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Ask the Expert Question-and-Answer Archive (Wastewater Treatment)

by Mike McGinness, EcoShield Environmental Systems, Inc.
April, 2005

Trouble Precipitating Nickel Stripping Solution

Q. I am in the process of treating a stripper tank that used meta-nitrobenzoic acid and etheylenediamine (I do not want to use their product names)to remove Ni plating from parts. The chemical supplier that provided the above chemicals said it could be treated using sodium dimethyldithiocarbamate (again I am not using their specific product name) This hasnt worked and I am now left with a mess on my hands that seems to be growing daily. I need avenues I can try to break the Ni so it will precipitate?

A. This sounds like a mess all right. First I would not try anything else until you have tested and proven a viable treatment method in a glass beaker, say 500 ml volume and verified the results. This will require some some lab supplies such as a titrator for dispensing small quantities (like 0.1 to 1.0 ml) of treatment chemicals.

I would need to know what all is in the solution now, including concentration (at least approximate concentration), total bath volume (for economic and volume/ mass calculation purposes), actual pH of the solution, and I would need to know what you want left after treating the solution.

I assume you want to remove the nickel from the solution, but what are you wanting to do with the removed nickel, and the treated solution afterwards?

What happens to the solution afterwards, what is the nickel limit after treatment?

I would be just as concerned about the liquid after removing the nickel as before especially if the organics (nitro benzoic acid, dithiocarbamate, and ethylenediamine) are any higher than about 50 to 500 ppm. The POTWs are not going to allow much nitrobenzoic acid or dithiocarbamate to be sewered. They will probably object to anything more than about 10 ppm of either one. They would probably allow higher amounts of ethylenediamine up to maybe 100 or 500 ppm.

Also, was this a chemical only nickel stripper or electro-chemical nickel stripper solution / process?

Based on your information I am going assume that equipment such as Electro-Dialisis, Electro-Coagulation or Nanofiltration is not going be an option due to their capital cost and the limited volume you generate. Your best bet on a small complex mix like this may be to slowly evaporate the water to reduce the final volume of waste, but if you do use evaporation watch out for the volatiles and odors from the organics in this mix. A slow ambient evaporator would be much safer and preferable to a heated evaporator (which might require a permit!).

You also might try electroplating the nickel out of solution using a small battery charger and some thick (consumable) aluminum plates for the anode and cathode. The dissolved aluminum would replace the nickel and free it up to co-precipitate with the rest of the dissolved aluminum as aluminum hydroxide.

There are several proprietary mixed clay & carbon powder based technologies that reportedly can remove the nickel in waste like yours but they are expensive and usually produce a large amount of sludge in relation to the treated water volume.



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