Effects of Soil Organic Matter on the Kinetics and Mechanisms of Pb(II) Sorption and Desorption in Soil

Abstract

make better predictions about the mobility of contaminants, it is critical that time-dependent metal sorption To improve predictions of the toxicity and threat from Pb contamiand desorption behavior on soil be understood, as well nated soil, it is critical that time-dependent sorption and desorption behavior be understood. In this paper, the sorption and desorption as the mechanism of the sorption-desorption reactions. behavior (pH ϭ 5.50, I ϭ 0.05 M) of Pb in a Matapeake silt loam Lead sorption behavior is often initially fast, followed soil (Typic Hapludult) were studied by stirred-flow and batch experiby a slow reaction (Benjamin et al., 1981; Hayes et al., ments. In addition, we studied the effects of soil organic matter (SOM) 1986; Strawn et al., 1998). The fast reaction is most likely on sorption and desorption behavior by treating the soil with sodium adsorption via electrostatic attraction, and/or innerhypochlorite to remove the SOM fraction, and using a soil with six sphere complexation with functional groups present on times as much SOM (St. Johns loamy sand [Typic Haplaquods]) as the soil components. There are several possible reasons the Matapeake soil. Lead sorption consisted of a fast initial reaction for the slow sorption steps, such as: slow interparticle in which all of the Pb added to the stirred-flow chamber was sorbed. diffusion in porous minerals and organic matter, forma-Following this initial fast reaction, sorption continued and appears to tion of precipitates on surfaces which can sometimes be be rate limited (indicated by a decrease in the outflow concentration when the flow rate was decreased, or when the flow was stopped). slower than typical sorption, and adsorption onto sites The total amount of Pb sorbed was 102, 44, and 27 mmol kg Ϫ1 for that have relatively large activation energies (Fuller et the St. Johns soil and the untreated and treated Matapeake soils,

Sequential sorption of lead and cadmium in three tropical soils

“…In the above studies, inner-sphere complexes were inferred in the original sorbed phases using either extended X-ray absorption fine structure spectroscopy (EXAFS) or the constant capaci tance model. However, Strawn and Sparks (2000) found only 32e76% of the sorbed Pb were desorbed from the soil after 6 h. …”

Competitive sorption and desorption of phosphate and citrate in clayey and sandy loam soils

“…Phosphorus sorption and desorption were assessed by the stirred flow technique (Figure 1), similar to the system described by Bar-Tal et al (1990) and Strawn & Sparks (2000). This technique has been used for many years in several countries in kinetic studies, but is little known in Brazil (Carski & Sparks, 1985;Bar-Tal et al, 1990;Strawn & Sparks, 2000;Staats et al, 2004;Pérez-Novo et al, 2011).…”

“…This technique has been used for many years in several countries in kinetic studies, but is little known in Brazil (Carski & Sparks, 1985;Bar-Tal et al, 1990;Strawn & Sparks, 2000;Staats et al, 2004;Pérez-Novo et al, 2011). The stirred-flow system consists of a tank with N, receptors for stock solutions of P and citrate, a peristaltic pump with a flow rate of 1.58 mL min -1 , a 12 mL reaction chamber, magnetic stirrer, two filters (diameter 25 mm, pore size 0.45 µm) to separate the soil from the reaction solution, and tubes for sample collection.…”

“…The stirred-flow system consists of a tank with N, receptors for stock solutions of P and citrate, a peristaltic pump with a flow rate of 1.58 mL min -1 , a 12 mL reaction chamber, magnetic stirrer, two filters (diameter 25 mm, pore size 0.45 µm) to separate the soil from the reaction solution, and tubes for sample collection. In the reaction chamber, a soil:solution ratio of 1:11 was used, as proposed by Bar-Tal et al (1990), Strawn & Sparks (2000) and Carski & Sparks (1985).…”

“…In this system, reactions are relatively fast and the sorption and desorption kinetics can be measured in a single experiment (Sparks et al, 1996;Yin et al, 1997). This technique has been used for many years in several countries to investigate sorption and desorption of metals (Carski & Sparks, 1985;Bar-Tal et al, 1990;Strawn & Sparks, 2000), and also of P, although in fewer studies (Staats et al, 2004;Pérez-Novo et al, 2011).…”