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In the United States, hazardous wastes are subject to regulations mandated by the Resource Conservation and Recovery Act (RCRA). Every month, we provide clear, in-depth guidance on a different aspect of the RCRA regulations. The information presented here is an excerpt from McCoy’s RCRA Unraveled, 2021 Edition.

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F006, F007, F008, F009, and F019 Wastes

Wastes that originate from electroplating operations are among the most complex from a RCRA regulatory perspective. The regulatory problems that are most common with these wastes involve determining which plating wastes are regulated, and deciding which hazardous waste codes apply. Because the listing descriptions for the plating wastes may appear to overlap, a review of EPA guidance is critical to understanding the applicability of these waste codes.

The plating process

A diagram of a hypothetical electroplating process appears in Figure 1.

Figure 1

The metal parts (solid lines) are conveyed through a series of different process baths. The electroplating step is defined as the application of a surface coating. This process usually, but not always, involves electrodeposition to provide corrosion protection, erosion resistance, and/or friction-reducing characteristics or to improve appearance. [RO 11103] Chemical etching and milling are typically nonelectrodeposition processes that are also considered to be electroplating processes.

Wastes from each process bath (dashed lines) are sometimes collected in a process sewer. The process sewer flows to a wastewater treatment system that produces two residues: sludge and treated water. Besides the process flows identified above, electroplating facilities also produce wastes from floor washings, accidental spills, and general maintenance activities. The process sewer also typically captures these episodic wastes.

F006 wastes

The current listing description for F006 in §261.31 is: Wastewater treatment sludges from electroplating operations except from the following processes:

  1. Sulfuric acid anodizing of aluminum;
  2. Tin plating on carbon steel;
  3. Zinc plating (segregated basis) on carbon steel;
  4. Aluminum or zinc-aluminum plating on carbon steel;
  5. Cleaning/stripping associated with tin, zinc, and aluminum plating on carbon steel; and
  6. Chemical etching and milling of aluminum.
In addition to the six processes cited above that are specifically excluded in the regulatory description, F006 sludges will also not be produced by the following processes [December 2, 1986; 51 FR 43351]:
  1. Chemical conversion coating (as we will discuss in Section 3.4.6, wastewater treatment sludges from chemical conversion coating of aluminum are F019 wastes);
  2. Electroless plating; and
  3. Printed circuit board manufacturing (unless the manufacturing process includes chemical etching or milling).

The nine exclusions given above describe processes that will not produce F006 wastewater treatment sludge. Perhaps what is more important is identifying the processes that will produce this listed waste. First, it is worth noting that F006 was originally listed because electroplating operations typically use cadmium, chromium, nickel, and complexed cyanides, all of which can partition into the wastewater treatment sludge. To carry the F006 code, the sludge must originate from the following processes [51 FR 43351]:

  • Common and precious metals electroplating [except tin, zinc (segregated basis), aluminum, and zinc-aluminum plating on carbon steel];
  • Anodizing (except sulfuric acid anodizing of aluminum);
  • Chemical etching and milling (except when performed on aluminum); and
  • Cleaning and stripping associated with the above processes (except when associated with tin, zinc, and aluminum plating on carbon steel).

The following subsections describe important details of how various types of wastes associated with electroplating operations are regulated.

Baths and rinsewaters

In plating shops, the two most common wastes are baths and rinsewaters. The baths are essentially concentrated solutions used during the electroplating process. If the spent baths are kept segregated, they (and any residues produced from their treatment) will typically have their own hazardous waste code (e.g., F007, F008, or F009, each of which will be described later in this section). If the baths become mixed with electroplating wastewaters, however, sludges generated from treatment of the mixture would be F006. [RO 11315]

When parts pass through the various baths, they typically carry out residual droplets of the bath chemicals (called “dragout”), which are then removed by rinsing. Because these droplets are considered to be chemicals that are still in use (i.e., they are not spent chemicals), they are not solid wastes, do not have a waste code yet, and will not cause the rinsewater to be listed hazardous waste via the mixture rule. [RO 11198, 11269, 11339, 14314] In other words, rinsewaters are not themselves listed hazardous wastes (although they may exhibit a characteristic). Only when these rinsewaters are treated in a wastewater treatment system that produces a sludge does the F006 waste code apply. [RO 11269]

As noted previously, electroplating processes include common and precious metals electroplating, anodizing, chemical etching and milling, and cleaning and stripping associated with these processes. The following guidance relates to how EPA has interpreted the scope of the last two of these processes.

Chemical etching and milling

Chemical etching and milling processes utilize chemical solutions to dissolve metal layers from a part. Etching and milling are essentially the same process, but etching only removes relatively small amounts of metal (1 to 5 mils). According to EPA, this category of processes includes “chemical milling, chemical etching, bright dipping, electropolishing, and electrochemical machining.” [RO 11214] “Bright dipping” of brass parts is an example of chemical etching; the process changes the brass surface appearance and/or improves coating adhesion. [RO 13387]

An example of chemical milling would be when a manufacturer produces gold beads by plating gold on a copper base metal. Nitric acid is then used to dissolve the copper (a chemical milling process). [RO 11315]

When parts are removed from the etching or milling process, they are typically rinsed to remove the etching/milling chemicals. If a sludge is produced when treating the rinsewater, it is F006.

Cleaning and stripping

Cleaning and stripping operations that are associated with electroplating processes can produce F006 sludge. The purpose of the cleaning/stripping steps is to remove any contaminants that might interfere with the electroplating process. Three phases of cleaning are typically considered to be integral steps in the electroplating process: precleaning (bulk removal of oil and dirt), electrocleaning, and pickling. Treatment of wastewaters from any of these steps, when conducted as part of an electroplating operation, would produce F006 sludge. For example, a pickling bath might be used to remove oxide scale from precious metals prior to electroplating. If the spent bath is neutralized, the resulting sludge is not F006 (because the bath is not wastewater). However, if the pickled part is subsequently rinsed, the sludge from treating the rinsewater would be F006. [RO 11315] In another example, a cleaning process associated with a bright dipping/chemical etching operation is also a process associated with the F006 listing description. [RO 14808]

Stripping steps in an electroplating operation are typically performed to remove metal from a base material. For example, if a part has been improperly plated, it might be stripped to dissolve the unwanted metal, followed by replating. Because the stripping solutions can contain significant metal concentrations and cyanides, sludges produced from the treatment of wastewaters from metal stripping operations are regulated under the F006 category. [RO 11340]

Confusion with K062—spent pickle-liquor wastes

Spent pickle liquor is essentially spent acid that has been used to remove metal oxide scale from a substrate. When these spent acids come from the iron and steel industry (SIC Codes 331 and 332), they are classified as K062 wastes. [RO 12972] If spent acids are produced as part of the electroplating process, and if these acids are dumped to a wastewater sewer (or if the metal is subsequently rinsed), the wastewater could produce an F006 sludge. [RO 11315] According to EPA:

“[T]he agency did not intend the K062 listing to include electroplating processes that generate spent pickle liquor. This would be duplicative since electroplating wastes are specifically covered under F006…. In considering petitions to delist electroplating waste, the agency has stated that the F006 listing includes acidic wastes (i.e., spent pickle liquor) from the electroplating process. Electroplating operations typically pretreat the metal using acidic baths prior to electroplating. The acidic wastes from this process are generally mixed with spent plating bath solutions and lime treated. Sludge generated from this process is considered F006…. In cases where acidic wastes from the electroplating operation remain untreated or are segregated from other process waste and treated separately, the waste is then considered K062….” [RO 12268]

Filtrate and supernatant

In the final sludge settling and dewatering step shown in Figure 1, supernatant (liquid overlying solids) results from gravity separation. Similarly, filtrate (the liquid that passes through a filter) is produced by mechanical filtration. With regards to these wastes, EPA stated:

“[S]upernatant from F006 generation is not considered to be F006, but simply wastewater from treatment of electroplating wastewaters. Filtrate from F006 sludges could be hazardous under the derived-from rule, but if it is similar in terms of identity and concentration of constituents in the influent to the wastewater treatment process, it is not considered to be derived from F006. Rather, it is the original influent wastewater.” [August 17, 1988; 53 FR 31153]

Sludge

The F006 listing applies to wastewater treatment “sludge.” The term “sludge” is defined in §260.10 as “any solid, semisolid, or liquid waste generated from a municipal, commercial, or industrial wastewater treatment plant, water supply treatment plant, or air pollution control facility exclusive of the treated effluent from a wastewater treatment plant.”

In most cases, F006 sludges are formed when heavy metals precipitate from electroplating wastewater as a result of adding sodium hydroxide, sulfides, lime, or some other precipitant to the wastewater. However, sometimes other types of materials are considered to be F006 sludge. For example, rinsewater from an electroplating process is pumped through a filter and ion-exchange column for removal of solids, metal ions, and cyanide. The treated water is then either recycled or disposed, and the used filter and ion-exchange resin are sent offsite for recycling. EPA considers the spent filter media and resin to be listed F006 sludges (even if they don’t exhibit a characteristic), which must be manifested when sent offsite to a recycling facility. [RO 11244] Even if treated or reclaimed wastewater is reinserted into the process, contaminant removal is considered to be pollution control and spent resins are F006 sludge. [RO 11857]

Sludge from sequential treatment of electroplating wastewaters

Sometimes, it is unclear where F006 sludges will appear in a sequential wastewater treatment system. In Figure 2, electroplating wastewaters are treated, and F006 sludge is produced in a settling and dewatering unit. Water (supernatant) from this unit is then mixed with sanitary wastes, and the combined mixture is treated in a surface impoundment (or it could alternatively be a tank). Sludge forms in this impoundment, and an issue arises as to whether this impoundment sludge is also regulated as F006.

Figure 2

Some facilities have tried to make the case that after some initial treatment (e.g., treatment to meet a CWA effluent limitation), the effluent is no longer “wastewater” and can, therefore, no longer generate F006 sludge. According to EPA, the F006 background documents provide no guidance as to when “wastewater” becomes a “treated effluent.” [RO 11139] As a result, the F006 listing includes sludges derived from the treatment of electroplating wastewater, regardless of where the sludges are formed. Thus, if a sludge is formed in a wastewater treatment tank, filtration device, or surface impoundment, it is F006 sludge. The units would be subject to all applicable hazardous waste regulations; the tank and filtration device might be wastewater treatment units that are exempt from permitting, but the surface impoundment would be a hazardous waste unit requiring a permit. [RO 12267]

A question that arises occasionally is: Would the F006 code apply to sludge from a POTW if the POTW receives rinsewater from electroplating operations? Assume that the rinsewater was mixed with domestic sewage and arrived at the POTW by way of the sewer. EPA has implied that sludge from a POTW will not carry the F006 code under these circumstances but doesn’t clearly explain why. [RO 11139, 14322] We suspect that this outcome results from the handoff between RCRA and CWA at the discharge to the POTW’s sewer line.

Surprise! You’ve got F006

F006 sludges can be generated from nonhazardous wastes or wastes that are hazardous only for a characteristic (e.g., D002 corrosive wastewater). [RO 11269] For example, rinsewater from an electroplating process may not exhibit any characteristics and doesn’t meet any listing descriptions. This nonhazardous waste could be shipped to an offsite facility without a manifest. However, if the offsite facility generates a sludge from processing the rinsewater, it has just generated F006 hazardous waste. [RO 11439]

Methods to avoid F006 generation

Two methods are available to help electroplaters minimize their production of F006 waste:

  1. Physically separate the electroplating step (e.g., chemical etching) from the other process steps (e.g., cleaning and stripping). This can be accomplished by rinsing and drying components such that hazardous contaminants are not carried downstream. [RO 11851]
  2. If a facility generates a waste that meets the listing description for F006, and if the sludge contains very low levels of contaminants, the facility can submit a delisting petition per §§260.20 and 260.22. Note that electroplating sludges are one of the most common delisted wastes in Part 261, Appendix IX.

Exemptions from the F006 listing

Nine different processes are excluded from the F006 listing. EPA has issued many interpretations concerning the scope of these exclusions, some of which are discussed in the next subsections.

Zinc plating

One of the processes that is not considered to involve electroplating is “zinc plating (segregated basis) on carbon steel.” The phrase “zinc plating (segregated basis)” refers to zinc plating processes that do not use cyanide. For example, wastewater treatment sludges from zinc plating using baths formulated from zinc oxide and/or sodium hydroxide would be excluded from the listing. Similarly, hot-dip galvanizing on carbon steel is not considered to be an electroplating process and, when operated on a segregated basis, would not result in the production of F006. [RO 11068] However, wastewater treatment sludges from zinc plating processes utilizing zinc cyanide and/or sodium cyanide would be considered to be F006 sludges. Where both cyanide- and noncyanide-containing processes are used at the same facility, the noncyanide-containing sludges must be kept segregated from the cyanide-containing sludges in order to remain excluded from the F006 listing. [December 2, 1986; 51 FR 43351]

Chemical conversion coating

Chemical conversion coating includes chromating, phosphating, immersion plating, and coloring. While chemical conversion coating of aluminum can result in the production of F019 sludge, other types of conversion coating were specifically excluded from the F006 listing on December 2, 1986. [51 FR 43351] For example, when zinc plating on steel is followed by zinc phosphating, wastewater treatment sludges from the process are not considered to be F006. [RO 12972]

Printed circuit board manufacturing

Although a general exclusion from the F006 listing exists for wastes from printed circuit board manufacturing, two circumstances have been identified where the general exclusion does not apply.

  1. When EPA decided that wastes from printed circuit board manufacturing were excluded from the definition of F006 [51 FR 43351], they added the following footnote:

“Wastewater treatment sludges from printed circuit board manufacturing operations that include processes which are within the scope of the listing (e.g., chemical etching) are regulated as EPA Hazardous Waste No. F006.”

  1. Depending on how printed circuit boards are manufactured, photoresist “skins” may be an F006 waste. The principle to be applied is described as follows:

“If there is any possibility of skins stripping solutions being mixed or commingled with other electroplating wastewater, or if the hazardous constituents generated by other electroplating processes can otherwise be ‘carried forward’ by the nature of the association of the two processes, the skins themselves could become contaminated with these hazardous constituents.” [RO 11851]

For example, if circuit boards are sequentially etched and then stripped of photoresist material, contaminants from chemical etching (an F006-generating process) could enter the stripping bath and contaminate the photoresist solids. Under these circumstances, when the solids are filtered from the contaminated stripping solution, they would be F006. In EPA’s language:

“If the stripping operation is in line with or contiguous with an electroplating operation, then the stripper solution itself becomes an electroplating wastewater. ‘In line with or contiguous with’ in this case would mean the stripping operation is not physically separated from these [electroplating] operations and the printed circuit boards are not rinsed and dried prior to the photoresist stripping operation. The stripper solutions thus could be mixed or intermingled with electroplating wastewater.” [RO 11851]

On the other hand, if the boards are etched, rinsed, dried, and then stripped, contaminants from the etching step would not be carried into the stripping step, and the photoresist solids would not be F006. [RO 11851]

F007 wastes

The listing description in §261.31 for F007 wastes is: “Spent cyanide plating bath solutions from electroplating operations.” Note that the plating bath solution is not an F007 waste until it is spent. Clearly, dumps of the bath are F007 wastes; however, EPA has given conflicting guidance on the status of bath dragout or carryover. In one interpretation, parts were transferred from a plating bath to a chlorination tank to stop the plating process. The agency stated that plating bath dragout is considered to be a spent bath solution; hence, any sludge that forms in the chlorination tank would be considered F007 waste. [RO 12269] In other interpretations, the agency concluded that dragout droplets are not spent materials and that rinsewater baths following the plating process are also not solid wastes. Therefore, these baths would not be F007, F008, or F009. [RO 11198, 11269, 11339, 14314] We believe that this second interpretation is the most defensible, and it certainly is the one EPA has confirmed most often.

F007 wastes can also be reactive due to their cyanide content. EPA gives this example: When anode bags are removed from a cyanide plating bath, they are considered to be a spent material. Washing the anode bags for reuse is considered to be reclamation; hence, according to Table 1 in §261.2(c), the bags are a solid waste. Because the bags are both reactive and have been soaked in spent plating bath, they carry both the D003 and F007 codes. [RO 13476] That’s what EPA said, but, per §268.9(b), the D003 code would not have to be reported on the LDR notification. Also note that per §261.4(a)(23–24), spent materials that will be reclaimed are not solid wastes if certain conditions are met.

Finally, note that spent baths are only F007 wastes if they are “electroplating baths.” As mentioned previously, electroless plating is not considered to be electroplating. [December 2, 1986; 51 FR 43351] EPA has stated that, even if electroless plating baths contain low concentrations of cyanide, they would not be considered F007 wastes when disposed. They could, however, be characteristic wastes. [RO 13311] Similarly, a cyanide-containing bath from an electrowinning process is not considered to be F007 waste. [RO 13304]

F008 wastes

F008 listed wastes are described in §261.31 as “Plating bath residues from the bottom of plating baths from electroplating operations where cyanides are used in the process.” In one case, a filter was used to remove residue from a plating bath. When the filter media were removed for disposal, EPA stated that the proper waste codes would be D003 and F008. [Per §268.9(b), however, the D003 code would not have to be reported on the LDR notification.] Although the filter residue could also contain spent plating bath (F007), the F008 listing is more specific and should be used instead of the F007 listing. [RO 13476]

F009 wastes

The listing description for F009 in §261.31 is “Spent stripping and cleaning bath solutions from electroplating operations where cyanides are used in the process.” Where cleaning solutions do not contain cyanides (e.g., they are detergent solutions), the F009 listing is not applicable. [RO 13476]

An example of a stripping process that produces F009 waste involves a chemical etching process. In the process, a potassium ferricyanide solution at pH >12.0 is used to remove tungsten or molybdenum substrate material. Although the waste might meet the listing description for F007 (spent cyanide plating bath from electroplating), EPA decided that the correct waste code was F009. [RO 11251]

One confusing issue related to F009 wastes is the source of the cyanides in the baths. Two possibilities exist: 1) cyanide can be an ingredient in the stripping and cleaning solution, or 2) cyanide can be carried into a noncyanide-containing stripping and cleaning bath via dragout from a previous cyanide-containing step. Clearly, the F009 code was meant to apply in the first situation. Regarding the second situation, EPA stated:

“A cleaning and stripping bath used prior to the cyanide plating bath would not contain cyanide contamination from carryover. Spent cleaning and stripping baths that follow cyanide plating baths at some point in the dip sequence would have levels of cyanide in them due to dragout. Therefore, it is EPA’s intent to regulate only those spent cleaning and stripping baths from electroplating processes that are used at some point after the cyanide bath. However, if cleaning and stripping baths are commingled with other baths occurring during or after the cyanide baths or if cyanide-containing solutions or wastes are introduced or recycled in the process upstream of the cyanide plating baths, then these cleaning or stripping baths would be F009.” [RO 13301]

Finally, if any sludges form in the bottom of the cleaning tank, they are also considered to be F009. [RO 14276]

F019 wastes

When EPA developed the listing description for F006, it listed wastewater treatment sludges from chemical conversion coating of aluminum separately as F019. This distinction was made because the aluminum-based sludges were not expected to contain significant concentrations of cadmium and nickel (constituents typically found in other F006 wastes). The current listing description for F019 in §261.31 is “Wastewater treatment sludges from the chemical conversion coating of aluminum except from zirconium phosphating in aluminum can washing when such phosphating is an exclusive conversion coating process. Wastewater treatment sludges from the manufacturing of motor vehicles using a zinc phosphating process will not be subject to this listing.…”

Because the F019 listing is similar to the F006 listing, many of the provisions applicable to F006 wastes also apply to F019 wastes. For example, supernatant and filtrate from processing F019 sludge are simply wastewaters and do not carry the F019 code. [RO 13323] Similarly, if wastewater from chemical conversion coating of aluminum is treated in sequential systems (e.g., two tanks in series followed by a surface impoundment), any sludge that appears in any of the units is F019. [RO 11507, 11961] Finally, wastewater treatment sludges generated from treatment of contaminated rinsewaters collected from stages prior to chromate conversion coating are not F019. [RO 11731]

Exemptions from the F019 listing

The exemption for zirconium phosphating was added in 1990. [February 14, 1990; 55 FR 5340] In the Federal Register notice, EPA stated:

“This final exclusion applies only to sludges from processes that exclusively use zirconium phosphating solutions that do not contain chromium or cyanides. Further, these processes are not associated with electroplating or conversion coating steps where hazardous constituents are used. For example, if a can maker employs a chromating step, separately or in conjunction with such zirconium phosphating, the wastewater treatment sludges would meet the F019 listing and would not be excluded under this rulemaking.”

Other types of phosphating on aluminum (e.g., tin phosphating) are not covered by the zirconium phosphating exclusion and would result in the production of F019 wastes. [RO 11547, 14103]

EPA states, “As to sludges from sulfuric acid anodizing, these wastes do not meet the F019 listing since anodizing is not considered to be a ‘conversion coating’ process. Anodizing is an electrical process wherein the part is made anodic, whereas conversion coating uses nonelectrical processes.” [RO 11551]

EPA excluded wastewater treatment sludges generated from zinc phosphating in the automotive assembly process on June 4, 2008. [73 FR 31756] Until this rule was issued, the zinc phosphating (conversion coating) step in the manufacture of motor vehicles containing aluminum parts resulted in generation of F019 sludge from the wastewater treatment systems at auto plants. The exclusion, which applies at the point of generation, is based on the following conditions:

  1. The waste must be generated from motor vehicle manufacturing. This is defined to include the manufacture of automobiles and light-duty trucks/vehicles (NAICS codes 336111 and 336112, respectively). The exclusion to the F019 listing does not apply to other motor vehicle manufacturing industries (such as heavy-duty truck or motor home manufacturing).
  2. Prior to offsite shipment, the waste must not be placed outside on the land.
  3. The waste must be disposed in a landfill that is either 1) a state-permitted or authorized Subtitle D (municipal or industrial) unit that is equipped with at least a single clay liner; or 2) subject to, or otherwise meeting, the requirements in §258.40, 264.301, or 265.301.
  4. Generators must maintain documentation onsite proving that they meet the above conditions excluding their wastewater treatment sludges from the F019 listing.

As a follow-up to the exclusion from F019 for wastewater treatment sludges generated from zinc phosphating in the automotive assembly process, EPA provided a May 2009 interpretation noting that sludges generated from zirconium oxide coating operations on automobile bodies containing aluminum are also excluded from the F019 listing. [RO 14806]


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