A410 POLLUTION PREVENTION IN THE CHROMIUM ELECTROPLATING INDUSTRY

INTRODUCTION

Recently published Environmental Protection Agency (EPA) air quality regulations require reductions in air toxic emissions fiom chromium electroplating and anodizing operations. The regulation requires that these facilities comply with technology based emissions limits, work practice standards, performance testing, recordkeepingheporting requirements and monitoring requirements. As electroplating facilities address these more stringent air regulations, some have taken a multimedia waste management approach to also minimize wastewater and hazardous waste residuals. Central to this multimedia approach is integration of pollution prevention techniques to reduce air emissions and waste through improved process and waste management modifications.

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Pollution prevention options should be considered as methods to reduce toxic emissions and waste fiom chromium electroplating operations. The advantages, disadvantages, and mode of operation for air emission reduction techniques such as fume suppressants, wetting agents, dry scrubbing systems, and polypropylene ball covers and for wastewater and residual waste reduction are discussed. In many cases pollution prevention strategies are relatively low technology approaches that are more cost effective than convention control and treatment technologies. The use of alternative metal finishes to chromium electroplating as a method to completely eliminate chromium emissions is also discussed. This paper addresses pollution prevention techniques for functional “hard” and decorative chromium electroplating using hexavalent chromium bath formulations. Two case studies are also presented of chromium electroplating facilities in North Carolina that have implemented a number of these multimedia pollution prevention techniques. The case studies were developed by the North Carolina Ofice of Waste Reduction which provides waste reduction assistance to industries.

- BACKGROUND AND PROCESS DESCRIPTION

Hard chromium electroplating, intended for items such as hydraulic cylinders and rods, industrial rolls, zinc die castings, plastic molds, enghe components, and marine hardware deposits a thick layer of chromium directly on the base metal. This thick layer of chromium provides certain desirable surface characteristics such as wear resistance, a low coefficient of fiction, hardness, and corrosion resistance. This process generally deposits a thickness of 0.1 mil and up to 20 mils or more. Decorative plating is generally used for items such as auto trim, mtal furniture, bicycles and plumbing fixtures. In this type of plating, the base material is plated with a layer of copper then nickel followed by a relatively thin layer of chromium. This provides the base material with a bright surfice that has wear and tarnish resistance. According to EPA estimates, there are 1,540 hard chromium electroplating and 2,800 decorative chromium electroplating operations in the United States?

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A410 . The first step in the chromium electroplating process is to prepare the part surface through pretreament operations. These operations include polishing, grinding, degreasing and cleaning of the metal part. Polishing and grinding are performed to smooth the surface of the part and degreasing is performed to remove oils and grease. Alkaline cleaning (sodium carbonate, sodium phosphate, or sodium hydroxide in solution ) is sometimes used to dislodge surface soil and prevent it fiom settling back onto the metal. For deposition of chromium, chromic acid plating baths are the most widely used. Chromium anhydride (Cr03), most commonly known as chromic acid, is the hexavalent compound of chromium used to make up the plating bath. Typical bath concentrations are 225 to 375 g/L (30 to 50 odgal of water) of chromic acid. In addition, small amounts of sulfuric acid (2.25 to 3.75 g/L [0.3 to 0.5 odgal]) are added as a bath catalyst? A s Cr03 is added to water, it reacts with the water to form a compound (H2Cr04), which is correctly called chromic acid. As more Cr03 is added to the plating bath, the H2Cr04 molecules combine to form dichromic acid (HZCr2O7) and water. As dichromic acid forms, it readily ionizes to form dichromate ions (Cr2O,'> and hydrogen ions (H3. The dichromate ions are then used in the chromium deposition reaction. The following reactions take place at the surface of the part to be plated. These are the deposition reaction and two side reactions?

1. Cr207= + 14H' + 12(e) -+ 2Cr" + 7H20 2. 2H' + 2(e) -+ H2? 3. Cr2O7- + 14H' + 6(e) + 2Cr'3 + 7H20

In the first reaction chromium metal is deposited on the part to be plated as the dichromate ion reacts with hydrogen ions and electrons to form chromium metal and water. This reaction requires the presence of a sulfate ion as a catalyst. Two side reactions occur in addition to this deposition reaction. The first side reaction consists of two hydrogen ions combining with two electrons to form hydrogen gas. When the hydrogen gas leaves the bath, it entrains chromic acid and which results in misting at the surface of the plating bath. The second side reaction involves the dichromate ion combining with hydrogen ions and electrons to form water and trivalent chromium. At the anode, the trivalent chromium is reoxidized to chromic acid. The anode area is always larger than the cathode area to ensure that most of the trivalent chromium formed at the cathode will react at the anode to form chromic acid. Generally, in chromium electroplating, the material used for the anode is a lead alloy. The following reactions take place at the anode during chromium electroplating?

1. 40H - 4(e) -+ 2H20 + 02? 2. Pb + 4 0 H - 4(e) + Pb02 $- 2H20 3. 2Cr'3 + 302? - 6(e) + 2Cr0,

The reactions discussed above result in the generation of both hydrogen and oxygen gases. As these gas bubbles rise through the plating solution, they entrain some of the plating solution. When the bubbles burst at the surface of the plating bath, a large amount of chromic acid mist is generated. The inherent inefficiency of the hexavalent chromium plating process is one of the reasons for emissions of chromic acid mist fiom chromic acid plating baths. In fact, only about 10 to 20 percent of the current applied actually is used to deposit chromium on the item plated.1J The remainder of the electrical current applied to the chrome plating solution goes into the formation of hydrogen and oxygen gases.

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A410 In addition to chromic acid a;: emissions, the electroplating process generates wastewater, hazardous residuals and emissions. Typically, flowing rinsewater baths after all process baths including alkaline cleaning, acid etches and electrolytic chromium generate rinse wastewater. All process baths must be periodically replaced due build up of contaminants leaving spent solution to be managed. Emissions in the form of alkaline and acid mists are also generated fiom the electroplating pretreatment operations.

POLLUTION PREVENTION TECHNIQUES

* Several pollution prevention techniques can be used in chromium electroplating operations to reduce the releases of toxic emissions, wastewater, and residual fiom the process. Most of these options are cost effective and improve the efficiency of the plating system. This section of the paper will describe these techniques and will be followed by a description of the pollution prevention options that two facilities in North Carolina that have implemented as a methods of waste reduction.

Pollution Prevention Techniques for Air Emissions Since the majority of emissions fiom the plating operations results fiom the misting fiom the chromic acid bath, emission reduction teckxiques focus on reducing the amount of mist released from the tank. These techniques include h e suppressants in the form of wetting agents and foam blankets, polypropylene balls, and dry mesh pad eliminators with a recycle stream.

Fume Suppressants. One pollution prevention technique involves the use of chemical fume suppressants that are typically added to the plating bath to reduce the amount of misting fiom the chromic acid plating bath. A h e suppressant is a chemical that forms a barrier on the surface of the plating bath to prevent misting. Chemical fume suppressants are mandactured in liquid, and free or compressed powder forms and are surface-active compounds that are added directly to chromium plating bath. Fume suppressants include wetting agents and foam blankets. Fume suppressants have two classifications: temporary or permanent. Temporary fume suppressants have to be replaced because of the degradation of the active ingredient and permanent fume suppressants are diminished through carry over of the solution on the plated parts. Fume suppressants operate by the principle of reducing bath surface tension or by mist impingement into a foam blanket. Although the use of fume suppressants alone can be effective with a ninety-five percent reduction in emissions many plants use them in conjunction with add-on control devices. Disadvantages of fiune suppressants are more notable pitting defects in parts and potential hydrogen explosion with foam blankets. Fume suppressants are used widely by decorative chromium electroplaters, however, hard chromium platers in the United States seldom use h e suppressants? Fluorinated wetting agents have a tendency to make pitting defects more visible. Also, when foam blankets ari used, there is a potential for explosion of the entrapped hydrogen gas. These tendencies are more pronounced in hard chromium plating than in decorative chromium plating because of the higher current densities and longer plating times associated with hard chromium electroplating operations.

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Wettin? Acents. Wetting agents reduce the surface tension of the chrome plating solution which in turn reduces the rate of misting as the hydrogen and oxygen bubbles burst with less intensity when they reach the surface. Fluorinated wetting agents are the most common wetting agents because they are very stable throughout a wide range of operating temperatures, current densities, chromic acid concentrations, and oxidation-reduction reactions. Examples of wetting agent formulations include potassium perfluorooctane sulfonate (C,F,,SO,K) and tetraethylammonium perfluorooctane sulfonate (C,F,,S03N'(C2H5)4)? One potential drawback with the use of fume suppressants is that fluorocarbon-based suppressants may aid pitting and defects in base metals when plating thickness is greater than 13 to 25 pm (0.5 to 1 mil)? Additionally, some h e suppressant vendors suggest caution when using these compounds if the chromium thickness increases beyond 25 to 100 pm (1 to 4 mils) (depending on the product). However, some mandzturers state that certain base metals have a tendency to pit and that this tendency is not aided by the use of fume suppressant additives. Some non-fluorinated h e suppressants are reported to be successllly used for hard chromium plating deposits. Another benefit of using wetting agents is the reduced amount of plating solution carry-over into subsequent tanks caused by more efficent draining.

Foam Blankets, During the plating operation, the h e suppressant generates a foam blanket and traps the process gases between the solution and the blanket or in the blanket itself. The foam blankets do not reduce or eliminate the formation of chromic acid mist, but rather prevent the mist fiom escaping. Foam blankets are usually 1.3 to 2.5 cm (0.5 to 1 .O in.) thick and cover the entire surface of the plating bath.. The thickness of the foam layer is critical to its effectiveness as a pollution prevention. If the foam layer gets too thick, a danger of an explosion is present. The trapped hydrogen gases can build up in the foam layer, and if a spark is generated, a hydrogen explosion can occur. As a result of this minor explosion, the foam layer along with a portion of the plating solution is blown out of the tank and the chromium plate on the part could be damaged. However, if the foam layer is not maintained at a minimum reasonable thickness, the ability of the foam layer to inhibit misting is reduced. The amount of foam blanket solution that is used is determined by the surface area of the solution, amount of current applied, and temperature and chromic acid concentration of the plating bath. Foam blankets are depleted primarily by decomposition; however depending on the thickness of the foam layer, drag-out of the foam may also be a factor. Also, foam blankets k y be pulled into the exhaust system ifthe solution level is too close to the hoods. Excessive air agitation of the bath due to liberation of hydrogen gas can deplete the foam layer. Visual monitoring of the thickness of the foam blanket is the most common method for determining when to add foam blanket solution to the bath.

Polypropylene Balls. Another technique to reduce the level of emissions fiom the plating bath is the use of polypropylene balls to reduce mist formation and evaporation of the plating solution. The balls are approximately 0.75 inches to 1.5 inches in diameter and are usually arranged in two layers deep across the surface of the plating solution. l2 Polypropylene balls may prevent up to 70 percent of the mist that escapes fiom the plating bath and can be used both in hard and decorative chrome plating operations.' Polypropylene balls are generally used on hard chromium plating baths to reduce evaporation of plating solution and inhibit misting. They are generally not used in automated plating or anodizing operations

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A410 because plating racks drag the balls out of the baths. The balls tend to be pushed away fiom the anodes and cathodes where the surface ofthe bath is agitated by gassing, thus reducing their effectiveness for inhibiting misting. -

Mesh Pad Eliminator with Recycle. Another pollution prevention technique involves the use of mesh pad eliminators systems to capture chromic acid mists and recycle them back into the plating bath. Usually traditional air emission control devices such are wet packed bed scrubber are not consider a waste reduction techniques since the dilute aqueous solutions captured must be treated and disposed. Mesh pad eliminator use very little water (sometimes termed “dry scrubbers”) and can capture the concentrated chromic acid solution for direct reuse. Mesh-pad mist eliminators consist of layers of intertwined fibers densely packed between two supporting grids. The mist eliminator is placed in the air stream to trap the liquid droplets entrained in the air flow. The droplets coalesce until they become large enough to flow off the mesh pad and the droplets drain to the bottom of the mist eliminator as a result of gravity. This solution can be piped directly back to the plating tank. The mesh pad eliminator system can achieve a 95% reduction in emissions.

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Pollution Prevention Techniques For Wastewater and Residuals A number of process optimization techniques can be utilized to minimize chromium and other pollutant loading in wastewater strear-:: ahd reduce solid residuals requiring waste management. These techniques ‘include drag-out loss reduction, rinsing efficiency improvements, chemical recovery techniques, and wastewater reuse techniques.

Drag-out Reduction Techniques, A wide range of techniques can be employed to reduce the amount of residual solution carried out (termed “dragout”) of the process bath by the parts. Potential dragout reduction techniques for hard chrome platers include: 1) operating bath formulations at a minimum chemical concentrations, 2) maximizing bath operating temperature to lower bath viscosity, 3) using wetting agent to reduce surface tension, 4) racking parts to minimize drainage, 5 ) extending drainage time over process tank or dead rinse tank, 6) using spray or fog rinsing over the process tank or dead rinse tank, and 7) positioning drainage boards between the process tank and next rinse tank. By reducing the volume of process solutions carried out of the plating tank, platers can conserve expensive bath formulations and directly reduce the pollutant mass loading to flowing rinsewater tanks which are typically treated in wastewater treatment systems. The difference in dragout rates for a flat-surfaced part in 33 ounce per gallon (397 gL) vs. a 55 ounce per gallon (247 g/L) hard chromium plating bath formulation has been calculated to be 74 percent less due to reduced bath viscosity. Wetting agent used to reduce chromium air emissions by lowering bath surface tension will also help reduce drag-out. Kusher estimates that wetting agents can reduce dragout by as much as fifty percent. Proper parts racking to incrsase drainage is one to the most common drag-out reduction measures. Based on Soderberg work, drag-out rates for very poorly drained parts were 3 to 12 times the rates for well drained parts with vertical, horizontal and cup shaped surfaces.’

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A410 . In a recent study by National Center for Manufacturing Sciences and the National Association of Metal Finishers (NCMSiNAMF), over sixty percent of electroplaters surveyed have increased the drainage time that parts can are allowed to drip over process tanks. Meltzer’s work with both theoretical and empirical data shows that increasing drip time fiom 3 to 10 second reduces the mass fiaction of plating solution remaining on a part by forty percent for common electroplating bath parameter! Proper control of drip time is especially important in manual process lines where rack weight and operator fatigue tend to inhibit appropriate drain times. Some electroplaters choose to use a still or dead rinse following the process bath. As process solution concentration increases in this still tank, the solution can be used to make up drag-out or evaporative losses from the process tank. One simple technique that an estimated 57 percent of eiectroplaters use is the installation of drip shields between tanks which channels dag-out back into the process tank from which the part came. Another way platers have reduce drag-out in chromium electroplating line is to rinse parts off directly over the process tank using low flow fog nozzles. Because water evaporation rates are relatively high in heated chromium process tank (130-14OoF), all rinsing can be done directly over process tanks and effectively “close the loop” of flowing rinsewater baths which must be later treated. Job shops with lower production rates have the high potential to fblly utilize this effective cost and waste saving technique.

Improving Rinsing Efficiency. Improving rinsing efficiency can greatly reduce water consumption and hydraulic capacity requirements for wastewater treatment systems. In a 1994 survey by NCMS/NAMF 68% percent of plating operations surveyed have made significant strides in reduction water usage. Several shops had reduced water usage by over ninety percent. Many methods including improved rinsing tank designs, better control of rinse water flows, and alternative rinse tank configurations have been employed by platers. Reduction in rinsewater flow is also the first step to enable chemical recovery from more concentrated wastestream and improves the potential of closed-looping the electroplating line. Optimum rinse tank designs provide fast removal of solution from the parts and complete mixing. By increasing turbulence via air agitation, mechanical mixing, or pumping/fltration system, better rinsing can be achieved with lower flesh water feed rates. Feed water short circuiting should be avoided by proper placement for inlets and outlets on opposite ends of the tank. Inlet flow distributors can also be used. Rinse inlet flows can be better controlled using flow restrictors, manual controls of inlet valves, conductivity flow control valves, timer control, and foot operated flow actuators. The use of any flow restriction device is dependent on proper determination of minimum purity requirements which still provide adequate rinsing. Once a measure of minimum rinsewater purity is established, typically a conductivity measurement, any of the above flow restriction measures can be used? Alternative rinse tank configurations include counter-flow rinsing, reactive rinses and other configurations. Counter-flow rinses utilize additional rinse baths in series with only one inlet feed which is pumped or gravity fed back through each rinse tank in a direction counter to the work flow. Counter current rinsing and reactive rinsing can each reduce rinsewater flows by 50 percent? Reactive rinsing in the pretreatment stages saves acid make-up chemicals because the reactive rinse better neutralizes the drag-in.

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Chemical Recovery Techniques. A number of chemical recovery technique exist for captured process bath solutions and rinsewater. Bath maintenance techniques can also be used to remove impurities and extend bath life. The most commonly reported chemical recovery techniques employed by chromium electroplaters include: atmospheric evaporation, vacuum evaporation, ion exchange, and porous pot technologies. In the case of hard chromium plating tanks, atmospheric evaporators can applied to recalculated side streams fiom the heated process tank. Evaporators are typically used to remove excess water added to the chromium plating tank from the counter flowing rinsewater bath. Atmospheric evaporators have also been used to evaporate mixed wastewater streams where no discharge option exist for the plater. Approximately 18 percent of electroplating atmospheric installations are used for this purpose.’ Ion exchange is also used to recover chromium fiom the rinsewater baths. Ion exchange cartridges can be regenerated on-site or off-site. The regenerate solution must be treated or sent off-site for recovery. Ion exchange has also been applied to closed circuit rinse tanks to remove drag-out contamination fiom the rinse tanks. The cationic and anionic exchange cartridges are then sent off-site for regeneration. The porous pot is a ceramic membrane pot which is used as an on-line filter for hexavalent chromium plating bath to remove contaminants. The porous pot uses an electrophoresis principal to drive chromium anhydride through the pot membrane without allowing other bath contaminant to past through. The use of porous pot can extent the life a chromic acid plating bath by several years.

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Wastewater Reuse Techniques. Some electroplating shop are reusing treated wastewater for non- critical rinsing steps such as after alkaline cleaners and acid pickling steps. The reuse of conventionally treated wastewater (via hydroxide precipitation) should be cautioned due to the introduction high dissolve solids into the plating line. Drag-out and drag-in fiom conventionally treated water can contaminate other process bath with contaminants such as sodium. In conjunction with advanced membrane separation techniques such as ultrafiltation andor reverse osmosis, wastewater reuse becomes more feasible fiom a operation standpoint but also becomes much more expensive. A relatively recent development in a electro-coagulatiodultraviolet process patented by Pasco, Inc. has been successfully applied to treat and reuse alkaline and acid rinsewaters and bath dumps. The process offers cost effective high water quality reuse and low sludge generation due to no needed chemical additions for solids coagulation and flocculation treatment stages (see case study: Amplate, Inc.).

Electroplating Alternatives to Hexavalent Chromium Electroplating Presently no alternatives to functional hard chrome plating exist that can replace all or even a majority of hard chromium’s physical, chemical, and operational properties. Properties of hexavalent chromium (functional chromium) platiq include: wear resistance, corrosion protection, ability to hold lubricant in microcracks, high temperature wear resistance, low fiiction coefficient, ability to produce thick deposits, ease of bath maintenance, ease of stripping rejects, hardness, and chemical resistance. While no substitute will replace all of these properties, alternative metal finishing techniques, both emerging and currently available, exist that can replace decorative and functional chrome plating for selected applications.

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Trivalent Chromium Formulations for Decorative Applications. Trivalent chromium formulations can be used to replace hexavalent bath formulations for decorative plating applications. Trivalent chromium is at least 100 times less toxic to humans and the environment than hexavalent.8 Trivalent decorative plating has been commercially available since 1975. As these formulation have improved, they prove to not only be environmentally safer but can also result in improved productivity and cost savings over hexavalent formulations. Trivalent chromium decorative electroplating has several processing and environmental advantages. Trivalent baths operate at lower metal concentrations (about 1 odgal vs, 15 to 40 odgal for hexavalent baths). solution, less pollutant mass loading in the wastewater stream, less environmental liability, and less hazardous sludge generation. Rinsewater from trivalent plating do not need to undergo a valence reduction treatment step which requires three pounds of sodium metabisulfite for every pound of chromic acid. Trivalent baths generate much less air emission misting due to less hydrogen gas evolution from the cathode.” Other processing improvements include: fewer rejects due to parts “burning”, higher rackin densities can be used, lower current densities can be used, and the process is more energy efficient.’0” Total operating cost savings have been shown with trivalent formulation? The visual differences between earlier trivalent and hexavalent formulations was their darker color. Modified trivalent formulations have more recently become commercially available that claim to have a blue-white color that is indistinguishable from hexavalent formulations. Trivalent plating chemicals are more expensive than hexavalent, and the bath is more susceptible to operating parameter such as temperature, concentration, and impurities. l2 While trivalent formulation are viable replacements for thinly deposited decorative hexavalent applications, no trivalent formulations exist for functional applications. Research shows promise to develop a trivalent formulation that can be applied at the thickness of functional chromium application of . 1 mils to 10 mils.12 Commercialization of a viable trivalent alternative for functional hard chrome make take as long as 5 years.13

This lower concentration equates to less drag-out

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Electroless Nickel AIternatives. Electroless nickel plating has existed for over 30 years as both a decorative and functional coating. Electroless nickel is an autocatalytic process in which nickel is deposited on the substrate without electric current. As an alternative to hard chromium plating, electroless nickel is somewhat limited by lower physical properties of wear rate, galling resistance, hardness, and cost effectively apply thick deposit. Heat treatment of electroless nickel plated parts is required to achieve full hardness. A low phosphorus (34%) electroless nickel formulations which is heat treated can provide a similar microhardness to haad chromium. Positive characteristics include greater corrosion resistance and low fatigue loss debit. The de osit thickness is much more uniform with than chrome which can reduce the need for over plating. sensitive to impurities, and baths have a finite life which requires more frequent waste management, but total waste management cost for electroless nickel system are slightly less due to fe.wer waste treatment steps. The process cost per square foot plate is equal to or slightly higher than hard chromium plating?

1B The chemical bath reactions are more

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A410 Nickel-Tungsten Electroplating Alternatives. Two electrolytic nickel-tungsten plating alternatives exist that can replace many properties of functional hexavalent chromium. These processes include a nickel-tungsten-boron (Ni-W-B) entitled Amplate and a nickel-tungsten-silicon carbide (Ni-W-Sic) developed by Takada. Both these processes use less energy than chrome plating and apply more uniform coatings. These coatings have favorable chemical and abrasion resistance, high ductility, low friction coefficients. Heat treating after plating produces a similar hardness to functional chrome.12 These nickel-tungsten process use comparable equipment and facilities as chromium plating. While these processes still use a regulated heavy metal, nickel, the concentrations of the electroplating baths are much less than those used in hexavalent chromium plating. The reduced concentration results in less dragout rates, less waste generation, and less mist emissions of heavy metal compounds. The disadvantage of these coating are their higher costs over chromium, their lack of maturity, their use of a regulated heavy metal, plating solution sensitivity to impurities, and other process control requirements of plating three alloying elements? Other potential metal f i sh ing alternatives to hexavalent chromium exist which include metal spray coating applications. In this category arc spray, flame spray, plasma spray, and high velocity oxygenated fuel (HVOF) sprays are include. The metal spray alternative are a mature technology which can offer some superior coating properties but, in general, are more expensive than chrome and have limited parts applications?

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CASE STUDY: AMPLATE, INC.

Background Amplate, Inc., is an electroplating job shop located in Charlotte, NC. Amplate performs cadmium, nickel, zinc, and decorative and hard chrome electroplating and heat chemical processes such as black oxidizing, chromate conversion, passivation, and electroless nickel. The company treated all rinse water and hauled it to the POTW for disposal, but in 1990, Amplate could not longer haul wastewater to the POTW because of new pump and haul laws. As the company had no wastewater disposal options, it had to adopt a closed loop system to continue operations. Amplate began to evaporate all the wastewater generated but quickly found that this practice limited production. Innovative source reduction and wastewater reuse were pursued and implemented.

Waste Reduction Activities The company installed a counter-current system on the rinse tanks and an ion exchange system to remove contaminants from the rinse water. Contaminated overflowing rinse water is pumped through a pre-filter unit, a cation column to remove metals, and then an anion column to further puri@ the water. The water is then returned tc the rinse tank for reuse. Once the ion exchange columns are exhausted, they are sGpped off site for regeneration. The company has been able to increase bath life of the alkaline cleaning solutions by proper selection of chemicals, in-tank filtration to remove insoluble contaminants, and treatment of other contaminants. These practices extended alkaline cleaner bath life from 3 to over 18 months. Similarly, a coagulant is used periodically in the acid pickle tanks to remove metal contamination without the usual pH adjustment. As a result, an acid pickle bath has not been dumped in over two years.

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Wastewater Reuse System. Amplate utilizes an electro-coagulation unit to treat and recycle the rinse water fiom the alkaline cleaners and the acid pickle rinses of the plating line. The pH of the wastewater is adjusted, but no chemicals are used to precipitate contaminates. Treatment is accomplished with an ionic generator which utilizes W light and a small rectifier. The W light produces oxygen in the water stream which then passes two probes powered by the rectifier. Wastewater floc accumulates on the probes, which reverse polarity every few minutes. When the polarity reverses, the floc is released from the probe and captured downstream by a conventional filter. Final treatment is accomplished when the water passes through an actkated carbon filter. Wastewater must be circulated through the system more -

than once to achieve desired quality standards, and, therefore, a batch approach is utilized. Treated water is stored in a holding tank and reused for alkaline cleaners and acid bath rinses. In response to more stringent air emission requirements for chromium electroplaters, Amplate asks customers to consider electroless nickel as an alternative to hard chrome, and many customers have found electroless nickel to be a suitable and sometimes superior replacement to hard chrome in some applications.

Waste Reduction SummaryKost Savings Since the implementation of Amplate’s water reuse and conservation systems and the drying of metal sludge in 199 1 , the following reductions have been realized: 0 In 1989, Amplate discharged 63,440 to the local POTW. Since 1990 Amplate has not discharged

any wastewater to the local POTW despite a five fold increase in production. 0 In 199 1 Amplate disposed of over 1 1,000 pounds of spent acid bath solution. With a new chemical

treatment technique and filtration, Amplate has been able to use hydrochloric and nitric acid baths for almost 3 years without a bath dump.

0 Hazardous waste generation has been reduce by 65 percent between 1991 and 1995. Corresponding hazardous waste disposal costs have dropped by 88 percent, equating to an mual saving of over $9000.

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- For more information on these activities contact: David Overcash, Vice President, (704) 597-0688.

CASE STUDY: C&R HARDCHROME AND ELECTROLESS NICKEL SERVICE

C&R Hardchrome is a small chrome and electroless nickel plating company located in Gastonia, NC that specializes in plating plastic injection mold apparatus and machined tool parts. To reduce the high costs associated with proper disposal of wastes generated at the facility, the company sought ways to keep wastes and liabilities to a minimum.

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Waste Reduction Activities

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A410 The compaby implemented a range of waste reduction programs to reduce air and water emissions and hazardous waste generation.

Fume Scrubber Modifications. To control emissions from the chrome plating operation, in 1990 the company installed a wet-packed fume scrubber with a recirculation system. This system collected chromium concentrate fiom two plating tanks; however, several problems occurred in this process. As different streams of chrome were being mixed from the different plating tanks, iron from the steel ducts was contaminating the chrome concentrate and wash out. This contamination required the off-site shipment each month of large quantities of chrome concentrate and wastewater for reclamation and hazardous waste disposal, respectively. Between 1990 and 1992, separate PVC pipes were installed on the baths. The new system employed a moisture extractor, double-baffle mesh pad mist eliminator, and an in-line vertical mist eliminator. The plating fumes are collected by two plenum arms on either side of the tank. The tops of these arms slant toward the tank to return drag-out chrome solution. The collected fumes are directed to a moisture extractor located above the tank. Moisture removal is accomplished centrifigally as air passes through a set of stationary blades. A spray system periodically washes these blades, and the solution is returned to the plating tank.

The final treatment involves an in-line vertical mist eliminator. A mesh pad is installed as a projection in the event the wash down spray system is not disengaged. A blower operating at a rate of 5,250 ft3/min is used for this system. The chromium could now be recaptured by the fume scrubbers and recirculated back to the solution with the rinsewater. This system eliminated the need to ship chromium- contaminated concentrate and wastewater off site, reduced the use of chromic acid used to make up the chrome plating bath, improved fume capture efficiency, and significantly reduced chromium emissions to the air. Part of the costs of the system were met with a Challenge Grant fiom the NC Ofice of Waste Reduction.

Electroless Nickel Line Modifications. In 1986, the company installed an electroless nickel plating line. During the electroless plating process, chemical reactions drive the process instead of an electric current. As contaminants fiom the parts shortened solution life, the company was generating 70 to 80 gallons of spent bath solution each month and discharging between 6,000 and 7,500 gallons to the POTW daily.

In 1993, with a Challenge Grant from the NC Office of Waste Reduction, the company upgraded its electroless nickel system.

0 Polypropylene tanks replaced steel tanks, and, for energy conservation, double-walled insulated tanks replaced all heated steel tanks. Single-rinse tanks were switched to a system of counterflow multiple rinse tanks to reduce water consumption. Also, restrictive flow nozzles on water inlets were added to better control and reduce water consumption.

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A410 0 The lifespans of solutions were extended with in-tank filtration systems installed on the alkaline

cleaner, hydrochloric acid, and electroless nickel tanks. With nitric acid stripping solution replaced by hydrogen peroxide, the generation of nitric acid hazardous waste was eliminated, and the hydrogen peroxide is sent to a recycler where nickel sulfate is reclaimed for reuse. An ion exchange system was added to the final rinse to enable reclamation of the plating solution, although ion exchange is rarely needed.

0 Finally, a new "dry" mesh-pad ventilation system reduced air emissions from the process and allowed reuse of any captured fumes.

Porous Pot. Contaminants fkom the parts entering the chrome plating bath reduced solution life and lowered plating efficiency. The reduced lifespans required frequent replacement and disposal of the chromium solution, while lower plating efficiency reduced plating quality and increased power consumption and plating time. In 1987, the company purchased a chrome solution purifier called a porous pot. During the plating operations, impurities collect on the pot instead of in the solution. The porous pot uses electrodialysis concepts in conjunction with ceramic membranes. The continual removal of contaminants significantly lengthened the bath life. The impurities are removed periodically and stored in a drum for later shipment and treatment.

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Operational Practices. Other waste reduction work practices conducted at C&R Hardchrome include educating operators to raise parts ftom solutions slowly and to rinse parts over tanks. Drain boards were installed between tanks to prevent solution loss. Also, parts are racked to maximize drainage and minimize solution losses.

Waste Reduction SummaqXost Savings The PVC fume scrubbing system eliminated the need to send 1,840 gallons of chromium concentrate and wastewater off site each year for treatment, and chromic acid consumption fell by almost 90 percent, from 5,400 pounds to less than 600 pounds per year. Chromium air emissions fell by 98 percent, fiom 6 1.4 pounds to less than 0.2 pounds emitted per year. Approximately $12,000 is saved annually in process bath chemical consumption. This savings gives a simple payback period of 8 years for the $95,000 of capital outlay for the fume scrubber systems. The electroless nickel line upgrade reduced water consumption by 87 percent, from 7,500 gallons to less than 1,000 gallons per day. Hazardous waste generation dropped 80 percent, f?om 70 to 80 gallons to 10 to 20 gallons per month. Air emissions were virtually eliminated, dropping fiom 265 pounds to 0.53 pounds per year. No waste bearing heavy metal is currently discharged to the city POTW. An additional benefit from the implementation of pollution prevention measures is that the city no longer requires the company to monitor its discharges. This regulatory relief represents a substantial savings in time and money for the company. An annual saving $7,000 will give C & R a four year payback period for the new upgraded electroless nickel process line (excluding the fume scrubbers). Since 1987 the porous pot has collected

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A410 55 gallons of contaminant sludge and prevented the disposal of at least four chrome baths or 2,300 gallons of solution. The payback time on the $600 pot was less than 3 months.

Other Activities In the 1994 Governor’s Awards for Excellence in Waste Reduction, C&R Hard Chrome Services, Inc., received an Outstanding Achievement Award in the Small Business Category. For more information on these waste reduction achievements contact Ms. Cheryl Cottingham, Office Manager, (704) 861 -883 1.

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CONCLUSIONS

Because of increasing environmental regulations in air and water quality and hazardous waste management, chromium electroplaters should address strict waste management requirements using integrated, cost effective, pollution prevention approaches. As shown by the case studies presented, facilities are employing a variety of pollution prevention practices, fiom low- technology fume suppressants, drag-out reduction, and improved rinsing efficiency, to innovative pollution controVreuse technologies and alternative metal finishes. In most instances the process modifications have improved material usage and processing efficiency while saving money and substantially reducing environmental releases. Traditional end-of-the-pipe control technology approaches and mentalities must be reexamined in a way that inextricably links the production process and pollution prevention.

REFERENCES

1. “Practical Pollution Prevention Guide: Chromium Emission Reduction for Electroplaters and Anodizers,” Program for Toxic Air Pollutant Studies, University of Northern Iowa. 2. Jectrodatbg and Chromic Ac’ id A n o b ODerat ions-

ound I nformmon for P ronosed S d a r d s . Volume I and Jl , EPA-453R-93-030A and B. 3. “Pollution Prevention Tips: Drag-out Management for Electroplaters,” Pollution Prevention Program, NC Department of Environment, Health and Natural Resources, Raleigh, 1985. 4. J. Kusher,”Water and Waste Control for the Plating Shop,” Gardener Publications, Inc., 1976 5. G. Cushnie Jr., Pollution Prevention and Co ntrol Technology for Platinv Onerat ions, 1st Edition, Ann Arbor, 1994 pp 25-80. 6. M.P. Meltzer, “Reducing Environmental Risk: Source Reduction for the Electroplating Industry,” University of California dissertation, Los Angeles, 1989 pp 8-33. 7. Audio Script: Rinsing Process Modification for Electroplaters, WRITER, Minneapolis, Mn, 1992 8. D. L. Snyder, “Performance Properties of Trivalent Chromium,” Atotech USA, Inc. Somerset, New Jersey.

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A410 9. “Fact Sheet: Plating with Trivalent Chrome,” Hazardous & Toxic Materials Project, Board of Public Works, Los Angeles, 1989. 10. N. Zaki, “Complying with Air Quality Standards with New Trivalent Chromium Plating Technology” in 10th AESF/EPA Conference on Environmental Control in the Metal Finishing Industry, American Electroplaters and Surface Finishers, Orlando, 1989. 1 1. “Technical Bulletin: Environchrome Decorative Trivalent Chromium Plating Process,” Frederick

, EPA/625/r-94/007, U.S. Environmental Gumm Chemical Company, Inc., Kearny NJ, 1989. 12. m d e to Cleaner Technologies: Altamtive Metal Fushes Protection Agency, Cincinnati, 1994. pp9-55. 13. K Newby, Atotech USA Inc., Somerset, New Jersey, personal communication, 1995. 14. B. Durkin and D. Crotty, “Electroless Nickel as a Replacement for Hard Chromium, the Phosphorus Content Makes the Difference,” in 79th AESF Annual Technical Conference, American Electroplaters and Surface Finishers Society, Orlando, 1992, pp 1151- 1171.

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