How to improve precipitation of nickel for waste treatment
Can anyone suggest an effective method of precipitating Ni from our batch tank? We adjust pH to 9.5 using NaOH, floc, settle, and then filter press. We still find that there is approx. 20 to 40 ppm Ni after the filter press. We've filtered the effluent and determined the Ni to be soluble (hence the need for more complete precipitation.) Presence of chelates is an unlikely possibility. Citrates and CN are present in the shop, but those particular rinses are segregated, and are latter in the process. Anyway, what precipitating agents might be more effective for Ni ?
Thanks in advance
Dear Gary ,
I would suggest that you use lime , instead of Caustic , you will produce more sludge , but the Filter Press will take care of that , it is also a little more messy being a fine powder .With sufficient mixing and settling time you will probably not need the Floc , so there will be some $$$ savings
- Victoria Australia
John's suggestion above is likely to work, but an even better method is to introduce a touch of magnesium hydroxide in the beginning of the precipitation (2-4 g/l) followed by the caustic you are presently using. Raise the pH to about 11 - 11.5, floc and you should knock the Ni down to less than 2 ppm. This treatment is easy to test and optimize in a 1 l beaker in the lab before implementation.
If you need more specifics, please feel free to contact me.
Good luck from PlaterB
"PlaterB" Berl Stein
Rochester, New York
I have used DTC products with some success, finding it helpful to start the process at pH 2.5 (it will give off odor) and then raising pH with NaOH to 10.2 pH. At other times DTC at a more neutral pH, followed by further pH adjustment works as well. My experience is mostly with EN, so the DTC is almost necessary to break chelation. Though you may not have direct contact with chelators in your stream, it may be that you are getting interference with other cleaners' rinsewater streams. I have found that to be the case when we are using strongly alkaline electrocleaners. You also might find ferrous sulfate (the old standby) as a suitable reducing agent/co-precipitant. Sometimes a touch of DTC will cause it to drop more readily as well. Nickel is problematic and sensitive to any possible chelators or ammonia, but iron especially is useful if the problem arises from electrocleaner formulations in the rinsewater stream. Bench testing is the only way to find your best results.Sometimes it is helpful to dilute the batch material 50% or 100%, which gives room for the floc to build. (Iron floc requires considerable expansion volume) Good luck from "PlaterC".Mike Solvie
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