600 700 800 T im e (h) Concentration (mmol/L) Cl/25 S Mg/2 Ca/10 K Na/40 REACTIVE TRANSPORT MODEL PHREEQC (Versión 2) is a computer program for speciation, batch reaction, and one- dimensional transport calculations, distributed free of charge by the U.S. Geological Survey (http://wwwbrr.cr.usgs.gov/projects/GWC_coupled/phreeqc/index.html). The windows version of the program has an intuitive, user-friendly interface. Numerous options and capabilities make PHREEQC useful for finding solutions to many practical problems in hydrogeochemistry. RESULTS The Saturation Index (SI) of gypsum has been modified in different scenarios. In the case of SI = 0 gypsum precipitation/disolution must have occurred. Differences can be attributed to local equilibrium. Simulation results are improved by taking SI = 0.65. The predicted elution curves in the first stages of advance of the intrusion front are in agreement with experimental results. Differences in the last stages are probably due to the variation in the value of the exchange coefficients with salinity. An attempt was made to study gypsum precipitation in processes simulating seawater intrusion [6] in a column filled with resin (Duolite C20) of a great cationic exchange capacity (CEC = 15.6 meq/kg). The goal of the 20 time increase in the CEC was to try to obtain a high concentration of calcium, which would produce gypsum precipitation into the column. However, only a very small amount of gypsum precipitated, as can be seen from the elution curve of sulphate (fig. 1), which was nearly synchronous to that of conservative chloride. OBJECTIVES Obtain column transport parameters with ACUAINTRUSION. Modelize with PHREEQC using the calculated transport parameters and exchange coefficients of resin. Different scenarios are considered for precipitation/disolution of gypsum.
Transcript of Modelling seawater intrusion in a resin-filled column to...
Boluda Botella, N., Gomis Yagües, V., Pedraza Berenguer, R. and Torres Prieto, N.Chemical Engineering Department, University of Alicante. Apdo. 99. E-03080
Alicante. Spain. E-mail: [email protected]
REFERENCES 55.[1] Appelo, C.A.J. and Postma, D., 2005. Geochemistry, groundwater and pollution. 2nd Ed. Balkema, Rotterdam, Netherlands. 535 pp. [6] Boluda-Botella, N., Gomis-Yagües, V., Ruiz-Beviá, F. and Saquete-Ferrándiz, MD., [2] Gomis, V., Boluda, N. and Ruiz, F., 1997. J. Cont. Hydrol., 29, 81-91. 2004. 18th SWIM. Cartagena (Spain).[3] Boluda-Botella, N., Gomis-Yagües, V. and Ruiz-Beviá, F., 2008. J. of Hydrol. (in press). [7] Boluda Botella, N., Gomis, V. and Pedraza, R., 2006. 1st SWIM-SWICA. Cagliary [4] Gomis, V., Boluda, N. and Ruiz, F., 1996. J. Cont. Hydrol., 22: 67-81. (Italy).[5] Gomis-Yagües, V., Boluda-Botella, N. and Ruiz-Beviá, F., 2000. J. of Hydrol., 228, 48- [8] Parkhurst, D.L. and Appelo, C.A.J., 1999. U.S. Geological Survey. Water Res. Inv.
INTRODUCTIONLaboratory column experiments are necessary to the understanding of the reactive transport behavior of inorganic chemical species when dealing with environmental problems such as fresh- or seawater intrusions into aquifers, landfill leaching plumes, or transport of heavy metals in soils and aquifers. In the case of seawater intrusion, cationic exchange is one of the main chemical reactions analyzed [1]. This process occurs when cations from seawater (mainly sodium and magnesium) displace calcium ions on sediment exchange sites.
In previous studies of the reactive transport processes of seawater intrusion [2,3], column experiments were carried out by displacing synthetic freshwater with seawater along a sediment column 100 cm in length. Moreover, application of a multicomponent reactive model [4] to the experimental data showed gypsum precipitation dissolution [5] to be taking place, in addition to cation exchange.
Modelling seawater intrusion in a resin-filled column to study cationic exchange and gypsum precipitation
Water composition Freshwater (mmol/L) (mmol/L)Sodium 0 522Potassium 0 10.3Calcium 3.13 11.3Magnesium 0 61.7Chloride 2.96 606Sulphate 0 30.2Bicarbonate 0 2.13
Seawater
Figure 1. Previous experimental results
0
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40
0 100 200 300 400 500 600 700 800
Time (h)
Co
nc
en
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l/L)
S Mg/2
Cl/25
Na/40
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Ca/10
COLUMN TRANSPORT PARAMETERS ACUAINTRUSION [7] a graphical user interface was designed with Microsoft Visual Basic 6.0 to calculate the best fit of the experimental data [chloride concentration (mmol/L) versus experimental time (h)]. This code uses the analytical solution of the convection-dispersion equation (Lapidus and Amundson, 1952) is
WhereC(L,t) is the chloride concentration at the output stream of the column,C , the initial concentration of the chloride in the freshwater,i,
C , the concentration of chloride in the seawater,0
L, column length,t, time,v, interstitial water velocity in the direction of propagation (equal to Darcy velocity divided by porosity, or u/e), andD , longitudinal dispersion coefficient.L
( ) ( )úû
ùêë
é÷÷ø
öççè
æ +÷÷ø
öççè
æ+÷÷
ø
öççè
æ --+=
tD4
vtLerfc
D
vLexp
tD4
vtLerfc
2
CCCt,LC
LLL
i0i
Column propertiesColumn length 19 cmColumn diameter 2.5 cmFlow 50 mg/min
Transport parametersPeclet number 167.6Residence time 14.67 hDarcy’s velocity 0.61 cm/hPorosity 0.47Interstitial velocity 1.29 cm/h
2Dispersion 0.146 cm /hDispersivity 0.113 cm
Chloride breakthrough curve
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0.6
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1.2
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Time (h)
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nle
ssc
hlo
ride
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Calculated
Figure 2. Chloride breakthrough curves: experimental (symbol), calculated
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Symbols: experimental. Lines: simulated (SI = 0).
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Symbols: experimental. Lines: simulated (SI = 0.65).
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Time (h)
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Cl/25
S Mg/2
Ca/10
K
Na/40
REACTIVE TRANSPORT MODELPHREEQC (Versión 2) is a computer program for speciation, batch reaction, and one-dimensional transport calculations, distributed free of charge by the U.S. Geological Survey (http://wwwbrr.cr.usgs.gov/projects/GWC_coupled/phreeqc/index.html). The windows version of the program has an intuitive, user-friendly interface. Numerous options and capabilities make PHREEQC useful for finding solutions to many practical problems in hydrogeochemistry.
RESULTSThe Saturation Index (SI) of gypsum has been modified in different scenarios. In the case of SI = 0 gypsum precipitation/disolution must have occurred. Differences can be attributed to local equilibrium. Simulation results are improved by taking SI = 0.65. The predicted elution curves in the first stages of advance of the intrusion front are in agreement with experimental results. Differences in the last stages are probably due to the variation in the value of the exchange coefficients with salinity.
An attempt was made to study gypsum precipitation in processes simulating seawater intrusion [6] in a column filled with resin (Duolite C20) of a great cationic exchange capacity (CEC = 15.6 meq/kg). The goal of the 20 time increase in the CEC was to try to obtain a high concentration of calcium, which would produce gypsum precipitation into the column. However, only a very small amount of gypsum precipitated, as can be seen from the elution curve of sulphate (fig. 1), which was nearly synchronous to that of conservative chloride.
OBJECTIVESObtain column transport parameters with ACUAINTRUSION. Modelize with PHREEQC using the calculated transport parameters and exchange coefficients of resin. Different scenarios are considered for precipitation/disolution of gypsum.
