THESIS
2006
xvii, 229 leaves : ill. ; 30 cm
Abstract
With increasing concern about soil and groundwater contamination, research on contaminant transport modeling and remediation technology has grown rapidly. Nonequilibrium transport of heavy metals resulting from rate-limited reactions in soils under natural and remediation conditions was investigated with batch, column, and sequential extraction experiments together with transport modeling in this study....[
Read more ]
With increasing concern about soil and groundwater contamination, research on contaminant transport modeling and remediation technology has grown rapidly. Nonequilibrium transport of heavy metals resulting from rate-limited reactions in soils under natural and remediation conditions was investigated with batch, column, and sequential extraction experiments together with transport modeling in this study.
Higher pore-water velocity that allowed shorter residence time and lower temperature that reduced the sorption rate resulted in nonequilibrium transport, whereas the reverse promotes equilibrium transport. Diffusion process was probably the rate-limiting step. The disparity of transport behavior was related to both residence time and reaction time.
Competition among heavy metals for sorption not only suppressed the sorption equilibrium but changed the corresponding transport behavior. The specific sorption of Cd, which was found rate-limited, was nearly eliminated by the presence of Cu, leading to shorter apparent equilibrium time and thereby equilibrium transport of Cd. In addition, the concentration-dependent relative contribution of nonlinear and rate-limited sorption to nonideal transport was assessed, in which rate-limited sorption was important only at sufficiently low metal loading. It has demonstrated that the multiple approaches using batch, sequential extraction and column experiments can provide a better analysis of the transport behavior.
Nonequilibrium transport of metal complexes was also demonstrated to be important during EDTA-flushing. While Cu extraction by EDTA was efficient, soil mineral and organic matter dissolution that would significantly alter the soil properties should not be neglected. The EDTA-promoted extraction and dissolution, which are rate-limited, could be described by the respective second-order kinetics. The proposed transport model successfully simultaneously simulated the nonequilibrium transport of all extracted and dissolved metals, taking into account the factors of metal competition for EDTA, concentration of EDTA and extractable amount of metals.
Post a Comment