Experimental and modeling investigation of metal release from metal‐spiked sediments

Abstract

In sediments that contain iron monosulfide, cadmium, nickel, lead, zinc, and silver(I) form insoluble metal sulfides that lower the metal ion activity in the sediment-pore water system, thereby reducing toxicity. However, metal sulfides are susceptible to oxidation by molecular oxygen resulting in metal solubilization. To better understand the sources and sinks of metal sulfides in sediments, iron monsulfide-rich freshwater sediments were spiked with cadmium, nickel, lead, zinc, or silver(I) and placed into cylindrical cores with an overlying layer of oxygen-saturated water. Measurements of the dissolved metal concentration in the overlying water were made as a function of time and the vertical profiles of acid-volatile sulfide (AVS) and simultaneously extracted metal (SEM) were measured after 150 d. A one-dimensional reactive and transport model has been employed to help elucidate processes controlling the fate of metals in sediments. The model incorporates metal-sulfide formation, metal-sulfide oxidation, and metal partitioning onto sediment organic carbon and iron oxyhydroxide to simulate the vertical transport of metals throughout the sediment core.

Effects of cyclic changes in pH and salinity on metals release from sediments

“…However, 11.2 mmol g À1 of Cd (25% of total Cd) was extracted by hydroxylamine hydrochloride, indicating that some of the spiked Cd might not be associated in sulfide phases because of incomplete formation of CdS (s) during precipitation or oxidation of CdS (s) during sediment mixing and aging. The recovery of sulfide as AVS from CdS (s) was 87%, which is similar to the recovery efficiencies of 85 to 94% observed in other studies [17]. Amorphous CdS (s) spiking did not change the Fe 2þ -Fe 3þ couple dominance of the redox chemistry and kept the sediment pH neutral.…”

“…Cadmium at 40 mmol g À1 was spiked to the sediment as amorphous CdS (s) to minimize pH decrease and redox condition changes from metals spiking to sediments [19] and aged for two weeks. The Cd concentration in sediment was confined to the range of reported values [17,18]. The CdS (s) used in the experiments was generated by dissolving equimolar quantities of Na 2 SÁ9H 2 O (s) and CdCl 2 Á2½H 2 O (s) in deaerated deionized water and aging the solution for 3 d in an anaerobic chamber [20].…”

“…Laboratory-scale microcosms were set up to simulate sediments exposed to saline water, sediments exposed to freshwater, and sediments exposed to alternating regimes of saline and freshwater. The resulting release of Cd, Zn, and Mn was monitored as model metals, because they have been commonly found and studied in contaminated sediments [17,18]. The model sediment from the Anacostia River (Washington, DC, USA) contained sufficient quantities of Zn and Mn for the experiment, but amorphous CdS (s) was added to the sediment prior to placement in the microcosms to allow evaluation of Cd release.…”

Assessing contaminated sediments in the context of multiple stressors

“…Carbonaro et al [94] created a one-dimensional reactive and transport model on metal fate in sediment that incorporates metal-sulfide formation/oxidation and partitioning to organic carbon and Fe oxyhydroxides. Nickel and Zn fluxed into overlying water, followed by slow decreases, and were related to the initial pore water concentrations that overwhelmed sulfide complexation.…”

Geochemistry of trace metals in a fresh water sediment: Field results and diagenetic modeling

“…Recently, Gallon et al (2004) used an inverse, steady state model to describe Pb diagenesis in sediments of a Canadian shield lake. Others have applied multi-component RTMs to assess metal sulfide oxidation (Carbonaro et al, 2005;Di Toro et al, 1996) and the controls on arsenic mobility in sediments (Smith and Jaffe, 1998).…”