Sequestration of metals in active cap materials: A laboratory and numerical evaluation

Abstract

9Active capping involves the use of capping materials that react with sediment contaminants to 10 reduce their toxicity or bioavailability. Although several amendments have been proposed for use 11 in active capping systems, little is known about their long-term ability to sequester metals. 12Recent research has shown that the active amendment apatite has potential application for metals 13 contaminated sediments. The focus of this study was to evaluate the effectiveness of apatite in 14 the sequestration of metal contaminants through the use of short-term laboratory column studies 15 in conjunction with predictive, numerical modeling. A breakthrough column study was 16 conducted using North Carolina apatite as the active amendment. Under saturated conditions, a 17 spike solution containing elemental As, Cd, Co, Se, Pb, Zn, and a non-reactive tracer was injected 18 into the column. A sand column was tested under similar conditions as a control. Effluent water 19 samples were periodically collected from each column for chemical analysis. Relative to the non-20 reactive tracer, the breakthrough of each metal was substantially delayed by the apatite.

Evaluation of Active Cap Materials for Metal Retention in Sediments

“…As was expected, all cap materials prevented desorption of metals from the underlying sediment over the six‐month period represented by the study. These data are in agreement with model predictions, which show that even sand will retain metals in sediment for one year in the absence of transport mechanisms other than diffusion (Dixon & Knox, ; Knox et al., ). Over longer periods, the metal binding capacity of active sequestering agents becomes critical, and it significantly retards the release of sediment contaminants compared with inert materials such as sand (Dixon & Knox, ; Knox et al., ).…”

A review of the in-situ capping amendments and modeling approaches for the remediation of contaminated marine sediments

“…A second experiment highlighted that the reactive materials limited Pb, Zn, Ni, Cr, and Cd potentially mobile fractions. These results were in agreement with the model simulations that showed that even sand can retain metals in sediment for one year in presence of only diffusion phenomenon (Dixon and Knox, 2012). However, in the long-term the metal binding capacity of reactive materials became crucial and they considerably retarded the release of pollutants compared with sand (Knox, Paller and Roberts, 2012b).…”

Experimental investigations and numerical modelling of in-situ reactive caps for PAH contaminated marine sediments

“…Both sediments and seawater samples were chemically characterized with EPA standard method 8275A. The column experiments were set up following the same methods used by U.S. Army Corps of Engineers (1987) and several researchers (Gidley et al, 2012;Dixon and Knox 2012;Silvani et al, 2017). Pyrene, benzo[a]pyrene and anthracene concentrations were equal respectively to 898, 519…”