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- Title
Ironstone and red mud barriers to reduce subsurface movement of soil phosphorus.
- Authors
Smith, Samantha; Gaston, Lewis; Beasley, Jeffery; Wang, Jim; Padilla, Josh; Sun, Wenguang
- Abstract
Loss of phosphorus in seepage may contribute to eutrophication of downstream water bodies. This study examined the potential use of pedogenic ironstone and untreated red mud (bauxite refining residue) as P sorbents in a permeable reactive barrier (PRB) to mitigate such loss. Effects of ironstone and red mud on P sorption (batch), transport (columns), saturated hydraulic conductivity (KS), and growth of common bermudagrass (Cynodon dactylon; greenhouse) were examined. Both materials had sorption maxima of ∼30 mmol P kg−1 or about five times that of a P‐enriched sandy soil; however, sorption by red mud greatly increased with decreasing pH. Transport of P through columns of ironstone and red mud (diluted with nonreactive sand) was similar and slower compared to soil + sand. However, when red mud was mixed with soil, increased sorption at lower pH resulted in greater P retention compared to ironstone + soil (76% vs. 13%). Although addition of ironstone to soil up to 20% did not reduce KS, red mud at even 5% did. Soil amendment with red mud increased bermudagrass growth and P uptake. Given long‐term neutralization of red mud in an acidic soil and increased P sorption, it may be suitable in a PRB if incorporated at a low rate and/or co‐incorporated with a coarser material. Core Ideas: Phosphate transport is reduced by ironstone and red mud.Red mud is more retentive than ironstone at acidic pH.Low hydraulic conductivity of red mud poses some limitation.Phytoextraction may help maintain sorption capacity over time. Plain Language Summary: Loss of fertilizer phosphorus from soil may foul water quality. One pathway of phosphorus loss from soil is lateral movement with groundwater. However, if one were to install a porous wall in soil that could capture phosphorus, less would be discharged to surface water. Results of this study indicate that such a permeable reactive barrier containing either ironstone (natural material) or red mud (nonhazardous industrial waste) would be effective in this way. Although red mud is likely better, design of the barrier must compensate for the effect of red mud on slowing groundwater flow. Results also indicate that plant uptake of phosphorus from the barrier zone may help preserve the long‐term capacity of the barrier to retain groundwater phosphorus.
- Subjects
PERMEABLE reactive barriers; ACID soils; SOIL amendments; HYDRAULIC conductivity; RED soils; BERMUDA grass
- Publication
Journal of Environmental Quality, 2024, Vol 53, Issue 5, p758
- ISSN
0047-2425
- Publication type
Article
- DOI
10.1002/jeq2.20601