| Summary: | 博士 === 國立交通大學 === 土木工程學系研究所 === 85 === Chemical fixation/solidification of wastes is one of the best demonstrated a
vailable technologies for treating wastes, especially those containing heavy m
etals. Cement-based solidification/stabilization (S/S) processes have proven s
uccessful on many sludges generated by the precipitation of heavy metals.
Cement-based waste forms, however, typically have a permeability value rangin
g from 10-5 to 10-9 cm/sec. The capillary pores, which serve as a trans-portat
ion conduit, have sizes ranging from 0.01 to 10(m in the hydrated cementpaste,
thereby decreasing the effectiveness of solidification/stabilization. The p
resent study is to investigate the mechanisms of solidification/ stabilization
of chromium with cement and cement/unsaturated polyester com- posite. When un
saturated polyester (UP) is added as modification, the cement/ UP causes polym
erization or crosslinking, thus reducing the permeability of treated wastes an
d improving the effectiveness of solidification/stabili-zation of wastes. Th
e fixing agents used include cement, cement/UP and cement constituents (i.e. (
-C2S, C3S, and C3A). The wastes were chromium-containing sludge, chromic oxid
e (Cr2O3) and chromium nitrate (Cr(NO3)3 ?9H2O). Scanning Elec-tron Microscop
y (SEM), Energy Dispe rsive Spectroscopy (EDS), X-ray Diff-raction (XRD) and M
agic Angle Spinning/Nuclear Magnetic Resonance (MAS/NMR ) were employed for th
e structural and molecular analysis of the solidified/stabilized samples. The
unconfined compressive strength (UCS) and the leach-ability by the Toxicity Ch
aracteristics Leaching Procedure (TCLP) of thesolidified/stabilized samples we
re measured. Three major S/S processes wereemployed in this study and some sig
nificant results are summarized as follows: I、Solidification/stabilization o
f chromium-containing sludge with cementand cement /unsaturated polyester comp
osite.1. All the solidified samples prepared with cement had compressive stren
gth higher than 10 Kg/cm2 and leachability values which met the Taiwan EPA re-
quirements for landfilldisposal. Nevertheless, they need to be disposed in se
gregated landfill.2. Most of the solidified samples prepared with cement/unsat
urated polyester composite had compressive strength higher than 150 Kg/cm2and
leachability values which met the Taiwan EPA requirements for recycle-reuse re
gulation.3. The samples prepared with cement exhibited loose structures,while
thosewith cement/unsaturated polyester composite exhibited denser structures i
n SEM observations.II、Solidification/stabilization of Cr2O3 or Cr(NO3)3 ?9H2
O with cement and cement/unsaturated polyester composite. 1. Crystalline CaCr
O4 was formed during the S/S of Cr2O3 with cement.This isattributed to the sub
stitution of chromium for silicon in hydrated cementproducts.2. The degree of
cement hydration decreased during the S/S of Cr(NO3)3 ?9H2O with cement, an
d it decreased more dramatically during the S/S of Cr(NO3)3 ?9H2O with cement
/unsaturated polyester composite ; indicating that chromium nitrate an
d un saturated polyester could retard the extent of cement hydration.III、
Solidification/stabilization of Cr(NO3)3 ?9H2O with cement constituents(i.e.
(-C2S, C3S, and C3A).1. Formation of (-calcium chromium oxide hydrate ((-CaCrO
4 ?2H2O) during the solidification/stabilization of chromium nitrate (Cr(NO3)
3 ?9H2O) with (-C2S indicates the probable replacement of silicon by chromium
in the calcium sili-cate hydrate (C-S-H). 2. Formation of calcium chromium si
licate (CaCrSi4O10),calcium chromium oxide hydrate (CaCrO4 ?2H2O), and calciu
m dichromate (CaCr2O7) during the solidifi-cation/stabilization of chromium ni
trate (Cr(NO3)3 ?9H2O) with C3S indicatesthe probable replacement of silicon
by chromium in the calcium silicate hydrate(C-S-H).3. Formation of aluminum ch
romium oxide hydroxide (Al2(OH)4CrO4) during thesolidification/stabilization o
f chromium nitrate (Cr(NO3)3 ?9H2O) with C3Aindicates the probable interactio
n between Cr and Al.
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