Waste Treatment for black oxide


Operators of an Insta-Blak process should be aware of the pollution implications and now the process is affected by EPA regulations. In the majority of Insta-Blak installations the rinse waters from the process do not need to be treated. After installation and initial operation of the Insta-Blak process, the sewer effluent from the plant should be checked for pH and concentration of copper and selenium. Only by this analysis will it be possible to determine if treatment is required.

The Federal EPA establishes minimum standards of quality for industrial effluent wastewater by defining an acceptable pH range and setting maximum allowable levels for specific metals discharge through a sewer line. While state, county and local agencies commonly adopt the Federal standards, they may set limits which are more stringent than the Federal limits.

Because many of the regulations are continually changing, it is difficult to make a blanket waste treating recommendation which will satisfy all current regulations. The recommendations given here are designed to satisfy the Federal regulations. It is suggested that the operator check with the authorities in his area to determine the local regulations.

In order to comply with the regulations, it is important to identify the source and type of chemicals in the sewer line. Other metal finishing or treatment processes in the plant should be examined along with the Insta-Blak process. Some of the baths in the Insta-Blak process line require maintenance that calls for periodic dumping of the bath. In this case, the proper dumping procedure is described below. Three (3) of the baths are designed to operate as permanent baths with no periodic dumping. If this is the case, the source of the chemicals in the sewer line is actually the rinse tank immediately following the bath. The treatment recommendations given will be based on normal operating conditions rather than unlikely possibilities.

Most Insta-Blak processing lines utilize several chemical products, each of which is designed to perform a specific function on the surface of the steel, iron or powdered metal parts.

The chemical content of each tank is as follows:

     Step 1. The E-KLEEN soak cleaning solution contains caustic soda, alkaline salts and biodegradable wetting agents. It operates at pH 9 to 13.

 This solution is designed to emulsify oils from the surface of the parts and hold them in suspension. Normal maintenance calls for initial makeup at 8-12 wt. oz./gal. or 10% by volume liquid concentrate followed by periodic additions of fresh powdered or liquid concentrate cleaner to maintain the alkalinity and oil-holding            capacity. At some point, the solution will lose its efficiency and will no longer be able to absorb more oil and therefore it must be dumped and a new solution prepared.     

The E-Kleen bath operates at pH of 9 - 13. Because of EPA regulations call for an allowable pH range of 5.0 - 10.0 in the sewer line, the pH of the E-Kleen bath may have to be lowered before disposal. Sulfuric acid is recommended and must be added slowly, with good stirring, until a pH of 10 is achieved. E-Kleen contains no other
regulated chemicals and therefore the solution can then be dumped without further treatment.  

     Step 2. RINSE - overflowing cold tap water containing small amount of E-Kleen solution from Step 1.

The pH of this rinse is usually well within the allowable range of 5-10. Therefore, the overflowing water can go directly into the drain without treatment.

During normal operation of the Insta-Blak process, this rinse will be slightly alkaline and when mixed with the slightly acidic rinse after Step 3 and Step 5, it will help to neutralize the combined rinse waters from Step 3 and Step 5.

     Step 3. E-PREP surface conditioner contains phosphoric acid and biodegradable wetting agents. It is not used in all Insta-Blak processes.

This bath is a mild phosphoric acid solution which has a pH of approximately 4.0 when fresh. During operation the bath is maintained with additions of fresh concentrate. This bath is only dumped when it becomes contaminated or cannot be maintained at proper strength. The E-Prep bath contains no regulated chemicals, but if it must be dumped, the pH must be raised above pH 5 with baking soda or caustic soda.

Often times, it is a good idea to drain the E-Kleen alkaline cleaner solution at the same time as the acidic E-Prep solution. In this way, the two solutions will help to neutralize each other. The E-Prep does not contain enough acid to completely neutralize the EKleen and therefore the addition of sulfuric acid may still be necessary in order to ensure a final pH of 5-10. This method will reduce the amount of sulfuric acid required to completely neutralize the E-Kleen solution. 

     Step 4. RINSE - overflowing cold tap water containing small amount of E-Prep from Step 2.

This tank will contain no regulated chemicals and the pH will be in the acceptable range of 5-10, and therefore it can be drained and/or dumped without treatment.

     Step 5. INSTA-BLAK blackening solution which contains low levels of phosphoric acid, copper and selenium. It operates at pH of 1.5 to 2.

Bath maintenance consists of monitoring the concentrations of the components (per the technical data sheet) which will call for periodic additions of fresh Insta-Blak concentrate. The Insta-Blak bath is designed to be operated as a permanent bath. It is not dumped unless it is grossly contaminated. If the bath becomes so contaminated it becomes unusable, the bath must be treated in the following manner: To precipitate the metal ions, (copper, iron and selenium) leaving a solution with only a few parts per million total metal ions:

1. Add Sulfuric Acid until the solution acquires a pH of 1.4 or less. This quantity will vary, depending upon the extent of depletion and the amount of water used in the original make-up.

2. Shred into hand-size pieces, 5-7 lbs. grade 00 steel wool per 100 gallons of spent solution. Add shredded steel wool to the solution and stir for 20 minutes. Check pH to be sure it has not risen above 2.2. If it has, add more Sulfuric Acid and stir for a few minutes longer. Let solution stand for 24 hours.

3. This is followed by additions of sufficient Sodium Hydroxide (in liquid form - 50% solution may be purchased) to raise the pH to 10.5 to 11.0. Stir thoroughly and continuously while adding the Sodium Hydroxide.

4. The treated solution is then allowed to stand for several days so the insoluble metallics and other solids drop to the bottom of the tank. The liquid portion may then be drawn off into a separate container. Lower the pH of this solution with Sulfuric Acid to meet local regulations. The sludge from the bottom of the tank, which will contain metallic ions deposited on the blackened steel wool should be accumulated and disposed of per local regulations.

Note: To minimize the amount of sludge, the steel wool can be contained in perforated plastic or stainless steel dip baskets. Stir the solution continuously to bring fresh solution in contact with the steel wool in the baskets. The blackened steel wool should be thoroughly rinsed with water and then disposed of separately from the sludge. If the steel wool is very oily, it may require pre-cleaning prior to immersion in the Insta-Blak solution.

     Step 6. RINSE - overflowing cold tap water containing small amount of Insta-Blak from Step 5.

The rinse water will contain small amounts of acid, copper and selenium. When operated properly, the concentrations of the above-mentioned materials will be quite low: The pH will be well above 5.0: The copper and selenium concentrations will be approximately 2-10 parts per million as the rinse water leaves the tank. Concentrations will vary, depending upon the drag-out rate. When combined with the rinse waters from Steps 2 and 4 the concentrations will be greatly reduced due to dilution. This water will undergo still further dilution when combined with the other waste water in the plant which is discharged to the sewer. The resulting concentration in the main sewer line leaving the plant will generally be in the range of 0.1-5.0 ppm and usually does not require treatment. If the concentration of copper and selenium exceed the regulated levels, then an Ion exchange unit must be installed on the overflowing rinse from this tank.

     Step 7. SEAL - may be one of several different materials which may be either water based or solvent based.
The sealant tank is operated as a permanent bath with no dumping as part of regular operation. Therefore, no sealant would be found in the sewer line. If solvent based water displacing sealants such as E-Tec 501, 502, 503, 504, 505 or 505+ are used, then the rinse water from Step 6 will be displaced to the bottom of the tank where it is periodically drawn off and treated as the overflow water from Step 6. 
If a water soluble (emulsifiable) sealers such as E-Tec 510, 512, 513 or 515 are used then the rinse water from Step 6 is contained in the emulsifier. Excess water is driven off by evaporation from the warm, 150°F emulsion. If the emulsion becomes contaminated and must be discarded, it must be sent to an oil and solvent recovery firm.
Note: If resin or wax sealants such as E-Tec 520, 521, 522 or 525 are used then the rinse water from Step 6 is dispersed in the resin solution or emulsion. When the solution becomes so contaminated it cannot be used, it should be disposed by a licensed disposal firm.