Formatted Title
Overcoming the Limitation of Zero Valent Iron (ZVI) Sequestration of Metals and Radionuclides in Groundwater Remediation and Wastewater Treatment
Background/Objectives
For the past 30 years, zero valent iron (ZVI) has been used for the remediation/treatment of a variety of organic and inorganic contaminants. ZVI is capable of a myriad of chemical processes, such as abiotic and biotic reductive transformations and sequestration reactions that are involved in these treatment processes. ZVI is easy to use, inexpensive, sustainable, and has a long treatment life. This presentation will focus on the limitations of the processes involved in the sequestration of metals and radionuclides in groundwater and wastewater treatment and how to overcome them. The major limitations of ZVI include passive oxide layers, narrow pH treatment ranges, precipitation of metal hydroxides and carbonates.
Approach/Activities
In laboratory-scale studies, the effects of pretreatment, physical methods to remove passive layers, combination with other adsorptive materials (e.g., iron oxides, activated carbon, zeolite, and silica), and ionic strength on the kinetics of the removal of metals and radionuclides have been studied. These absorptive materials can provide additional adsorption sites for oxidized metal species, thus reducing the inhibitory effects on ZVI treatment. In addition, oxygen and the formation of oxides play a complex role in the effectiveness of ZVI. The conditions for improving contaminant removal and broadening the applicable pH range have been identified.
Results/Lessons Learned
Using conditions to enhance ZVI corrosion can lead to enhanced mass transfer H+ and oxygen on the surface and broadened the application pH range for ZVI. Pretreatment of pristine ZVI with acid or H2 can remove the passive layer and enhance the reactivity of ZVI. Physical methods, such as ultrasound and microwave technologies can do the same. Finally, in chloride and sulfate matrices with higher ionic strengths, there is a more effective reduction in metals and radionuclides. Ideal conditions for overcoming limitations of ZVI effectiveness in treating metals and radionuclides are proposed. However, there is a need for large-scale studies to demonstrate their efficiency and cost-effectiveness.