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51.
Daniel?E.?HarlovEmail author Richard?Wirth Hans-Jürgen?F?rster 《Contributions to Mineralogy and Petrology》2005,150(3):268-286
In a series of timed experiments, monazite inclusions are induced to form in the Durango fluorapatite using 1 and 2 N HCl
and H2SO4 solutions at temperatures of 300, 600, and 900°C and pressures of 500 and 1,000 MPa. The monazite inclusions form only in
reacted areas, i.e. depleted in (Y+REE)+Si+Na+S+Cl. In the HCl experiments, the reaction front between the reacted and unreacted
regions is sharp, whereas in the H2SO4 experiments it ranges from sharp to diffuse. In the 1 N HCl experiments, Ostwald ripening of the monazite inclusions took
place both as a function of increased reaction time as well as increased temperature and pressure. Monazite growth was more
sluggish in the H2SO4 experiments. Transmission electron microscopic (TEM) investigation of foils cut across the reaction boundary in a fluorapatite
from the 1 N HCl experiment (600°C and 500 MPa) indicate that the reacted region along the reaction front is characterized
by numerous, sub-parallel, 10–20 nm diameter nano-channels. TEM investigation of foils cut from a reacted region in a fluorapatite
from the 1 N H2SO4 experiment at 900°C and 1,000 MPa indicates a pervasive nano-porosity, with the monazite inclusions being in direct contact
with the surrounding fluorapatite. For either set of experiments, reacted areas in the fluorapatite are interpreted as replacement
reactions, which proceed via a moving interface or reaction front associated with what is essentially a simultaneous dissolution–reprecipitation
process. The formation of a micro- and nano-porosity in the metasomatised regions of the fluorapatite allows fluids to permeate
the reacted areas. This permits rapid mass transfer in the form of fluid-aided diffusion of cations to and from the growing
monazite inclusions. Nano-channels and nano-pores also serve as sites for nucleation and the subsequent growth of the monazite
inclusions. 相似文献
52.
53.
Oxygen-enhanced biodegradation of phenoxy acids in ground water at contaminated sites 总被引:1,自引:0,他引:1
The effects of adding oxygen to anaerobic aquifer materials on biodegradation of phenoxy acid herbicides were studied by laboratory experiments with aquifer material from two contaminated sites (a former agricultural machinery service and an old landfill). At both sites, the primary pollutants were phenoxy acids and related chlorophenols. It was found that addition of oxygen enhanced degradation of the six original phenoxy acids and six original chlorophenols. Inverse modeling on 14C 4-chloro-2-methylphenoxypropanoic acid (MCPP) degradation curves revealed that increasing the oxygen concentrations from <0.3 mg/L up to 7 to 8 mg/L shortened the lag phases (from approximately 150 d to 5 to 25 d) and increased first-order degradation rate constants by 1 order of magnitude (from approximately 5 x 10(-2) d(-1) to up to 30 x 10(-2) d(-1)). Additionally, the degree of MCPP mineralization was increased (30% to 50% mineralized at low oxygen concentrations and 50% to 70% mineralized at high oxygen concentrations, based on 14CO2 recovery). These positive effects on degradation were observed even at relatively low oxygen concentrations (2 mg/L). Furthermore, effects related to the addition of oxygen on the general geochemistry were studied. An oxygen consumption of 2.2 to 2.6 mg O2/g dw was observed due to oxidation of solid organic matter and, to some extent (0.5% to 11% of the total oxygen consumption), water-soluble compounds such as Fe2+, dissolved Mn, nonvolatile organic carbon, and NH4+. Overall, the results suggest that stimulated biodegradation by addition of oxygen might be a feasible remediation technology at herbicide-contaminated sites, although oxygen consumption by the sediment could limit the applicability. 相似文献