Aging Effects on Cadmium Transport in Undisturbed Contaminated Sandy Soil Columns

Abstract

Limited information is available on the effects of contaminant aging (i.e., the contact time of Cd with the soil) on Cd transport in soils. We conducted displacement experiments in which indigenous Cd and freshly applied Cd were leached simultaneously from undisturbed samples of three Spodosol horizons. Sorption of Cd was described using Freundlich isotherms, whereas transport was described as a convection-dispersion process. Parameter optimization analysis using a mobile-immobile transport model applied to nonsorbing tracer displacement data showed that 16 to 22% of the water in the columns was immobile. The low dimensionless mass transfer coefficients in the mobile-immobile model were indicative of diffusion-limited transfer between mobile and immobile water, and hence physical nonequilibrium. A two-site kinetic sorption model could be fitted closely to breakthrough curves of the non-aged Cd for three soil horizons. No conclusive evidence was found that contaminant aging in soil affects cadmium transport. On the one hand, predictions of aged Cd leaching, using parameters estimated from displacement experiments with nonaged Cd, differed from those for the aged Cd in the E horizon. On the other hand, no meaningful differences in transport behavior between aged and non-aged Cd were found for the humus Bh and Bh/C horizons. The two-site kinetic rate coefficient alphac was found to depend on water flux, further indicating that mass transfer between sorption sites and the liquid is limited by diffusion rather than by kinetic sorption.

Mobility of Cr, Pb, Cd, Cu and Zn in a loamy sand soil: A comparative study

“…The results with respect to Pb transport and sorption are less conclusive. The mass transfer coefficient points to a nonequilibrium process (ω b 1), but the value of β reveals that a larger amount of these cations are sorbed at equilibrium sites than at nonequilibrium sites (Candela et al, 2007;Seuntjens et al, 2001;van Genuchten, 1981). According to the batch experiment results, both Cr and Pb cations were retained at sites with high sorption energies; therefore, sorption at nonequilibrium sites seems to be predominant, as this reaction is kinetically controlled.…”

Effects of rice straw on the speciation of cadmium (Cd) and copper (Cu) in soils

“…In the mean time, the "ageing effects" of ion adsorption to clay minerals will also take place, which has generally been attributed to micropore diffusion, cavity entrapment, occlusion in solid phases by coprecipitation and co-flocculation, and surface precipitation/crystal growth (Alexander, 2000;Seuntjens et al, 2001;Ma et al, 2006). With ageing, metal is generally subject to transformation or incorporation into a more stable solid phase that can lead to a decrease in metal bioavailability.…”

Sewage Sludge Application and Soil Properties Effects on Short-Term Zinc Leaching in Soil Columns

“…The latter explanation is more plausible. Seuntjens et al (2001) reported that solutes can migrate into less accessible soil regions and become strongly bound over time. Except soil A, from which 8.02 mg Zn per column were eluted in the unamended treatment (Table 2), in the other soils total amounts of eluted Zn were never higher than 35% of the added (i.e., 3.41 mg per column in the unamended treatment in soil G).…”