Enhancement of phosphorus sorption onto light expanded clay aggregates by means of aluminum and iron oxide coatings
Autor: | Helinä Hartikainen, Nader Yaghi |
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Rok vydání: | 2013 |
Předmět: |
Environmental Engineering
Sorbent Health Toxicology and Mutagenesis Inorganic chemistry Oxide Iron oxide chemistry.chemical_element 010501 environmental sciences 01 natural sciences Ferric Compounds Waste Disposal Fluid chemistry.chemical_compound Adsorption Aluminum Oxide Environmental Chemistry Environmental Restoration and Remediation 0105 earth and related environmental sciences Phosphorus Public Health Environmental and Occupational Health Sorption 04 agricultural and veterinary sciences General Medicine General Chemistry Phosphate Pollution 6. Clean water chemistry Wetlands 040103 agronomy & agriculture 0401 agriculture forestry and fisheries Clay Aluminum Silicates Saturation (chemistry) Water Pollutants Chemical |
Zdroj: | Chemosphere. 93(9) |
ISSN: | 1879-1298 |
Popis: | Phosphorus (P) loading from non-point or point sources increases the eutrophication risk of natural waters. The functioning of constructed wetlands (CWs) used as natural water treatment systems can be improved by means of additional materials adsorbing soluble P. In this study, light expanded clay aggregates (LECA) and LECA coated with aluminum (Al) oxide (Al-LECA) or iron (Fe) oxide (Fe-LECA) were tested for their efficiency as P sorbents in the pH range 3–8. The oxide coatings duplicated the actual sorption capacity calculated from the sorption isotherms at the P concentration in the equilibrium solution of 20 μg L−1, assumed to be the allowable P level in purified water. In the oxide-coated LECAs the sorption was fast and followed both the first- and second-order Lagergren kinetic models, suggesting that the formation of a binuclear surface complex was feasible. In LECA, sorption was markedly slower and followed the first-order kinetic model, indicating that retention occurred through a monodentate attachment. These findings were in harmony with the degree of P saturation (DPS) of the sorbent surfaces at the highest P addition level (200 μg L−1), DPS being decisively higher for LECA than for the oxide-coated sorbents. Accordingly, at higher pH values the competition by hydroxyl ions diminished the sorption in LECA relatively more than that in the coated sorbents. In agreement with the acidity of Al3+ being 100 times lower than that of Fe3+, at elevated pH the sorption by Al-LECA proved to be less reversible than that by Fe-LECA. The results provide evidence that in CWs Al-coated sorbents are superior to Fe-coated ones that are also redox-sensitive and may lose their sorption properties in anoxic conditions. |
Databáze: | OpenAIRE |
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