Scavenger material

Vanadium raw materials are processed to produce vanadium chemicals, eg, the pentoxide and ammonium metavanadate (AMV) primary compounds, by salt roasting or acid leaching. Interlocking circuits, in which unfinished or scavenged material from one process is diverted to the other, are sometimes used. Such interlocking to enhance vanadium recovery and product grade became more feasible in the late 1950s with the advent of solvent extraction. 

In order to explore the potential of CHD resins as scavenger materials, 1-ethyl-3,5-dimethoxycydohexa-2,5-dienecarboxylic acid was anchored to a commercially available trisamine resin (Scheme 7.106), which yielded a high-loading cyclohexane-1,3-dione scavenger resin (CHD-SR) [125]. 

Some rather interesting custom made electrophilic resins that have been developed lately as nucleophile scavenging materials are the acid chloride (25) and arenesulfonyl chloride (26) resin shown in Fig. 9. Resin 26 is stable to various reaction conditions over resin 18 and can be used while conducting subsequent chemical steps.62... 

The sediments represent the major sink for material in the oceans. The main pathway to the sediments is the deposition of suspended particles. Such particles may be only in transit through the ocean from a continental origin or be formed in situ by chemical and biological processes. Sinking particles can scavenge material from solution. Accordingly, this section introduces the components found in marine sediments, but emphasises processes that occur within the water column that lead to the formation and alteration of the deposited material. 

Scavenger processes are used only for trace sulfur removal and are in many cases not suitable for in-situ regeneration. They are typically designed with two or more vessels operating in a lead/lag mode. When the scavenger material reaches the end if its useful life, it must be removed from the vessel and anew charge loaded in. 

Zerdin, K., Rooney, M.L., and Vermue, J. 2003. The vitamin C content of orange juice packed in an oxygen scavenger material. Food Chem. 82, 387 395. 

A result is that new products have been developed based on the use of recycled materials as a cotton yam substitute. Using scavenged materials certainly allowed women to continue their weaving, anpower their imagination, and contribute to the spirit of community by providing inexpensive raw materials at a time when the cost of traditional cotton yams was prohibitive. Even after cotton prices fell in late 2011, the Guatemalan women continued making products from recycled materials. 

Small quantities of zirconium are also used for special applications. In photo flash equipment the very high flame temperature, 4660°C, can be used. Another use is as a scavenger material in the vacuum technique. The scavenger function implies that zirconium, when present in a heated evacuated container, removes any traces of oxygen present. 

Substituted Hydantoins. 5-Methylhydantoin [616-03-5] has been selected from several stmctures as a formaldehyde scavenger for color photosensitive materials and water-thinned inks and coatings (102,103). 

Figure 5 illustrates the type of encapsulation process shown in Figure 4a when the core material is a water-immiscible Hquid. Reactant X, a multihmctional acid chloride, isocyanate, or combination of these reactants, is dissolved in the core material. The resulting mixture is emulsified in an aqueous phase that contains an emulsifier such as partially hydroly2ed poly(vinyl alcohol) or a lignosulfonate. Reactant Y, a multihmctional amine or combination of amines such as ethylenediamine, hexamethylenediamine, or triethylenetetramine, is added to the aqueous phase thereby initiating interfacial polymerisation and formation of a capsule shell. If reactant X is an acid chloride, base is added to the aqueous phase in order to act as an acid scavenger. 

Environmental Impact of Ambient Ozone. Ozone can be toxic to plants, animals, and fish. The lethal dose, LD q, for albino mice is 3.8 ppmv for a 4-h exposure (156) the 96-h LC q for striped bass, channel catfish, and rainbow trout is 80, 30, and 9.3 ppb, respectively. Small, natural, and anthropogenic atmospheric ozone concentrations can increase the weathering and aging of materials such as plastics, paint, textiles, and mbber. For example, mbber is degraded by reaction of ozone with carbon—carbon double bonds of the mbber polymer, requiring the addition of aromatic amines as ozone scavengers (see Antioxidants Antiozonants). An ozone decomposing polymer (noXon) has been developed that destroys ozone in air or water (157). 

Another way to minimise nitrosamine exposure is to use scavengers, which are reported to function by reacting rapidly with nitrosamines to render them harmless, but the relative effectiveness of each scavenger remains to be better quantified. Materials that have been investigated include the following (30) ... 

Hot-Water Process. The hot-water process is the only successflil commercial process to be appHed to bitumen recovery from mined tar sands in North America as of 1997 (2). The process utilizes linear and nonlinear variations of bitumen density and water density, respectively, with temperature so that the bitumen that is heavier than water at room temperature becomes lighter than water at 80°C. Surface-active materials in tar sand also contribute to the process (2). The essentials of the hot-water process involve conditioning, separation, and scavenging (Fig. 9). 

Aromatic Amines. Antioxidants derived from -phenylenediarnine and diphenylamine are highly effective peroxy radical scavengers. They are more effective than phenoHc antioxidants for the stabilization of easily oxidized organic materials, such as unsaturated elastomers. Because of their intense staining effect, derivatives of -phenylenediamine are used primarily for elastomers containing carbon black (qv). 

Nickel—beryllium casting alloys are readily air melted, in electric or induction furnaces. Melt surface protection is suppHed by a blanket of argon gas or an alumina-base slag cover. Furnace linings or cmcibles of magnesia are preferred, with zirconium siUcate or mullite also adequate. Sand, investment, ceramic, and permanent mold materials are appropriate for these alloys. Beryllium ia the composition is an effective deoxidizer and scavenger of sulfur and nitrogen. 

Metal or metal oxides may be added to perform specific functions. Brass chips and copper powder are frequently used in heavy-duty organics where these metaUics act as scavengers to break up undesirable surface films. Zinc chips used in Class A organics contribute significantly to recovery of normal performance following fade. Aluminum is also used. Most of these inorganic materials tend to detract from antinoise properties and mating surface compatibihty. 

A significant use of butylene oxide [26249-20-7] is as an acid scavenger for chlorine-containing materials such as trichloroethylene. Inclusion of about 0.25—0.5% of butylene oxide, based on the solvent weight, during preparation of vinyl chloride and copolymer resin solutions minimizes container corrosion which may be detrimental to resin color and properties. 

Catalysts commonly lose activity in operation as a result of accumulation of materials from the reactant stream. Catalyst poisoning is a chemical phenomenon, A catalyst poison is a component such as a feed impurity that as a result of chemisorption, even in smaH amounts, causes the catalyst to lose a substantial fraction of its activity. For example, sulfur compounds in trace amounts poison metal catalysts. Arsenic and phosphoms compounds are also poisons for a number of catalysts. Sometimes the catalyst surface has such a strong affinity for a poison that it scavenges it with a high efficiency. The... 

When the ore contains a large amount of clay minerals, these form difficult to separate slimes, which hinder the recovery of the minerals (see Clays). The tailing from the scavenger cells can be cycloned to remove the slimes before the coarse material is floated in a tailings retreatment plant. The flotation product from the rougher cells of this plant can be reground and cleaned. This additional treatment of the tailings from the main copper flotation plant may improve the recovery of metal values by 1—3%. 

The destiny of most biological material produced in lakes is the permanent sediment. The question is how often its components can be re-used in new biomass formation before it becomes eventually buried in the deep sediments. Interestingly, much of the flux of phosphorus is held in iron(lll) hydroxide matrices and its re-use depends upon reduction of the metal to the iron(ll) form. The released phosphate is indeed biologically available to the organisms which make contact with it, so the significance attributed to solution events is understandable. It is not clear, however, just how well this phosphorus is used, for it generally remains isolated from the production sites in surface waters. Moreover, subsequent oxidation of the iron causes re-precipitation of the iron(lll) hydroxide floes, simultaneously scavenging much of the free phosphate. Curiously, deep lakes show almost no tendency to recycle phosphorus, whereas shallow... 

Today, the plastics industry is heavily integrated with the oil industry. In fact a popular view is that it would not be able to produce plastics if oil were not available. This is very different from the situation 40-50 years ago when the plastics industry was being described as a scavenger of raw materials . 

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