Waste treating nitric acid nickel strips
We are a metal plating shop in Minnesota that has recently rebuilt our facility and installed a new waste treatment system. We plate electroless and electrolytic nickel, acid and cyanide copper, gold, cyanide silver, acid and alkaline tin, and cyanide cadmium. We also perform passivate, chromating of aluminum, and sulfuric anodize. Our waste system is an automated clarifier based system with batch treat capabilities. We have not found an economic way to run our nitric acid nickel strips through the system or to batch treat them. Everything we try ends up using too much DTC to make it cost effective or we end up with too high of nickel in our effluent. It costs us $220 per 55 gallon drum to ship the waste off site for treatment. Do you know of any ways of treating the nitric acid nickel strips in house that will cost us less than this in chemicals and sludge formation and will keep our nickel metal within our discharge limits?Steve Ganiere
- Fridley, Minnesota
- What is the starting ppm of nickel of this waste stream?
- Is it just nitric acid?
- At what dilution do you run your nitric strip into the pH adjustment tank?
- At what pH do you try to precipitate the nickel?
- Have you optimized the pH for that particular waste stream?
- The DTC should be used to scavenge only the last few ppm of nickel.
- What is the ppm of nickel of the clarified wastewater when you start adding DTC?
In response to the questions from Tom Pullizzi:
1. Our nitric nickel strips are approximately 5000 ppm nickel.
2. Yes. It is just nitric acid, water, nickel, and copper.
3. If we try to run it through the system it goes into a spent acid tank which feeds into our AA tank at rates as low as 12 gph.
4. We use a 2 stage pH process. Stage 1 is a pH of 4-5.5 and stage 2 is a pH of 9.3-9.8.
5. Yes. This pH range works well for all waste streams.
7. The waste system is set up so that DTC is added on batch treats only. We add an aluminum chloride based chemistry to stage 1 of the pH adjust and a flocculant after stage 2.Steve Ganiere
- Fridley, Minnesota
This may sound over-simplified. Why not just neutralize the stripper to a pH of 8 to 10 in your batch treatment tank with sodium hydroxide? You will probably want to dilute it first, since it is likely to get quite hot during the neutralization, and the sludge will be rather thick. Then pump the slurry through your filter press, returning the clear filtrate to the headworks (equalization tank, or whatever the first tank is in the treatment system). The only thing that will shock the system at that point will be the soluble salts (mostly sodium nitrate), which aren't too hard on sludge making systems. There should be less than 10 ppm nickel in the filter press filtrate so that shouldn't upset the system either. Unless the stripper is some sort of weird proprietary blend there shouldn't be any chelators present, so DTC is unnecessary.
microwave & cable assemblies
Mesa (what a place-a), Arizona
Why not use diffusion dialysis to purify rather than dump the acid? The savings in caustic for neutralization plus new acid should justify the cost of a system.Lyle Kirman
consultant - Cleveland, Ohio
Diffusion Dialysis can help with some of your problems. These systems allow you to reuse your acid while the waste effluent from the system is very low in acid strength. This makes the waste easier to waste treat because less chemicals are necessary for neutralization and there is almost no heat generated during treatment. These systems also operate continuously so this waste stream is fed to your waste treatment process at a constant, slow flow rate.Tony D'Amato
- Chicopee, Massachusetts
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