Theme: 08. Metals

Topic Area: 8c. Precipitation and Stabilization of Metals

Formatted Title:

Innovative and Cost-Effective Boron Absorbent Media

Background/Objectives:

Boron naturally occurs as borates in oceans, sedimentary rock, and some soils and is released into the environment due to weathering as well as anthropogenically. Anthropogenic sources include agricultural runoff, industrial processes, landfills and coal combustion residual (CCR) impoundments. Although it is well recognized as a micronutrient, boron is classified as a moderate to high toxic element in aquatic environments and due to its high mobility in water easily enters surface- and groundwater systems. As such, boron is used as an indicator of CCR impacts to groundwater due to its elevated concentration within CCR materials and is currently included as a detection monitoring constituent under the Federal CCR Rule (40 CFR 257 Subpart D) and may be added to the list of assessment monitoring constituents. If boron is part of assessment monitoring programs, exceedances would need to be addressed in order to satisfy applicable remedy selection criteria. Additionally, some states regulate boron in groundwater and/or drinking water, with variable compliance criteria. Current options for in situ treatment of boron via remedial technologies such as permeable reactive barriers (PRBs) are limited by low efficiency of boron removal or high costs.

Approach/Activities:

Initial testing involved the use of an absorbent media in a two-phased column treatment configuration. The initial test evaluated groundwater collected from a site which is impacted by boron and other CCR constituents to simulate field treatment conditions as closely as possible. In addition, a bench treatability study using the absorbent media as a permeable reactive barrier to remove boron and other metals from non-CCR groundwater was performed.

Results/Lessons Learned:

Results from the column study found that boron concentrations were reduced from 30 mg/L to less than 2 mg/L for approximately 230 pore volumes, This resulted in a boron loading rate similar to those observed for commercially available ion exchange resins. Testing was also completed to evaluate boron behavior under post-closure conditions, with artificial groundwater representing background conditions with no boron passed through the column. Desorption equilibria in the media seems to allow leaching at a concentration similar to the breakthrough concentration, suggesting concentration reductions will be maintained long-term.

Evaluating the media as a PRB to treat site groundwater resulted in successful treatment of not only boron, but also cobalt, selenium and manganese. The results suggest that the patented boron removal technology is a promising cost-effective alternative to currently available commercial technologies and the applicability of this removal technology for both in situ and ex situ applications will continue to be evaluated.

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Rosemary Le