Iron Filings Cement Engineered Soil Mix

Abstract

Engineered soil mixes are expected to maintain plant growth while minimizing nutrient leaching in greenhouse and bioretention applications. Iron (Fe) has been suggested within plant growth mixtures as a sorbent for phosphorus. The purpose of this study was to determine if Fe filings are an appropriate component of engineered plant growth mixtures. Iron filings were added to engineered soil mixes in laboratory columns, and plants were grown for 2 mo. Unfortunately, Fe filings partially cemented the engineered mixes, especially the treatment with sand and compost but no soil. After completing the study, orange and red aggregates were apparent. Although Fe filings might be useful in filter beds, they were not suitable within engineered plant growth mixes.Core Ideas Iron added to sand mix resulted in partial cementation. New red and orange aggregates were formed in the sand mix. Iron should not be added to soil mixes where plants will be grown.

Nutrient Leaching When Soil Is Part of Plant Growth Media

“…At least for P leaching, sorption to soils in the mixes was adequate in the absence of inorganic non-soil P sorption products. The soils were not harmful to plant growth as sorbent materials could be [6]; however, excess nitrate leaching occurred over time. Overall, it is recommended that bioretention cells and other plant growth media include soil as a component to reduce P leaching.…”

“…Addition of biochar and perlite or dolomite (3% by volume) did not retain P [19]. Addition of iron filings (3% by volume) resulted in partial cementation of the sand or soil mixes [6]. Addition of manure compost resulted in unacceptable leaching loss of nitrate [19]; however, layering the compost on top rather than mixing throughout reduced nitrate leaching.…”

“…Sometimes, sorbents [4,5] are added to sand to increase P retention, especially in filters in which no plants are growing. Unfortunately, sorbents used in these filters may not be suitable for filter systems where plants are grown [6].…”

Urban Stormwater Characterization, Control, and Treatment

“…However, leaching of Zn was significantly reduced by combining scrap tire rubber with the water treatment residuals. When comparing batch study and column study results for six different amendments, found that column studies were a more realistic test than batch studies when determining removal efficiencies and service lives of amended media Logsdon and Sauer (2016a). published the findings of laboratory studies demonstrating that iron filings were not suitable as soil amendments for engineering media because they caused cementation of the soils.…”