Dechlorination metal particles

Carbon is a prominent catalyst support material as it allows the anchoring of metal particles on a substrate which docs not exhibit solid acid-base properties. Carbon is finally a catalyst in its own right, enabling the activation of oxygen and chlorine for selective oxidation, chlorination, and dechlorination reactions. 

The operation of a short reactor column (Figure 1) designed to be interposed within a flowing stream of SCCO2 has bemi optimized for dechlorinations (3). The cohinm ass iibly (25 x 1cm) was filled with ZV metal particles - iron (Fe 0... 

Figure 1. A dechlorination assembly consisting of source of scC02, a tenqterature andpressare equilibratitm vessel (TPEV), a presswe transducer (PT), a three- ay subsUate inlet tee, a reactor column filled with zero-valent (ZV) metal particles (jacketed with a heated alumina tube) and a terminating ccpillary restrictin. (Adcq/ted with permission from refereme 3. O yri t 2000,...

That dechlorinations w re accelerated by the ZV-metal particles was demonstrated by replacing the metal particles with silica (acid washed sea sand). For the silica column operated under dechlorinating conditions that had been optimal for ZV metal (400 C, 31.0 MPa), the recovery of organically bound chlorine from the eluate was virtually quantitative. In further trials, acetone-hexane extract of a sandy loam soil (spiked with 600 ppm Aroclor 1254) was fed to the reactor at 0.1 mLymin and dechlorinated efficiently. Chlorinated residues were not detected in the reactor effluent by GC-MS. More importantly, soil co-extractives in the PCB solution did not seem to affect the course or the efficiency of the reaction perceptibly. 

Zhang W, Wang C. (1997). Nanoscale metal particles for dechlorination of PCE and PCBs. Environmental Science and Technology 31 2154-2156. 

Other studies use soil or sediment samples for a more accurate indication of microbial activity in natural environments. In these samples, organic matter and clay particles play a role in metal toxicity.76112113 Both organic material and clay particles in soil can bind metals and reduce their bioavailability. For example, Pardue et al.87 demonstrated that much less solution-phase cadmium was required to inhibit trichloroaniline (TCA) dechlorination in a mineral-based soil than in a soil containing a higher concentration of organic matter. Other studies have shown that adding clay minerals to a medium mitigates toxicity. Clay minerals, such as kaolinite, montmorillonite, bentonite, and vermiculite, can bind to metals to decrease the amount that is bioavailable.112 115... 

The graded and cleaned particles of waste plastic are then introduced into a melt-ing/preheating system with an extruder feeder. The hard metal, clay and sand, glass, etc. are separated here by sedimentation, and then the waste plastic is charged in the dechlorination section. The solid metal, glass, etc. is removed from the melting/preheating section periodically. 

Reductive dechlorination of HCB can be achieved with the combination of electrokinetics with the appropriate catalysts such as nanoscale zero valent iron (NZVl). The electric field can be used as a mechanism for the delivery of NZVl into the soil [10]. Reductive dechlorination can be achieved in the soil or even upon the cathode if the contaminant reaches the cathode compartment. Other metallic catalysts such as Cu/Fe or Pd/Fe bimetal microscale particles were satisfactorily used with the same purpose. Dechlorination of hexachlorobenzene up to 98 % was achieved with Cu/Fe [27] and only 60 % with Pd/Fe [20]. 

Xu Jiao-Xing et al. have investigated the effect of the dechlorination temperature on the metal dispersion and the catal3dic activity for ruthenium-based catalyst (Table 6.26). For Ru/AC catalyst, when the temperature is lower than 400°C, ruthenium particles are stable and the chlorines can be removed effectively. But the dechlorination at the higher temperatures will result in the sintering of the ruthenium particles. They considered that the dechlorination at 400°C-450°C would be more suitable for the catalyst with activated carbons as supports. The key of H2... 

Another means to promote in situ abiotic transformation is the construction of a reactive wall, physically similar to a slurry wall but with a porous backfill, containing chemical reactants, through which contaminated groundwater can flow. One such reactant, often referred to as zero-valent iron, is made up of fine particles of elemental (metallic) iron. Reactions between elemental iron and some dissolved chlorinated solvents, for example, can result in dechlorination of the solvents to species that are more susceptible to subsequent biodegradation. 

Various methods of synthetizing finely divided bronzes HxMo03 with or without the presence of metallic activator particles are available. The starting molybdenum trioxide can be prepared in a flame reactor, under conditions where nucleation and growth processes of the oxide particles in the hot zone of the flame are optimized in order to obtain high surface areas ( 30 m g-l) and a stable structure (orthothombic phase) after a standard dechlorination treatment of M0O3. 

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