Effect of pore-water velocity on chemical nonequilibrium transport of Cd, Zn, and Pb in alluvial gravel columns

Pang, Liping; Close, Murray E.; Schneider, Daniela Ribeiro; Stanton, Greg

doi:10.1016/s0169-7722(01)00223-6

Cited by 71 publications

(49 citation statements)

References 32 publications

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“…The high k1/k 2 ratios of Cd resulted in high R values of 101-108 for Cd transport, whereas the low k1/k 2 ratios of RWT gave low R values of 5-7 for RWT transport. As R values are related to pore-water velocity under non-equilibrium conditions (Pang et al 2002), the R values estimated in this study are relevant/related to the groundwater velocity 1.7-1.8 m/day and may be different at other flow velocities. However, this flow velocity is typical in pumice sand groundwater and hence the results of the study should be readily applicable to these aquifer systems.…”

Section: Adsorption/desorption and Retardationmentioning

confidence: 88%

“…In the past, we have studied the adsorption and transport of Cd in alluvial gravel aquifers. These investigations include a field study (Pang & Close 1999a), the effects of transport scale (Pang & Close 1999b), and flow velocity (Pang et al 2002) on Cd transport, and bacteria-facilitated Cd transport (Pang & Close 1999a). However, little information is available in the literature on the adsorption and transport of Cd in pumice sand aquifers.…”

Section: Introductionmentioning

confidence: 99%

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Adsorption and transport of cadmium and rhodamine WT in pumice sand columns

Pang

Greenfield

et al. 2004

New Zealand Journal of Marine and Freshwater Research

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The transport and attenuation of cadmium (Cd) and rhodamine WT (RWT) in a pumice sand aquifer media was investigated using column experiments to study a scenario of point-source contamination. A pore-water velocity of 1.7-1.8 m/day, which is a typical field groundwater velocity in a pumice sand aquifer system, was applied to triplicate columns. A pulse of a solution containing Cd and RWT, together with the conservative tracer tritiated water ( 3 H 2 O) at pH = 7, was introduced into the columns. Experimental results showed that concentration breakthrough curves (BTCs) of 3 H 2 O were symmetrical and fitted well into an equilibrium model. In contrast, BTCs of Cd and RWT were asymmetrical with significant tailings and fitted well with a two-site adsorption/desorption model. The symmetric 3 H 2 O BTCs suggest that physical nonequilibrium was absent in the experimental system, therefore the asymmetrical BTCs of Cd and RWT were attributed to chemical non-equilibrium. Modelling results showed that, in comparison with 3 H 2 O, Cd was apparently retarded by 101-108 times in pumice sand aquifer media (apparent adsorption coefficient 7.33-9.24 ml/g) and underwent a mass loss of 20-30% that was probably because of precipitation of CdCO 3 . As CdCO 3 is extremely insoluble, Cd precipitation would be irreversible and therefore it would not contribute to the tailing of the Cd BTCs. The experimental results suggest that the adsorption and desorption of Cd in pumice sand aquifer media in hydrodynamic conditions was a kinetic process. Cd desorption rates were two orders-of-magnitude slower than its adsorption rates. This resulted in a prolonged mean residence time for Cd in pumice sand aquifer media, which was 10-12 days in the 18-cm-long columns under a flow velocity of 1.7-1.8 m/day. Since the mean residence time is only indicative for the arrival of the central of mass in a contaminant BTC, the time required for the total disappearance of Cd will be much longer than the mean residence time because of the significantly long tailing of the BTC. This implies that natural attenuation of Cd from a contaminated pumice sand aquifer would take a time period from decades to centuries. Batch isotherm experiments were also carried out to obtain Cd adsorption coefficients at equilibrium conditions. In comparison with the column results obtained from non-equilibrium conditions, adsorption coefficients of 20 ml/g obtained from the batch equilibrium experiments were 2-3 times higher for Cd. This finding suggests that care should be taken when using batch adsorption isotherm results to predict field problems because the delay in the appearance of contaminants in drinking water wells and springs could be overestimated. In comparison with 3 H 2 O, RWT was retarded 5-7 times and had BTCs that were significantly more spread out. Hence the use of RWT to indicate groundwater flow in pumice sand aquifers will underestimate groundwater velocity and overestimate aquifer dispersivity. About 4-14% of RWT mass was lost during its transport, prob...

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Section: Adsorption/desorption and Retardationmentioning

confidence: 88%

Section: Introductionmentioning

confidence: 99%

Adsorption and transport of cadmium and rhodamine WT in pumice sand columns

Pang

Greenfield

et al. 2004

New Zealand Journal of Marine and Freshwater Research

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“…Although repacked soils are usually considered homogenous media, both physical and chemical nonequilibrium models have been applied to describe the transport of heavy metals in repacked soil columns (Pang et al, 2002;Hutchison et al, 2003). The nonequilibrium model is based on the theory that the water contained in soil pores is composed of two regions: mobile region where the water is relatively mobile and immobile region where the advection is minimal.…”

Section: Nonequilibrium Modelmentioning

confidence: 99%

“…CXTFIT, a computer program that has been used to estimate CDE parameters in steady state onedimensional flow (Toride et al, 1999), has been successfully used to fit R d and D values for Cd transport in soil columns (Kookana and Naidu, 1998;Pang et al, 2002). Most Cd breakthrough curves have been evaluated by analyzing Cd concentration in the outflow leachate from small soil cores with inner diameter around 6 cm and length about 10 cm.…”

Section: Introductionmentioning

confidence: 99%

Modeling Cadmium Transport in Neutral and Alkaline Soil Columns at Various Depths

Qi¹,

Feng

Helmers

2012

Pedosphere

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Human health has been potentially threatened by cadmium (Cd) contained in sewage irrigation water. Previous studies of Cd transport in soils were mainly conducted using small soil cores with pH values less than 6. The objectives of this study were to determine the parameters of the convection-dispersion equation (CDE) for Cd transport in relatively larger columns with neutral and alkaline soils, and to investigate the parameters' variability with depth. The soil columns were 50 cm in length and 12.5 cm in diameter. Ceramic suction lysimeters were buried at depths of 2.5, 7.5, 17.5, 27.5, and 37.5 cm to abstract soil solution. Cd concentration in the soil solution samples were subsequently analyzed to obtain breakthrough curves (BTCs). Equilibrium and nonequilibrium models in CXTFIT program were used to estimate parameters of the CDE. The results suggested that both equilibrium and non-equilibrium models performed well in modeling Cd transport. The hydrodynamic dispersion coefficient (D) ranged from 0.18 to 10.70 cm 2 h −1 , showing large differences among different depths. The retardation factor (R d ) ranged from 25.4 to 54.7 and the standard deviation of R d value was lower than 30% of the mean value. Precipitation coefficient (R p ) decreased consistently with increasing depth, varying from 1.000 × 10 −10 to 0.661 h −1 . Sensitivity tests showed that Dwas less sensitive than R d . These results would be helpful in understanding the transport and retention of Cd in non-acidic soils. RightsWorks produced by employees of the U.S. Government as part of their official duties are not copyrighted within the U.S. The content of this document is not copyrighted. ABSTRACTHuman health has been potentially threatened by cadmium (Cd) contained in sewage irrigation water. Previous studies of Cd transport in soils were mainly conducted using small soil cores with pH values less than 6. The objectives of this study were to determine the parameters of the convection-dispersion equation (CDE) for Cd transport in relatively larger columns with neutral and alkaline soils, and to investigate the parameters' variability with depth. The soil columns were 50 cm in length and 12.5 cm in diameter. Ceramic suction lysimeters were buried at depths of 2.5, 7.5, 17.5, 27.5, and 37.5 cm to abstract soil solution. Cd concentration in the soil solution samples were subsequently analyzed to obtain breakthrough curves (BTCs). Equilibrium and nonequilibrium models in CXTFIT program were used to estimate parameters of the CDE. The results suggested that both equilibrium and non-equilibrium models performed well in modeling Cd transport. to 0.661 h −1 . Sensitivity tests showed that D was less sensitive than R d . These results would be helpful in understanding the transport and retention of Cd in non-acidic soils.

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“…Few studies have examined the influence of flow rate on the mobility of HM (Pang et al, 2002;Wehrer and Totche 2008;Lo et al, 2011). In these works, the washing liquid which is a mixing of water and a reagent is operated in saturated columns.…”

Section: Introductionmentioning

confidence: 99%

Polluted soil leaching: unsaturated conditions and flow rate effects

Mathlouthi

Kacem

Mesticou

et al. 2017

Eurasian Journal of Soil Science (Ejss)

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Article Info Received : 12.09.2016 Accepted : 12.12.2016 In this study, soil samples are extracted from a polluted site at different depths. Soils texture and pollutant presence are different with depth. Preliminary analyzes showed pollution by heavy metals. To simulate soil leaching operation in static condition, a series of leaching tests are conducted in laboratory column under conditions of upflow unsaturated soil. Electrical conductivity and pH measurements on the recovered leachate are performed. Different flow rates are tested. Comparison of different profiles shows that the dissolved pollutants are concentrated in the upper soil levels and disperse weakly in the lower parts which confirm the nature of anthropogenic pollution of heavy metals. Water mobilizes a high amount of dissolved ionic substances up to 80% of the initial concentration. The increase in flow rate requires more pore volume injected to achieve the maximum clearance rate. The down flow condition extracts a small amount of dissolved substances.

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Effect of pore-water velocity on chemical nonequilibrium transport of Cd, Zn, and Pb in alluvial gravel columns

Cited by 71 publications

References 32 publications

Adsorption and transport of cadmium and rhodamine WT in pumice sand columns

Adsorption and transport of cadmium and rhodamine WT in pumice sand columns

Modeling Cadmium Transport in Neutral and Alkaline Soil Columns at Various Depths

Polluted soil leaching: unsaturated conditions and flow rate effects

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