heavy metals, emulsion, remediation, sediments
Sediments can act as both a sink for pollutants and a source for aquatic contaminants. Natural and human disturbances of the sediments can release the contaminants to the overlying water where bottom dwelling, or benthic, organisms may be exposed through direct contact, ingestion of sediment particles, or uptake of dissolved contaminants present in the water. Dredging, the most common remediation technology for heavy metals, exacerbates this process. The in situ use of emulsified metal has been studied for its ability to pull heavy metals from aqueous solution and from saturated soils. It has proven successful in the laboratory with removal of lead, cadmium, copper, nickel, and uranium from aqueous solution and removal of lead and cadmium from saturated spiked soils. The use of zero-valent metal particles, particularly those of zero-valent iron (Fe0), as an in situ remediation technique, is currently undergoing evaluation. The basic mechanism for removal appears to be reduction of contaminant metals followed by the subsequent precipitation of their insoluble forms. This is accompanied by the oxidation of the zero-valent metal. In the case of iron, Fe0 undergoes oxidation to Fe2+ and then to the Fe3+ state. Particulate Fe0 has been shown to precipitate Cr6+ to Cr3+ and Pb2+ undergoes reduction to Pb0. Initially, zero-valent iron filings were used to reduce the metal contaminants, but it has been shown that smaller size iron particles, such as nano-scale iron, have higher initial reduction rates as well as a higher concentration of contaminant removal per mole of iron. Emulsion liquid membrane (ELM) technology has been employed as a remediation technique for the removal of metals from wastewater where extraction and stripping processes are performed in a single operation. The ELMs are made by forming an emulsion between two immiscible liquids, such as oil and water, and are often stabilized by a surfactant. We have attempted to demonstrate the application of the combination of these two technologies through the use of emulsified zero-valent metal (EZVM) to treat sediments with heavy metal contamination. Emulsions were prepared using vegetable oil, water, Span 85, and either nanoscale Fe, 1-3 [micro]m Fe, 4 [micro]m Mg, or a 20 wt % Fe-Mg mixture. The results presented in this study demonstrate that EZVM is a viable technique for in situ remediation of heavy metals in sediments. Laboratory scale studies have shown high levels of removal of lead and cadmium from solution using emulsified zero-valent iron. Additionally, the use of emulsified magnesium has shown the ability for high levels of removal of copper, cadmium, nickel, lead, and uranium from solution. A variety of solution matrices were also explored for a lead solution including seawater, the presence of complexing agents and humic acids. Small-scale laboratory studies have shown 65% removal of lead and 45% removal of cadmium from saturated, spiked soils. A bench scale test to demonstrate the applicability of this technique in the environment revealed similar results for the removal of lead.
Master of Science (M.S.)
College of Arts and Sciences
Length of Campus-only Access
Masters Thesis (Open Access)
Milum, Kristen Marie, "In Situ Remediation Of Heavy Metal Contaminated Sediments Using Emulsified Zero-valent Metal Particles" (2005). Electronic Theses and Dissertations. 469.