1. EXECUTIVE SUMMARY

This report gives a brief overview of the state of the U.S. metal fabrication industry, with an emphasis on efforts to incorporate pollution prevention and clean technologies into metal-processing operations. This report is not intended to be a thoroughly comprehensive industry guide or study. Rather, it was written as guidance material for those who are seeking general information about the U.S. metal fabrication industry and its use of technologies and processes that reduce or prevent pollution.

This report concentrates on three areas of metal fabrication, with an emphasis on the automobile industry. Metal fabrication encompasses three distinct sectors: metal formation (casting, forging, and shaping), metal preparation, and metal finishing (plating, painting, coating, and so on). The latter two sectors are usually grouped as one because of the similar nature of their operations.

Product demand from the automotive sector has continued to increase, and automotive demand has outpaced U.S. production. The U.S. industry is one of the largest producers and exporters in the world. Exports of metal products are expected to continue to expand to developing countries in Asia and South America. Canada still receives the largest amount of finished U.S. metal components.

Key resources used by the industry include the following:

Water. Water is used extensively in metal preparation and finishing. It is an active part in most metal immersion processes. In metal-forming operations, the use of water is not as big a factor as in other metal fabrication processes.

Protective Metals. The most common protective metals used by the finishing industry include nickel, copper, zinc, and chromium. These metals provide a chemistry that makes them less likely to form surface oxides; these metals can also provide an attractive appearance. The automobile industry has long used these metals in their component manufacturing.

Energy. Metal formation, particularly metal casting, is the most energy-intensive process in metal fabrication. More than 60% of the energy used by an iron foundry goes to molten metal operations. Significant amounts of fossil fuels (e.g., coke and coal) are needed to keep the molten metal in liquid form. Coal is readily available in the United States and is not considered a limiting natural resource, but stack air emissions from fossil fuel use have become a major pollution concern. The industry is just beginning to utilize economical alternative fuels that create less environmental pollution.

Raw Materials. There are a multitude of raw materials that go into the metal fabrication process. Most of the more toxic and hazardous materials are used in the surface preparation and finishing sectors, whereas metal formation and casting use less toxic materials. Metals (e.g., steel, iron, and aluminum), water, fossil fuels, aqueous cleaners, solvents, cooling fluids, abrasives, and complexing metal bath agents are the major raw materials used in metal fabrication.

Key environmental issues for the U.S. industry include the following:

Wastewater. Metal fabrication wastewaters are high in inorganic materials and have a high chemical oxygen demand (COD). Like other industrial operations, a majority of the companies have started to recycle their wastewater within a plant. Cyanide and heavy metal waste streams from metal preparation and finishing operations are the more difficult wastewaters to treat. In the past, wastewater was combined and then treated, but today most operations only combine waste streams when the combination would be beneficial to the treatment process.

Air Emissions. Air emissions from metal preparation and finishing operations represent one of the greatest areas of concern for pollution prevention. For many years, air emissions were viewed as an unseen hazard, because they were more difficult to quantify and regulate than solid and liquid wastes. Attempts have been made to restrict the volatilization of toxic chemicals from solvent and plating bath operations. Although both fugitive and point air emissions have been reduced in the past 10 years, fugitive emissions represent the greatest area of reduction.

Solid and Liquid Waste. For the metal-forming industry, the introduction and subsequent disposal of machining and forming fluids is a source of pollution once they outlive their usefulness. These cooling and cutting oils are recycled and reused in the original process or left as a petroleum oil lubricant (POL) waste stream.

Typically, solid waste streams (hazardous and nonhazardous) result from excess metal material that is trimmed from manufactured metal products or is a rejected metal component. In both cases, the scrap metal is almost always recycled back into the metal formation process. Used foundry sand and wastewater treatment processes generate most other solid wastes for the industry.

The various federal environmental regulations and statutes that affect the metal fabrication industry are the following:

• Federal Water Pollution Control Act or the Clean Water Act (CWA)
• Clean Air Act (CAA)
• Resource Conservation and Recovery Act (RCRA)
• Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA), commonly known as "Superfund"
• Pollution Prevention Act (PPA)

Clean technologies described in this document include the following:

• Best Management Practices (BMPs) include improving inventory control, preventing accidental spills, segregating waste streams, and scheduling production runs that maximize production and minimize waste.
• Recycling Metal-Working/Cutting Fluids, Foundry Sand, and Lost Foam Casting reduces both the amount of hazardous materials (HMs) procured and hazardous waste (HW) generated for working fluids. Fluid life can be extended by 40% and foundry sand can be used in construction fill applications.
• Alternatives to Solvent Cleaning utilize ultrasonic cleaning or product substitution to reduce and eliminate hazardous air emissions.
• Component Parts Washers represent a contained system to reduce the amount and toxicity of fugitive and point source air emissions.
• Water Use Reduction (Closed Loop/Zero Emission Systems) reduces effluent from the manufacturing process by either recycling or making waste material become a useful raw material.
• Improved Sensors and Process Control involve use of advanced techniques to control specific portions of the manufacturing process to reduce wastes and increase productivity.
• Mechanical Blast Media use mechanical means to prepare and clean a metal surface for finishing.
• Electrodialysis Technology for Bath Solutions efficiently maintain a low metal ion concentration in the anodizing bath solution by transporting metal ions from the bath solution through a selective membrane into a capture media using an electrical current to induce flow.
• Hexavalent Chromium Plating Substitution Options replace toxic chromium plating operations with either physical plating or reduced toxicity plating operations.
• Electroless Plating Bath Life Extension is used to extend the useful life of a plating bath through addition of bath chemicals (reducing agents, complexing agents, hypophosphite, and bath stabilizers).
• Ion Vapor Deposition is fundamentally an evaporative coating process that gradually builds a film on the metal surface to be coated.
• Electrolytic Recovery Technology for Metal Cyanide Recycling uses an electrical current to plate out the metals and oxidize the cyanides in the rinse waters.

The metal-forming industries have been switching to continuous casting operations that allow the molten metal to be formed directly into sheets to eliminate interim forming stages. Companies are starting to utilize alternative fuels that create less pollution. Mechanical surface preparation is expected to increase in use over traditional chemical preparation. The more apparent trends concerning clean technologies and pollution prevention (P2) are source reduction and process recycling. Gradually, the industry is beginning to move from the more hazardous heavy metals (e.g., chromium and cadmium) to less hazardous metals such as nickel and zinc. Although improved HM/HW management is one of the more difficult BMPs to implement quickly and efficiently, it will continue to be a part of most companies' pollution prevention plans. Ion Vapor Deposition (IVD) practices are expected to continue to replace aqueous plating operations. Zero emissions and closed-loop systems are expected to gain in importance as the industry tightens its "wastewater and air emission" belts.

The U.S. metal fabrication industry will continue to face some of the most stringent environmental regulations in the world. The development of new and innovative pollution prevention technologies will be needed to ensure the industry can achieve proposed and pending discharge limitations. Pollution prevention and clean technologies will allow the industry to meet environmental standards and still provide quality, cost-competitive products.

ACRONYMS
 

2. INDUSTRY BACKGROUND

2.1 Description and History

The metal fabrication industry, most notably foundry operations, has existed since the first Spanish and British colonies were established in North America. Yet, it was not until the American Industrial Revolution in the mid-1800s that the first modern large-scale metal fabrication industry took root and grew both domestically and internationally. As the industry has become more sophisticated, it has branched into more unique metal-finishing operations.

The automobile industry is one of the largest consumers of fabricated and finished metal products in the United States. The automobile industry relies on metals to provide a safe and durable, building block material for finished automobiles. The automobile industry recognized the need for prefabricated and corrosion-resistant components for production line manufacturing processes. The corrosive nature of the environment coupled with consumer investment concerns created the need for protecting and extending the life span of automobiles. Technology improvements in corrosion protection have helped the metal-finishing sector to grow significantly since the late 1800s. The states of the Ohio valley (most notably, Michigan, Ohio, and Pennsylvania) were the first to develop large-scale, steel- and iron-processing and finishing operations.

The steel and metal fabrication industry has seen many down cycles during the past 200 years in the United States, but in the late 1970s and early 1980s the industry was at one of its lowest levels of productivity. Many underlying reasons exist for the near collapse of the industry, and experts differ on the exact cause. It is generally accepted that the industry failed to (1) modernize, (2) capitalize on the growing international market of post"World War II, and (3) keep executive and union workers" wages in check. The industry also operates under some of the world's strictest environmental laws and regulations.

Since its low point in the early 1980s, the industry has been regenerated by modernization and reinvestment, as well as restructuring and controlling overhead and other costs. The industry has returned to its competitive spirit in both the domestic and international marketplace. The overall industry is expected to continue to regain lost market share and prosper into the next millennium.

2.2 Industry Demographics

This report concentrates on three areas of metal fabrication, with an emphasis on the automobile industry. Metal fabrication encompasses three distinct sectors: metal formation (e.g., casting, forging, and shaping), metal preparation, and metal finishing (e.g., plating, painting, coating, and so on). The latter two sectors are usually grouped together because of the similar nature of their operations.

The metal fabrication industry has long been concentrated in the Ohio Valley because of the area's rich iron ore and coal deposits and because the area is located close to urban centers with good access to rail and water transportation (i.e., the Ohio River and the Great Lakes). Gradually, the metal fabrication industry, particularly the metal-finishing sector, has branched out to different geographical regions of the United States. Today, California has the largest concentration of companies that produce metal-related products. This is attributed to the concentration of the aerospace and defense industries in Southern California and the small shop demographics of the industry (detailed below in sections 2.2.1, and 2.2.2). For automotive products, Michigan, Ohio, and Pennsylvania still tend to have the highest concentration of companies. Metal-processing companies tend to prosper in areas that supply a skilled, but cost-effective labor force (i.e., in urban areas), have a local source of inexpensive raw materials, and support an adequate transportation infrastructure.

Table 1 provides a brief listing of some of the largest companies and organizations associated with the U.S. industry. This list is not intended to be exhaustive but rather provide a short overview of industry players, which include metal-forming, metal preparation, and metal-finishing companies; equipment and chemical suppliers; process design and consulting engineers; professional trade associations; and research institutions. Small companies tend to work directly with the supplier community to meet their day-to-day needs for operation and maintenance of equipment. For large-scale retrofits and redesigns, however, companies typically work with design and consulting engineers, who in turn work directly with manufacturers to specify the processes and equipment needed.

Product demand from the automotive sector has continued to increase, and automotive demand has outpaced U.S. production. Exports of metal products have also continued to expand to developing countries in Asia and South America. Canada is still the largest export market for the United States.

 

By restricting workers' access to hazardous materials, there is less chance of stockpiling or misusing products or products passing their expiration dates without use. A worker can only exchange empty hazardous material containers for new material on a one-for-one basis, and HM inventory follows the first-in/first-out (FIFO) management principle. Efforts are made to reduce the number of different hazardous materials being purchased and stocked. An example is reducing the number of cutting fluid products used for the same metal-forming process. Quick and accurate inventorying can be achieved by centralizing HM storage to assure that only usable quantities of hazardous materials are stored at any one time.

Segregation of HW and non-HW streams prevents an entire waste stream from becoming hazardous and reduces the volume of waste requiring treatment or disposal. Maintaining separate waste streams can enhance a company's ability to reuse or recycle waste materials. Waste treatment practices for the metal fabrication industry involve changing the pH of a wastewater to make it easier to remove contaminants. Sometimes different waste streams are mixed to help change the pH of a wastewater, but if the total amount of hazardous waste is increased and the new wastewater interacts, it may become unsafe for workers. Special attention should be given whenever mixing waste streams.

Scheduling production runs to maximize production and minimize waste is a basic principle that can easily be applied to metal fabrication. An example of smart scheduling would be performing operations using light paints first, leaving darker paint operations for the end of a production run. Typically, switching to the darker paints later in the cycle will decrease the amount of clean outs needed over the entire run. Efficient scheduling includes performing material quality control before a finishing process is started. For example, removing rejected metal components before applying a finish reduces the number of wasteful product operations and maintains a longer life for the finishing material.

A trained work force is often an overlooked part of a company's pollution prevention plan. Training not only helps avert or limit accidents, it also empowers workers and makes them feel more valued by their company. Many companies have developed training and documents for Spill Response Control and Countermeasures Plans for their facilities and practice events to simulate how workers can respond in an emergency.

Benefits. BMPs save in three ways: by decreasing (1) procurement costs, (2) hazardous waste disposal costs, and (3) compliance costs. BMPs cost little to implement, but savings can be realized by tracking the annual expired shelf life of HM, total volume of spilled HM, total HM used, and the like.

Status of Use in the United States. Both private industry and federal government facilities actively implement BMPs. In particular, the DOD community aggressively implements these procedures because they are cost effective and relatively easy to incorporate into existing operations. The U.S. Navy has estimated that after the initial set-up phase of HM inventory control, most installations will have an immediate reduction in procurement costs and materials that have passed their expiration dates. In short, these types of inventory management systems end up saving money.

4.2 Recycling Metal-Working/-Cutting Fluids, Foundry Sand, and Lost Foam Casting

Description. Generation of waste metal-working fluids can be minimized by extending the useful life of the fluids. Useful life is a function of various factors, including the type of metal-working operation, type/quality of fluid used, housekeeping practices, bacterial and other contamination, and water quality (see section 2.4 above). Off-the-shelf systems are available for on-site batch recycling of metal-working fluids. These systems clean the fluids by removing solids, bacteria, and oil contaminants. Water or fluid concentrate may be added to the reclaimed fluid to adjust the fluid concentration to the desired level. Capital costs for a fluid collection device and recycling equipment vary depending on unit size. An alternative to the purchase, operation, and maintenance of recycling equipment is to use an off-site recycling service. The economics of recycling metal-working fluids improves as a metal-forming operation decreases the number of different metal-working fluids used in the manufacturing process.

As noted in section 2.4, foundry sand is subject to contamination by binding agents and metal debris from casting operations. Recycling of foundry sand involves material encapsulation. The foundry sand must past EPA's Toxic Characteristic Leaching Process (TCLP) analysis to be recycled into construction activities. Earth fill material and highway construction fill are the two primary means of recycling.

Another new technology being implemented is called lost foam casting. The process operates by creating a polystyrene foam copy of the part to be cast and packing it with foundry sand. The polystyrene cast is vaporized when the molten metal is poured into the foam copy and the cast metal part is left.

Benefits. Recycling metal-working fluids will reduce both the amount of hazardous material procured and hazardous waste generated. Fluid life can be extended by 40%, and the extended service life will reduce labor and machine downtime (clean out) costs. Recycling also improves fluid and machine tool cleanliness, which can lead to reduced operation and maintenance costs. Recycling of foundry sands provides the generator with hazardous waste disposal cost savings.

Lost foam casting produces less foundry sand waste and results in cast parts that require much less machining to achieve tolerances, therefore, reducing metal turnings and machining fluids.

Status of Use in the United States. Almost all metal formation companies are starting to implement either on-site or off-site metal fluid recyclers. This technology is well tested and easily implemented and is expected to continue being used throughout the industry. Foundry sand testing procedures vary from state to state but are expected to be increasingly scrutinized as states look to limit the amount of solid waste disposal in landfills. Lost foam casting is being used at the Saturn Corporation and is expected to be used at other General Motors foundries.

4.3 Alternatives to Solvent Cleaning

Description. Conventional solvent substitutions simply involve utilizing a more environmentally friendly cleaner in lieu of a hazardous material. The Defense Logistics Agency produces an annual catalog that lists acceptable substitutes for specific hazardous aqueous cleaners, degreasers, lubricants, and other products used in critical military applications.

Ultrasonic cleaning is a process enhancement used in immersion cleaning to improve the cleaning efficiency of most liquids, including neutral, alkaline, acidic aqueous solutions, and semiaqueous solutions. It is a viable alternative to traditional solvent-based cleaning operations such as vapor degreasing. Ultrasonic cleaning can be used to clean from gross to precision levels and effectively removes particles, machining chips, grease, oils, and other contaminants. Ultrasonic cleaning is usually employed in a multistage process of ultrasonic wash, rinse, and dry.

An ultrasonic cleaning system consists of transducers, a generator, a tank, and a liquid medium. The transducers convert the energy supplied by the generator to sonic energy vibrations. These vibrations are transmitted through the tank and produce cavitation bubbles in the liquid medium in the tank. The formation and collapse of these bubbles create a scrubbing action that is effective at removing contaminants. The energy provided by the ultrasonics raises the temperature of the liquid; thermostats and cooling coils are required to control the operating temperature.

A second alternative is conventional solvent substitutions, which simply involve utilizing a more environmentally friendly cleaner in lieu of a hazardous material. The Defense Logistics Agency produces an annual catalog that lists acceptable substitutes for specific hazardous aqueous cleaners, degreasers, lubricants, and other products used in critical military applications.

Benefits. Ultrasonic cleaning can achieve high levels of cleanliness for metal surfaces and is capable of removing extremely small particles. Ultrasonic cleaning can remove debris from parts with complex geometries more quickly than immersion dipping processes that utilize the same cleaning solution. Advantages to ultrasonic cleaning and other solvent substitutions are decreased air emissions (ODSs and other toxic air hazards) and decreased hazardous waste generation. Also, because these cleaners are less hazardous, worker safety is improved and the need for compliance reporting is reduced.

Status of Use in the United States. Solvent substitution has long been an accepted practice in the United States and most metal fabrication companies are implementing changes when feasible. Companies have been slower to use ultrasonic systems because they are new to the industry and have just become affordable. Ultrasonic systems vary in size from 5 to 35 gallons of capacity and, as a result, are not used in larger metal component applications. Custom systems are expected to make ultrasonic cleaning available to a wider number of industrial cleaning applications.

4.4 Component Parts Washers

Description. Aqueous jet parts washers use a combination of water and detergent as a cleaning solution, whereas nonaqueous washers utilize low-hazard cleaning solutions. These parts washers make up a cleaning cabinet with spray nozzles that apply high pressure streams of water at the metal components to be cleaned. The cleaning process will remove contaminants, oil, and grease. Aqueous part washers are frequently compared to household dishwashing machines.

The detergent solution used in these systems is typically biodegradable, and the solution may be discharged into the local POTW if it meets discharge limitations. Nonaqueous washers use solvents similar to mineral spirits to clean component parts in a contained vessel. Most of the washers have a purifying/recycling system that allow the detergent or solvent solution to be recycled and reused. These purifying/recycling systems skim oil from the solution and remove sludge waste that settles to the bottom of the washer. These closed-loop systems enable the user to reuse the cleaning solutions several times before requiring fresh solution. Many systems, particularly those that are solvent based, are employed through a service contract with an outside contractor. The washer units come in a variety of sizes from 75- to 400-gallon capacities.

Benefits. Aqueous parts washers replace hazardous solvents with biodegradable detergents and minimize the disposal of hazardous waste. Spent water or detergent solutions may be discharged to the local POTW. Solvent-based parts washers capture and reuse evaporated cleaning fluid, which in turn decreases the amount of cleaner needed. This saves on material and disposal costs for spent solvent. The enclosed cleaning process eliminates and lessens workers' exposure to hazardous substances. Both aqueous and nonaqueous part washers reduce the amount and toxicity of fugitive and point source air emissions (e.g., ODSs).

Status of Use in the United States. The use of parts washers has increased since 1,1,1-trichloroethane vapor degreasing and other ODS cleaning technologies have been curtailed. Parts washers are used in all types of industries in the United States, and many support companies have been created as a result. The unit cost for these washers has decreased as they become more commonplace in today's metal-cleaning and preparation operations. The current technology and practice has been to make these parts washers as closed-loop and low maintenance as possible.

4.5 Water Use Reduction (Closed-Loop/Zero Emission Systems)

Description. An increasingly viable option for companies is the "zero discharge" system. The decision point for this option is when it is more expensive to discharge a company's wastewater than to treat it and recycle it back into the plant. A large capital expenditure and a customized treatment solution are required to handle this option. Furthermore, the uniqueness of various metal fabrication operations makes it difficult, if not impossible, to find off-the-shelf treatment designs to fit a user's needs.

A more plausible approach is that of achieving a "zero emissions" strategy that relies on a network of companies that utilize waste streams from other companies as their raw material. It should be noted that the term "zero emissions" is an ideal. This strategy is a more economically efficient system than a "closed loop" because the waste products do not have to be fully treated. Although facilities are moving toward decreased volumes of effluent, material mass balances still dictate that process residuals such as sludges will require management and possibly off-site disposal.

Benefits. Both zero discharge and zero emission systems improve effluent water quality and have fewer negative impact on the environment.

Status of Use in the United States. A zero discharge or emission facility is a lofty goal. Through regulation and other restrictions, the U.S. metal fabrication industry is expected to invest more time, money, and effort in reducing effluent levels and contamination to the lowest economically feasible levels. Improved communication among companies will help foster the principle of "one company's waste is another's raw material."

4.6 Improved Sensors and Process Control

Description. Automation has always been a part of the metal fabrication industry due to concerns about worker safety and exposure. Improvements in technology and reductions in costs have made analytical sensors, PC interfaces, and closed-loop control systems more attractive. These types of automated products allow the user to improve efficiency, control raw material inputs, and limit the amount of wastes generated. Sensors can be used to control process temperature, humidity, pH, flow rates, and contamination levels.

Sensor technology has advanced to the point that computers can now be used for assessing conditions that in the past only human workers could access. Artificial intelligence was the phrase coined in the 1980s to describe the capabilities of these new pieces of equipment. Sensors are now capable of characterizing physical and chemical properties of processing materials.

Benefits. Use of automation further reduces the chance of human error in manufacturing processes. Automation improves speed and accuracy in measuring process variables and also reduces labor costs. Through the use of automation, workers are now able to dedicate their time to other more pressing production issues. Automated equipment makes real-time data available to plant personnel without interrupting the production run.

Status of Use in the United States. Since the mid-1980s, facilities have continued to modernize and make these sensor technologies a larger part of metal manufacturing. A new wave of cost-effective automated products are becoming available for all aspects of metal fabrication. Sensors and process controls have made great inroads in pretreatment technologies for metal fabrication wastewaters.

4.7 Mechanical Blast Media

Description. Mechanical cleaning and preparation of almost any metallic surface is possible if it is sturdy enough to withstand the friction and force produced by the mechanical work of cleaning operations such as sanding, grinding, polishing, brushing, and scraping. Mechanical operations remove surface imperfections and prepare metal components for future coating or plating operations. These technologies are not meant to be used on precision or delicate parts. Mechanical cleaning processes are viable alternatives to traditional solvent-based, metal-cleaning and preparation operations. They reduce waste production and eliminate potential safety problems with the handling and usage of toxic, ODS-type, and often flammable solvents. Mechanical blast media vary from the use of plastic media to baking soda and solid carbon dioxide pellets.

Benefits. Mechanical preparation significantly reduces the amount and cost of handling hazardous waste compared to chemical preparation. The elimination of solvents provides cost savings in terms of procurement. Mechanical preparation reduces worker exposure to toxic solvents, hazardous waste, and hazardous air emissions.

Status of Use in the United States. High capital costs and a large facility space requirement have slowed the use of mechanical cleaning and preparation processes, but the tightening of air emission standards is expected to make this a more cost-effective option. Cleaning operations for precision parts or removal of viscous compounds are expected to continue to use chemical methods, but these operations are expected to use solvents that are more environmentally friendly. The percentage of companies that use mechanical processes is expected to rise steadily.

4.8 Electrodialysis Technology for Bath Solutions

Description. Electrodialysis is a process that efficiently maintains a low metal ion concentration in the anodizing bath solution by transporting metal ions from the bath solution through a selective membrane into a capture media using an electrical current to induce flow. When anodizing aluminum, for example, the bath solution must be changed out and disposed of when the aluminum concentration reaches 80-100 grams/liter. The spent solution contains high levels of sulfuric acid and aluminum, requiring neutralization and metal removal prior to disposal to a POTW. Electrodialysis does not affect the anodizing process but is simply a process that can indefinitely extend the useful life of the bath solution by maintaining a low concentration of metal ions. The capture media, catholyte, captures the metal ions and forms a concentrated sludge. The sludge must be removed from the unit and the catholyte changed out on a regular basis to ensure effective metal removal from the anodizing bath solution. The recovered sludge is a hazardous waste containing high concentrations of metal that can be reclaimed.

Benefits. Electrodialysis reduces hazardous waste volume and associated disposal costs associated with anodizing baths. First, heavy metals can be reclaimed and reused. Second, electrodialysis can extend the useful life of the anodizing bath solution; as a result, a company can lower its annual costs for chemical makeup and bath replacement. Third, controlling the metal ion concentration in the anodizing bath solution improves the production quality of manufactured parts.

Status of Use in the United States. Due to the moderately high capital cost for this equipment, most companies have been slow to accept this technology. Locating companies that will recover and reclaim metals from the sludge has proved difficult at times, but an organization called the Center for Byproduct Utilization (see Table 1) helps to link companies for this purpose. As disposal costs increase, electrodialysis will prove more economically beneficial.

4.9 Hexavalent Chromium Plating Substitution Options

Description. Hexavalent chromium is an extremely toxic substance that proves difficult to treat and remove from industrial waste streams. Recent industrial practices have been directed at removing or decreasing the use of hexavalent chromium.

High Velocity Oxy-Fuel (HVOF) thermal spray technology is a dry process that produces a dense metallic coating whose desired physical properties are equal to or surpass those of hard chrome plating with hexavalent chromium. HVOF thermal spray uses a fuel/oxygen mixture (i.e., propylene, hydrogen, and kerosene) in a combustion chamber. This combustion process melts a metal powder that is continually fed into a gun using a carrier gas (argon) and propels it at high speeds (3,000-4,000 feet/second) toward the surface of the part to be coated. The high speed of the spray produces a coating on impact that can be used as an alternative to chromium plating. The metal powder is available in many compositions, including nickel, chrome carbide, and tungsten carbide. Uniform coating thickness of up to 0.250 inches can be achieved.

Other substitution options for hexavalent chromium plating are the use of trivalent chromium plating or the use of the sulfuric/boric acid anodizing (SBAA) process. Only minor process changes are needed for trivalent chromium plating, and waste trivalent chromium is much easier to precipitate from wastewater. The SBAA process is a direct replacement for the chromic acid anodizing process used on aluminum production pieces. The SBAA process consists of a sulfuric/boric acid anodizing bath and a chromate sealer bath. The SBAA process contains a small amount of chromium in a separate sealer bath in which the parts are dipped after the SBAA process. The rinse waters still contain metals and acids that must be pretreated prior to being released to a POTW, but the overall level of chromium needing treatment is much less than in conventional finishing operations.

Benefits. The HVOF process gives performance properties similar to chrome plating, which include wear resistance, corrosion resistance, low oxide content, low stress, low porosity, and high bonding strength to the base metal. The only waste stream produced by HVOF is from overspray. The current technique to limit overspray is to install a water curtain filter system or a particulate air filter. Because the overspray contains only the pure metal or alloy, it is feasible to recycle or reclaim it as a raw material. By using HVOF, annual costs will decrease, along with air emissions, hazardous waste generation, and associated disposal costs.

Trivalent chromium is less viscous and toxic compared to hexavalent chromium. The lower viscosity decreases the amount of drag out from a plating bath and lessens the frequency of countercurrent flow operations. SBAA offers a significant reduction in the treatment of chromic acid, as well as a reduction in toxic air emissions from the chromium plating. SBAA operating costs are similar to existing chromium plating operations.

Status of Use in the United States. The estimated payback period for using HVOF is 2-4 years, depending on the size of operations. HVOF is steadily gaining acceptance, whereas substitution of trivalent chromium has been slow because the level of plating quality is lower than using hexavalent chromium. Automobile manufacturers continue to demand the high quality, high-gloss finish that hexavalent chromium delivers. Reductions in allowed chromium levels to U.S. waters are expected to make all three clean technologies (HVOF, SBAA, and trivalent chromium) more prevalent alternatives in metal-finishing operations in the next 5-10 years.

4.10 Electroless Plating Bath Life Extension

Description. Electroless plating consists of a chemical process in which a reaction occurs to reduce charged metal ions to a neutral solid state; the ions (primarily nickel ions) then deposit onto another metallic part. The current practice is to change out the plating bath solution as it becomes contaminated with byproducts of the chemical reactions that interfere with the plating process and dispose of it as hazardous waste. Typical electroless plating waste streams include orthophosphite, sulfate, plating metal ions, and sodium ions. The electroless plating bath life extension technology accomplishes this by performing two functions: (1) it removes the chemical byproducts formed during the plating process and (2) it maintains the overall chemical balance of the electroless plating bath (metal ion concentration, pH, and phosphite) through the addition of bath chemicals (reducing agents, complexing agents, hypophosphite, and bath stabilizers).

Benefits. Utilizing the electroless plating bath life extension technology to augment current electroless plating operations can increase the life of the plating bath up to tenfold and reduce the volume of hazardous waste generated by up to 90% along with the associated disposal costs. Production quality is improved due to the stability of plating bath parameters and quick removal of bath impurities that can cause poor plating quality. Also, there is a reduction in the need to replate poorly plated materials.

Status of Use in the United States. Electroless plating extension technology involves no major capital costs and only requires purchasing additional bath chemicals. The metal-finishing industry is always looking for new ways to reduce the amount of wastewater produced in a plating process. Electroless plating extension is gaining acceptance and similar bath extension technologies are making inroads within the industry. Another trend seen in the finishing sector is replacement of more hazardous cadmium and chromium operations with zinc and nickel chemistries, respectively.

4.11 Ion Vapor Deposition

Description. Ion Vapor Deposition (IVD) comprises a group of surface-coating technologies used for decorative-coating, tool-coating, and other metal-coating applications. It is fundamentally an evaporative coating process that gradually builds a film on the metal surface to be coated.

Benefits. IVD is a desirable alternative to electroplating and some painting applications. IVD can be applied using a wide variety of materials to coat an equally diverse number of substrates. IVD coating processes are even compatible with some plastics, either as coatings or as substrates. The application of IVD surface-coating technologies at large-scale, high volume operations will result in reduction of hazardous waste generated compared to electroplating and other metal-finishing processes that use large quantities of toxic and hazardous material. Up to 90% of all water use in electroplating goes to rinsing operations, and IVD virtually eliminates all rinse water.

Status of Use in the United States. Many companies are replacing aqueous plating operations with IVD, most notably electroplating processes such as cadmium plating. One limitation of IVD is that coatings do not work well where lubrication is required; they are also not a good choice for fastener parts. Also, IVD has limited success in applications that involve coating annular-shaped objects. The IVD process requires detailed attention to operate. Apart from these limitations and similar to other clean technologies listed in this report, IVD processes are expected to grow in their uses in metal-finishing applications.

4.12 Electrolytic Recovery Technology for Metal Cyanide Recycling

Description. Wastewater generated from the rinsing of metal cyanide-plated parts contains metals (primarily cadmium, copper, and silver) and cyanide-containing compounds (cyanides). These waste streams require pretreatment to reduce toxic loadings prior to discharge to a POTW. Typically, the treatment requires the use of hazardous chemicals, including acids, alkalis, and chlorine-containing chemicals. Electrolytic recovery technology uses an electrical current to plate out the metals and oxidize the cyanides in the rinse waters. The metal is recovered from the electrolytic recovery unit (ERU) as a foil that can be returned to the cyanide plating bath as an anode source. The ERU is plumbed to a stagnant rinse tank in a closed-loop fashion. The cyanides are partially oxidized to cyanates in the ERU, which can remove more than 90% of the metal ions used in the rinse waste stream and oxidize up to 50% of the cyanides.

Benefits. The benefits of electrolytic recovery for metal cyanide recycling include cost savings and reduction of hazardous waste. Cost savings result from a reduction in the use of treatment chemicals for cyanides and heavy metals; the reuse of heavy metals, which reduces the costs for anodes or chemicals; and a reduction in the volume of metal-containing hazardous sludge. This technology is applicable to other plating baths, such as nickel, zinc, and lead.

Because the ERU is run in a batch mode, few process changes are required. ERU is a pretreatment operation that has a relatively short payback period, estimated at two years for operations that generate more than 300,000 gallons of metal silver-cyanide rinse wastewater.

Status of Use in the United States. Electrolytic recovery is only feasible for highly concentrated metal wastewaters. The efficiency of the operation decreases as the concentration of metal ions decreases. Typically, it is used to recover and recycle more valuable metals (e.g., silver and gold) and has not been widely used in the metal-finishing industry.

5. FUTURE TRENDS

Regulations and Standards

The U.S. metal fabrication industry will continue to prosper in the foreseeable future. Industry standards and business practices will continue to be driven by both government intervention and economical reality. The strengthening of the CWA and CAA and concerns about RCRA's solid waste disposal issues will continue to drive the industry closer to "sustainable development."

EPA, through new guidelines, will propose further limitations in wastewater effluents from metal fabrication operations. As mentioned earlier in the report, EPA has proposed standards on Maximum Achievable Control Technology (MACT)?based performance standards that set limits on air emissions based on concentration values. EPA has targeted vapor degreasers that use the following HAPs: methylene chloride, perchloroethylene, trichloroethylene, 1,1,1-trichloroethane, carbon tetrachloride, and chloroform. MACT standards have been proposed for various metal fabrication operations.

International standards developed by the Geneva-based International Organization of Standardization, called ISO, represent an attempt to provide a global environmental management system. ISO 14000 was designed to help organizations manage and evaluate the environmental aspects of their operations without being prescriptive. The International Organization of Standardization intends to provide companies with a framework to comply with both domestic and foreign environmental regulations. ISO 14000 contains sections calling for implementation of pollution prevention programs; many U.S. companies are evaluating the pros and cons of becoming fully certified in ISO 14000. Furthermore, EPA is talking about easing reporting requirements for U.S. companies that earn ISO 14000 certification.

Industry Trends

There are several ongoing trends and research and development activities apparent within the metal fabrication community in the areas of pollution prevention and clean technology implementation.

The metal-forming industries have been switching to continuous casting operations that allow molten metal to be formed directly into sheets to eliminate interim forming stages. As mentioned earlier in this report, companies are starting to utilize alternative fuels that create less pollution. Mechanical surface preparation is expected to increase in use over traditional chemical preparation. The more apparent trends concerning clean technologies and pollution prevention are source reduction and process recycling. The phasing out of Class 1 and Class 2 ODSs has pushed the industry to find alternative solvent and cleaning operations. Gradually, the industry is beginning to move from the more hazardous heavy metals (e.g., chromium and cadmium) to lesser metals such as nickel and zinc. Although improved HM/HW management is one of the more difficult BMPs to implement quickly and efficiently, it will continue to be a part of most companies' pollution prevention plans. Ion Vapor Deposition (IVD) practices are expected to continue to replace aqueous plating operations. Zero emissions and closed-loop systems are expected to gain in importance as the industry tightens its "wastewater and air emission" belts.

Mechanical versus Chemical Preparation

Companies will increasingly consider using mechanical methods for surface preparation. Mechanical processes can be used to perform many of the same functions as chemical processes. The costs and benefits of using mechanical versus chemical processes will be further quantified to aid in decision making.

Water Conservation and Wastewater Reduction

Water use will continue to be the principal target for pollution prevention source reduction practices in the metal fabrication industry. Water used in plating and finishing, facility cleanup, or other noningredient uses will be reduced, which in turn will reduce the wastewater volume from metal fabrication facilities. Wastewater treatment will continue to be the pollution prevention treatment focus for metal fabrication companies. The industry will continue to implement advanced innovative techniques to lessen the environmental impact of metal fabrication discharge wastewaters.

In summary, the U.S. metal fabrication industry will continue to face some of the most stringent environmental regulations in the world. The development of new and innovative pollution prevention technologies will be needed to ensure that the industry can achieve proposed and pending discharge limitations. Pollution prevention and clean technologies will be a means to let the industry meet environmental standards and still provide quality, cost-competitive products.

REFERENCES

Chalfant, Robert V. "The new emphasis on pollution prevention," New Steel, v12, n3, p82, March 1996.

Gedlinske, Brian. "Aqueous parts washing and pollutant loadings," Pollution Prevention Review, v7, n2, p47, Spring 1997.

Hanson, David. "EPA to shift focus from pollutants to industries," Chemical & Engineering News, v72, n30, p9, July 25, 1994.

Katzel, Jeanine. "Managing nonhazardous solid wastes," Plant Engineering, v48, n11, p42, September 1994.

Mason, Keith D. Richard J. Dauksys, Terry A. Cullum. "Improved management of automotive painting operations," Automotive Engineering, v104, n2, p79, February 1996.

Sheridan, John H. "Pollution solutions," Industry Week, v243, n7, p32, April 4, 1994.

Zuckerman, Amy. "Don't rush into ISO 14000," Machine Design, v68, n1, p38, January 11, 1996.

Other Readings:

Joint Service Pollution Prevention Opportunity Handbook, Naval Facilities Engineering Service Center, June 1997.

Profile of the Fabricated Metal Products Industry, EPA Office of Compliance Sector Notebook, EPA/310-R-95-007, September 1995.

Guides to Pollution Prevention: Municipal Pretreatment Programs, EPA Office of Research and Development, EPA/625/R-93/006, October 1993.

Guides to Pollution Prevention: The Fabricated Metal Products Industry, EPA Office of Research and Development, EPA/625/7-90/006, July 1990.

Environmental Products Catalog, 2nd edition, Defense Logistics Agency, December 1995.

Pollution Equipment News, 1997 Buyer's Guide.

Chemical Engineering Magazine, McGraw Hill.

Hazardous and Industrial Wastes, Proceedings of the Twenty-Fifth Mid-Atlantic Industrial Waste Conference, July 9-13, 1993.
 

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