Iron Phosphate-Contaminated Rinsewater Disposal/Recycle

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Q. We own and operate a metal finishing facility that has a three-stage iron phosphate washer. The three stages consist of a pre rinse, iron phosphate dip and a final rinse. Due to the physical characteristics of the metal parts we are processing, there is a fairly significant amount of drag-out from the iron phosphate solution into our final rinse. In order to maintain the rinse quality needed in the final rinse, this bath is frequently pumped into an external holding tank and the rinse completely refreshed. Since we do not have a wastewater permit allowing direct (stream) or indirect (local sewer district) discharge, we utilize an evaporator to evaporate the phosphate contaminated rinse waters in an effort to reduce the volume prior to shipping off-site for proper disposal.

Could you provide us readers with some advice as to the potential to recycle or reuse our waste iron phosphate? C.H.


A. I am sure you have already discussed this with your chemical supplier and are not satisfied with their answer. Based upon our experience with several clients, they had attempted to do so and found that it wreaked havoc on process chemistry and quickly abandoned the project. The best “recycle” concept that we have heard is to have enough dip time between the iron phosphate tank and final rinse and, possibly, adding a halo rinse of de-ionized water equal to the evaporation rate of the iron phosphate tank; in both cases, the water is directed back into the iron phosphate stage. Unless your process allows these changes, you will need to dispose of the waste iron phosphate solution and/or sludge/scale.

In that you do not have a wastewater permit authorizing discharge, your most likely option is direct disposal using an approved service provider. You must determine if the iron phosphate solution is hazardous waste per Subtitle C of the Resource Conservation and Recovery Act (RCRA). In determining if your spent solution is a hazardous waste, you need to look at both the process and the type of parts being processed. Waste streams are classified as a hazardous waste if it is identified as a “characteristic” or “listed” waste.
Characteristic wastes are those materials that exhibit a trait that is known to be harmful to the environment under certain conditions or concentrations. For example, a material is classified as hazardous if it has a pH of =/<2.0 su or =/>12.5 su Characteristic wastes are the D waste. Here is a summary of the “characteristic” wastes:

D001 – Ignitability
D002 – Corrosivity
D003 – Reactivity
D004 through D043 – Toxicity

For an expanded definition of the characteristic waste refer to USEPA regulations, 40 CFR 261.20 through 24.

We strongly recommend obtaining a representative sample of this waste stream and submit to a laboratory to determine whether or not this waste material is a hazardous or non-hazardous waste based on US EPA’s parameters for characteristic waste. Whether liquid or solid, make sure the sample is well mixed so that the resulting analysis is representative of the sample.

Based on the aqueous nature of iron phosphate and knowledge of the process, ignitability, reactivity (sulfide or cyanide containing) and many of the toxicity parameters should not be a concern. We would recommend analysis be performed for corrosivity (pH) and a “total” metal scan for the eight RCRA metals (arsenic, barium, cadmium, chromium, lead, mercury, selenium and silver). If the total metal scan finds less than 19 times a metal’s characteristic limit (i.e., Chromium = 5 mg/l × 19 = 95 mg/l), then no further analytical for that metal parameter needed; this is because lab procedure requires the portion of the sample be mixed with 19 parts by weight of leaching solution. If the total metal scan result is greater than the 19 times rule of thumb, then a TCLP (Total Characteristic Leaching Procedure) would be required to verify whether or not the particular RCRA toxicity characteristic threshold is exceeded.

Based on our experience, we would not expect a typical waste iron phosphate solution or iron phosphate sludge/scale to exceed any of the characteristic parameters deeming it a hazardous waste; much of this has to do with the types of parts being processed, such a leaded steel (Lead = D008).

Listed waste are those materials that US EPA has deemed hazardous due to past experiences regardless of its characteristics or concentrations. Therefore, if a waste meets any of the listed waste definitions defined in US EPA regulations, 40 CFR 261.31 through 35, the waste is hazardous regardless of analytical results. The listed waste are classified as F, K, P, & U wastes in the above regulations.

The listed waste category of most concern regarding an iron phosphate waste solution or sludge/scale is F019. F019 is defined as, “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 at the point of generation if the wastes are not placed outside on the land prior to shipment to a landfill for disposal and are either: disposed in a Subtitle D municipal or industrial landfill unit that is equipped with a single clay liner and is permitted, licensed or otherwise authorized by the state; or disposed in a landfill unit subject to, or otherwise meeting, the landfill requirements in §258.40, §264.301 or §265.301.
For the purposes of this listing, motor vehicle manufacturing is defined in paragraph (b)(4)(i) of this section and (b)(4)(ii) of this section describes the record-keeping requirements for motor vehicle manufacturing facilities.”
Even if a waste has been determined to be a listed waste, it should also be evaluated to see if it also qualifies as a characteristic waste.  Additional rules may apply to it in some cases. Also, its hazardous characteristic likely impacts acceptability and/or cost at a permitted Treatment, Storage or Disposal Facility (TSDF).

In summary, waste classification and characterization can be a very complex process. Furthermore, whether a RCRA hazardous or non-hazardous waste, it is very important to have the documentation on site to demonstrate how you determined its classification. If you are not comfortable in evaluating your waste stream, you may wish to request assistance from your chemical supplier, local EPA office or a professional consultant.

We hope the above information gets you pointed in the right direction.


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