Powder recovery

No better way exists to produce a thick, run- and sag-free plastic coating on an object. When the coating or powder applications are used, steps must always be carried out in a ventilated enclosure. The system is not 100% efficient so the oversprayed powder must be retained by a flowing air stream. This oversprayed powder—usually about 20-30% of that directed toward the object—is picked up and carried by the exhaust air to a filter system where it is removed from the air. Such a filter, or separation system, usually consists of a cyclone filter followed by a bag type filter. In some of the newer systems, the powder recovery system operates in conjunction with belts that move over... 

When it comes to finding more complex systems of reusing the scrap rubber powder, recovery alternatives include pyrolysis, gasification, tire derived fuel, reuse and recycling, rubber reclaim, and retreading [3]. 

Criteria for spray cabins, powder recovery systems, and powder preparation systems are mainly determined by the time required to change colors. A compact unit... 

In other study, it was proved that the same oil previously cited can be successfully complexed with pCD by the coprecipitation method using hydroethanolic medium with a 96% powder recovery. The product obtained was similar to the original Mentha x villosa oil with respect to the major volatile components. The retention of volatiles was approximately 78%, while the total volatile compounds in the original oil was 99%. From the detected compounds in the original oil, 13 are monoterpenes, 10 are sesquiterpenes, 1 is ester, 1 is phenylpropanoid, and 3 were not identified. The major component of the oil is piperitenone oxide and its degree of complexation was 72%. Twelve compounds were totally complexed, 11 compounds were partially complexed, and 5 compounds were not complexed. It is supposed that 3 were only adsorbed on the pCD surface and 2 were absent. The calculated complexation efficiency was 13.6% (Martins et al., 2007). 

The EU s requirements are put forward in EU Directive 96/61/EF (IPPC Directive, Integrated Pollution Prevention and Control). The IPPC Directive with BREF (BAT REFerence document) will regulate all environmental aspects in one concession including energy and silica powder recovery. 

Fig. 6.1 Typical spray-d ing system consisting of a feed pump, an atomizer, an air heater, an air dispenser, a drying chamber, and equipment for exhaust air cleaning and powder recovery.

Flock spraying. Cold powder is sprayed, under air pressure, onto the pre-heated metalwork. Depending on the type of powder used, so post-sintering may be required. The process is essentially a manual one relying on operator skill and speed and is, as a consequence, rather slow. Powder recovery is not always easy. 

Into a 1-litre beaker, provided with a mechanical stirrer, place 36 - 8 g. (36 ml.) of aniline, 50 g. of sodium bicarbonate and 350 ml. of water cool to 12-15° by the addition of a little crushed ice. Stir the mixture, and introduce 85 g. of powdered, resublimed iodine in portions of 5-6 g, at intervals of 2-3 minutes so that all the iodine is added during 30 minutes. Continue stirring for 20-30 minutes, by which time the colour of the free iodine in the solution has practically disappeared and the reaction is complete. Filter the crude p-iodoaniline with suction on a Buchner funnel, drain as completely as possible, and dry it in the air. Save the filtrate for the recovery of the iodine (1). Place the crude product in a 750 ml. round-bottomed flask fitted with a reflux double surface condenser add 325 ml. of light petroleum, b.p. 60-80°, and heat in a water bath maintained at 75-80°. Shake the flask frequently and after about 15 minutes, slowly decant the clear hot solution into a beaker set in a freezing mixture of ice and salt, and stir constantly. The p-iodoaniline crystallises almost immediately in almost colourless needles filter and dry the crystals in the air. Return the filtrate to the flask for use in a second extraction as before (2). The yield of p-iodoaniline, m.p. 62-63°, is 60 g. 

Decant the ethereal solution from the yellow aldimine stannichloride which has separated, rinse the solid with two 50 ml. portions of ether, and transfer the solid to a 2-5 litre flask fitted for steam distillation and immersed in an oil bath at 110-120°. Pass steam through a trap (compare Fig. 11,40, 1,6) to remove condensed water, then through a superheater heated to 260° (Fig. I, 7, 2), and finally into the mixture (2). Continue the passage of y steam until the aldehyde is completely removed (4-5 litres 8-10 hours). Filter the white soUd at the pump, and dry in the air. The resulting p-naphthaldehyde, m.p. 53-54°, weighs 12 g. It may be further purified by distillation under diminished pressure (Fig. II, 19, ) -, pour the colourless distillate, b.p. 156-158°/15 mm., while hot into a mortar and powder it when cold. The m.p. is 57- 58°, and the recovery is over 90 per cent. 

Metal passivation Metal pickling Metal powders Metal recovery... 

Guar gum [9000-30-0] derived from the seed of a legume (11,16), is used as a flocculant in the filtration of mineral pulps leached with acid or cyanide for the recovery of uranium and gold (16). It is also used as a retention aid, usually in a chemically modified form (14,17). Starch and guar gum are subject to biological degradation in solution, so they are usually sold as dry powders that are dissolved immediately before use. Starch requires heating in most cases to be fully dissolved. 

Nickel sulfide, NiS, can be prepared by the fusion of nickel powder with molten sulfur or by precipitation usiag hydrogen sulfide treatment of a buffered solution of a nickel(II) salt. The behavior of nickel sulfides ia the pure state and ia mixtures with other sulfides is of iaterest ia the recovery of nickel from ores, ia the high temperature sulfide corrosion of nickel alloys, and ia the behavior of nickel-containing catalysts. 

Transportation and Disposal. Only highly alkaline forms of soluble sihcates are regulated by the U.S. Department of Transportation (DOT) as hazardous materials for transportation. When discarded, these ate classified as hazardous waste under the Resource Conservation and Recovery Act (RCRA). Typical members of this class are sodium sihcate solutions having sihca-to-alkah ratios of less than 1.6 and sodium sihcate powders with ratios of less than 1.0. In the recommended treatment and disposal method, the soluble sihcates are neutralized with aqueous acid (6 Af or equivalent), and the resulting sihca gel is disposed of according to local, state, and federal regulations. The neutral hquid, a salt solution, can be flushed iato sewer systems (86). 

Fig. 13. Spray-dryer system designed for production of agglomerated food powders with instant properties (82) A, Hquid-feed system B, spray-dryer chamber C, drying air heater D, cyclones for fines recovery E, vibrofluidizer as afterdryer F, vibrofluidizer as aftercooler and G, fines return to drying...

High density tungsten alloy machine chips are recovered by oxidation at about 850°C, foUowed by reduction in hydrogen at 700—900°C. Typically, the resultant powders are about 3-p.m grain size and resinter readily. There can be some pickup of refractory materials used in furnace constmction, which must be controUed. This process is important commercially. Eor materials that may be contaminated with other metals or impurities, the preferred recovery process is the wet chemical conversion process used for recovery of tungsten from ores and process wastes. Materials can always be considered for use as additions in alloy steel melting. 

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