Long Live Acid Baths!

Article From: Products Finishing, , from Products Finishing

Posted on: 11/1/2002

David French, president of Amplate, wouldn't believe it until he tried it, but this acid bath extender has allowed him to go 18 to 20 months with his acid baths without dumping them…and they are still going strong without any sign of failing!

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Amplate, Inc. (Charlotte, NC) is a typical job shop plating company offering nickel, zinc, and decorative chromium electroplating, as well as black oxide, passivation and electroless nickel plating. Since Amplate is a typical shop, it is confronted by the same challenges as most shops face: government regulations, chemical costs, waste treatment and handling costs, improving production, etc.

Amplate is always looking for ways to improve all aspects of the business, whether it is to lower chemical costs, save on water or improve production efficiency. So when David French, president, learned about a product that would allow 30 plus turnovers on his acid baths, he wanted to know more. He lunched with Gwen Wagner, the widow of the developer Dr. John C. Wagner, who told him about PRO-pHx Acid Bath Extender, a reagent chemistry. He found it difficult to believe what Mrs. Wagner was telling him, but he decided to try the product in his plant initially in exchange for free chemistry. Amplate, now a customer, first added the reagent chemistry to its pickling baths with success, and eleven months later added it to its recycle water system with equal success.

The chemistry, a catalyzed reagent for extending acid bath life, is a proprietary blend of soluble silicates that allow for the effective immobilization of soluble metals by reacting with them to form insoluble metal silicates. Silicon can form polymers, which are in a special class of compounds in which sodium oxide is associated with silicon dioxide generally in ranges varying from 1:1 to 1:3.22. In dilute solution, the compound depolymerizes to form chains of silica and oxygen. Negative charges on some oxygen atoms react with positive metal ions to form stable, insoluble metal silicates. The ingredients in the catalytic reagents will also react with volatile and non-volatile organic compounds to produce a non-volatile, non-toxic, non-hazardous waste. The carbon dioxide formed reacts with the silicates and does not escape.

Zero Acid Disposal: Use and History.

The acid bath extender, a reagent chemistry that requires simple filtration, is used in the acid pickling, stripping and activating baths for the zinc, electrolytic nickel, electroless nickel, and decorative chromium plating lines. It is also used in the acid baths for the black oxide and passivation lines. In addition, the acid extender is also used in the citric and nitric passivation baths. At Amplate these plating operations are performed on all basic metal substrates except for aluminum and zinc die-castings.

Prior to the use of the acid bath extender, Amplate sought to increase the bath life of its cleaning solutions with the proper selection of chemicals and in-tank filtration to remove insoluble contaminants and treatment of other contaminants. These practices extended cleaner bath life from three to 24 months. A coagulant (DTC) was used periodically in the acid pickle tanks to remove metal contamination without the usual pH adjustment; however, organics would eventually build up, and the acid baths would have to be disposed of.

In November of 2000, Amplate replaced the DTC with the acid bath extender chemistry. Since replacing it, the company has not disposed of any acids. Acid addition is now required only to makeup for drag out and evaporation. See Table I.

The chloride zinc-plating bath uses hydrochloric acid. It features clear and yellow chromate and uses a 50-micron filter in the treated acids. The acid bath extender was added to the spent acid and restored it to approximately two-days old. The tank is used 60 + hrs/week. Treatment has extended the acid life more than 34 times during the course of 20 months.

The nickel-plating lines use nitric, hydrochloric and sulfuric acids with 5-micron filters. The acid extender was added to these spent acids to restore them. The baths run 40+ hrs/week.

TABLE I: Acid Bath Extender Addition Records for Some Lines
Plating Line: Zinc Pickle and Activate
Type of Acid: 45% Hydrochloric at 20 Baume and 55% water
Tank Size: 200 gal
Date of Add Quantity in Gal
1/11/01 2
6/25/01 0.5
9/13/01 0.5
11/21/01 0.5
1/7/02 0.5
6/5/02 0.5
Note: Tank was one month old at first addition
Waste Treatment Line: Recycling Rinse Waters
Type of Material: Rinse water with organics and metals
Tank Size: 2,300 gal
Date of Add Quantity in Gal
10/22/01 1
11/7/01 2
11/20/01 1
2/27/02 1
4/27/02 1
6/5/02 1
Note: The carbon filtration used to remove organics from the recycling wastewater system was eliminated on 10/4/01.

This pattern continues for the decorative chrome, electroless nickel, passivation and chrome stripping lines, using 10-micron filtration.

After more than 23 months of using the acid bath extender, the black oxide finishing line, which is used 40+ hrs/week, continues to perform as a two-day8-old acid.

The hydrochloric acid tank on the zinc line, which was previously disposed of every two weeks, ran five months before needing additional acid extender chemistry.

Recycle Water System Uses Same Reagent Chemistry.
In 1995, Amplate installed a system to treat and recycle water that featured an electro coagulation unit. It was used to treat and recycle the rinse water from the alkaline cleaners and acid pickle rinses on the plating lines. The pH of the wastewater was adjusted, but only simple coagulates were used to precipitate the contaminants. Treatment was accomplished with an ionic generator that used UV light and a small rectifier. The UV light produced oxygen in the rinse water stream, which then passed two probes powered by a rectifier. Wastewater floc accumulated on the probes, which reversed polarity every few minutes. When the polarity reversed, floc was released from the probes and was captured downstream by a conventional filter. Final treatment was accomplished when the water passed through an activated carbon filter to remove organics.

In October of 2001, Amplate removed the carbon filtration from the system and replaced it with the acid extending reagent chemistry. It was added at 1/10 of 1% to remove metals and organics. This chemistry has also replaced the need for the electro coagulation unit. Wastewater is continuously circulated through the system and filtered to achieve desired water quality. A batch approach is used. Treated and filtered water is stored in a holding tank and reused in both the alkaline cleaner and acid bath rinses.

The chromate tank rinse waters use a countercurrent and ion exchange system to remove contaminants. Contaminated overflowing rinse water is pumped through a prefilter unit; a cation column to remove metals; and then an anion column to further purify the water and adjust pH. The water is then returned to the rinse tanks for reuse. Once the ion exchange columns are exhausted, they are shipped off site for regeneration.

Return on Investment

Normally the return on an investment is realized in years, not weeks. However, after adding the acid regeneration chemistry, the return on investment was two weeks. "We saved a ton of money and significantly reduced sludge shipped to the landfill," noted Mr. French. Prior to this, the company was disposing of more than 11,000 lb of neutral salts generated from acids last year. Last year Amplate's acid disposal was zero and their F006 waste shipments were reduced more than 40%. The chemistry has saved the company more than $25,000 annually.

Amplate has also used other innovative approaches to wastewater reuse and sludge reduction. The company was recognized for Outstanding Achievement in the small business category of the North Carolina Governor's Award for Excellence in Waste Reduction.

TABLE II: Savings from Extending Acid Bath Life
Based on 1,000 gal tank
Acid strength of 40% with
A 30-day acid life.
Untreated Acid Treated Acid Savings
Weekly
Hydrochloric acid at $0.86/gal
15 gal
$12.90/week
10 gal
$8.60
$4.30/week
Monthly
Acid + water used and disposed
1,000 gal total
400 gal acid +
600 gal water
Zero 100%
Monthly
Hydrochloric acid at $0.86/gal
1,065 gal total
465 gal acid + 600 gal water = $399.90/month
43.3 gal acid
$37.24/month
$362/month
Monthly
Filtered solids for disposal
F006 at $295/cu yd.
1,500-3,000 lb
1-3 cu yds F006
20-40 lb $295-885/month
month
Monthly
Caustic for pH adjustment
At $4.04/gal
222 gal
$896.88
Zero $896
Annual
Acid + water used and disposed
12,000 gal
4,800 gal acid +
7,200 gal water
Zero 100%
Annual
Replacement acid and water
Hydrochloric at $0.86/gal
12,780 gal
5,580 gal acid +
7,200 gal water
520 gal
$447.20
$4,351
Annual
Filter solids/F006 wastes
At $295/cu yd
18,000-36,000
12-36 cu yds
240-480 lb
less than 1 cu yd
$3,245-
10/3,25
Annual
Caustic for pH adjustment
At $4.04/gal
2,664 gal
$10,762.56
Zero $10.762
Total Annual Savings $18,358- $24,438
Typical Yearly Savings: Based on monthly waste treatments* savings should be a minimum of: Based on the number of gallons a tank holds × 1.84 × number of times the tank is dumped and waste treated per year = subtotal. Subtotal × 94.716% = savings per year.
Example: Based on 1,000 G tank @ 12 dumps per year = $20,913 savings per year.
Typical yearly savings: Based on a monthly Pump and Haul Disposal** method savings should be a minimum of: Based on the number of gallons a tank holds × 1.18 × number of times the tank is dumped and waste treated per year = subtotal. Subtotal × 91.76% = savings per year.
Example: Based on 1,000 G tank @ 12 dumps per year = $12,993 savings per year.
*Calculations are based on an on-going total drag out and evaporation of acid of @ 6.5% per month.
**Based on $.90 per Gal. Pump & Haul Disposal costs.


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