Drag out

To reduce costs of the more expensive platiag solutioas and decrease the amount of hazardous or regulated material ia a waste stream, recovery and reuse of the drag-out is a common practice. This is done by closing off the water flow to the first tinse tank foHowiag the process tank, and periodicaHy... 

RoUs and other relatively simple shapes make use of inert shields and thieves to avoid edge buildup and produce a more even plate thickness. For more compUcated shapes having deeper recesses thicker deposits from cyanide copper baths have been used as an undercoat to the copper sulfate deposit. Acid copper baths operate near 100% efficient over a wide current density range. The cathode efficiency is usuaUy slightly less than the anode efficiency, bringing about a slow increase in copper unless drag-out losses are high. 

From all these factors, it is clear that the approval and construction of major new industrial plants or expansions is a far more complicated operation than it has been in the past, even the recent past. Stringent environmental restric tions are hkely to preclude construction of certain facilities at locations where they otherwise might have been built. In other cases, acquisition of required approves mav generate a heated technical and pohtical debate that can drag out the regulatoiy process for several years. 

Self-induced spray wet collectors This is the most common type, and relies on its separating action by the induced air from the fan pulling the contaminated air through a curtain of water. It is simple in operation with no pumps or moving parts except for the fan, which is set on the clean side of the collector. The scrubbing action is dependent on the pressure drop across the collector. When set, this is constant and is determined by the water level within the collector. The removal of sludge is either by automatic ejection or manual drag-out. 

Surface-active agents are often added to the pickle if the inhibitor has no surface-active properties. They assist the penetration of the acid into the scale, reduce drag-out losses, and form a foam blanket on the pickle. This blanket reduces heat losses and cuts down the acid spray caused by the hydrogen evolution. 

In USA a patent is awarded to the person first producing an invention, not necessarily who first applied for a patent. The opposite policy prevails in the rest of the world with USA policy probably changing in order to achieve worldwide patent law harmonization. USA utility patents (machines, equipment, etc.) in the past where good for at least 17 years after date the patent was issued. As of 1995, the patent is good for 20 years after the date the patent is filed (prior to the date it is issued) that eliminated those who would file for a patent and let it drag out for many years prior to being issued when it would be needed for infringement, etc. 

Pollutant parameters found in the common metals subcategory raw waste stream from sampled plants are shown in Table 9.4. The major constituents shown are parameters, which originate in process solutions (such as from plating or galvanizing) and enter wastewaters by drag-out to rinses. These metals appear in waste streams in widely varying concentrations. 

Wetting agents and longer workpiece withdrawal/drainage times are two techniques that significantly control drag-out. These and other techniques are discussed below. 

In barrel plating, the barrel should be rotated for a time just above the plating tank in order to reduce the volume of dragged-out chemical. Holes in the barrels should be as large as possible to improve solution drainage while still containing the pieces. A fog spray directed at the barrel or its... 

FIGURE 9.1 Typical drag-out drainage rates. (Adapted from U.S. EPA, Meeting Hazardous Waste Requirements for Metal Finishers, Report EPA/625/4-87/018, U.S. Environmental Protection Agency, Cincinnati, OH, 1987.)... 

Low-concentration plating solutions reduce the total mass of chemicals being dragged-out. The mass of chemicals removed from a bath is a function of the solution concentration and the volume of solution carried from the bath. Traditionally, the bath concentration is maintained at a midpoint within a range of operating conditions. With the high cost of replacement, treatment, and disposal of dragged-out chemicals, the economics of low-concentration baths are favorable. 

As an illustration, a typical nickel plating operation with five nickel tanks has an annual nickel drag-out of about 10,000 L. Assuming the nickel baths are maintained at the midpoint operating concentration, as shown in Table 9.12, the annual cost of chemical replacement, treatment, and disposal is about USD 20,700 in terms of 2007 USD. If the bath is converted to the modified operating condition as shown in the table, the annual cost of chemical replacement, treatment, and disposal are approximately USD 18,700, a savings of about USD 2000/yr. Generally, any percent... 

Contaminated plating baths, for example, carbonate buildup in cyanide baths, can increase drag-out as much as 50% by increasing the viscosity of the bath. Excessive impurities also make the application of recovery technology difficult, if not impossible. 

Bath viscosity indexes are available from chemical suppliers. As the bath viscosity increases, drag-out volume also increases. 

High-temperature baths reduce surface tension and viscosity, thus decreasing drag-out volume. Disadvantages to be considered are more rapid solution decomposition, higher energy consumption, and possible dry-on pattern on the workpiece. 

Additional bath components (chemicals) tend to increase both viscosity and drag-out. 

Every workpiece has at least one racking position in which drag-out will be at a minimum. In general, to minimize drag-out... 

Capture/Concentration with Full Reuse of Drag-Out... 

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