Sequestering Agents for Active Caps—Remediation of Metals and Organics

Abstract

This research evaluated organoclays, zeolites, phosphates, and a biopolymer as sequestering agents for inorganic and organic contaminants. Batch experiments were conducted to identify amendments and mixtures of amendments for metal and organic contaminant removal and retention. Contaminant removal was evaluated by calculating partitioning coefficients. Metal retention was evaluated by desorption studies in which residue from the removal studies was extracted with 1 M MgCl₂ solution. The results indicated that phosphate amendments, some organoclays, and the biopolymer, chitosan, were very effective sequestering agents for metals in fresh and salt water. Organoclays were very effective sorbents for phenanthrene, pyrene, and benzo(a)pyrene. Partitioning coefficients for the organoclays were 3000–3500 L g⁻¹ for benzo(a)pyrene, 400–450 L g⁻¹ for pyrene, and 50–70 L g⁻¹ for phenanthrene. Remediation of sites with a mixture of contaminants is more difficult than sites with a single contaminant because metals and organic contaminants have different fate and transport mechanisms in sediment and water. Mixtures of amendments (e.g., organoclay and rock phosphate) have high potential for remediating both organic and inorganic contaminants under a broad range of environmental conditions, and have promise as components in active caps for sediment remediation.

Keywords:

• rock phosphate
• zeolite
• organoclay
• biopolymer
• active caps
• contaminants
• sediments

Acknowledgements

This research was supported wholly by the U.S. Department of Defense, through the Strategic Environmental Research and Development Program (SERDP) under project ER 1501. Additionally, the manuscript preparation was supported by the SRNL's Mini-Sabbatical Program. Performers of this project would like to thank to all commercial companies for supplying sequestering agents.

Notes

^a Rock phosphate from Tennessee (RPT), rock phosphate from North Carolina (NCA), biological apatite (BA), calcium phytate (CaP), organoclays from Biomin, Inc.: Clayfloc^TM 200 (OCB-200), Clayfloc^TM 202 (OCB-202), and Clayfloc^TM 750 (OCB-750), clinoptilolite (ZC), phillipsite (ZP), chitosan (BPC)

^b 50% indicates 0.1g of each constituent and 100% indicates 0.2 g of each constituent

^aX–retention at 30–50%; XX–retention at 50–80%; XXX–retention at 80–100%

^a X–retention at 30–50%; XX–retention at 50–80%; XXX–retention at 80–100%