Critical Evaluation of Desorption Phenomena of Heavy Metals from Natural Sediments

Abstract

In natural sediments, the majority of heavy metal ions are generally associated with the solid phase. To become bioavailable, the metal ions must desorb from the solid. Numerous studies of heavy metals in sediments have suggested that sorption and desorption exhibit hysteresis (i.e., the two processes are not reversible), while other studies have suggested that desorption hysteresis does not exist. In this study, sorption/desorption hysteresis of lead (Pb) and cadmium (Cd) was evaluated over the following range of conditions: (i) desorption induced by replacing the supernatant liquid with contaminant-free electrolyte solution; (ii) desorption induced by lowering the solution pH with mineral acid; and (iii) desorption induced by sequestration with EDTA. Given the importance of dissolved organic and inorganic ligands in regulating heavy metal behavior in nature sediments, sorption/desorption experiments were conducted on both untreated and prewashed sediments. Prewashing treatment increases the sorption potential of Cd but not Pb. Desorption hysteresis is observed in both the untreated and the prewashed sediments using the replaced supernatant method, and the desorption hysteresis appears to increase with aging time. Hysteresis is not observed when desorption is initiated by lowering the solution pH. A large fraction of the sorbed heavy metal ions can be easily desorbed by EDTA; between 0.04 and 1.2 mmol/kg Cd and Pb ions are resistant to desorption.

Kinetics of neptunium(V) sorption and desorption on goethite: An experimental and modeling study

“…In the literature, the term hysteresis is often used as an equivalent to some degree of irreversible sorption behavior, which implies a non-equilibrium transfer of contaminants between solution phase and mineral surfaces (e.g., (Laird et al, 1994;Gao et al, 2003;Sander et al, 2005)). Under constant solution conditions, the contaminant fraction that remains sorbed after desorption equilibration is often larger than the one during the initial (ad)sorption step.…”

Binding strength-associated toxicity reduction by birnessite and hydroxyapatite in Pb and Cd contaminated sediments

“…Although sediment sorbs heavy metals and restrains their mobility under favorable conditions, previous studies have reported that sediment-sorbed heavy metals are released into the water body according to the changes in environmental conditions (i.e., pH, redox potential, ionic strength, etc. ), and consequently the free metal ions accumulate in aquatic organisms and exhibit their toxicity [3][4][5][6]. Unlike soil and groundwater remediation, sediment remediation technologies that are effective and proven in the field are limited.…”

Trace Element Management in Rice

“…Thus a majority of TEs are associated with the solid phase of soil where they occur as precipitate or co-precipitate of mineral salts. Co-precipitation usually occurs with newly formed chemical species such as carbonates, phosphates, oxides and hydroxides [24,25]. These kinds of co-precipitation help to limit exposure of toxic TEs to biota, and also slow down the release of TEs into the soil solution.…”