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Description:
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Fe (II ) -based degradative solidification /stabilization (Fe (II ) -DS /S ) technology is
the modification of conventional solidification /stabilization (S /S ) . Inorganic pollutants
are immobilized by Fe (II ) -DS /S while organic pollutants are destroyed . Experimental
studies were conducted to identify the active agents for Tetrachloroethylene (PCE )
degradation as well as the conditions that enhance the formation of the active agents in
the Fe (II ) -DS /S system . PCE was chosen as a model chlorinated aliphatic hydrocarbon
in this study .
First , the conditions that lead to maximizing production of the active agents were
identified by measuring the ability of various chemical mixtures to degrade PCE . Results
showed that Fe (II ) , Fe (III ) , Ca , and Cl were the the important elements that affect
degradation activity . Elemental compositions of the mixtures and the conditions
affecting solid formation might be the important factors in determining how active solids
are formed . Second , instrumental analyses (XRD , SEM , SEM -EDS ) were used to identify
minerals in chemical mixtures that have high activities . Results indicate that active
agents for PCE degradation in Portland cement slurries and in cement extracts might be
one of several AFm phases . However , systems without cement did not form the same
solids as those with cement or cement extract . Ferrous hydroxide was identified as a
major solid phase formed in systems without cement .
Finally , the effect of using different types of ordinary Portland cement (OPC ) on
PCE degradation rate during Fe (II ) -DS /S was examined and the solids were examined
by instrumental analyses (XRD , SEM , SEM -EDS ) . Four different OPC (Txi , Lehigh ,
Quikrete , and Capitol ) showed different PCE degradation behaviors . Pseudo first -order
kinetics was observed for Capitol and Txi OPC and second -order kinetics was observed
for Quikrete . In the case of Lehigh cement , pseudo first -order kinetics was observed in
cement slurry and second -order kinetics in cement extract . Calcium aluminum hydroxide
hydrates dominated solids made with Txi , Quikrete , and Lehigh cements and Friedel s
salt was the major phase found in solids made with Capitol cements . Fe tended to be
associated with hexagonal thin plate particles , which were supposed to be a LDH . |