Evaluation of Active Cap Materials for Metal Retention in Sediments

Abstract

This study evaluated chemically active amendments used to construct active caps for remediating contaminated sediments. Three experiments assessed the effects of apatite, organoclay, zeolite, and biopolymers (chitosan and xanthan) on metal mobility, retention, and speciation. The first showed that the amendments individually and in mixtures (2 percent dry weight) reduced the concentrations of Cr, Co, Ni, and Pb in water extracts from reduced sediment. The second experiment, which used sequential extraction procedures to evaluate the effects of the amendments on metal speciation, showed that the amendments reduced the potentially mobile fractions of Pb, Zn, Ni, Cr, and Cd that are likely to be bioavailable. Last, column studies showed that active caps composed of the amendments prevented the diffusive transport of metals from contaminated sediment over six months. In addition, there was a “zone of influence” beneath the caps in which water extractable concentrations of metals declined substantially compared with untreated sediment. © 2014 Wiley Periodicals, Inc.

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

“…Another material particularly effective to also remove metal(loids) is organoclay (OC), widely described in section 3, which consists of a bentonite layer modified with quaternary amines. Knox et al (2014) evaluated the effects of apatite, OC, zeolite, and biopolymers (i.e., chitosan and xanthan) on metal speciation, mobility, and retention. Their main results revealed that amendments reduced chromium (Cr), cobalt (Co), Pb, and Ni concentrations in water in reduced conditions.…”

Reactive amendment saltstone (RAS). A novel approach for improved sorption/retention of radionuclides such as technetium and iodine

“…Chemically reactive amendments have been used to improve contaminant retention in active capping systems (Knox et al 2014) and have potential to improve the retention properties of saltstone. Additionally, Li et al (2014) demonstrated the effectiveness of several active amendments (i.e.…”

Application of calcium-rich mineral under nonwoven fabric mats and sand armor as cap layer for interrupting N and P release from river sediments

“…Capping materials used in laboratories and eld studies include activated carbon (Gu et al 2017), phoslock (Wang et al 2017), and natural/modi ed zeolites (Hong et al 2019;Jacobs and Waite 2004;Xiong et al 2018;Zhan et al 2019). Other materials newly studied include apatite (Knox et al 2014), attapulgite (ATT) (Yin et al 2016), biochar (Wang et al 2018;Zhu et al 2019), calcium peroxide (Zhou et al 2020), illite (Gu et al 2019), layered double hydroxide (Wu et al 2020), lanthanum-modi ed bentonite (Kong et al 2020), and zero-valent iron (Todaro et al in press).…”