Need to Electrowin Nickel Metal from Nickel Sulfate IX Col Regenerant
I am looking to remove dilute concentrations of nickel in the rinse water from a nickel sulfate plating bath. Currently I've found that @ pH 3-4 using a chelating type IX resin removal from the rinse is near 100%.
After complete loading of the IX column I find that removal of the nickel from the resin (regeneration) is easily accomplished via 10-15% sulfuric. My resultant is a volume of @ 10-15 g/l Nickel in the sulfuric solution. Precipitation of this material is then very simple.
My question then becomes, is it possible to electrowin this acid solution to attain a 1 g/l Nickel-sulfuric solution which could be reused as regenerant? Currently, the hydrolysis of the water/acid mixture prevails and all that happens is the liberation of H2/O2. Assuming this to be impossible, how about electrowinning the solution at an increased pH level, or alternate temp, or from a different regenerant... For the sole purpose of recovering the nickel.
Has anyone experience with this?Brad Dirkman
- Fergus Falls, Minnesota
One possibility is to dilute it to the desired nickel strength, adjust the pH to what you need, carbon treat it and drum it for future use. I would have it analyzed for other metals that could affect your bath. Like copper and iron. Ion chromatography works well for this and atomic adsorption is a little bit more specific.
You may have to peroxide treat to remove the iron.
Dummying helps the solution also.
For electrowinning, you need to raise the pH to about 4 to 4.5 and check it several times a day as it will change because you will be using an insoluble anode. Yes, you will get some H2 and O2 given off, but it will be minimal. Stay below 4 volts and you will have a lot less. Intense agitation speeds up the process, so you could use a lower voltage. This nickel will include some of the copper, so you are are right back where you started above.James Watts
- Navarre, Florida
You might consider using another type of resin that doesn't require 10-15% sulphuric acid for regeneration. Resins are available that will remove nickel from your rinsing bath only requiring 2-3% sulphuric acid for regeneration. You will need less alkali chemicals for pH-adjustment to pH 3-4 for electrowinning and of course save on H2SO4 consumption.Ruud Gerritsen
- Simpelveld, Netherlands
I have personally accomplished this task several times, and in varying scales up to several hundred pounds of recovered nickel per day.
We have a process that we use to regenerate ion exchange resins that gives us 120-130 g/L of metal in the solution (and for the doubting thomases out there, we are NOT taking cuts of the regeneration!)
You could use a weak acid resin, as is suggested previously, however you may find that this resin will scavenge other unwanted items from the solution too, and render it unacceptable for plate-out. I would stick with a good quality chelated resin. Pound for pound, it will hold more nickel.
I could fill several pages discussing this. You're on the right track - just have to make a few adjustments in the approach.
wastewater treatment specialist
Electrowinning is a process that requires special equipment, mainly special cathodes with high surface area.
chemical process supplier
Actually, your suggestion to use high surface area cathodes is a good one, however not necessarily always required. You can plate out quite effectively on low surface area (2 dimensional cathodes - basically plates) with the correct plating parameters. Remember the 5 basics - concentration, current density, agitation, temperature, chemistry. Keep control of these, and you can just about plate out anything.
Nickel is no different, but does require careful control over the free acidity present in the solution (creates hydrogen, which burns the plate and passivates it). Many of our earlier clients used to use boric acid to give the solutions some stability, however with boron limits getting tighter, that may not be the best option anymore. We use an acid recovery unit on the system to remove the free acid as it is created (1 lb metal plated makes 1 lb of acid).
High surface area cathodes were originally developed to plate out of very dilute solutions as an effluent control device. As limits dropped, their effectiveness was challenged to meet sub-ppm requirements. However, they gained acceptance as a straightforward electrowinning system for certain applications, such as plating out of IX regenerants. Care should be taken, however, to evaluate the cost effectiveness of using consumable cathodes in a high concentration application. Based on the resale value of the metal, you might spend more on replacement cathodes than the metal is worth. In that case, you could use a low surface area cell, followed by a high surface area cell to get all the metal out.
Good design and understanding these costs is critical.
wastewater treatment specialist
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