Precipitate the heavy metal from EDTA complex ???

[Jeffrop]

Hi every body,

We want to precipitate the nickel ion from complex EDTA-nickel by hydroxide (OH from lime) but did not work ! The EDTA-Ni is so stable, Ni ion can not form a complex with OH to be precipitate ! !.

We try to break down the EDTA-Ni complex before precipitate by oxidation (HNO3/H2O2, Hypochlorite, O3/UV, thermal hydrolysis ..., ) but Ni can not be free from EDTA !

Any body who know how to precipitate the heavy metal from EDTA complex (EDTA-m) please let we know !!.

Thanks

 

[bimr]

Sulfide precipitation should work fine. Metal sulfide solubility is extremely low with sulfide precipitation that it works even in the presence of complexing agents. US Filter (Permutit Co.) has or had a sulfide precipitation process called sulfex. The beauty of the sulfex process is that it ties up the sulfide ion so you do not have to be greatly concerned about hydrogen sulfide.

A potential disadvantage of sulfide precipitation is the release of hydrogen sulfide should the pH drop. The sulfex process minimizes this potential.

If you can not find information about this process, get back to me and I can send you something.

http://www.usace.army.mil/inet/usace-docs/eng-manuals/em1110-1-4012/chap4.pdf

 

[Jeffrop]

Hi bimr,

Thanks for your suggestion ! Could you pls sent me more information about the preciptation of Sulfide with heavy metal complex with EDTA and Sulfex process.

Regards

Jeff

 

[RGCook]

Further to the sound advice from bimr, a "big gun" last resort that I have also fallen back on is the use of DTC. DTC is a carbamate-based precipitant that is not significantly affected by complexation via EDTA. However, like sulfide, it comes with its own set of issues, not the least of which are cost and potential toxicity. Carbamates are very good biocides so you must handle them with care or they can create a bigger problem than you started with in the outfall.

Some chemical companies have recently come out with some innovative chemicals to deal with the issues of the old Sulfide and DTC techniques, but you need to assess these for your own situation.

 

[bimr]

There is information available regarding sulfex on the web. Please review the available web information and talk to US Filter, as a first step. If you have no luck finding the information, I have technical papers and the process design for a project.

http://yosemite.epa.gov/R10/WATER.N...6f45e21cbb1bf8825683f006eafb9/$FILE/app_e.PDF

http://es.epa.gov/techpubs/6/3426.html

 

[Jeffrop]

Dear bimr,

Thanks you for the information, we will look it carefully !

Regards !

Jeff

 

[Stevecort]

Dear Jeff,
EDTA/Nickel complexes are very stable and difficult to break to precipitate the nickel. Sulfide treatment is the best hope but suggest that ferrous also be added as a chelate breaker. Also suggest a high ph around 10-11. We specialize in heavy metal removal and sell inorganic sulfide metal precipitatant. Please contact me if you are interested in our help.
Steve

 

[Jeffrop]

Dear Steve

Could you give me the telephone number and/or email address of your company, We will get in touch with you.

Thanks

 

[kenvlach]

Jeffrop,
Since you posted your April 29 results (thread127-49084),
I ordered up some DTC and did a low-budget experiment on precipitating Ni. Three chelants present (ammonia, EDTA and a proprietary one from electroless nickel solution), also some Cr⁺³ & Fe⁺². Initial pH 9.5, ORP 10 mV, dark blue color (Ni-ammonia complex). Added 20% DTC solution until ORP -25 mV (pH dropped to 9.1). Results: ND (< 0.05 mg/L), crystal clear filter press effluent.

So, I am thinking that, in your experiment, there may have been other cations, e.g., Ca⁺², Mg⁺², that depleted the DTC. Also, was the 1 g DTC the actual amount (corrected for concentration)?

 

[Jeffrop]

Dear Kenvlach,

I will check Ca+2, Mg+2, in our waste, repead the experience as you did and will let you know.

Regards

 

[Stevecort]

Dear Jeffrop,
I have not been keeping up with responses and apologige for the delay in getting back to you. I hope you have your problem solved by now.
Steve

 

[cookerrr]

You may add sulfide into wastewater, maybe the efficiency is better

 

[JaccoH]

Dear Jeffrop

What kind of concentrations and flows are you dealing with. I suppose that that is quite important information in order to give you advice on useful methods.

Regards,

Jacco

 

[BertGielen]

Dear all

THERE IS AN ALTERNATIVE TO PRECIPITATION AND TO FINAL TREATMENT !

Why ?
1) The alternative is probably financially more attractive
2) All proposed methods solve only the environmental burden of Nickel but ignore the environmental effects of EDTA. Once released into surface water, EDTA will form again metal complexes which are toxic for fish, simply by leaching out metals out of the soil.

Consider elektrolysis:
- Elektrolytic Ni-precipitation (generaly done on the 1st rinsing stage after the plating bath ; also possible on spent plating baths)
- other elektrode : elektrolytic destruction of EDTA
- can be done without pH-change, but generally done at pH 7 - 9 (in this way the high pH values mentioned in other proposals in this discussion are avoided; high pH in combination with the presence of NH3 in the plating solution would lead to very unpleasant fumes).

Rough financial picture:
- working costs of elektrolysis : 0.5 - 1 USD / kg Ni
- scrap value of precipitated Ni : 2 - 4 USD / kg Ni
- avoiding disposal costs of Ni-sludge (say 5% Ni) : 0.5 - 2 USD / kg Ni
- avoiding cost of carbamate, TMT15, sulfide, ... : ?

 

[exti]

Bert,
How much power is used? What is power A/C or DC? What is the power unit? What What are the anode and cathode made of? What is the cell size? How many GPM can it handle? How low can the nickel be plated out in PPM? will it go below 1PPM? Do you have a working model?
EXTi.biz

 

[BertGielen]

Dear exti

Being a water treatment specialist and not an plating professional, I can give you only rough and partial answers to your questions.

I prefer to give you some adresses of companies who developped and eventually can supply such a process :
- Siemens Europe (in house development)
- L. Danneels (laurent.danneels@kahosl.be) (consultant who is familiar with this technique)
- ESMIL (Ratingen, Germany) has build such installations
- ROWCAT project (serveral leading companies in plating world; for quick presentation of the project see

http://www.intellectuk.org/sectors/components_and_manufacturing/environmental/rocwat.pdf)