ENVR 29 |
| Surface modification of nano-scale zero-valent iron (NZVI) is necessary for its placement in groundwater DNAPL (dense non aqueous phase liquid) source zones. However, the transport of anionic polyelectrolyte-modified NZVI in sand columns can be affected by many factors including groundwater pH and the presence of clay particles. A fundamental understanding of how these factors affect NZVI mobility will aid in planning an injection or placement scheme for a desired NZVI distribution and treatment effectiveness. The effect of pH (5 to 8) and the presence of silica sand fines (2 to 15 wt %) and clay fines (2 to 15 wt %) on the mobility of modified nanoiron were evaluated in water-saturated sand columns. Modifiers included a high MW (125 kg/mol) tri-block co-polymer (PMAA-PMMA-PSS) and polyaspartate which is a low MW (2 to 3 kg/mol) biopolymer. Without excess polymer in solution, polyelectrolyte-modified NZVI was immobile in 15-cm sand columns at pH 6, but mobile at pH=8. The presence of 2 wt% kaolinite clay particles greatly reduced mobility at pH=8. Low transport of NZVI at low pH was caused by the aggregation of NZVI and higher attachment to the sand grains. The existence of silica fines did not inhibit the transport of NZVIs. On the other hand, clay fines limited the mobility of these particles significantly which is attributed to the pH dependent charge heterogeneity on clay mineral surfaces. A kaolinite-NZVI hetero-aggregation study and column transport studies with kaolinite and nano-iron over the pH range 5 to 8 confirmed the attachment of modified NZVI to kaolinite at pH<8. These results indicate that the hydrogeochemical conditions of an aquifer must be considered when selecting surface modifiers. |
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Environmental Behavior and Fate of Manufactured Nanomaterials
1:30 PM-5:35 PM, Sunday, April 6, 2008 Morial Convention Center -- Rm. 235, Oral
Division of Environmental Chemistry |