title: Influence of injection conditions on EDDS-flushing of metal-contaminated soil.
abstract: This study evaluated the design of step-gradient, single-pulse, multi-pulse, and continuous injection of biodegradable EDDS ([S,S]-ethylene-diamine-disuccinic acid, under the same total dosage) and the significance of pore-water velocities during in situ soil flushing. In view of the metal breakthrough and extraction efficiency of each injection mode, single-pulse injection was found to be the least effective for all metals. Multi-pulse injection was consistently more effective than single-pulse injection, although the efficiency of second and third pulse injections significantly diminished. Continuous injection offered a simple operation and the greatest Ni and Cu extraction, whereas step-gradient injection was the best option for Zn and Pb extraction because it mitigated the influence of metal exchange. Moreover, a rinsing step with a background solution following the initial injection of the multi-pulse injection removed newly formed metal-EDDS complexes from soil pores effectively before further EDDS-flushing. A decrease in pore-water velocity provided a longer residence time for greater Ni and Cu extraction, but also enhanced the rate-limited metal exchange of Zn-EDDS and Pb-EDDS complexes and thus hindered Zn and Pb extraction. These results suggest a slower and continuous injection for the best Ni or Cu removal, but a faster and step-gradient injection for Zn or Pb removal.
authors.affiliation: Department of Civil and Environmental Engineering, The Hong Kong University of Science and Technology, Hong Kong, China. cemclo@ust.hk
authors.forename: Irene M C
authors.initials: IM
authors.lastname: Lo
authors.forename: Daniel C W
authors.initials: DC
authors.lastname: Tsang
authors.forename: Theo C M
authors.initials: TC
authors.lastname: Yip
authors.forename: Fei
authors.initials: F
authors.lastname: Wang
authors.forename: Weihua
authors.initials: W
authors.lastname: Zhang
mesh_terms: D005029:Ethylenediamines / Q000737:chemistry*; D008670:Metals / Q000737:chemistry*; D012989:Soil Pollutants / Q000737:chemistry*; D013386:Succinates / Q000737:chemistry*
chemical_list: D005029:Ethylenediamines; D008670:Metals; D012989:Soil Pollutants; D013386:Succinates; C041447:N,N'-ethylenediamine disuccinic acid